Expr functions now act as closures

- fraction type renamed as FractionType and moved from operator-fraction.go to fraction-type.go
- ListType moved from operator-list.go to list-type.go
- all test file were renamed adding the "t_" prefix
- defined a test template in file t_temple_test.go
- new test file t_relational_test.go where relational tests are collected
- lists can now compared as set using operators <, <=, >, and >= (IMPORTANT: here = menas same content, not same list)

ast.go

@@ -60,7 +60,7 @@ func (self *ast) addToken(tk *Token) (err error) {
 }
 
 func (self *ast) addToken2(tk *Token) (t *term, err error) {
-	if t = newTerm(tk, nil); t != nil {
+	if t = newTerm(tk); t != nil {
 		err = self.addTerm(t)
 	} else {
 		err = tk.Errorf("unexpected token %q", tk.String())
@@ -119,7 +119,7 @@ func (self *ast) eval(ctx ExprContext, preset bool) (result any, err error) {
 		if self.forest != nil {
 			for _, root := range self.forest {
 				if result, err = root.compute(ctx); err == nil {
-					ctx.setVar(ControlLastResult, result)
+					ctx.UnsafeSetVar(ControlLastResult, result)
 				} else {
 					//err = fmt.Errorf("error in expression nr %d: %v", i+1, err)
 					break
@@ -128,6 +128,7 @@ func (self *ast) eval(ctx ExprContext, preset bool) (result any, err error) {
 		}
 		if err == nil {
 			result, err = self.root.compute(ctx)
+			ctx.UnsafeSetVar(ControlLastResult, result)
 		}
 		// } else {
 		// 	err = errors.New("empty expression")

common-errors.go

@@ -8,6 +8,20 @@ import (
 	"fmt"
 )
 
+func errTooFewParams(minArgs, maxArgs, argCount int) (err error) {
+	if maxArgs < 0 {
+		err = fmt.Errorf("too few params -- expected %d or more, got %d", minArgs, argCount)
+	} else {
+		err = fmt.Errorf("too few params -- expected %d, got %d", minArgs, argCount)
+	}
+	return
+}
+
+func errTooMuchParams(maxArgs, argCount int) (err error) {
+	err = fmt.Errorf("too much params -- expected %d, got %d", maxArgs, argCount)
+	return
+}
+
 // --- General errors
 
 func errCantConvert(funcName string, value any, kind string) error {
@@ -18,11 +32,15 @@ func errExpectedGot(funcName string, kind string, value any) error {
 	return fmt.Errorf("%s() expected %s, got %T (%v)", funcName, kind, value, value)
 }
 
+func errDivisionByZero(funcName string) error {
+	return fmt.Errorf("%s() division by zero", funcName)
+}
+
 // --- Parameter errors
 
-func errOneParam(funcName string) error {
+// func errOneParam(funcName string) error {
-	return fmt.Errorf("%s() requires exactly one param", funcName)
+// 	return fmt.Errorf("%s() requires exactly one param", funcName)
-}
+// }
 
 func errMissingRequiredParameter(funcName, paramName string) error {
 	return fmt.Errorf("%s() missing required parameter %q", funcName, paramName)

common-params.go

@@ -5,7 +5,26 @@
 package expr
 
 const (
+	paramCount     = "count"
+	paramItem      = "item"
 	paramParts     = "parts"
 	paramSeparator = "separator"
 	paramSource    = "source"
+	paramSuffix    = "suffix"
+	paramPrefix    = "prefix"
+	paramStart     = "start"
+	paramEnd       = "end"
+	paramValue     = "value"
+	paramEllipsis  = "..."
+	typeFilepath   = "filepath"
+	typeDirpath    = "dirpath"
 )
+
+// const (
+// 	typeInteger  = "int"
+// 	typeFloat    = "float"
+// 	typeString   = "string"
+// 	typeFraction = "fract"
+// 	typeList     = "list"
+// 	typeDict     = "dict"
+// )

common-type-names.go

@@ -5,10 +5,14 @@
 package expr
 
 const (
+	typeAny      = "any"
 	typeBoolean  = "boolean"
-	typeFloat    = "decimal"
+	typeFloat    = "float"
 	typeFraction = "fraction"
+	typeHandle   = "handle"
 	typeInt      = "integer"
+	typeItem     = "item"
 	typeNumber   = "number"
+	typePair     = "pair"
 	typeString   = "string"
 )

context-helpers.go

@@ -15,14 +15,16 @@ func exportVar(ctx ExprContext, name string, value any) {
 	if name[0] == '@' {
 		name = name[1:]
 	}
-	ctx.setVar(name, value)
+	ctx.UnsafeSetVar(name, value)
 }
 
 func exportFunc(ctx ExprContext, name string, info ExprFunc) {
 	if name[0] == '@' {
 		name = name[1:]
 	}
-	ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
+	// ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
+	// ctx.RegisterFuncInfo(name, info)
+	ctx.RegisterFunc(name, info.Functor(), info.ReturnType(), info.Params())
 }
 
 func exportObjects(destCtx, sourceCtx ExprContext) {

context.go

@@ -4,39 +4,45 @@
 // context.go
 package expr
 
-// ---- Function template
-type FuncTemplate func(ctx ExprContext, name string, args []any) (result any, err error)
-
 // ---- Functor interface
 type Functor interface {
 	Invoke(ctx ExprContext, name string, args []any) (result any, err error)
+	SetFunc(info ExprFunc)
+	GetFunc() ExprFunc
 }
 
-type simpleFunctor struct {
+// ---- Function Param Info
-	f FuncTemplate
+type ExprFuncParam interface {
-}
+	Name() string
-
+	Type() string
-func (functor *simpleFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
+	IsOptional() bool
-	return functor.f(ctx, name, args)
+	IsRepeat() bool
+	DefaultValue() any
 }
 
 // ---- Function Info
 type ExprFunc interface {
+	Formatter
 	Name() string
 	MinArgs() int
 	MaxArgs() int
 	Functor() Functor
+	Params() []ExprFuncParam
+	ReturnType() string
 }
 
 // ----Expression Context
 type ExprContext interface {
 	Clone() ExprContext
+	Merge(ctx ExprContext)
 	GetVar(varName string) (value any, exists bool)
 	SetVar(varName string, value any)
-	setVar(varName string, value any)
+	UnsafeSetVar(varName string, value any)
 	EnumVars(func(name string) (accept bool)) (varNames []string)
 	EnumFuncs(func(name string) (accept bool)) (funcNames []string)
 	GetFuncInfo(name string) (item ExprFunc, exists bool)
 	Call(name string, args []any) (result any, err error)
-	RegisterFunc(name string, f Functor, minArgs, maxArgs int)
+	// RegisterFunc(name string, f Functor, minArgs, maxArgs int)
+	RegisterFuncInfo(info ExprFunc)
+	RegisterFunc(name string, f Functor, returnType string, param []ExprFuncParam) error
 }

doc/Expr.adoc

@@ -22,49 +22,242 @@ Expressions calculator
 
 toc::[]
 
-#TODO: Work in progress#
+#TODO: Work in progress (last update on 2024/05/20, 06:58 a.m.)#
 
 == Expr
 _Expr_ is a GO package capable of analysing, interpreting and calculating expressions.
 
-
 === Concepts and terminology
 #TODO#
 
+image::expression-diagram.png[]
+
+=== `dev-expr` test tool
+`dev-expr` is a simple program that can be used to evaluate expressions interactively. As its name suggests, it was created for testing purpose.  In fact, in additon to the automatic verification test suite based on the Go test framework, `dev-expr` provides an important aid for quickly testing of new features during their development.
+
+`dev-expr` can work as a _REPL_, _**R**ead-**E**xecute-**P**rint-**L**oop_, or it can process expression acquired from files or standard input.
+
+The program can be downloaded from https://git.portale-stac.it/go-pkg/-/packages/generic/dev-expr/[dev-expr].
+
+Here are some examples of execution.
+
+.Run `dev-expr` in REPL mode and ask for help
+[source,shell]
+----
+# Type 'exit' or Ctrl+D to quit the program.
+
+[user]$ ./dev-expr
+expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@portale-stac.it)
+	Based on the Expr package v0.10.0
+	Type help to get the list of available commands
+	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
+
+>>> help
+--- REPL commands:
+      source -- Load a file as input
+         tty -- Enable/Disable ansi output <1>
+        base -- Set the integer output base: 2, 8, 10, or 16
+        exit -- Exit the program
+        help -- Show command list
+          ml -- Enable/Disable multi-line output
+        mods -- List builtin modules
+
+--- Command line options:
+    -b <builtin>       Import builtin modules.
+                       <builtin> can be a list of module names or a glob-pattern.
+                       Use the special value 'all' or the pattern '*' to import all modules.
+    -e <expression>    Evaluate <expression> instead of standard-input
+    -i                 Force REPL operation when all -e occurences have been processed
+    -h, --help, help   Show this help menu
+    -m, --modules      List all builtin modules
+    -p                 Print prefix form
+    -t                 Print tree form <2>
+
+>>> 
+----
+
+<1> Only available for single fraction values
+<2> Work in progress
+
+.REPL examples
+[source,shell]
+----
+[user]$ ./dev-expr
+expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@portale-stac.it)
+	Based on the Expr package v0.10.0
+	Type help to get the list of available commands
+	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
+
+>>> 2+3
+5
+>>> 2+3*(4-1.5)
+9.5
+>>> 0xFD + 0b1 + 0o1 <1>
+255
+>>> 1|2 + 2|3 <2>
+7|6
+>>> ml <3>
+>>> 1|2 + 2|3
+7
+-
+6
+>>> 1+2 but 5|2+0.5 <4>
+3
+>>> 1+2; 5|2+0.5 <5>
+3
+>>>
+----
+
+<1> Number bases: 0x = hexadecimal, 0o = octal, 0b = binary.
+<2> Fractions: numerator | denominator.
+<3> Activate multi-line output of fractions.
+<4> But operator, see <<_but_operator>>.
+<5> Multi-expression: the same result of the previous single expression but this it is obtained with two separated calculations.
+
 == Data types
 _Expr_ supports numerical, string, relational, boolean expressions, and mixed-type lists.
 
 === Numbers
-Numbers can be integers (GO int64) or float (GO float64). In mixed operations involving integers and floats, integers are automatically promoted to floats.
+_Expr_ supports three type of numbers:
+
+. [blue]#Integers#
+. [blue]#Floats#
+. [blue]#Factions#
+
+In mixed operations involving integers, fractions and floats, automatic type promotion to the largest type take place.
+
+==== Integers
+__Expr__'s integers are a subset of the integer set. Internally they are stored as Golang _int64_ values.
+
+.Integer literal syntax
+====
+*_integer_* = [_sign_] _digit-seq_ +
+_sign_ = "**+**" | "**-**" +
+_digit-seq_ = _dec-seq_ | _bin-seq_ | _oct-seq_ | _hex-seq_ +
+_dec-seq_ = {__dec-digit__} +
+_dec-digit_ = "**0**"|"**1**"|...|"**9**" +
+_bin-seq_ = "**0b**"{__bin-digit__} +
+_bin-digit_ = "**0**"|"**1**" +
+_oct-seq_ = "**0o**"{__oct-digit__} +
+_oct-digit_ = "**0**"|"**1**"|...|"**7**" +
+_hex-seq_ = "**0x**"{__hex-digit__} +
+_hex-digit_ = "**0**"|"**1**"|...|"**9**"|"**a**"|...|"**z**"|"**A**"|...|"**Z**"
+====
+
+Value range: *-9223372036854775808* to *9223372036854775807*
 
 .Arithmetic operators
 [cols="^1,^2,6,4"]
 |===
 | Symbol    | Operation     | Description               | Examples
-
+| [blue]`+` | _sum_         | Add two values            | [blue]`-1 + 2` -> 1
-| [blue]`+` / [blue]`-` | _change sign_ | Change the sign of values | [blue]`-1` _[-1]_ +
+| [blue]`-` | _subtraction_ | Subtract the right value from the left one | [blue]`3 - 1` -> 2
-[blue]`-(+2)` _[-2]_
+| [blue]`*` | _product_     | Multiply two values       | [blue]`-1 * 2` -> -2
-
+| [blue]`/` | _Division_    | Divide the left value by the right one^(*)^ | [blue]`-10 / 2` -> 5
-| [blue]`+` | _sum_ | Add two values | [blue]`-1 + 2` _[1]_ +
+| [blue]`%` | _Modulo_      | Remainder of the integer division | [blue]`5 % 2` -> 1
-[blue]`4 + 0.5` _[4.5]_
-
-| [blue]`-` | _subtraction_ | Subtract the right value from the left one | [blue]`3 - 1` _[2]_ +
-[blue]`4 - 0.5` _[3.5]_
-
-| [blue]`*` | _product_ | Multiply two values | `-1 * 2` _[-2]_ +
-[blue]`4 * 0.5` _[2.0]_
-
-| [blue]`/` | _Division_ | Divide the left value by the right one | [blue]`-1 / 2` _[0]_ +
-[blue]`1.0 / 2` _[0.5]_
-
-| [blue]`./` | _Float division_ | Force float division | [blue]`-1 ./ 2` _[-0.5]_
-
-| [blue]`%` | _Modulo_ | Remainder of the integer division | [blue]`5 % 2` _[1]_
-
 |=== 
 
-=== String
+^(*)^ See also the _float division_ [blue]`./` below.
-Strings are character sequences enclosed between two double quote [blue]`"`. Example: [blue]`"I'm a string"`.
+
+
+==== Floats
+__Expr__'s floats are a subset of the rational number set. Note that they can't hold the exact value of an unlimited number; floats can only approximate them. Internally floats are stored as Golang's _float64_ values.
+
+
+.Float literal syntax
+====
+*_float_* = [_sign_] _dec-seq_ "**.**" [_dec-seq_] [("**e**"|"**E**") [_sign_] _dec-seq_] +
+_sign_ = "**+**" | "**-**" +
+_dec-seq_ = _see-integer-literal-syntax_
+====
+
+.Examples
+`>>>` [blue]`1.0` +
+[green]`1` +
+`>>>` [blue]`0.123` +
+[green]`0.123` +
+`>>>` [blue]`4.5e+3` +
+[green]`4500` +
+`>>>` [blue]`4.5E-33` +
+[green]`4.5e-33` +
+`>>>` [blue]`4.5E-3` +
+[green]`0.0045` +
+`>>>` [blue]`4.5E10` +
+[green]`4.5e+10`
+
+
+.Arithmetic operators
+[cols="^1,^2,6,4"]
+|===
+| Symbol    | Operation     | Description               | Examples
+| [blue]`+` | _sum_         | Add two values            | [blue]`4 + 0.5` -> 4.5
+| [blue]`-` | _subtraction_ | Subtract the right value from the left one | [blue]`4 - 0.5` -> 3.5
+| [blue]`*` | _product_     | Multiply two values       | [blue]`4 * 0.5` -> 2.0
+| [blue]`/` | _Division_    | Divide the left value by the right one | [blue]`1.0 / 2` -> 0.5
+| [blue]`./`| _Float division_ | Force float division   | [blue]`-1 ./ 2` -> -0.5
+|===
+
+==== Fractions
+_Expr_ also supports fractions. Fraction literals are made with two integers separated by a vertical bar `|`.
+
+.Fraction literal syntax
+====
+*_fraction_* = [__sign__] (_num-den-spec_ | _float-spec_) +
+_sign_ = "**+**" | "**-**" +
+_num-den-spec_ = _digit-seq_ "**|**" _digit-seq_ +
+_float-spec_ = _dec-seq_ "**.**" [_dec-seq_] "**(**" _dec-seq_ "**)**" +
+_dec-seq_ = _see-integer-literal-syntax_ +
+_digit-seq_ = _see-integer-literal-syntax_
+====
+
+.Examples
+// [source,go]
+// ----
+`>>>` [blue]`1 | 2` +
+[green]`1|2` +
+`>>>` [blue]`4|6`  [gray]_// Fractions are always reduced to their lowest terms_ +
+[green]`2|3` +
+`>>>` [blue]`1|2 + 2|3` +
+[green]`7|6` +
+`>>>` [blue]`1|2 * 2|3` +
+[green]`1|3` +
+`>>>` [blue]`1|2 / 1|3` +
+[green]`3|2` +
+`>>>` [blue]`1|2 ./ 1|3` [gray]_// Force decimal division_ +
+[green]`1.5` +
+`>>>` [blue]`-1|2` +
+[green]`-1|2` +
+`>>>` [blue]`1|-2` [gray]_// Invalid sign specification_ +
+[red]_Eval Error: [1:3] infix operator "|" requires two non-nil operands, got 1_ +
+`>>>` [blue]`1|(-2)` +
+[green]`-1|2`
+// ----
+
+Fractions can be used together with integers and floats in expressions.
+
+.Examples
+`>>>` [blue]`1|2 + 5` +
+[green]`11|2` +
+`>>>` [blue]`4 - 1|2` +
+[green]`7|2` +
+`>>>` [blue]`1.0 + 1|2` +
+[green]`1.5`
+
+
+
+=== Strings
+Strings are character sequences enclosed between two double quote [blue]`"`.
+
+.Examples
+`>>>` [blue]`"I'm a string"` +
+[green]`I'm a string` +
+`>>>` [blue]`"123abc?!"` +
+[green]`123abc?!` +
+`>>>` [blue]`"123\nabc"` +
+[green]`123` +
+[green]`abc` +
+`>>>` [blue]`"123\tabc"` +
+[green]`123{nbsp}{nbsp}{nbsp}{nbsp}abc`
 
 Some arithmetic operators can also be used with strings.
 
@@ -73,55 +266,75 @@ Some arithmetic operators can also be used with strings.
 |===
 | Symbol    | Operation     | Description               | Examples
 
-| [blue]`+` | _concatenation_ | Join two strings or two _stringable_ values | [blue]`"one" + "two"` _["onetwo"]_ +
+| [blue]`+` | _concatenation_ | Join two strings or two _stringable_ values | [blue]`"one" + "two"` -> _"onetwo"_ +
-[blue]`"one" + 2` _["one2"]_
+[blue]`"one" + 2` -> _"one2"_
 
-| [blue]`*` | _repeat_ | Make _n_ copy of a string  | [blue]`"one" * 2` _["oneone"]_
+| [blue]`*` | _repeat_ | Make _n_ copy of a string  | [blue]`"one" * 2` -> _"oneone"_
 |===
 
+The items of strings can be accessed using the dot `.` operator.
 
-=== Boolean
+.Item access syntax
-Boolean data type has two values only: _true_ and _false_. Relational and Boolean expressions produce Boolean values.
+====
+_item_ = _string-expr_ "**.**" _integer-expr_
+====
+
+.String examples
+`>>>` [blue]`s="abc"`  [gray]_// assign the string to variable s_ +
+[green]`abc` +
+`>>>` [blue]`s.1`      [gray]_// char at position 1 (starting from 0)_ +
+[green]`b` +
+`>>>` [blue]`s.(-1)`   [gray]_// char at position -1, the rightmost one_ +
+[green]`c` +
+`>>>` [blue]`\#s`       [gray]_// number of chars_ +
+[gren]`3` +
+`>>>` [blue]`#"abc"`   [gray]_// number of chars_ +
+[green]`3`
 
 
-.Relational operators
+=== Booleans
+Boolean data type has two values only: [blue]_true_ and [blue]_false_. Relational and boolean expressions result in boolean values.
+
+.Relational operators^(*)^
 [cols="^1,^2,6,4"]
 |===
 | Symbol    | Operation     | Description               | Examples
 
-| [blue]`==` | _Equal_ | True if the left value is equal to the right one | [blue]`5 == 2` _[false]_ +
+| [blue]`==` | _Equal_ | True if the left value is equal to the right one | [blue]`5 == 2` -> _false_ +
-[blue]`"a" == "a"` _[true]_
+[blue]`"a" == "a"` -> _true_
-| [blue]`!=` | _Not Equal_ | True if the left value is NOT equal to the right one | [blue]`5 != 2` _[true]_ +
+| [blue]`!=` | _Not Equal_ | True if the left value is NOT equal to the right one | [blue]`5 != 2` -> _true_ +
-[blue]`"a" != "a"` _[false]_
+[blue]`"a" != "a"` -> _false_
-| [blue]`<` | _Less_ | True if the left value is less than the right one | [blue]`5 < 2` _[false]_ +
+| [blue]`<` | _Less_ | True if the left value is less than the right one | [blue]`5 < 2` -> _false_ +
-[blue]`"a" < "b"` _[true]_
+[blue]`"a" < "b"` -> _true_
-| [blue]`\<=` | _Less or Equal_ | True if the left value is less than or equal to the right one | [blue]`5 \<= 2` _[false]_ +
+| [blue]`\<=` | _Less or Equal_ | True if the left value is less than or equal to the right one | [blue]`5 \<= 2` -> _false_ +
-[blue]`"b" \<= "b"` _[true]_
+[blue]`"b" \<= "b"` -> _true_
-| [blue]`>` | _Greater_ | True if the left value is greater than the right one | [blue]`5 > 2` _[true]_ +
+| [blue]`>` | _Greater_ | True if the left value is greater than the right one | [blue]`5 > 2` -> _true_ +
-[blue]`"a" < "b"` _[false]_
+[blue]`"a" < "b"` -> _false_
-| [blue]`>=` | _Greater or Equal_ | True if the left value is greater than or equal to the right one | [blue]`5 >= 2` _[true]_ +
+| [blue]`>=` | _Greater or Equal_ | True if the left value is greater than or equal to the right one | [blue]`5 >= 2` -> _true_ +
-[blue]`"b" \<= "b"` _[true]_
+[blue]`"b" \<= "b"` -> _true_
 |===
 
+^(*)^ See also the  [blue]`in` operator in the _list_ and _dictionary_ sections.
+
 
 .Boolean operators
 [cols="^2,^2,5,4"]
 |===
 | Symbol    | Operation     | Description               | Examples
 
-| [blue]`NOT` | _Not_ | True if the right value is false | [blue]`NOT true` _[false]_ +
+| [blue]`NOT` | _Not_ | True if the right value is false | [blue]`NOT true` -> _false_ +
-[blue]`NOT (2 < 1)` _[true]_
+[blue]`NOT (2 < 1)` -> _true_
 
-| [blue]`AND` / [blue]`&&` | _And_ | True if both left and right values are true  | [blue]`false && true` _[false]_ +
+| [blue]`AND` / [blue]`&&` | _And_ | True if both left and right values are true  | [blue]`false && true` -> _false_ +
-[blue]`"a" < "b" AND NOT (2 < 1)` _[true]_
+[blue]`"a" < "b" AND NOT (2 < 1)` -> _true_
 
-| [blue]`OR` / [blue]`\|\|` | _Or_ | True if at least one of the left and right values integers true| [blue]`false or true` _[true]_ +
+| [blue]`OR` / [blue]`\|\|` | _Or_ | True if at least one of the left and right values integers true| [blue]`false or true` -> _true_ +
-[blue]`"a" == "b" OR (2 == 1)` _[false]_
+[blue]`"a" == "b" OR (2 == 1)` -> _false_
 |===
 
 [CAUTION]
 ====
-Currently, boolean operations are evaluated using _short cut evaluation_. This means that, if the left expression of operators [blue]`and` and [blue]`or` is sufficient to establish the result of the whole operation, the right expression would not evaluated at all.
+Currently, boolean operations are evaluated using _short cut evaluation_. This means that, if the left expression of the [blue]`and` and [blue]`or` operators is sufficient to establish the result of the whole operation, the right expression would not evaluated at all.
 
 .Example
 [source,go]
@@ -131,113 +344,240 @@ Currently, boolean operations are evaluated using _short cut evaluation_. This m
 <1> This multi-expression returns _1_ because in the first expression the left value of [blue]`or` is _true_ and as a conseguence its right value is not computed. Therefore the _a_ variable only receives the integer _1_.
 ====
 
-=== List
+=== Lists
-_Expr_ supports list of mixed-type values, also specified by normal expressions.
+_Expr_ supports list of mixed-type values, also specified by normal expressions. Internally, _Expr_'s lists are Go arrays.
 
-.List examples
+.List literal syntax
-[source,go]
+====
-----
+*_list_* = _empty-list_ | _non-empty-list_ +
-[1, 2, 3]                   // List of integers
+_empty-list_ = "**[]**" +
-["one", "two", "three"]     // List of strings
+_non-empty-list_ = "**[**" _any-value_ {"**,**" _any-value} "**]**" +
-["one", 2, false, 4.1]      // List of mixed-types
+====
-["one"+1, 2.0*(9-2)]        // List of expressions
-[ [1,"one"], [2,"two"]]     // List of lists
-----
 
+.Examples
+`>>>` [blue]`[1,2,3]`                     [gray]_// List of integers_ +
+[green]`[1, 2, 3]` +
+`>>>` [blue]`["one", "two", "three"]`     [gray]_// List of strings_ +
+[green]`["one", "two", "three"]` +
+`>>>` [blue]`["one", 2, false, 4.1]`      [gray]_// List of mixed-types_ +
+[green]`["one", 2, false, 4.1]` +
+`>>>` [blue]`["one"+1, 2.0*(9-2)]`        [gray]_// List of expressions_ +
+[green]`["one1", 14]` +
+`>>>` [blue]`[ [1,"one"], [2,"two"]]`     [gray]_// List of lists_ +
+[green]`[[1, "one"], [2, "two"]]`
 
 .List operators
 [cols="^2,^2,5,4"]
 |===
 | Symbol    | Operation     | Description               | Examples
 
-| [blue]`+` | _Join_ | Joins two lists | [blue]`[1,2] + [3]` _[ [1,2,3] ]_
+| [blue]`+` | _Join_ | Joins two lists | [blue]`[1,2] + [3]` -> _[1,2,3]_
-
+| [blue]`-` | _Difference_ | Left list without elements in the right list  | [blue]`[1,2,3] - [2]` -> _[1,3]_
-| [blue]`-` | _Difference_ | Left list without elements in the right list  | [blue]`[1,2,3] - [2]` _[ [1,3] ]_
+| [blue]`>>` | _Front insertion_ | Insert an item in front | [blue]`0 >> [1,2]` -> _[0,1,2]_
+| [blue]`<<` | _Back insertion_ | Insert an item at end | [blue]`[1,2] << 3` -> _[1,2,3]_
+| [blue]`.` | _List item_ | Item at given position | [blue]`[1,2.3].1` -> _2_
+| [blue]`in` | _Item in list_ | True if item is in list | [blue]`2 in [1,2,3]` -> _true_ +
+[blue]`6 in [1,2,3]` -> _false_
 |===
 
-== Variables
+The items of array can be accessed using the dot `.` operator.
-A variable is an identifier with an assigned value. Variables are stored in the object that implements the _ExprContext_ interface.
+
+.Item access syntax
+====
+_item_ = _list-expr_ "**.**" _integer-expr_
+====
+
+.Items of list
+`>>>` [blue]`[1,2,3].1` +
+[green]`2` +
+`>>>` [blue]`list=[1,2,3]; list.1` +
+[green]`2` +
+`>>>` [blue]`["one","two","three"].1` +
+[green]`two` +
+`>>>` [blue]`list=["one","two","three"]; list.(2-1)` +
+[green]`two` +
+`>>>` [blue]`list.(-1)` +
+[green]`three` +
+`>>>` [blue]`list.(10)` +
+[red]`Eval Error: [1:9] index 10 out of bounds` +
+`>>>` [blue]`#list` +
+[green]`3` +
+`>>>` [blue]`index=2; ["a", "b", "c", "d"].index` +
+[green]`c`
+
+
+
+=== Dictionaries
+The _dictionary_, or _dict_, data-type is set of pairs _key/value_. It is also known as _map_ or _associative array_.
+
+Dictionary literals are sequences of pairs separated by comma [blue]`,` enclosed between brace brackets.
+
+.Dict literal syntax
+====
+*_dict_* = _empty-dict_ | _non-empty-dict_ +
+_empty-dict_ = "**{}**" +
+_non-empty-dict_ = "**{**" _key-scalar_ "**:**" _any-value_ {"**,**" _key-scalar_ "**:**" _any-value} "**}**" +
+====
 
 .Examples
-[source,go]
+`>>>` [blue]`{1:"one", 2:"two"}` +
-----
+[green]`{1: "one", 2: "two"}` +
-a=1
+`>>>` [blue]`{"one":1, "two": 2}` +
-x = 5.2 * (9-3)
+[green]`{"one": 1, "two": 2}` +
-x = 1; y = 2*x
+`>>>` [blue]`{"sum":1+2+3, "prod":1*2*3}` +
-----
+[green]`{"sum": 6, "prod": 6}`
+
+
+.Dict operators
+[cols="^2,^2,4,5"]
+|===
+| Symbol    | Operation     | Description               | Examples
+
+| [blue]`+` | _Join_ | Joins two dicts | [blue]`{1:"one"}+{6:"six"}` -> _{1: "one", 6: "six"}_
+| [blue]`.` | _Dict item value_ | Item value of given key | [blue]`{"one":1, "two":2}."two"` -> _2_
+| [blue]`in` | _Key in dict_ | True if key is in dict | [blue]`"one" in {"one":1, "two":2}` -> _true_ +
+[blue]`"six" in {"one":1, "two":2}` -> _false_
+|===
+
+
+== Variables
+_Expr_, like most programming languages, supports variables. A variable is an identifier with an assigned value. Variables are stored in _contexts_.
+
+.Variable literal syntax
+====
+*_variable_* = _identifier_ "*=*" _any-value_ +
+_identifier_ = _alpha_ {(_alpha_)|_dec-digit_|"*_*"} +
+__alpha__ = "*a*"|"*b*"|..."*z*"|"*A*"|"*B*"|..."*Z*"
+====
+
+NOTE: The assign operator [blue]`=` returns the value assigned to the variable.
+
+.Examples
+`>>>` [blue]`a=1` +
+[green]`1` +
+`>>>` [blue]`a_b=1+2` +
+[green]`1+2` +
+`>>>` [blue]`a_b` +
+[green]`3` +
+`>>>` [blue]`x = 5.2 * (9-3)`  [gray]_// The assigned value has the approximation error typical of the float data-type_ +
+[green]`31.200000000000003` +
+`>>>` [blue]`x = 1; y = 2*x` +
+[green]`2` +
+`>>>` [blue]`_a=2` +
+[red]`Parse Error: [1:2] unexpected token "_"` +
+`>>>` [blue]`1=2` +
+[red]`Parse Error: assign operator ("=") must be preceded by a variable`
+
 
 == Other operations
 
 === [blue]`;` operator
-The semicolon operator [blue]`;` is an infixed pseudo-operator. It evaluates the left expression first and then the right expression. The latter is the final result.
+The semicolon operator [blue]`;` is an infixed pseudo-operator. It evaluates the left expression first and then the right expression. The value of the latter is the final result.
+
+An expression that contains [blue]`;` is called a _multi-expression_ and each component expressione is called a _sub-expression_.
 
 IMPORTANT: Technically [blue]`;` is not treated as a real operator. It acts as a separator in lists of expressions.
 
 TIP: [blue]`;` can be used to set some variables before the final calculation.
 
 .Example
-[source,go]
+`>>>` [blue]`a=1; b=2; c=3; a+b+c` +
-----
+[green]`6`
-a=1; b=2; c=3; a+b+c    // returns 6
+
-----
+The value of each sub-expression is stored in the automatica variable _last_.
+
+.Example
+`>>>` [blue]`2+3; b=last+10; last` +
+[green]`15`
+
 
 === [blue]`but` operator
-[blue]`but` is an infixed operator. Its operands can be any type of expression. It evaluates the left expression first, then the right expression. The value of the right expression is the final result. Examples: [blue]`5 but 2` returns 2, [blue]`x=2*3 but x-1` returns 5.
+[blue]`but` is an infixed operator. Its operands can be expressions of any type. It evaluates the left expression first, then the right expression. The value of the right expression is the final result.
 
-[blue]`but` is very similar to [blue]`;`. The only difference is that [blue]`;` can't be used inside parenthesis [blue]`(` and [blue]`)`.
+.Examples
+[blue]`5 but 2` +
+[green]`2` +
+[blue]`x=2*3 but x-1` +
+[green]`5`.
+
+[blue]`but` behavior is very similar to [blue]`;`. The only difference is that [blue]`;` is not a true operator and can't be used inside parenthesis [blue]`(` and [blue]`)`.
 
 === Assignment operator [blue]`=`
-The assignment operator [blue]`=` is used to define variables in the evaluation context or to change their value (see _ExprContext_).
+The assignment operator [blue]`=` is used to define variables or to change their value in the evaluation context (see _ExprContext_).
+
 The value on the left side of [blue]`=` must be an identifier. The value on the right side can be any expression and it becomes the result of the assignment operation.
 
 .Example
-[source,go]
+`>>>` [blue]`a=15+1`
-----
+[green]`16`
-a=15+1    // returns 16
+
-----
 
 === Selector operator [blue]`? : ::`
 The _selector operator_ is very similar to the _switch/case/default_ statement available in many programming languages.
 
-.Syntax
+.Selector literal Syntax
-[source,bnf]
+_selector-operator_ = _select-expression_ "*?*" _selector-case_ { "*:*" _selector-case_ } ["*::*" _default-multi-expression_] +
-----
+_selector-case_ = [_match-list_] _case-value_ +
-<selector-operator> ::= <select-expression> "?" <selector-case> { ":" <selector-case> } ["::" <default-multi-expression>]
+_match-list_ = "*[*" _item_ {"*,*" _items_} "*]*" +
-<selector-case> ::= [<match-list>] <case-value>
+_item_ = _expression_ +
-<match-list> ::= "["<item>{","<items>}"]"
+_case-multi-expression_ = "*{*" _multi-expression_ "*}*" +
-<item> ::= <expression
+_multi-expression_ = _expression_ { "*;*" _expression_ } +
-<case-multi-expression> ::= "{" <multi-expression> "}"
+_default-multi-expression_ = _multi-expression_
-<multi-expression> ::= <expression> {";" <expression>}
-----
 
-In other words, the selector operator evaluates the expression (`<select-expression>`) on the left-hand side of the `?` symbol; it then compares the result obtained with the values listed in the `<match-list>`'s. If the comparision find a match with a value in a match-list, the associated  `<case-multi-expression>` is evaluted, and its result will be the final result of the selection operation.
+In other words, the selector operator evaluates the _select-expression_ on the left-hand side of the [blue]`?` symbol; it then compares the result obtained with the values listed in the __match-list__'s, from left to right. If the comparision finds a match with a value in a _match-list_, the associated _case-multi-expression_ is evaluted, and its result will be the final result of the selection operation.
 
-The match lists are optional. In that case, the position, from left to right, of the `<selector-case>` is used as match-list. Of course, that only works if the select-expression results in an integer.
+The match lists are optional. In that case, the position, from left to right, of the _selector-case_ is used as _match-list_. Of course, that only works if the _select-expression_ results in an integer.
-
-The `:` symbol (colon) is the separator of the selector-cases. Note that if the value of the select-expression does not match any match-list, an error will be issued. Therefore, it is strongly recommended to provide a default (multi-)expression introduced by the `::` symbol (double-colon). Also note that the default expression has no match-list.
 
+The [blue]`:` symbol (colon) is the separator of the selector-cases. Note that if the value of the _select-expression_ does not match any _match-list_, an error will be issued. Therefore, it is strongly recommended to provide a default (multi-)expression introduced by the [blue]`::` symbol (double-colon). Also note that the default expression has no _match-list_.
 
 .Examples
-[source,go]
+`>>>` [blue]`1 ? {"a"} : {"b"}` +
-----
+[green]`b` +
-1 ? {"a"} : {"b"}                           // returns "b"
+`>>>` [blue]`10 ? {"a"} : {"b"} :: {"c"}` +
-10 ? {"a"} : {"b"} :: {"c"}                 // returns "c"
+[green]`c' +
-10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}      // returns "b"
+[green]`>>>` [blue]`10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}` +
-10 ? {"a"} :[true, 2+8] {"b"} ::[10] {"c"}  // error:  "... case list in default clause"
+[green]`b` +
-10 ? {"a"} :[10] {x="b" but x} :: {"c"}     // returns "b"
+`>>>` [blue]`10 ? {"a"} :[true, 2+8] {"b"} ::[10] {"c"}` +
-10 ? {"a"} :[10] {x="b"; x} :: {"c"}        // returns "b"
+[red]`Parse Error: [1:34] case list in default clause` +
-10 ? {"a"} : {"b"}                          // error:  "... no case catches the value (10) of the selection expression
+[green]`>>>` [blue]`10 ? {"a"} :[10] {x="b" but x} :: {"c"}` +
-----
+[green]`b` +
+`>>>` [blue]`10 ? {"a"} :[10] {x="b"; x} :: {"c"}` +
+[green]`b` +
+`>>>` [blue]`10 ? {"a"} : {"b"}` +
+[red]`Eval Error: [1:3] no case catches the value (10) of the selection expression`
+
+
+=== Variable default value [blue]`??` and [blue]`?=`
+The left operand of these two operators must be a variable. The right operator can be any expression. They return the value of the variable if this is define; otherwise they return the value of the right expression.
+
+IMPORTANT: If the left variable is defined, the right expression is not evuated at all.
+
+The [blue]`??` do not change the status of the left variable.
+
+The [blue]`?=` assigns the calculated value of the right expression to the left variable.
+
+.Examples
+`>>>` [blue]`var ?? (1+2)`'
+[green]`3` +
+`>>>` [blue]`var` +
+[red]`Eval Error: undefined variable or function "var"` +
+`>>>` [blue]`var ?= (1+2)` +
+[green]`3` +
+`>>>` [blue]`var` +
+[green]`3`
+
+NOTE: These operators have a high priority, in particular higher than the operator [blue]`=`.
 
 == Priorities of operators
 The table below shows all supported operators by decreasing priorities.
 
 .Operators priorities
-[cols="^2,^2,^2,^5,^5"]
+[cols="^2,^2,^2,^5,^6"]
 |===
 | Priority | Operators     | Position | Operation | Operands and results
 
-.1+|*ITEM*| [blue]`.` | _Infix_ | _Item_| _collection_ `"."` _key_ -> _any_
+.2+|*ITEM*| [blue]`.` | _Infix_ | _List item_| _list_ `"."` _integer_ -> _any_
+| [blue]`.` | _Infix_ | _Dict item_ | _dict_ `"."` _any_ -> _any_
 .2+|*INC*| [blue]`++` | _Postfix_ | _Post increment_| _integer-variable_ `"++"` -> _integer_
 | [blue]`++` | _Postfix_ | _Next item_ | _iterator_ `"++"` -> _any_
 .1+|*FACT*| [blue]`!` | _Postfix_ | _Factorial_| _integer_ `"!"` -> _integer_
@@ -249,24 +589,29 @@ The table below shows all supported operators by decreasing priorities.
 | [blue]`/` | _Infix_ | _Division_ | _number_ `"/"` _number_ -> _number_
 | [blue]`./` | _Infix_ | _Float-division_ | __number__ `"./"` _number_ -> _float_
 | [blue]`%` | _Infix_ | _Integer-remainder_ | _integer_ `"%"` _integer_ -> _integer_
-.5+|*SUM*| [blue]`+` | _Infix_ | _Sum_ | _number_ `"+"` _number_ -> _number_
+.6+|*SUM*| [blue]`+` | _Infix_ | _Sum_ | _number_ `"+"` _number_ -> _number_
 | [blue]`+` | _Infix_ |  _String-concat_ | (_string_\|_number_) `"+"` (_string_\|_number_) -> _string_
 | [blue]`+` | _Infix_ |  _List-join_ | _list_ `"+"` _list_ -> _list_
+| [blue]`+` | _Infix_ |  _Dict-join_ | _dict_ `"+"` _dict_ -> _dict_
 | [blue]`-` | _Infix_ | _Subtraction_ | _number_ `"-"` _number_ -> _number_
 | [blue]`-` | _Infix_ | _List-difference_ | _list_ `"-"` _list_ -> _list_
-.6+|*RELATION*| [blue]`<` | _Infix_ | _less_ | _comparable_ `"<"` _comparable_ -> _boolean_
+.8+|*RELATION*| [blue]`<` | _Infix_ | _less_ | _comparable_ `"<"` _comparable_ -> _boolean_
 | [blue]`\<=` | _Infix_ |  _less-equal_ | _comparable_ `"\<="` _comparable_ -> _boolean_
 | [blue]`>` | _Infix_ |  _greater_ | _comparable_ `">"` _comparable_ -> _boolean_
 | [blue]`>=` | _Infix_ |  _greater-equal_ | _comparable_ `">="` _comparable_ -> _boolean_
 | [blue]`==` | _Infix_ |  _equal_ | _comparable_ `"=="` _comparable_ -> _boolean_
 | [blue]`!=` | _Infix_ |  _not-equal_ | _comparable_ `"!="` _comparable_ -> _boolean_
+| [blue]`in` | _Infix_ |  _member-of-list_ | _any_ `"in"` _list_ -> _boolean_
+| [blue]`in` | _Infix_ |  _key-of-dict_ | _any_ `"in"` _dict_ -> _boolean_
 .1+|*NOT*| [blue]`not` | _Prefix_ | _not_ | `"not"` _boolean_ -> _boolean_
 .2+|*AND*| [blue]`and` | _Infix_ | _and_ | _boolean_ `"and"` _boolean_ -> _boolean_
 | [blue]`&&` | _Infix_ | _and_ | _boolean_ `"&&"` _boolean_ -> _boolean_
 .2+|*OR*| [blue]`or` | _Infix_ | _or_ | _boolean_ `"or"` _boolean_ -> _boolean_
 | [blue]`\|\|` | _Infix_ | _or_ | _boolean_ `"\|\|"` _boolean_ -> _boolean_
-.1+|*ASSIGN*| [blue]`=` | _Infix_ | _assignment_ | _identifier_ "=" _any_ -> _any_
+.3+|*ASSIGN*| [blue]`=` | _Infix_ | _assignment_ | _identifier_ "=" _any_ -> _any_
-.1+|*BUT*| [blue]`but` | _Infix_ | _but_ | _any_ "but" _any_ -> _any_
+| [blue]`>>` | _Infix_ | _front-insert_ | _any_ ">>" _list_ -> _list_
+| [blue]`<<` | _Infix_ | _back-insert_ | _list_ "<<" _any_ -> _list_
+ .1+|*BUT*| [blue]`but` | _Infix_ | _but_ | _any_ "but" _any_ -> _any_
 |===
 
 == Functions

formatter.go

@@ -4,13 +4,62 @@
 // formatter.go
 package expr
 
+import "fmt"
+
 type FmtOpt uint16
 
 const (
 	TTY FmtOpt = 1 << iota
 	MultiLine
+	Truncate
+	Base2
+	Base8
+	Base10
+	Base16
 )
 
+const (
+	TruncateEllipsis = "(...)"
+	MinTruncateSize  = 10
+	TruncateSize     = MinTruncateSize + 15
+)
+
+func TruncateString(s string) (trunc string) {
+	finalPart := len(s) - (MinTruncateSize - len(TruncateEllipsis))
+	trunc = s[0:len(s)-MinTruncateSize] + TruncateEllipsis + s[finalPart:]
+	return
+}
+
 type Formatter interface {
 	ToString(options FmtOpt) string
 }
+
+func getFormatted(v any, opt FmtOpt) (text string) {
+	if v == nil {
+		text = "(nil)"
+	} else if s, ok := v.(string); ok {
+		text = s
+	} else if formatter, ok := v.(Formatter); ok {
+		text = formatter.ToString(opt)
+	} else {
+		text = fmt.Sprintf("%v", v)
+	}
+	return
+}
+
+type Typer interface {
+	TypeName() string
+}
+
+func getTypeName(v any) (name string) {
+	if typer, ok := v.(Typer); ok {
+		name = typer.TypeName()
+	} else if IsInteger(v) {
+		name = "integer"
+	} else if IsFloat(v) {
+		name = "float"
+	} else {
+		name = fmt.Sprintf("%T", v)
+	}
+	return
+}

fraction-type.go

@@ -0,0 +1,401 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// fraction-type.go
+package expr
+
+//https://www.youmath.it/lezioni/algebra-elementare/lezioni-di-algebra-e-aritmetica-per-scuole-medie/553-dalle-frazioni-a-numeri-decimali.html
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+)
+
+type FractionType struct {
+	num, den int64
+}
+
+func newFraction(num, den int64) *FractionType {
+	num, den = simplifyIntegers(num, den)
+	return &FractionType{num, den}
+}
+
+func float64ToFraction(f float64) (fract *FractionType, err error) {
+	var sign string
+	intPart, decPart := math.Modf(f)
+	if decPart < 0.0 {
+		sign = "-"
+		intPart = -intPart
+		decPart = -decPart
+	}
+	dec := fmt.Sprintf("%.12f", decPart)
+	s := fmt.Sprintf("%s%.f%s", sign, intPart, dec[1:])
+	// fmt.Printf("S: '%s'\n",s)
+	return makeGeneratingFraction(s)
+}
+
+// Based on https://cs.opensource.google/go/go/+/refs/tags/go1.22.3:src/math/big/rat.go;l=39
+/*
+func _float64ToFraction(f float64) (num, den int64, err error) {
+	const expMask = 1<<11 - 1
+	bits := math.Float64bits(f)
+	mantissa := bits & (1<<52 - 1)
+	exp := int((bits >> 52) & expMask)
+	switch exp {
+	case expMask: // non-finite
+		err = errors.New("infite")
+		return
+	case 0: // denormal
+		exp -= 1022
+	default: // normal
+		mantissa |= 1 << 52
+		exp -= 1023
+	}
+
+	shift := 52 - exp
+
+	// Optimization (?): partially pre-normalise.
+	for mantissa&1 == 0 && shift > 0 {
+		mantissa >>= 1
+		shift--
+	}
+
+	if f < 0 {
+		num = -int64(mantissa)
+	} else {
+		num = int64(mantissa)
+	}
+	den = int64(1)
+
+	if shift > 0 {
+		den = den << shift
+	} else {
+		num = num << (-shift)
+	}
+	return
+}
+*/
+
+func makeGeneratingFraction(s string) (f *FractionType, err error) {
+	var num, den int64
+	var sign int64 = 1
+	var parts []string
+	if len(s) == 0 {
+		goto exit
+	}
+	if s[0] == '-' {
+		sign = int64(-1)
+		s = s[1:]
+	} else if s[0] == '+' {
+		s = s[1:]
+	}
+	if strings.HasSuffix(s, "()") {
+		s = s[0 : len(s)-2]
+	}
+	parts = strings.SplitN(s, ".", 2)
+	if num, err = strconv.ParseInt(parts[0], 10, 64); err != nil {
+		return
+	}
+	if len(parts) == 1 {
+		f = newFraction(sign*num, 1)
+	} else if len(parts) == 2 {
+		subParts := strings.SplitN(parts[1], "(", 2)
+		if len(subParts) == 1 {
+			den = 1
+			dec := parts[1]
+			lsd := len(dec)
+			for i := lsd - 1; i >= 0 && dec[i] == '0'; i-- {
+				lsd--
+			}
+			for _, c := range dec[0:lsd] {
+				if c < '0' || c > '9' {
+					return nil, errExpectedGot("fract", "digit", c)
+				}
+				num = num*10 + int64(c-'0')
+				den = den * 10
+			}
+			f = newFraction(sign*num, den)
+		} else if len(subParts) == 2 {
+			sub := num
+			mul := int64(1)
+			for _, c := range subParts[0] {
+				if c < '0' || c > '9' {
+					return nil, errExpectedGot("fract", "digit", c)
+				}
+				num = num*10 + int64(c-'0')
+				sub = sub*10 + int64(c-'0')
+				mul *= 10
+			}
+			if len(subParts) == 2 {
+				if s[len(s)-1] != ')' {
+					goto exit
+				}
+				p := subParts[1][0 : len(subParts[1])-1]
+				for _, c := range p {
+					if c < '0' || c > '9' {
+						return nil, errExpectedGot("fract", "digit", c)
+					}
+					num = num*10 + int64(c-'0')
+					den = den*10 + 9
+				}
+				den *= mul
+			}
+			num -= sub
+			f = newFraction(sign*num, den)
+		}
+	}
+exit:
+	if f == nil {
+		err = errors.New("bad syntax")
+	}
+	return
+}
+
+func (f *FractionType) toFloat() float64 {
+	return float64(f.num) / float64(f.den)
+}
+
+func (f *FractionType) String() string {
+	return f.ToString(0)
+}
+
+func (f *FractionType) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	if opt&MultiLine == 0 {
+		sb.WriteString(fmt.Sprintf("%d|%d", f.num, f.den))
+	} else {
+		var s, num string
+		if f.num < 0 && opt&TTY == 0 {
+			num = strconv.FormatInt(-f.num, 10)
+			s = "-"
+		} else {
+			num = strconv.FormatInt(f.num, 10)
+		}
+		den := strconv.FormatInt(f.den, 10)
+		size := max(len(num), len(den))
+		if opt&TTY != 0 {
+			sb.WriteString(fmt.Sprintf("\x1b[4m%[1]*s\x1b[0m\n", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, s+num)))
+		} else {
+			if len(s) > 0 {
+				sb.WriteString("  ")
+			}
+			sb.WriteString(fmt.Sprintf("%[1]*s", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, num)))
+			sb.WriteByte('\n')
+			if len(s) > 0 {
+				sb.WriteString(s)
+				sb.WriteByte(' ')
+			}
+			sb.WriteString(strings.Repeat("-", size))
+			sb.WriteByte('\n')
+			if len(s) > 0 {
+				sb.WriteString("  ")
+			}
+		}
+		sb.WriteString(fmt.Sprintf("%[1]*s", -size, fmt.Sprintf("%[1]*s", (size+len(den))/2, den)))
+	}
+
+	return sb.String()
+}
+
+func (f *FractionType) TypeName() string {
+	return "fraction"
+}
+
+// -------- fraction utility functions
+
+// greatest common divider
+func gcd(a, b int64) (g int64) {
+	if a < 0 {
+		a = -a
+	}
+	if b < 0 {
+		b = -b
+	}
+	if a < b {
+		a, b = b, a
+	}
+	r := a % b
+	for r > 0 {
+		a, b = b, r
+		r = a % b
+	}
+	g = b
+	return
+}
+
+// lower common multiple
+func lcm(a, b int64) (l int64) {
+	g := gcd(a, b)
+	l = a * b / g
+	return
+}
+
+// Sum two fractions
+func sumFract(f1, f2 *FractionType) (sum *FractionType) {
+	m := lcm(f1.den, f2.den)
+	sum = newFraction(f1.num*(m/f1.den)+f2.num*(m/f2.den), m)
+	return
+}
+
+// Multiply two fractions
+func mulFract(f1, f2 *FractionType) (prod *FractionType) {
+	prod = newFraction(f1.num*f2.num, f1.den*f2.den)
+	return
+}
+
+func anyToFract(v any) (f *FractionType, err error) {
+	var ok bool
+	if f, ok = v.(*FractionType); !ok {
+		if n, ok := v.(int64); ok {
+			f = intToFraction(n)
+		}
+	}
+	if f == nil {
+		err = errExpectedGot("fract", typeFraction, v)
+	}
+	return
+}
+
+func anyPairToFract(v1, v2 any) (f1, f2 *FractionType, err error) {
+	if f1, err = anyToFract(v1); err != nil {
+		return
+	}
+	if f2, err = anyToFract(v2); err != nil {
+		return
+	}
+	return
+}
+
+func sumAnyFract(af1, af2 any) (sum any, err error) {
+	var f1, f2 *FractionType
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	f := sumFract(f1, f2)
+	if f.num == 0 {
+		sum = 0
+	} else {
+		sum = simplifyFraction(f)
+	}
+	return
+}
+
+// Returns
+//
+//		 <0 if af1 < af2
+//		 =0 if af1 == af2
+//		 >0 if af1 > af2
+//	 err if af1 or af2 is not convertible to fraction
+func cmpAnyFract(af1, af2 any) (result int, err error) {
+	var f1, f2 *FractionType
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	result = cmpFract(f1, f2)
+	return
+}
+
+// Returns
+//
+//	<0 if af1 < af2
+//	=0 if af1 == af2
+//	>0 if af1 > af2
+func cmpFract(f1, f2 *FractionType) (result int) {
+	f2.num = -f2.num
+	f := sumFract(f1, f2)
+	if f.num < 0 {
+		result = -1
+	} else if f.num > 0 {
+		result = 1
+	} else {
+		result = 0
+	}
+	return
+}
+
+func subAnyFract(af1, af2 any) (sum any, err error) {
+	var f1, f2 *FractionType
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	f2.num = -f2.num
+	f := sumFract(f1, f2)
+	if f.num == 0 {
+		sum = 0
+	} else {
+		sum = simplifyFraction(f)
+	}
+	return
+}
+
+func mulAnyFract(af1, af2 any) (prod any, err error) {
+	var f1, f2 *FractionType
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	if f1.num == 0 || f2.num == 0 {
+		prod = 0
+	} else {
+		f := &FractionType{f1.num * f2.num, f1.den * f2.den}
+		prod = simplifyFraction(f)
+	}
+	return
+}
+
+func divAnyFract(af1, af2 any) (quot any, err error) {
+	var f1, f2 *FractionType
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	if f2.num == 0 {
+		err = errors.New("division by zero")
+		return
+		return
+	}
+	if f1.num == 0 || f2.den == 0 {
+		quot = 0
+	} else {
+		f := &FractionType{f1.num * f2.den, f1.den * f2.num}
+		quot = simplifyFraction(f)
+	}
+	return
+}
+
+func simplifyFraction(f *FractionType) (v any) {
+	f.num, f.den = simplifyIntegers(f.num, f.den)
+	if f.den == 1 {
+		v = f.num
+	} else {
+		v = &FractionType{f.num, f.den}
+	}
+	return v
+}
+
+func simplifyIntegers(num, den int64) (a, b int64) {
+	if num == 0 {
+		return 0, 1
+	}
+	if den == 0 {
+		panic("fraction with denominator == 0")
+	}
+	if den < 0 {
+		den = -den
+		num = -num
+	}
+	g := gcd(num, den)
+	a = num / g
+	b = den / g
+	return
+}
+
+func intToFraction(n int64) *FractionType {
+	return &FractionType{n, 1}
+}
+
+func isFraction(v any) (ok bool) {
+	_, ok = v.(*FractionType)
+	return ok
+}

func-base.go

@@ -10,16 +10,69 @@ import (
 )
 
 func isNilFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	if len(args) == 1 {
 	result = args[0] == nil
-	} else {
+	return
-		err = errOneParam(name)
+}
+
+func isIntFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsInteger(args[0])
+	return
+}
+
+func isFloatFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsFloat(args[0])
+	return
+}
+
+func isBoolFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsBool(args[0])
+	return
+}
+
+func isStringFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsString(args[0])
+	return
+}
+
+func isFractionFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsFract(args[0])
+	return
+}
+
+func isRationalFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsRational(args[0])
+	return
+}
+
+func isListFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsList(args[0])
+	return
+}
+
+func isDictionaryFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsDict(args[0])
+	return
+}
+
+func boolFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	switch v := args[0].(type) {
+	case int64:
+		result = (v != 0)
+	case *FractionType:
+		result = v.num != 0
+	case float64:
+		result = v != 0.0
+	case bool:
+		result = v
+	case string:
+		result = len(v) > 0
+	default:
+		err = errCantConvert(name, v, "bool")
 	}
 	return
 }
 
 func intFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	if len(args) == 1 {
 	switch v := args[0].(type) {
 	case int64:
 		result = v
@@ -39,8 +92,63 @@ func intFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	default:
 		err = errCantConvert(name, v, "int")
 	}
+	return
+}
+
+func decFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	switch v := args[0].(type) {
+	case int64:
+		result = float64(v)
+	case float64:
+		result = v
+	case bool:
+		if v {
+			result = float64(1)
 		} else {
-		err = errOneParam(name)
+			result = float64(0)
+		}
+	case string:
+		var f float64
+		if f, err = strconv.ParseFloat(v, 64); err == nil {
+			result = f
+		}
+	case *FractionType:
+		result = v.toFloat()
+	default:
+		err = errCantConvert(name, v, "float")
+	}
+	return
+}
+
+func fractFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	switch v := args[0].(type) {
+	case int64:
+		var den int64 = 1
+		if len(args) > 1 {
+			var ok bool
+			if den, ok = args[1].(int64); !ok {
+				err = errExpectedGot(name, "integer", args[1])
+			} else if den == 0 {
+				err = errDivisionByZero(name)
+			}
+		}
+		if err == nil {
+			result = newFraction(v, den)
+		}
+	case float64:
+		result, err = float64ToFraction(v)
+	case bool:
+		if v {
+			result = newFraction(1, 1)
+		} else {
+			result = newFraction(0, 1)
+		}
+	case string:
+		result, err = makeGeneratingFraction(v)
+	case *FractionType:
+		result = v
+	default:
+		err = errCantConvert(name, v, "float")
 	}
 	return
 }
@@ -50,8 +158,27 @@ func iteratorFunc(ctx ExprContext, name string, args []any) (result any, err err
 }
 
 func ImportBuiltinsFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("isNil", &simpleFunctor{f: isNilFunc}, 1, -1)
+	anyParams := []ExprFuncParam{
-	ctx.RegisterFunc("int", &simpleFunctor{f: intFunc}, 1, -1)
+		newFuncParam(paramValue),
+	}
+
+	ctx.RegisterFunc("isNil", newGolangFunctor(isNilFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("isInt", newGolangFunctor(isIntFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("isFloat", newGolangFunctor(isFloatFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("isBool", newGolangFunctor(isBoolFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("isString", newGolangFunctor(isStringFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("isFract", newGolangFunctor(isFractionFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("isRational", newGolangFunctor(isRationalFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("isList", newGolangFunctor(isListFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("isDict", newGolangFunctor(isDictionaryFunc), typeBoolean, anyParams)
+
+	ctx.RegisterFunc("bool", newGolangFunctor(boolFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("int", newGolangFunctor(intFunc), typeInt, anyParams)
+	ctx.RegisterFunc("dec", newGolangFunctor(decFunc), typeFloat, anyParams)
+	ctx.RegisterFunc("fract", newGolangFunctor(fractFunc), typeFraction, []ExprFuncParam{
+		newFuncParam(paramValue),
+		newFuncParamFlagDef("denominator", pfOptional, 1),
+	})
 }
 
 func init() {

func-import.go

@@ -35,7 +35,7 @@ func importGeneral(ctx ExprContext, name string, args []any) (result any, err er
 }
 
 func checkStringParamExpected(funcName string, paramValue any, paramPos int) (err error) {
-	if !(isString(paramValue) /*|| isList(paramValue)*/) {
+	if !(IsString(paramValue) /*|| isList(paramValue)*/) {
 		err = fmt.Errorf("%s(): param nr %d has wrong type %T, string expected", funcName, paramPos+1, paramValue)
 	}
 	return
@@ -137,8 +137,12 @@ func doImport(ctx ExprContext, name string, dirList []string, it Iterator) (resu
 }
 
 func ImportImportFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("import", &simpleFunctor{f: importFunc}, 1, -1)
+	ctx.RegisterFunc("import", newGolangFunctor(importFunc), typeAny, []ExprFuncParam{
-	ctx.RegisterFunc("importAll", &simpleFunctor{f: importAllFunc}, 1, -1)
+		newFuncParamFlag(typeFilepath, pfRepeat),
+	})
+	ctx.RegisterFunc("importAll", newGolangFunctor(importAllFunc), typeAny, []ExprFuncParam{
+		newFuncParamFlag(typeFilepath, pfRepeat),
+	})
 }
 
 func init() {

func-math.go

@@ -10,7 +10,7 @@ import (
 )
 
 func checkNumberParamExpected(funcName string, paramValue any, paramPos, level, subPos int) (err error) {
-	if !(isNumber(paramValue) || isFraction(paramValue)) /*|| isList(paramValue)*/ {
+	if !(IsNumber(paramValue) || isFraction(paramValue)) /*|| isList(paramValue)*/ {
 		err = fmt.Errorf("%s(): param nr %d (%d in %d) has wrong type %T, number expected",
 			funcName, paramPos+1, subPos+1, level, paramValue)
 	}
@@ -21,7 +21,7 @@ func doAdd(ctx ExprContext, name string, it Iterator, count, level int) (result
 	var sumAsFloat, sumAsFract bool
 	var floatSum float64 = 0.0
 	var intSum int64 = 0
-	var fractSum *fraction
+	var fractSum *FractionType
 	var v any
 
 	level++
@@ -45,7 +45,7 @@ func doAdd(ctx ExprContext, name string, it Iterator, count, level int) (result
 		count++
 
 		if !sumAsFloat {
-			if isFloat(v) {
+			if IsFloat(v) {
 				sumAsFloat = true
 				if sumAsFract {
 					floatSum = fractSum.toFloat()
@@ -61,9 +61,9 @@ func doAdd(ctx ExprContext, name string, it Iterator, count, level int) (result
 		if sumAsFloat {
 			floatSum += numAsFloat(v)
 		} else if sumAsFract {
-			var item *fraction
+			var item *FractionType
 			var ok bool
-			if item, ok = v.(*fraction); !ok {
+			if item, ok = v.(*FractionType); !ok {
 				iv, _ := v.(int64)
 				item = newFraction(iv, 1)
 			}
@@ -95,7 +95,7 @@ func doMul(ctx ExprContext, name string, it Iterator, count, level int) (result
 	var mulAsFloat, mulAsFract bool
 	var floatProd float64 = 1.0
 	var intProd int64 = 1
-	var fractProd *fraction
+	var fractProd *FractionType
 	var v any
 
 	level++
@@ -120,7 +120,7 @@ func doMul(ctx ExprContext, name string, it Iterator, count, level int) (result
 		count++
 
 		if !mulAsFloat {
-			if isFloat(v) {
+			if IsFloat(v) {
 				mulAsFloat = true
 				if mulAsFract {
 					floatProd = fractProd.toFloat()
@@ -136,9 +136,9 @@ func doMul(ctx ExprContext, name string, it Iterator, count, level int) (result
 		if mulAsFloat {
 			floatProd *= numAsFloat(v)
 		} else if mulAsFract {
-			var item *fraction
+			var item *FractionType
 			var ok bool
-			if item, ok = v.(*fraction); !ok {
+			if item, ok = v.(*FractionType); !ok {
 				iv, _ := v.(int64)
 				item = newFraction(iv, 1)
 			}
@@ -167,8 +167,13 @@ func mulFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 }
 
 func ImportMathFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("add", &simpleFunctor{f: addFunc}, 0, -1)
+	ctx.RegisterFunc("add", &golangFunctor{f: addFunc}, typeNumber, []ExprFuncParam{
-	ctx.RegisterFunc("mul", &simpleFunctor{f: mulFunc}, 0, -1)
+		newFuncParamFlagDef(paramValue, pfOptional|pfRepeat, 0),
+	})
+
+	ctx.RegisterFunc("mul", &golangFunctor{f: mulFunc}, typeNumber, []ExprFuncParam{
+		newFuncParamFlagDef(paramValue, pfOptional|pfRepeat, 1),
+	})
 }
 
 func init() {

func-os.go

@@ -158,12 +158,26 @@ func readFileFunc(ctx ExprContext, name string, args []any) (result any, err err
 }
 
 func ImportOsFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("openFile", &simpleFunctor{f: openFileFunc}, 1, 1)
+	ctx.RegisterFunc("openFile", newGolangFunctor(openFileFunc), typeHandle, []ExprFuncParam{
-	ctx.RegisterFunc("appendFile", &simpleFunctor{f: appendFileFunc}, 1, 1)
+		newFuncParam(typeFilepath),
-	ctx.RegisterFunc("createFile", &simpleFunctor{f: createFileFunc}, 1, 1)
+	})
-	ctx.RegisterFunc("writeFile", &simpleFunctor{f: writeFileFunc}, 1, -1)
+	ctx.RegisterFunc("appendFile", newGolangFunctor(appendFileFunc), typeHandle, []ExprFuncParam{
-	ctx.RegisterFunc("readFile", &simpleFunctor{f: readFileFunc}, 1, 2)
+		newFuncParam(typeFilepath),
-	ctx.RegisterFunc("closeFile", &simpleFunctor{f: closeFileFunc}, 1, 1)
+	})
+	ctx.RegisterFunc("createFile", newGolangFunctor(createFileFunc), typeHandle, []ExprFuncParam{
+		newFuncParam(typeFilepath),
+	})
+	ctx.RegisterFunc("writeFile", newGolangFunctor(writeFileFunc), typeInt, []ExprFuncParam{
+		newFuncParam(typeHandle),
+		newFuncParamFlagDef(typeItem, pfOptional|pfRepeat, ""),
+	})
+	ctx.RegisterFunc("readFile", newGolangFunctor(readFileFunc), typeString, []ExprFuncParam{
+		newFuncParam(typeHandle),
+		newFuncParamFlagDef("limitCh", pfOptional, "\\n"),
+	})
+	ctx.RegisterFunc("closeFile", newGolangFunctor(closeFileFunc), typeBoolean, []ExprFuncParam{
+		newFuncParam(typeHandle),
+	})
 }
 
 func init() {

func-string.go

@@ -5,6 +5,7 @@
 package expr
 
 import (
+	"fmt"
 	"io"
 	"strings"
 )
@@ -32,9 +33,9 @@ func doJoinStr(funcName string, sep string, it Iterator) (result any, err error)
 }
 
 func joinStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	if len(args) < 1 {
+	//	if len(args) < 1 {
-		return nil, errMissingRequiredParameter(name, paramSeparator)
+	//		return nil, errMissingRequiredParameter(name, paramSeparator)
-	}
+	//	}
 	if sep, ok := args[0].(string); ok {
 		if len(args) == 1 {
 			result = ""
@@ -61,9 +62,6 @@ func subStrFunc(ctx ExprContext, name string, args []any) (result any, err error
 	var source string
 	var ok bool
 
-	if len(args) < 1 {
-		return nil, errMissingRequiredParameter(name, paramSource)
-	}
 	if source, ok = args[0].(string); !ok {
 		return nil, errWrongParamType(name, paramSource, typeString, args[0])
 	}
@@ -92,9 +90,6 @@ func trimStrFunc(ctx ExprContext, name string, args []any) (result any, err erro
 	var source string
 	var ok bool
 
-	if len(args) < 1 {
-		return nil, errMissingRequiredParameter(name, paramSource)
-	}
 	if source, ok = args[0].(string); !ok {
 		return nil, errWrongParamType(name, paramSource, typeString, args[0])
 	}
@@ -102,13 +97,122 @@ func trimStrFunc(ctx ExprContext, name string, args []any) (result any, err erro
 	return
 }
 
+func startsWithStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var source string
+	var ok bool
+
+	result = false
+
+	if source, ok = args[0].(string); !ok {
+		return result, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	for i, targetSpec := range args[1:] {
+		if target, ok := targetSpec.(string); ok {
+			if strings.HasPrefix(source, target) {
+				result = true
+				break
+			}
+		} else {
+			err = fmt.Errorf("target item nr %d is %T, expected string", i+1, targetSpec)
+			break
+		}
+	}
+	return
+}
+
+func endsWithStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var source string
+	var ok bool
+
+	result = false
+
+	if source, ok = args[0].(string); !ok {
+		return result, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	for i, targetSpec := range args[1:] {
+		if target, ok := targetSpec.(string); ok {
+			if strings.HasSuffix(source, target) {
+				result = true
+				break
+			}
+		} else {
+			err = fmt.Errorf("target item nr %d is %T, expected string", i+1, targetSpec)
+			break
+		}
+	}
+	return
+}
+
+func splitStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var source, sep string
+	var count int = -1
+	var parts []string
+	var ok bool
+
+	if source, ok = args[0].(string); !ok {
+		return result, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	if len(args) >= 2 {
+		if sep, ok = args[1].(string); !ok {
+			return nil, fmt.Errorf("separator param must be string, got %T (%v)", args[1], args[1])
+		}
+		if len(args) >= 3 {
+			if count64, ok := args[2].(int64); ok { // TODO replace type assertion with toInt()
+				count = int(count64)
+			} else {
+				return nil, fmt.Errorf("part count must be integer, got %T (%v)", args[2], args[2])
+			}
+		}
+	}
+	if count > 0 {
+		parts = strings.SplitN(source, sep, count)
+	} else if count < 0 {
+		parts = strings.Split(source, sep)
+	} else {
+		parts = []string{}
+	}
+	list := make(ListType, len(parts))
+	for i, part := range parts {
+		list[i] = part
+	}
+	result = &list
+	return
+}
+
 // --- End of function definitions
 
 // Import above functions in the context
 func ImportStringFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("joinStr", &simpleFunctor{f: joinStrFunc}, 1, -1)
+	ctx.RegisterFunc("joinStr", newGolangFunctor(joinStrFunc), typeString, []ExprFuncParam{
-	ctx.RegisterFunc("subStr", &simpleFunctor{f: subStrFunc}, 1, -1)
+		newFuncParam(paramSeparator),
-	ctx.RegisterFunc("trimStr", &simpleFunctor{f: trimStrFunc}, 1, -1)
+		newFuncParamFlagDef(paramItem, pfOptional|pfRepeat, ""),
+	})
+
+	ctx.RegisterFunc("subStr", newGolangFunctor(subStrFunc), typeString, []ExprFuncParam{
+		newFuncParam(paramSource),
+		newFuncParamFlagDef(paramStart, pfOptional, 0),
+		newFuncParamFlagDef(paramCount, pfOptional, -1),
+	})
+
+	ctx.RegisterFunc("splitStr", newGolangFunctor(splitStrFunc), "list of "+typeString, []ExprFuncParam{
+		newFuncParam(paramSource),
+		newFuncParamFlagDef(paramSeparator, pfOptional, ""),
+		newFuncParamFlagDef(paramCount, pfOptional, -1),
+	})
+
+	ctx.RegisterFunc("trimStr", newGolangFunctor(trimStrFunc), typeString, []ExprFuncParam{
+		newFuncParam(paramSource),
+	})
+
+	ctx.RegisterFunc("startsWithStr", newGolangFunctor(startsWithStrFunc), typeBoolean, []ExprFuncParam{
+		newFuncParam(paramSource),
+		newFuncParamFlag(paramPrefix, pfRepeat),
+	})
+
+	ctx.RegisterFunc("endsWithStr", newGolangFunctor(endsWithStrFunc), typeBoolean, []ExprFuncParam{
+		newFuncParam(paramSource),
+		newFuncParamFlag(paramSuffix, pfRepeat),
+	})
 }
 
 // Register the import function in the import-register.

funcs_test.go

@@ -1,45 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// funcs_test.go
-package expr
-
-import (
-	"errors"
-	"testing"
-)
-
-func TestFuncs(t *testing.T) {
-	inputs := []inputType{
-		/*   1 */ {`isNil(nil)`, true, nil},
-		/*   2 */ {`v=nil; isNil(v)`, true, nil},
-		/*   3 */ {`v=5; isNil(v)`, false, nil},
-		/*   4 */ {`int(true)`, int64(1), nil},
-		/*   5 */ {`int(false)`, int64(0), nil},
-		/*   6 */ {`int(3.1)`, int64(3), nil},
-		/*   7 */ {`int(3.9)`, int64(3), nil},
-		/*   8 */ {`int("432")`, int64(432), nil},
-		/*   9 */ {`int("1.5")`, nil, errors.New(`strconv.Atoi: parsing "1.5": invalid syntax`)},
-		/*  10 */ {`int("432", 4)`, nil, errors.New(`int() requires exactly one param`)},
-		/*  11 */ {`int(nil)`, nil, errors.New(`int() can't convert <nil> to int`)},
-		/*  12 */ {`two=func(){2}; two()`, int64(2), nil},
-		/*  13 */ {`double=func(x) {2*x}; (double(3))`, int64(6), nil},
-		/*  14 */ {`double=func(x){2*x}; double(3)`, int64(6), nil},
-		/*  15 */ {`double=func(x){2*x}; a=5; double(3+a) + 1`, int64(17), nil},
-		/*  16 */ {`double=func(x){2*x}; a=5; two=func() {2}; (double(3+a) + 1) * two()`, int64(34), nil},
-		/*  17 */ {`builtin "import"; import("./test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
-		/*  18 */ {`builtin "import"; import("test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
-		/*  19 */ {`@x="hello"; @x`, nil, errors.New(`[1:3] variable references are not allowed in top level expressions: "@x"`)},
-		/*  20 */ {`f=func(){@x="hello"}; f(); x`, "hello", nil},
-		/*  21 */ {`f=func(@y){@y=@y+1}; f(2); y`, int64(3), nil},
-		/*  22 */ {`f=func(@y){g=func(){@x=5}; @y=@y+g()}; f(2); y+x`, nil, errors.New(`undefined variable or function "x"`)},
-		/*  23 */ {`f=func(@y){g=func(){@x=5}; @z=g(); @y=@y+@z}; f(2); y+z`, int64(12), nil},
-		/*  24 */ {`f=func(@y){g=func(){@x=5}; g(); @z=x; @y=@y+@z}; f(2); y+z`, int64(12), nil},
-		/*  25 */ {`f=func(@y){g=func(){@x=5}; g(); @z=x; @x=@y+@z}; f(2); y+x`, int64(9), nil},
-		/*  26 */ {`builtin "import"; importAll("./test-funcs.expr"); six()`, int64(6), nil},
-		/*  27 */ {`builtin "import"; import("./sample-export-all.expr"); six()`, int64(6), nil},
-	}
-
-	// parserTest(t, "Func", inputs[25:26])
-	parserTest(t, "Func", inputs)
-}

function.go

@@ -0,0 +1,237 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// function.go
+package expr
+
+import (
+	"fmt"
+	"strings"
+)
+
+// ---- Function template
+type FuncTemplate func(ctx ExprContext, name string, args []any) (result any, err error)
+
+// ---- Common functor definition
+type baseFunctor struct {
+	info ExprFunc
+}
+
+func (functor *baseFunctor) ToString(opt FmtOpt) (s string) {
+	if functor.info != nil {
+		s = functor.info.ToString(opt)
+	} else {
+		s = "func() {<body>}"
+	}
+	return s
+}
+
+func (functor *baseFunctor) SetFunc(info ExprFunc) {
+	functor.info = info
+}
+
+func (functor *baseFunctor) GetFunc() ExprFunc {
+	return functor.info
+}
+
+// ---- Linking with Go functions
+type golangFunctor struct {
+	baseFunctor
+	f FuncTemplate
+}
+
+func newGolangFunctor(f FuncTemplate) *golangFunctor {
+	return &golangFunctor{f: f}
+}
+
+func (functor *golangFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
+	return functor.f(ctx, name, args)
+}
+
+// ---- Linking with Expr functions
+type exprFunctor struct {
+	baseFunctor
+	params []string
+	expr   Expr
+	defCtx ExprContext
+}
+
+func newExprFunctor(e Expr, params []string, ctx ExprContext) *exprFunctor {
+	return &exprFunctor{expr: e, params: params, defCtx: ctx}
+}
+
+func (functor *exprFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
+	if functor.defCtx != nil {
+		ctx.Merge(functor.defCtx)
+	}
+
+	for i, p := range functor.params {
+		if i < len(args) {
+			arg := args[i]
+			if funcArg, ok := arg.(Functor); ok {
+				// ctx.RegisterFunc(p, functor, 0, -1)
+				ctx.RegisterFunc(p, funcArg, typeAny, []ExprFuncParam{
+					newFuncParam(paramValue),
+				})
+			} else {
+				ctx.UnsafeSetVar(p, arg)
+			}
+		} else {
+			ctx.UnsafeSetVar(p, nil)
+		}
+	}
+	result, err = functor.expr.eval(ctx, false)
+	return
+}
+
+// ---- Function Parameters
+type paramFlags uint16
+
+const (
+	pfOptional paramFlags = 1 << iota
+	pfRepeat
+)
+
+type funcParamInfo struct {
+	name         string
+	flags        paramFlags
+	defaultValue any
+}
+
+func newFuncParam(name string) ExprFuncParam {
+	return &funcParamInfo{name: name}
+}
+
+func newFuncParamFlag(name string, flags paramFlags) ExprFuncParam {
+	return &funcParamInfo{name: name, flags: flags}
+}
+
+func newFuncParamFlagDef(name string, flags paramFlags, defValue any) *funcParamInfo {
+	return &funcParamInfo{name: name, flags: flags, defaultValue: defValue}
+}
+
+func (param *funcParamInfo) Name() string {
+	return param.name
+}
+
+func (param *funcParamInfo) Type() string {
+	return "any"
+}
+
+func (param *funcParamInfo) IsOptional() bool {
+	return (param.flags & pfOptional) != 0
+}
+
+func (param *funcParamInfo) IsRepeat() bool {
+	return (param.flags & pfRepeat) != 0
+}
+
+func (param *funcParamInfo) DefaultValue() any {
+	return param.defaultValue
+}
+
+// --- Functions
+type funcInfo struct {
+	name       string
+	minArgs    int
+	maxArgs    int
+	functor    Functor
+	params     []ExprFuncParam
+	returnType string
+}
+
+func newFuncInfo(name string, functor Functor, returnType string, params []ExprFuncParam) (info *funcInfo, err error) {
+	var minArgs = 0
+	var maxArgs = 0
+	if params != nil {
+		for _, p := range params {
+			if maxArgs == -1 {
+				return nil, fmt.Errorf("no more params can be specified after the ellipsis symbol: %q", p.Name())
+			}
+			if p.IsOptional() {
+				maxArgs++
+			} else if maxArgs == minArgs {
+				minArgs++
+				maxArgs++
+			} else {
+				return nil, fmt.Errorf("can't specify non-optional param after optional ones: %q", p.Name())
+			}
+			if p.IsRepeat() {
+				maxArgs = -1
+			}
+		}
+	}
+	info = &funcInfo{
+		name: name, minArgs: minArgs, maxArgs: maxArgs, functor: functor, returnType: returnType, params: params,
+	}
+	functor.SetFunc(info)
+	return info, nil
+}
+
+func newUnnamedFuncInfo(functor Functor, returnType string, params []ExprFuncParam) (info *funcInfo, err error) {
+	return newFuncInfo("unnamed", functor, returnType, params)
+}
+
+func (info *funcInfo) Params() []ExprFuncParam {
+	return info.params
+}
+
+func (info *funcInfo) ReturnType() string {
+	return info.returnType
+}
+
+func (info *funcInfo) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	if len(info.Name()) == 0 {
+		sb.WriteString("func")
+	} else {
+		sb.WriteString(info.Name())
+	}
+	sb.WriteByte('(')
+	if info.params != nil {
+		for i, p := range info.params {
+			if i > 0 {
+				sb.WriteString(", ")
+			}
+			sb.WriteString(p.Name())
+
+			if p.IsOptional() {
+				sb.WriteByte('=')
+				if s, ok := p.DefaultValue().(string); ok {
+					sb.WriteByte('"')
+					sb.WriteString(s)
+					sb.WriteByte('"')
+				} else {
+					sb.WriteString(fmt.Sprintf("%v", p.DefaultValue()))
+				}
+			}
+		}
+	}
+	if info.maxArgs < 0 {
+		sb.WriteString(" ...")
+	}
+	sb.WriteString("): ")
+	if len(info.returnType) > 0 {
+		sb.WriteString(info.returnType)
+	} else {
+		sb.WriteString(typeAny)
+	}
+	sb.WriteString(" {<body>}")
+	return sb.String()
+}
+
+func (info *funcInfo) Name() string {
+	return info.name
+}
+
+func (info *funcInfo) MinArgs() int {
+	return info.minArgs
+}
+
+func (info *funcInfo) MaxArgs() int {
+	return info.maxArgs
+}
+
+func (info *funcInfo) Functor() Functor {
+	return info.functor
+}

global-context.go

@@ -0,0 +1,55 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// global-context.go
+package expr
+
+import "path/filepath"
+
+var globalCtx *SimpleStore
+
+func ImportInContext(name string) (exists bool) {
+	var mod *module
+	if mod, exists = moduleRegister[name]; exists {
+		mod.importFunc(globalCtx)
+		mod.imported = true
+	}
+	return
+}
+
+func ImportInContextByGlobPattern(pattern string) (count int, err error) {
+	var matched bool
+	for name, mod := range moduleRegister {
+		if matched, err = filepath.Match(pattern, name); err == nil {
+			if matched {
+				count++
+				mod.importFunc(globalCtx)
+				mod.imported = true
+			}
+		} else {
+			break
+		}
+	}
+	return
+}
+
+func GetVar(ctx ExprContext, name string) (value any, exists bool) {
+	if value, exists = ctx.GetVar(name); !exists {
+		value, exists = globalCtx.GetVar(name)
+	}
+	return
+}
+
+func GetFuncInfo(ctx ExprContext, name string) (item ExprFunc, exists bool, ownerCtx ExprContext) {
+	if item, exists = ctx.GetFuncInfo(name); exists {
+		ownerCtx = ctx
+	} else if item, exists = globalCtx.GetFuncInfo(name); exists {
+		ownerCtx = globalCtx
+	}
+	return
+}
+
+func init() {
+	globalCtx = NewSimpleStore()
+	ImportBuiltinsFuncs(globalCtx)
+}

helpers.go

@@ -34,12 +34,15 @@ func EvalStringA(source string, args ...Arg) (result any, err error) {
 }
 
 func EvalStringV(source string, args []Arg) (result any, err error) {
-	ctx := NewSimpleFuncStore()
+	ctx := NewSimpleStore()
 	for _, arg := range args {
 		if isFunc(arg.Value) {
 			if f, ok := arg.Value.(FuncTemplate); ok {
-				functor := &simpleFunctor{f: f}
+				functor := newGolangFunctor(f)
-				ctx.RegisterFunc(arg.Name, functor, 0, -1)
+				// ctx.RegisterFunc(arg.Name, functor, 0, -1)
+				ctx.RegisterFunc(arg.Name, functor, typeAny, []ExprFuncParam{
+					newFuncParamFlagDef(paramValue, pfOptional|pfRepeat, 0),
+				})
 			} else {
 				err = fmt.Errorf("invalid function specification: %q", arg.Name)
 			}

list-type.go

@@ -0,0 +1,149 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// list-type.go
+package expr
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+type ListType []any
+
+func newListA(listAny ...any) (list *ListType) {
+	return newList(listAny)
+}
+
+func newList(listAny []any) (list *ListType) {
+	if listAny != nil {
+		ls := make(ListType, len(listAny))
+		for i, item := range listAny {
+			ls[i] = item
+		}
+		list = &ls
+	}
+	return
+}
+
+func (ls *ListType) ToString(opt FmtOpt) (s string) {
+	var sb strings.Builder
+	sb.WriteByte('[')
+	if len(*ls) > 0 {
+		if opt&MultiLine != 0 {
+			sb.WriteString("\n  ")
+		}
+		for i, item := range []any(*ls) {
+			if i > 0 {
+				if opt&MultiLine != 0 {
+					sb.WriteString(",\n  ")
+				} else {
+					sb.WriteString(", ")
+				}
+			}
+			if s, ok := item.(string); ok {
+				sb.WriteByte('"')
+				sb.WriteString(s)
+				sb.WriteByte('"')
+			} else {
+				sb.WriteString(fmt.Sprintf("%v", item))
+			}
+		}
+		if opt&MultiLine != 0 {
+			sb.WriteByte('\n')
+		}
+	}
+	sb.WriteByte(']')
+	s = sb.String()
+	if opt&Truncate != 0 && len(s) > TruncateSize {
+		s = TruncateString(s)
+	}
+	return
+}
+
+func (ls *ListType) String() string {
+	return ls.ToString(0)
+}
+
+func (ls *ListType) TypeName() string {
+	return "list"
+}
+
+func (list *ListType) indexDeepCmp(target any) (index int) {
+	index = -1
+	for i, item := range *list {
+		if reflect.DeepEqual(item, target) {
+			index = i
+			break
+		}
+	}
+	return
+}
+
+func (ls *ListType) contains(t *ListType) (answer bool) {
+	if len(*ls) >= len(*t) {
+		answer = true
+		for _, item := range *t {
+			if answer = ls.indexDeepSameCmp(item) >= 0; !answer {
+				break
+			}
+		}
+	}
+	return
+}
+
+func (list *ListType) indexDeepSameCmp(target any) (index int) {
+	var eq bool
+	var err error
+	index = -1
+	for i, item := range *list {
+		if eq, err = deepSame(item, target, sameContent); err != nil {
+			break
+		} else if eq {
+			index = i
+			break
+		}
+	}
+	return
+}
+
+func sameContent(a, b any) (same bool, err error) {
+	la, _ := a.(*ListType)
+	lb, _ := b.(*ListType)
+	if len(*la) == len(*lb) {
+		same = true
+		for _, item := range *la {
+			if pos := lb.indexDeepSameCmp(item); pos < 0 {
+				same = false
+				break
+			}
+		}
+	}
+	return
+}
+
+func deepSame(a, b any, deepCmp deepFuncTemplate) (eq bool, err error) {
+	if isNumOrFract(a) && isNumOrFract(b) {
+		if IsNumber(a) && IsNumber(b) {
+			if IsInteger(a) && IsInteger(b) {
+				li, _ := a.(int64)
+				ri, _ := b.(int64)
+				eq = li == ri
+			} else {
+				eq = numAsFloat(a) == numAsFloat(b)
+			}
+		} else {
+			var cmp int
+			if cmp, err = cmpAnyFract(a, b); err == nil {
+				eq = cmp == 0
+			}
+		}
+	} else if deepCmp != nil && IsList(a) && IsList(b) {
+		eq, err = deepCmp(a, b)
+	} else {
+		eq = reflect.DeepEqual(a, b)
+	}
+
+	return
+}

module-register.go

@@ -6,7 +6,6 @@ package expr
 
 import (
 	"fmt"
-	"path/filepath"
 )
 
 type module struct {
@@ -31,30 +30,30 @@ func registerImport(name string, importFunc func(ExprContext), description strin
 	moduleRegister[name] = newModule(importFunc, description)
 }
 
-func ImportInContext(ctx ExprContext, name string) (exists bool) {
+// func ImportInContext(ctx ExprContext, name string) (exists bool) {
-	var mod *module
+// 	var mod *module
-	if mod, exists = moduleRegister[name]; exists {
+// 	if mod, exists = moduleRegister[name]; exists {
-		mod.importFunc(ctx)
+// 		mod.importFunc(ctx)
-		mod.imported = true
+// 		mod.imported = true
-	}
+// 	}
-	return
+// 	return
-}
+// }
 
-func ImportInContextByGlobPattern(ctx ExprContext, pattern string) (count int, err error) {
+// func ImportInContextByGlobPattern(ctx ExprContext, pattern string) (count int, err error) {
-	var matched bool
+// 	var matched bool
-	for name, mod := range moduleRegister {
+// 	for name, mod := range moduleRegister {
-		if matched, err = filepath.Match(pattern, name); err == nil {
+// 		if matched, err = filepath.Match(pattern, name); err == nil {
-			if matched {
+// 			if matched {
-				count++
+// 				count++
-				mod.importFunc(ctx)
+// 				mod.importFunc(ctx)
-				mod.imported = true
+// 				mod.imported = true
-			}
+// 			}
-		} else {
+// 		} else {
-			break
+// 			break
-		}
+// 		}
-	}
+// 	}
-	return
+// 	return
-}
+// }
 
 func IterateModules(op func(name, description string, imported bool) bool) {
 	if op != nil {

operand-const.go

@@ -1,32 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// operand-const.go
-package expr
-
-// -------- const term
-func newConstTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- eval func
-func evalConst(ctx ExprContext, self *term) (v any, err error) {
-	v = self.tk.Value
-	return
-}
-
-// init
-func init() {
-	registerTermConstructor(SymString, newConstTerm)
-	registerTermConstructor(SymInteger, newConstTerm)
-	registerTermConstructor(SymFloat, newConstTerm)
-	registerTermConstructor(SymBool, newConstTerm)
-	registerTermConstructor(SymKwNil, newConstTerm)
-}

operand-dict.go

@@ -4,6 +4,125 @@
 // operand-dict.go
 package expr
 
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+type DictType map[any]any
+
+func newDict(dictAny map[any]*term) (dict *DictType) {
+	var d DictType
+	if dictAny != nil {
+		d = make(DictType, len(dictAny))
+		for i, item := range dictAny {
+			d[i] = item
+		}
+	} else {
+		d = make(DictType)
+	}
+	dict = &d
+	return
+}
+
+func (dict *DictType) toMultiLine(sb *strings.Builder, indent int) {
+	sb.WriteString(strings.Repeat("\t", indent))
+	sb.WriteString("{\n")
+
+	first := true
+	for name, value := range *dict {
+		if first {
+			first = false
+		} else {
+			sb.WriteByte(',')
+			sb.WriteByte('\n')
+		}
+
+		sb.WriteString(strings.Repeat("\t", indent+1))
+		if key, ok := name.(string); ok {
+			sb.WriteString(string('"') + key + string('"'))
+		} else {
+			sb.WriteString(fmt.Sprintf("%v", name))
+		}
+		sb.WriteString(": ")
+		if f, ok := value.(Formatter); ok {
+			sb.WriteString(f.ToString(MultiLine))
+		} else if _, ok = value.(Functor); ok {
+			sb.WriteString("func(){}")
+		} else {
+			sb.WriteString(fmt.Sprintf("%v", value))
+		}
+	}
+	sb.WriteString(strings.Repeat("\t", indent))
+	sb.WriteString("\n}")
+}
+
+func (dict *DictType) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	if opt&MultiLine != 0 {
+		dict.toMultiLine(&sb, 0)
+	} else {
+		sb.WriteByte('{')
+		first := true
+		for key, value := range *dict {
+			if first {
+				first = false
+			} else {
+				sb.WriteString(", ")
+			}
+			if s, ok := key.(string); ok {
+				sb.WriteString(string('"') + s + string('"'))
+			} else {
+				sb.WriteString(fmt.Sprintf("%v", key))
+			}
+			sb.WriteString(": ")
+			if formatter, ok := value.(Formatter); ok {
+				sb.WriteString(formatter.ToString(opt))
+			} else if t, ok := value.(*term); ok {
+				sb.WriteString(t.String())
+			} else {
+				sb.WriteString(fmt.Sprintf("%#v", value))
+			}
+		}
+		sb.WriteByte('}')
+	}
+	return sb.String()
+}
+
+func (dict *DictType) String() string {
+	return dict.ToString(0)
+}
+
+func (dict *DictType) TypeName() string {
+	return "dict"
+}
+
+func (dict *DictType) hasKey(target any) (ok bool) {
+	for key := range *dict {
+		if ok = reflect.DeepEqual(key, target); ok {
+			break
+		}
+	}
+	return
+}
+
+func (dict *DictType) clone() (c *DictType) {
+	c = newDict(nil)
+	for k, v := range *dict {
+		(*c)[k] = v
+	}
+	return
+}
+
+func (dict *DictType) merge(second *DictType) {
+	if second != nil {
+		for k, v := range *second {
+			(*dict)[k] = v
+		}
+	}
+}
+
 // -------- dict term
 func newDictTerm(args map[any]*term) *term {
 	return &term{
@@ -19,7 +138,7 @@ func newDictTerm(args map[any]*term) *term {
 // -------- dict func
 func evalDict(ctx ExprContext, self *term) (v any, err error) {
 	dict, _ := self.value().(map[any]*term)
-	items := make(map[any]any, len(dict))
+	items := make(DictType, len(dict))
 	for key, tree := range dict {
 		var param any
 		if param, err = tree.compute(ctx); err != nil {
@@ -28,7 +147,7 @@ func evalDict(ctx ExprContext, self *term) (v any, err error) {
 		items[key] = param
 	}
 	if err == nil {
-		v = items
+		v = &items
 	}
 	return
 }

operand-expr.go

@@ -7,7 +7,8 @@ package expr
 import "fmt"
 
 // -------- expr term
-func newExprTerm(tk *Token) *term {
+func newExprTerm(root *term) *term {
+	tk := NewValueToken(root.tk.row, root.tk.col, SymExpression, root.source(), root)
 	return &term{
 		tk:       *tk,
 		parent:   nil,
@@ -20,8 +21,8 @@ func newExprTerm(tk *Token) *term {
 
 // -------- eval expr
 func evalExpr(ctx ExprContext, self *term) (v any, err error) {
-	if expr, ok := self.value().(Expr); ok {
+	if expr, ok := self.value().(*term); ok {
-		v, err = expr.eval(ctx, false)
+		v, err = expr.compute(ctx)
 	} else {
 		err = fmt.Errorf("expression expected, got %T", self.value())
 	}

operand-func.go

@@ -23,12 +23,16 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 
 // -------- eval func call
 func checkFunctionCall(ctx ExprContext, name string, params []any) (err error) {
-	if info, exists := ctx.GetFuncInfo(name); exists {
+	if info, exists, owner := GetFuncInfo(ctx, name); exists {
 		if info.MinArgs() > len(params) {
-			err = fmt.Errorf("too few params -- expected %d, got %d", info.MinArgs(), len(params))
+			err = errTooFewParams(info.MinArgs(), info.MaxArgs(), len(params))
 		}
-		if info.MaxArgs() >= 0 && info.MaxArgs() < len(params) {
+		if err == nil && info.MaxArgs() >= 0 && info.MaxArgs() < len(params) {
-			err = fmt.Errorf("too much params -- expected %d, got %d", info.MaxArgs(), len(params))
+			err = errTooMuchParams(info.MaxArgs(), len(params))
+		}
+		if err == nil && owner != ctx {
+			// ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
+			ctx.RegisterFuncInfo(info)
 		}
 	} else {
 		err = fmt.Errorf("unknown function %s()", name)
@@ -72,27 +76,30 @@ func newFuncDefTerm(tk *Token, args []*term) *term {
 
 // -------- eval func def
 // TODO
-type funcDefFunctor struct {
+// type funcDefFunctor struct {
-	params []string
+// 	params []string
-	expr   Expr
+// 	expr   Expr
-}
+// }
 
-func (functor *funcDefFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
+// func (funcDef *funcDefFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
-	for i, p := range functor.params {
+// 	for i, p := range funcDef.params {
-		if i < len(args) {
+// 		if i < len(args) {
-			arg := args[i]
+// 			arg := args[i]
-			if functor, ok := arg.(Functor); ok {
+// 			if functor, ok := arg.(Functor); ok {
-				ctx.RegisterFunc(p, functor, 0, -1)
+// 				// ctx.RegisterFunc(p, functor, 0, -1)
-			} else {
+// 				ctx.RegisterFunc2(p, functor, typeAny, []ExprFuncParam{
-				ctx.setVar(p, arg)
+// 					newFuncParam(paramValue),
-			}
+// 				})
-		} else {
+// 			} else {
-			ctx.setVar(p, nil)
+// 				ctx.UnsafeSetVar(p, arg)
-		}
+// 			}
-	}
+// 		} else {
-	result, err = functor.expr.eval(ctx, false)
+// 			ctx.UnsafeSetVar(p, nil)
-	return
+// 		}
-}
+// 	}
+// 	result, err = funcDef.expr.eval(ctx, false)
+// 	return
+// }
 
 func evalFuncDef(ctx ExprContext, self *term) (v any, err error) {
 	bodySpec := self.value()
@@ -101,10 +108,7 @@ func evalFuncDef(ctx ExprContext, self *term) (v any, err error) {
 		for _, param := range self.children {
 			paramList = append(paramList, param.source())
 		}
-		v = &funcDefFunctor{
+		v = newExprFunctor(expr, paramList, ctx)
-			params: paramList,
-			expr:   expr,
-		}
 	} else {
 		err = errors.New("invalid function definition: the body specification must be an expression")
 	}

operand-iterator.go

@@ -66,14 +66,16 @@ func evalFirstChild(ctx ExprContext, self *term) (value any, err error) {
 }
 
 func getDataSourceDict(ctx ExprContext, self *term, firstChildValue any) (ds map[string]Functor, err error) {
-	if dictAny, ok := firstChildValue.(map[any]any); ok {
+	// if dictAny, ok := firstChildValue.(map[any]any); ok {
+	if dictAny, ok := firstChildValue.(*DictType); ok {
 		requiredFields := []string{currentName, nextName}
 		fieldsMask := 0b11
 		foundFields := 0
 		ds = make(map[string]Functor)
-		for keyAny, item := range dictAny {
+		for keyAny, item := range *dictAny {
 			if key, ok := keyAny.(string); ok {
-				if functor, ok := item.(*funcDefFunctor); ok {
+				//if functor, ok := item.(*funcDefFunctor); ok {
+				if functor, ok := item.(Functor); ok {
 					ds[key] = functor
 					if index := slices.Index(requiredFields, key); index >= 0 {
 						foundFields |= 1 << index

operand-list.go

@@ -4,56 +4,14 @@
 // operand-list.go
 package expr
 
-import (
-	"fmt"
-	"strings"
-)
-
-type ListType []any
-
-func (ls *ListType) ToString(opt FmtOpt) string {
-	var sb strings.Builder
-	sb.WriteByte('[')
-	if len(*ls) > 0 {
-		if opt&MultiLine != 0 {
-			sb.WriteString("\n  ")
-		}
-		for i, item := range []any(*ls) {
-			if i > 0 {
-				if opt&MultiLine != 0 {
-					sb.WriteString(",\n  ")
-				} else {
-					sb.WriteString(", ")
-				}
-			}
-			if s, ok := item.(string); ok {
-				sb.WriteByte('"')
-				sb.WriteString(s)
-				sb.WriteByte('"')
-			} else {
-				sb.WriteString(fmt.Sprintf("%v", item))
-			}
-		}
-		if opt&MultiLine != 0 {
-			sb.WriteByte('\n')
-		}
-	}
-	sb.WriteByte(']')
-	return sb.String()
-}
-
-func (ls *ListType) String() string {
-	return ls.ToString(0)
-}
-
 // -------- list term
 func newListTermA(args ...*term) *term {
-	return newListTerm(args)
+	return newListTerm(0, 0, args)
 }
 
-func newListTerm(args []*term) *term {
+func newListTerm(row, col int, args []*term) *term {
 	return &term{
-		tk:       *NewValueToken(0, 0, SymList, "[]", args),
+		tk:       *NewValueToken(row, col, SymList, "[]", args),
 		parent:   nil,
 		children: nil,
 		position: posLeaf,

operand-literal.go

@@ -0,0 +1,33 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-literal.go
+package expr
+
+// -------- literal term
+func newLiteralTerm(tk *Token) *term {
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: nil,
+		position: posLeaf,
+		priority: priValue,
+		evalFunc: evalLiteral,
+	}
+}
+
+// -------- eval func
+func evalLiteral(ctx ExprContext, self *term) (v any, err error) {
+	v = self.tk.Value
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymString, newLiteralTerm)
+	registerTermConstructor(SymInteger, newLiteralTerm)
+	registerTermConstructor(SymFloat, newLiteralTerm)
+	registerTermConstructor(SymFraction, newLiteralTerm)
+	registerTermConstructor(SymBool, newLiteralTerm)
+	registerTermConstructor(SymKwNil, newLiteralTerm)
+}

operand-var.go

@@ -8,7 +8,7 @@ import "fmt"
 
 // -------- variable term
 func newVarTerm(tk *Token) *term {
-	return &term{
+	t := &term{
 		tk: *tk,
 		// class:    classVar,
 		// kind:     kindUnknown,
@@ -18,14 +18,16 @@ func newVarTerm(tk *Token) *term {
 		priority: priValue,
 		evalFunc: evalVar,
 	}
+	t.tk.Sym = SymVariable
+	return t
 }
 
 // -------- eval func
 func evalVar(ctx ExprContext, self *term) (v any, err error) {
 	var exists bool
 	name := self.source()
-	if v, exists = ctx.GetVar(name); !exists {
+	if v, exists = GetVar(ctx, name); !exists {
-		if info, exists := ctx.GetFuncInfo(name); exists {
+		if info, exists, _ := GetFuncInfo(ctx, name); exists {
 			v = info.Functor()
 		} else {
 			err = fmt.Errorf("undefined variable or function %q", name)

operator-assign.go

@@ -1,5 +1,5 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
+// All rights reserightChilded.
 
 // operator-assign.go
 package expr
@@ -22,23 +22,32 @@ func evalAssign(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	leftTerm := self.children[0]
-	if leftTerm.tk.Sym != SymIdentifier {
+	if leftTerm.tk.Sym != SymVariable {
 		err = leftTerm.tk.Errorf("left operand of %q must be a variable", self.tk.source)
 		return
 	}
 
-	if v, err = self.children[1].compute(ctx); err == nil {
+	rightChild := self.children[1]
-		if functor, ok := v.(Functor); ok {
-			var minArgs, maxArgs int = 0, 0
 
-			if funcDef, ok := functor.(*funcDefFunctor); ok {
+	if v, err = rightChild.compute(ctx); err == nil {
-				l := len(funcDef.params)
+		if functor, ok := v.(Functor); ok {
-				minArgs = l
+			funcName := rightChild.source()
-				maxArgs = l
+			if info, exists, _ := GetFuncInfo(ctx, funcName); exists {
-			}
+				// ctx.RegisterFuncInfo(info)
-			ctx.RegisterFunc(leftTerm.source(), functor, minArgs, maxArgs)
+				ctx.RegisterFunc(leftTerm.source(), info.Functor(), info.ReturnType(), info.Params())
+			} else if funcDef, ok := functor.(*exprFunctor); ok {
+				paramSpecs := ForAll(funcDef.params, newFuncParam)
+				// paramCount := len(funcDef.params)
+				// paramSpecs := make([]ExprFuncParam, paramCount)
+				// for i := range paramSpecs {
+				// 	paramSpecs[i] = newFuncParam(funcDef.params[i])
+				// }
+				ctx.RegisterFunc(leftTerm.source(), functor, typeAny, paramSpecs)
 			} else {
-			ctx.setVar(leftTerm.source(), v)
+				err = self.Errorf("unknown function %s()", funcName)
+			}
+		} else {
+			ctx.UnsafeSetVar(leftTerm.source(), v)
 		}
 	}
 	return

operator-builtin.go

@@ -26,15 +26,15 @@ func evalBuiltin(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	count := 0
-	if isString(childValue) {
+	if IsString(childValue) {
 		module, _ := childValue.(string)
-		count, err = ImportInContextByGlobPattern(ctx, module)
+		count, err = ImportInContextByGlobPattern(module)
 	} else {
 		var moduleSpec any
 		it := NewAnyIterator(childValue)
 		for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {
 			if module, ok := moduleSpec.(string); ok {
-				if ImportInContext(ctx, module) {
+				if ImportInContext(module) {
 					count++
 				} else {
 					err = self.Errorf("unknown module %q", module)

operator-coalesce.go

@@ -9,8 +9,6 @@ package expr
 func newNullCoalesceTerm(tk *Token) (inst *term) {
 	return &term{
 		tk:       *tk,
-		// class:    classOperator,
-		// kind:     kindUnknown,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priCoalesce,
@@ -26,7 +24,7 @@ func evalNullCoalesce(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	leftTerm := self.children[0]
-	if leftTerm.tk.Sym != SymIdentifier {
+	if leftTerm.tk.Sym != SymVariable {
 		err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		return
 	}
@@ -34,11 +32,7 @@ func evalNullCoalesce(ctx ExprContext, self *term) (v any, err error) {
 	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists {
 		v = leftValue
 	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		// if _, ok := rightValue.(Functor); ok {
-		// 	err = errCoalesceNoFunc(self.children[1])
-		// } else {
 		v = rightValue
-		// }
 	}
 	return
 }
@@ -63,7 +57,7 @@ func evalAssignCoalesce(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	leftTerm := self.children[0]
-	if leftTerm.tk.Sym != SymIdentifier {
+	if leftTerm.tk.Sym != SymVariable {
 		err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		return
 	}
@@ -72,20 +66,18 @@ func evalAssignCoalesce(ctx ExprContext, self *term) (v any, err error) {
 		v = leftValue
 	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
 		if functor, ok := rightValue.(Functor); ok {
-			ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
+			//ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
+			ctx.RegisterFunc(leftTerm.source(), functor, typeAny, []ExprFuncParam{
+				newFuncParamFlag(paramValue, pfOptional|pfRepeat),
+			})
 		} else {
 			v = rightValue
-			ctx.setVar(leftTerm.source(), rightValue)
+			ctx.UnsafeSetVar(leftTerm.source(), rightValue)
 		}
 	}
 	return
 }
 
-// utils
-// func errCoalesceNoFunc(t *term) error {
-// 	return t.Errorf("the right operand of a coalescing operation cannot be a function definition")
-// }
-
 // init
 func init() {
 	registerTermConstructor(SymDoubleQuestion, newNullCoalesceTerm)

operator-context.go

@@ -20,18 +20,18 @@ func evalContextValue(ctx ExprContext, self *term) (v any, err error) {
 	var childValue any
 
 	var sourceCtx ExprContext
-	if len(self.children) == 0 {
+	if self.children == nil || len(self.children) == 0 {
 		sourceCtx = ctx
+	} else if self.children[0].symbol() == SymVariable && self.children[0].source() == "global" {
+		sourceCtx = globalCtx
 	} else if childValue, err = self.evalPrefix(ctx); err == nil {
 		if dc, ok := childValue.(*dataCursor); ok {
 			sourceCtx = dc.ctx
 		}
-	} else {
-		return
 	}
 
 	if sourceCtx != nil {
-		if formatter, ok := ctx.(Formatter); ok {
+		if formatter, ok := sourceCtx.(Formatter); ok {
 			v = formatter.ToString(0)
 		} else {
 			keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })

operator-dot.go

@@ -4,8 +4,6 @@
 // operator-dot.go
 package expr
 
-import "fmt"
-
 // -------- dot term
 func newDotTerm(tk *Token) (inst *term) {
 	return &term{
@@ -17,23 +15,6 @@ func newDotTerm(tk *Token) (inst *term) {
 	}
 }
 
-func verifyIndex(ctx ExprContext, indexTerm *term, maxValue int) (index int, err error) {
-	var v int
-	var indexValue any
-	if indexValue, err = indexTerm.compute(ctx); err == nil {
-		if v, err = indexTerm.toInt(indexValue, "index expression value must be integer"); err == nil {
-			if v >= 0 && v < maxValue {
-				index = v
-			} else if index >= -maxValue {
-				index = maxValue + v
-			} else {
-				err = indexTerm.Errorf("index %d out of bounds", v)
-			}
-		}
-	}
-	return
-}
-
 func evalDot(ctx ExprContext, self *term) (v any, err error) {
 	var leftValue, rightValue any
 
@@ -47,39 +28,8 @@ func evalDot(ctx ExprContext, self *term) (v any, err error) {
 	indexTerm := self.children[1]
 
 	switch unboxedValue := leftValue.(type) {
-	case *ListType:
-		var index int
-		array := ([]any)(*unboxedValue)
-		if index, err = verifyIndex(ctx, indexTerm, len(array)); err == nil {
-			v = array[index]
-		}
-	case string:
-		var index int
-		if index, err = verifyIndex(ctx, indexTerm, len(unboxedValue)); err == nil {
-			v = unboxedValue[index]
-		}
-	case map[any]any:
-		var ok bool
-		var indexValue any
-		if indexValue, err = indexTerm.compute(ctx); err == nil {
-			if v, ok = unboxedValue[indexValue]; !ok {
-				err = fmt.Errorf("key %v does not belong to the dictionary", rightValue)
-			}
-		}
-	// case *dataCursor:
-	// 	if indexTerm.symbol() == SymIdentifier {
-	// 		opName := indexTerm.source()
-	// 		if opName == resetName {
-	// 			_, err = unboxedValue.Reset()
-	// 		} else if opName == cleanName {
-	// 			_, err = unboxedValue.Clean()
-	// 		} else {
-	// 			err = indexTerm.Errorf("iterators do not support command %q", opName)
-	// 		}
-	// 		v = err == nil
-	// 	}
 	case ExtIterator:
-		if indexTerm.symbol() == SymIdentifier {
+		if indexTerm.symbol() == SymVariable /*|| indexTerm.symbol() == SymString */ {
 			opName := indexTerm.source()
 			if unboxedValue.HasOperation(opName) {
 				v, err = unboxedValue.CallOperation(opName, []any{})
@@ -87,10 +37,14 @@ func evalDot(ctx ExprContext, self *term) (v any, err error) {
 				err = indexTerm.Errorf("this iterator do not support the %q command", opName)
 				v = false
 			}
+		} else {
+			err = indexTerm.tk.ErrorExpectedGot("identifier")
 		}
 	default:
+		if rightValue, err = self.children[1].compute(ctx); err == nil {
 			err = self.errIncompatibleTypes(leftValue, rightValue)
 		}
+	}
 	return
 }
 

operator-fact.go

@@ -25,7 +25,7 @@ func evalFact(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isInteger(leftValue) {
+	if IsInteger(leftValue) {
 		if i, _ := leftValue.(int64); i >= 0 {
 			f := int64(1)
 			for k := int64(1); k <= i; k++ {

operator-fraction.go

@@ -4,72 +4,13 @@
 // operand-fraction.go
 package expr
 
+//https://www.youmath.it/lezioni/algebra-elementare/lezioni-di-algebra-e-aritmetica-per-scuole-medie/553-dalle-frazioni-a-numeri-decimali.html
+
 import (
 	"errors"
 	"fmt"
-	"strconv"
-	"strings"
 )
 
-type fraction struct {
-	num, den int64
-}
-
-func newFraction(num, den int64) *fraction {
-	/*	if den < 0 {
-		den = -den
-		num = -num
-	}*/
-	num, den = simplifyIntegers(num, den)
-	return &fraction{num, den}
-}
-
-func (f *fraction) toFloat() float64 {
-	return float64(f.num) / float64(f.den)
-}
-
-func (f *fraction) String() string {
-	return f.ToString(0)
-}
-
-func (f *fraction) ToString(opt FmtOpt) string {
-	var sb strings.Builder
-	if opt&MultiLine == 0 {
-		sb.WriteString(fmt.Sprintf("%d|%d", f.num, f.den))
-	} else {
-		var s, num string
-		if f.num < 0 && opt&TTY == 0 {
-			num = strconv.FormatInt(-f.num, 10)
-			s = "-"
-		} else {
-			num = strconv.FormatInt(f.num, 10)
-		}
-		den := strconv.FormatInt(f.den, 10)
-		size := max(len(num), len(den))
-		if opt&TTY != 0 {
-			sb.WriteString(fmt.Sprintf("\x1b[4m%[1]*s\x1b[0m\n", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, s+num)))
-		} else {
-			if len(s) > 0 {
-				sb.WriteString("  ")
-			}
-			sb.WriteString(fmt.Sprintf("%[1]*s", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, num)))
-			sb.WriteByte('\n')
-			if len(s) > 0 {
-				sb.WriteString(s)
-				sb.WriteByte(' ')
-			}
-			sb.WriteString(strings.Repeat("-", size))
-			sb.WriteByte('\n')
-			if len(s) > 0 {
-				sb.WriteString("  ")
-			}
-		}
-		sb.WriteString(fmt.Sprintf("%[1]*s", -size, fmt.Sprintf("%[1]*s", (size+len(den))/2, den)))
-	}
-
-	return sb.String()
-}
-
 // -------- fraction term
 func newFractionTerm(tk *Token) *term {
 	return &term{
@@ -114,168 +55,11 @@ func evalFraction(ctx ExprContext, self *term) (v any, err error) {
 	if den == 1 {
 		v = num
 	} else {
-		v = &fraction{num, den}
+		v = &FractionType{num, den}
 	}
 	return
 }
 
-func gcd(a, b int64) (g int64) {
-	if a < 0 {
-		a = -a
-	}
-	if b < 0 {
-		b = -b
-	}
-	if a < b {
-		a, b = b, a
-	}
-	r := a % b
-	for r > 0 {
-		a, b = b, r
-		r = a % b
-	}
-	g = b
-	return
-}
-
-func lcm(a, b int64) (l int64) {
-	g := gcd(a, b)
-	l = a * b / g
-	return
-}
-
-func sumFract(f1, f2 *fraction) (sum *fraction) {
-	m := lcm(f1.den, f2.den)
-	sum = newFraction(f1.num*(m/f1.den) + f2.num*(m/f2.den), m)
-	return
-}
-
-func mulFract(f1, f2 *fraction) (prod *fraction) {
-	prod = newFraction(f1.num * f2.num, f1.den * f2.den)
-	return
-}
-
-func anyToFract(v any) (f *fraction, err error) {
-	var ok bool
-	if f, ok = v.(*fraction); !ok {
-		if n, ok := v.(int64); ok {
-			f = intToFraction(n)
-		}
-	}
-	if f == nil {
-		err = errExpectedGot("fract", typeFraction, v)
-	}
-	return
-}
-
-func anyPairToFract(v1, v2 any) (f1, f2 *fraction, err error) {
-	if f1, err = anyToFract(v1); err != nil {
-		return
-	}
-	if f2, err = anyToFract(v2); err != nil {
-		return
-	}
-	return
-}
-
-func sumAnyFract(af1, af2 any) (sum any, err error) {
-	var f1, f2 *fraction
-	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
-		return
-	}
-	f := sumFract(f1, f2)
-	if f.num == 0 {
-		sum = 0
-	} else {
-		sum = simplifyFraction(f)
-	}
-	return
-}
-
-func subAnyFract(af1, af2 any) (sum any, err error) {
-	var f1, f2 *fraction
-	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
-		return
-	}
-	f2.num = -f2.num
-	f := sumFract(f1, f2)
-	if f.num == 0 {
-		sum = 0
-	} else {
-		sum = simplifyFraction(f)
-	}
-	return
-}
-
-func mulAnyFract(af1, af2 any) (prod any, err error) {
-	var f1, f2 *fraction
-	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
-		return
-	}
-	if f1.num == 0 || f2.num == 0 {
-		prod = 0
-	} else {
-		f := &fraction{f1.num * f2.num, f1.den * f2.den}
-		prod = simplifyFraction(f)
-	}
-	return
-}
-
-func divAnyFract(af1, af2 any) (quot any, err error) {
-	var f1, f2 *fraction
-	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
-		return
-	}
-	if f2.num == 0 {
-		err = errors.New("division by zero")
-		return
-		return
-	}
-	if f1.num == 0 || f2.den == 0 {
-		quot = 0
-	} else {
-		f := &fraction{f1.num * f2.den, f1.den * f2.num}
-		quot = simplifyFraction(f)
-	}
-	return
-}
-
-func simplifyFraction(f *fraction) (v any) {
-	f.num, f.den = simplifyIntegers(f.num, f.den)
-	if f.den == 1 {
-		v = f.num
-	} else {
-		v = &fraction{f.num, f.den}
-	}
-	return v
-}
-
-func simplifyIntegers(num, den int64) (a, b int64) {
-	if num == 0 {
-		return 0, 1
-	}
-	if den == 0 {
-		panic("fraction with denominator == 0")
-	}
-	if den < 0 {
-		den = -den
-		num = -num
-	}
-	g := gcd(num, den)
-	a = num / g
-	b = den / g
-	return
-}
-
-func intToFraction(n int64) *fraction {
-	return &fraction{n, 1}
-}
-
-func isFraction(v any) (ok bool) {
-	_, ok = v.(*fraction)
-	return ok
-}
-
 // init
 func init() {
 	registerTermConstructor(SymVertBar, newFractionTerm)

operator-in.go

@@ -0,0 +1,46 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-in.go
+package expr
+
+//-------- in term
+
+func newInTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priRelational,
+		evalFunc: evalIn,
+	}
+}
+
+// func hasKey(d map[any]any, target any) (ok bool) {
+// 	_, ok = d[target]
+// 	return
+// }
+
+func evalIn(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+
+	if IsList(rightValue) {
+		list, _ := rightValue.(*ListType)
+		v = list.indexDeepSameCmp(leftValue) >= 0
+	} else if IsDict(rightValue) {
+		dict, _ := rightValue.(*DictType)
+		v = dict.hasKey(leftValue)
+	} else {
+		err = self.errIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymKwIn, newInTerm)
+}

operator-include.go

@@ -24,7 +24,7 @@ func evalInclude(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	count := 0
-	if isList(childValue) {
+	if IsList(childValue) {
 		list, _ := childValue.([]any)
 		for i, filePathSpec := range list {
 			if filePath, ok := filePathSpec.(string); ok {
@@ -39,7 +39,7 @@ func evalInclude(ctx ExprContext, self *term) (v any, err error) {
 				break
 			}
 		}
-	} else if isString(childValue) {
+	} else if IsString(childValue) {
 		filePath, _ := childValue.(string)
 		v, err = EvalFile(ctx, filePath)
 	} else {

operator-index.go

@@ -0,0 +1,123 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-index.go
+package expr
+
+// -------- index term
+func newIndexTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priDot,
+		evalFunc: evalIndex,
+	}
+}
+
+func verifyKey(indexTerm *term, indexList *ListType) (index any, err error) {
+	index = (*indexList)[0]
+	return
+}
+
+func verifyIndex(indexTerm *term, indexList *ListType, maxValue int) (index int, err error) {
+	var v int
+
+	if v, err = toInt((*indexList)[0], "index expression"); err == nil {
+		if v < 0 && v >= -maxValue {
+			v = maxValue + v
+		}
+		if v >= 0 && v < maxValue {
+			index = v
+		} else {
+			err = indexTerm.Errorf("index %d out of bounds", v)
+		}
+	}
+	return
+}
+
+func verifyRange(indexTerm *term, indexList *ListType, maxValue int) (startIndex, endIndex int, err error) {
+	v, _ := ((*indexList)[0]).(*intPair)
+	startIndex = v.a
+	endIndex = v.b
+	if startIndex < 0 && startIndex >= -maxValue {
+		startIndex = maxValue + startIndex
+	}
+	if endIndex < 0 && endIndex >= -maxValue {
+		endIndex = maxValue + endIndex + 1
+	}
+	if startIndex < 0 || startIndex > maxValue {
+		err = indexTerm.Errorf("range start-index %d is out of bounds", startIndex)
+	} else if endIndex < 0 || endIndex > maxValue {
+		err = indexTerm.Errorf("range end-index %d is out of bounds", endIndex)
+	} else if startIndex > endIndex {
+		err = indexTerm.Errorf("range start-index %d must not be greater than end-index %d", startIndex, endIndex)
+	}
+	return
+}
+
+func evalIndex(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+	var indexList *ListType
+	var ok bool
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+
+	indexTerm := self.children[1]
+	if indexList, ok = rightValue.(*ListType); !ok {
+		err = self.Errorf("invalid index expression")
+		return
+	} else if len(*indexList) != 1 {
+		err = indexTerm.Errorf("one index only is allowed")
+		return
+	}
+
+	if IsInteger((*indexList)[0]) {
+		switch unboxedValue := leftValue.(type) {
+		case *ListType:
+			var index int
+			if index, err = verifyIndex(indexTerm, indexList, len(*unboxedValue)); err == nil {
+				v = (*unboxedValue)[index]
+			}
+		case string:
+			var index int
+			if index, err = verifyIndex(indexTerm, indexList, len(unboxedValue)); err == nil {
+				v = string(unboxedValue[index])
+			}
+		case *DictType:
+			var ok bool
+			var indexValue any
+			if indexValue, err = verifyKey(indexTerm, indexList); err == nil {
+				if v, ok = (*unboxedValue)[indexValue]; !ok {
+					err = indexTerm.Errorf("key %v does not belong to the dictionary", rightValue)
+				}
+			}
+		default:
+			err = self.errIncompatibleTypes(leftValue, rightValue)
+		}
+	} else if isIntPair((*indexList)[0]) {
+		switch unboxedValue := leftValue.(type) {
+		case *ListType:
+			var start, end int
+			if start, end, err = verifyRange(indexTerm, indexList, len(*unboxedValue)); err == nil {
+				sublist := ListType((*unboxedValue)[start:end])
+				v = &sublist
+			}
+		case string:
+			var start, end int
+			if start, end, err = verifyRange(indexTerm, indexList, len(unboxedValue)); err == nil {
+				v = unboxedValue[start:end]
+			}
+		default:
+			err = self.errIncompatibleTypes(leftValue, rightValue)
+		}
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymIndex, newIndexTerm)
+}

operator-insert.go

@@ -33,10 +33,13 @@ func evalInsert(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isList(rightValue) {
+	if IsList(rightValue) {
 		list, _ := rightValue.(*ListType)
 		newList := append(ListType{leftValue}, *list...)
 		v = &newList
+		if self.children[1].symbol() == SymVariable {
+			ctx.UnsafeSetVar(self.children[1].source(), v)
+		}
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
@@ -50,16 +53,37 @@ func evalAppend(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isList(leftValue) {
+	if IsList(leftValue) {
 		list, _ := leftValue.(*ListType)
 		newList := append(*list, rightValue)
 		v = &newList
+		if self.children[0].symbol() == SymVariable {
+			ctx.UnsafeSetVar(self.children[0].source(), v)
+		}
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
+// func evalAssignAppend(ctx ExprContext, self *term) (v any, err error) {
+// 	var leftValue, rightValue any
+
+// 	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+// 		return
+// 	}
+
+// 	if IsList(leftValue) {
+// 		list, _ := leftValue.(*ListType)
+// 		newList := append(*list, rightValue)
+// 		v = &newList
+// 		if
+// 	} else {
+// 		err = self.errIncompatibleTypes(leftValue, rightValue)
+// 	}
+// 	return
+// }
+
 // init
 func init() {
 	registerTermConstructor(SymInsert, newInsertTerm)

operator-length.go

@@ -23,12 +23,16 @@ func evalLength(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isList(childValue) {
+	if IsList(childValue) {
-		list, _ := childValue.([]any)
+		ls, _ := childValue.(*ListType)
-		v = int64(len(list))
+		v = int64(len(*ls))
-	} else if isString(childValue) {
+	} else if IsString(childValue) {
 		s, _ := childValue.(string)
 		v = int64(len(s))
+	} else if IsDict(childValue) {
+		// m, _ := childValue.(map[any]any)
+		m, _ := childValue.(*DictType)
+		v = int64(len(*m))
 	} else if it, ok := childValue.(Iterator); ok {
 		if extIt, ok := childValue.(ExtIterator); ok && extIt.HasOperation(countName) {
 			count, _ := extIt.CallOperation(countName, nil)

operator-post-inc.go

@@ -25,7 +25,7 @@ func evalPostInc(ctx ExprContext, self *term) (v any, err error) {
 
 	if it, ok := childValue.(Iterator); ok {
 		v, err = it.Next()
-	} else if isInteger(childValue) && self.children[0].symbol() == SymIdentifier {
+	} else if IsInteger(childValue) && self.children[0].symbol() == SymVariable {
 		v = childValue
 		i, _ := childValue.(int64)
 		ctx.SetVar(self.children[0].source(), i+1)

operator-prod.go

@@ -30,20 +30,20 @@ func evalMultiply(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isString(leftValue) && isInteger(rightValue) {
+	if IsString(leftValue) && IsInteger(rightValue) {
 		s, _ := leftValue.(string)
 		n, _ := rightValue.(int64)
 		v = strings.Repeat(s, int(n))
-	} else if isNumber(leftValue) && isNumber(rightValue) {
+	} else if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
 			v = numAsFloat(leftValue) * numAsFloat(rightValue)
+		} else if isFraction(leftValue) || isFraction(rightValue) {
+			v, err = mulAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt * rightInt
 		}
-	} else if isFraction(leftValue) || isFraction(rightValue) {
-		v, err = mulAnyFract(leftValue, rightValue)
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
@@ -71,14 +71,16 @@ func evalDivide(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
+	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
 			d := numAsFloat(rightValue)
 			if d == 0.0 {
 				err = errors.New("division by zero")
 			} else {
 				v = numAsFloat(leftValue) / d
 			}
+		} else if isFraction(leftValue) || isFraction(rightValue) {
+			v, err = divAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			if rightInt, _ := rightValue.(int64); rightInt == 0 {
@@ -87,8 +89,6 @@ func evalDivide(ctx ExprContext, self *term) (v any, err error) {
 				v = leftInt / rightInt
 			}
 		}
-	} else if isFraction(leftValue) || isFraction(rightValue) {
-		v, err = divAnyFract(leftValue, rightValue)
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
@@ -114,7 +114,7 @@ func evalDivideAsFloat(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
+	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
 		d := numAsFloat(rightValue)
 		if d == 0.0 {
 			err = errors.New("division by zero")
@@ -148,7 +148,7 @@ func evalReminder(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isInteger(leftValue) && isInteger(rightValue) {
+	if IsInteger(leftValue) && IsInteger(rightValue) {
 		rightInt, _ := rightValue.(int64)
 		if rightInt == 0 {
 			err = errors.New("division by zero")

operator-range.go

@@ -0,0 +1,69 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-range.go
+package expr
+
+import "fmt"
+
+// -------- range term
+type intPair struct {
+	a, b int
+}
+
+func (p *intPair) TypeName() string {
+	return typePair
+}
+
+func (p *intPair) ToString(opt FmtOpt) string {
+	return fmt.Sprintf("(%d, %d)", p.a, p.b)
+}
+
+func isIntPair(v any) bool {
+	_, ok := v.(*intPair)
+	return ok
+}
+
+func newRangeTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priDot,
+		evalFunc: evalRange,
+	}
+}
+
+func evalRange(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	// if err = self.checkOperands(); err != nil {
+	// 	return
+	// }
+	if len(self.children) == 0 {
+		leftValue = int64(0)
+		rightValue = int64(-1)
+	} else if len(self.children) == 1 {
+		if leftValue, err = self.children[0].compute(ctx); err != nil {
+			return
+		}
+		rightValue = int64(-1)
+	} else if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+	if !(IsInteger(leftValue) && IsInteger(rightValue)) {
+		err = self.errIncompatibleTypes(leftValue, rightValue)
+		return
+	}
+
+	startIndex, _ := leftValue.(int64)
+	endIndex, _ := rightValue.(int64)
+
+	v = &intPair{int(startIndex), int(endIndex)}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymColon, newRangeTerm)
+}

operator-rel.go

@@ -4,13 +4,13 @@
 // operator-rel.go
 package expr
 
+import "reflect"
+
 //-------- equal term
 
 func newEqualTerm(tk *Token) (inst *term) {
 	return &term{
 		tk:       *tk,
-		// class:    classOperator,
-		// kind:     kindBool,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priRelational,
@@ -18,6 +18,33 @@ func newEqualTerm(tk *Token) (inst *term) {
 	}
 }
 
+type deepFuncTemplate func(a, b any) (eq bool, err error)
+
+func equals(a, b any, deepCmp deepFuncTemplate) (eq bool, err error) {
+	if isNumOrFract(a) && isNumOrFract(b) {
+		if IsNumber(a) && IsNumber(b) {
+			if IsInteger(a) && IsInteger(b) {
+				li, _ := a.(int64)
+				ri, _ := b.(int64)
+				eq = li == ri
+			} else {
+				eq = numAsFloat(a) == numAsFloat(b)
+			}
+		} else {
+			var cmp int
+			if cmp, err = cmpAnyFract(a, b); err == nil {
+				eq = cmp == 0
+			}
+		}
+	} else if deepCmp != nil && IsList(a) && IsList(b) {
+		eq, err = deepCmp(a, b)
+	} else {
+		eq = reflect.DeepEqual(a, b)
+	}
+
+	return
+}
+
 func evalEqual(ctx ExprContext, self *term) (v any, err error) {
 	var leftValue, rightValue any
 
@@ -25,21 +52,7 @@ func evalEqual(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
+	v, err = equals(leftValue, rightValue, nil)
-		if isInteger(leftValue) && isInteger(rightValue) {
-			li, _ := leftValue.(int64)
-			ri, _ := rightValue.(int64)
-			v = li == ri
-		} else {
-			v = numAsFloat(leftValue) == numAsFloat(rightValue)
-		}
-	} else if isString(leftValue) && isString(rightValue) {
-		ls, _ := leftValue.(string)
-		rs, _ := rightValue.(string)
-		v = ls == rs
-	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
-	}
 	return
 }
 
@@ -48,8 +61,6 @@ func evalEqual(ctx ExprContext, self *term) (v any, err error) {
 func newNotEqualTerm(tk *Token) (inst *term) {
 	return &term{
 		tk:       *tk,
-		// class:    classOperator,
-		// kind:     kindBool,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priRelational,
@@ -65,38 +76,11 @@ func evalNotEqual(ctx ExprContext, self *term) (v any, err error) {
 	return
 }
 
-// func evalNotEqual(ctx exprContext, self *term) (v any, err error) {
-// 	var leftValue, rightValue any
-
-// 	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
-// 		return
-// 	}
-
-// 	if isNumber(leftValue) && isNumber(rightValue) {
-// 		if isInteger(leftValue) && isInteger(rightValue) {
-// 			li, _ := leftValue.(int64)
-// 			ri, _ := rightValue.(int64)
-// 			v = li != ri
-// 		} else {
-// 			v = numAsFloat(leftValue) != numAsFloat(rightValue)
-// 		}
-// 	} else if isString(leftValue) && isString(rightValue) {
-// 		ls, _ := leftValue.(string)
-// 		rs, _ := rightValue.(string)
-// 		v = ls != rs
-// 	} else {
-// 		err = self.errIncompatibleTypes(leftValue, rightValue)
-// 	}
-// 	return
-// }
-
 //-------- less term
 
 func newLessTerm(tk *Token) (inst *term) {
 	return &term{
 		tk:       *tk,
-		// class:    classOperator,
-		// kind:     kindBool,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priRelational,
@@ -104,28 +88,44 @@ func newLessTerm(tk *Token) (inst *term) {
 	}
 }
 
+func lessThan(self *term, a, b any) (isLess bool, err error) {
+	if isNumOrFract(a) && isNumOrFract(b) {
+		if IsNumber(a) && IsNumber(b) {
+			if IsInteger(a) && IsInteger(b) {
+				li, _ := a.(int64)
+				ri, _ := b.(int64)
+				isLess = li < ri
+			} else {
+				isLess = numAsFloat(a) < numAsFloat(b)
+			}
+		} else {
+			var cmp int
+			if cmp, err = cmpAnyFract(a, b); err == nil {
+				isLess = cmp < 0
+			}
+		}
+	} else if IsString(a) && IsString(b) {
+		ls, _ := a.(string)
+		rs, _ := b.(string)
+		isLess = ls < rs
+		// Inclusion test
+	} else if IsList(a) && IsList(b) {
+		aList, _ := a.(*ListType)
+		bList, _ := b.(*ListType)
+		isLess = len(*aList) < len(*bList) && bList.contains(aList)
+	} else {
+		err = self.errIncompatibleTypes(a, b)
+	}
+	return
+}
+
 func evalLess(ctx ExprContext, self *term) (v any, err error) {
 	var leftValue, rightValue any
 
 	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
 		return
 	}
-
+	v, err = lessThan(self, leftValue, rightValue)
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isInteger(leftValue) && isInteger(rightValue) {
-			li, _ := leftValue.(int64)
-			ri, _ := rightValue.(int64)
-			v = li < ri
-		} else {
-			v = numAsFloat(leftValue) < numAsFloat(rightValue)
-		}
-	} else if isString(leftValue) && isString(rightValue) {
-		ls, _ := leftValue.(string)
-		rs, _ := rightValue.(string)
-		v = ls < rs
-	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
-	}
 	return
 }
 
@@ -141,6 +141,19 @@ func newLessEqualTerm(tk *Token) (inst *term) {
 	}
 }
 
+func lessThanOrEqual(self *term, a, b any) (isLessEq bool, err error) {
+	if isLessEq, err = lessThan(self, a, b); err == nil {
+		if !isLessEq {
+			if IsList(a) && IsList(b) {
+				isLessEq, err = sameContent(a, b)
+			} else {
+				isLessEq, err = equals(a, b, nil)
+			}
+		}
+	}
+	return
+}
+
 func evalLessEqual(ctx ExprContext, self *term) (v any, err error) {
 	var leftValue, rightValue any
 
@@ -148,21 +161,8 @@ func evalLessEqual(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
+	v, err = lessThanOrEqual(self, leftValue, rightValue)
-		if isInteger(leftValue) && isInteger(rightValue) {
+
-			li, _ := leftValue.(int64)
-			ri, _ := rightValue.(int64)
-			v = li <= ri
-		} else {
-			v = numAsFloat(leftValue) <= numAsFloat(rightValue)
-		}
-	} else if isString(leftValue) && isString(rightValue) {
-		ls, _ := leftValue.(string)
-		rs, _ := rightValue.(string)
-		v = ls <= rs
-	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
-	}
 	return
 }
 
@@ -171,8 +171,6 @@ func evalLessEqual(ctx ExprContext, self *term) (v any, err error) {
 func newGreaterTerm(tk *Token) (inst *term) {
 	return &term{
 		tk:       *tk,
-		// class:    classOperator,
-		// kind:     kindBool,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priRelational,
@@ -181,10 +179,13 @@ func newGreaterTerm(tk *Token) (inst *term) {
 }
 
 func evalGreater(ctx ExprContext, self *term) (v any, err error) {
-	if v, err = evalLessEqual(ctx, self); err == nil {
+	var leftValue, rightValue any
-		b, _ := toBool(v)
+
-		v = !b
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
 	}
+
+	v, err = lessThan(self, rightValue, leftValue)
 	return
 }
 
@@ -193,8 +194,6 @@ func evalGreater(ctx ExprContext, self *term) (v any, err error) {
 func newGreaterEqualTerm(tk *Token) (inst *term) {
 	return &term{
 		tk:       *tk,
-		// class:    classOperator,
-		// kind:     kindBool,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priRelational,
@@ -203,10 +202,13 @@ func newGreaterEqualTerm(tk *Token) (inst *term) {
 }
 
 func evalGreaterEqual(ctx ExprContext, self *term) (v any, err error) {
-	if v, err = evalLess(ctx, self); err == nil {
+	var leftValue, rightValue any
-		b, _ := toBool(v)
+
-		v = !b
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
 	}
+
+	v, err = lessThanOrEqual(self, rightValue, leftValue)
 	return
 }
 

operator-sign.go

@@ -35,14 +35,14 @@ func evalSign(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isFloat(rightValue) {
+	if IsFloat(rightValue) {
 		if self.tk.Sym == SymChangeSign {
 			f, _ := rightValue.(float64)
 			v = -f
 		} else {
 			v = rightValue
 		}
-	} else if isInteger(rightValue) {
+	} else if IsInteger(rightValue) {
 		if self.tk.Sym == SymChangeSign {
 			i, _ := rightValue.(int64)
 			v = -i

operator-sum.go

@@ -28,25 +28,21 @@ func evalPlus(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if (isString(leftValue) && isNumberString(rightValue)) || (isString(rightValue) && isNumberString(leftValue)) {
+	if (IsString(leftValue) && isNumberString(rightValue)) || (IsString(rightValue) && isNumberString(leftValue)) {
 		v = fmt.Sprintf("%v%v", leftValue, rightValue)
-	} else if isNumber(leftValue) && isNumber(rightValue) {
+	} else if IsNumber(leftValue) && IsNumber(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
 			v = numAsFloat(leftValue) + numAsFloat(rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt + rightInt
 		}
-	} else if isList(leftValue) || isList(rightValue) {
+	} else if IsList(leftValue) && IsList(rightValue) {
 		var leftList, rightList *ListType
-		var ok bool
+		leftList, _ = leftValue.(*ListType)
-		if leftList, ok = leftValue.(*ListType); !ok {
+		rightList, _ = rightValue.(*ListType)
-			leftList = &ListType{leftValue}
+
-		}
-		if rightList, ok = rightValue.(*ListType); !ok {
-			rightList = &ListType{rightValue}
-		}
 		sumList := make(ListType, 0, len(*leftList)+len(*rightList))
 		for _, item := range *leftList {
 			sumList = append(sumList, item)
@@ -55,8 +51,18 @@ func evalPlus(ctx ExprContext, self *term) (v any, err error) {
 			sumList = append(sumList, item)
 		}
 		v = &sumList
-	} else if isFraction(leftValue) || isFraction(rightValue) {
+	} else if (isFraction(leftValue) && IsNumber(rightValue)) || (isFraction(rightValue) && IsNumber(leftValue)) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
+			v = numAsFloat(leftValue) + numAsFloat(rightValue)
+		} else {
 			v, err = sumAnyFract(leftValue, rightValue)
+		}
+	} else if IsDict(leftValue) && IsDict(rightValue) {
+		leftDict, _ := leftValue.(*DictType)
+		rightDict, _ := rightValue.(*DictType)
+		c := leftDict.clone()
+		c.merge(rightDict)
+		v = c
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
@@ -82,15 +88,17 @@ func evalMinus(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
+	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
 			v = numAsFloat(leftValue) - numAsFloat(rightValue)
+		} else if isFraction(leftValue) || isFraction(rightValue) {
+			v, err = subAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt - rightInt
 		}
-	} else if isList(leftValue) && isList(rightValue) {
+	} else if IsList(leftValue) && IsList(rightValue) {
 		leftList, _ := leftValue.(*ListType)
 		rightList, _ := rightValue.(*ListType)
 		diffList := make(ListType, 0, len(*leftList)-len(*rightList))
@@ -100,8 +108,6 @@ func evalMinus(ctx ExprContext, self *term) (v any, err error) {
 			}
 		}
 		v = &diffList
-	} else if isFraction(leftValue) || isFraction(rightValue) {
-		v, err = subAnyFract(leftValue, rightValue)
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}

parser.go

@@ -119,7 +119,7 @@ func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 	for lastSym != SymClosedRound && lastSym != SymEos {
 		tk = scanner.Next()
 		if tk.IsSymbol(SymIdentifier) {
-			param := newTerm(tk, nil)
+			param := newTerm(tk)
 			args = append(args, param)
 			tk = scanner.Next()
 		} else if itemExpected {
@@ -154,15 +154,34 @@ func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 	return
 }
 
-func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
+func (self *parser) parseList(scanner *scanner, parsingIndeces bool, allowVarRef bool) (subtree *term, err error) {
+	r, c := scanner.lastPos()
 	args := make([]*term, 0)
 	lastSym := SymUnknown
 	itemExpected := false
 	for lastSym != SymClosedSquare && lastSym != SymEos {
 		var subTree *ast
+		zeroRequired := scanner.current.Sym == SymColon
 		if subTree, err = self.parseItem(scanner, allowVarRef, SymComma, SymClosedSquare); err == nil {
-			if subTree.root != nil {
+			root := subTree.root
-				args = append(args, subTree.root)
+			if root != nil {
+				if !parsingIndeces && root.symbol() == SymColon {
+					err = root.Errorf("unexpected range expression")
+					break
+				}
+				args = append(args, root)
+				if parsingIndeces && root.symbol() == SymColon && zeroRequired { //len(root.children) == 0 {
+					if len(root.children) == 1 {
+						root.children = append(root.children, root.children[0])
+					} else if len(root.children) > 1 {
+						err = root.Errorf("invalid range specification")
+						break
+					}
+					zeroTk := NewValueToken(root.tk.row, root.tk.col, SymInteger, "0", int64(0))
+					zeroTerm := newTerm(zeroTk)
+					zeroTerm.setParent(root)
+					root.children[0] = zeroTerm
+				}
 			} else if itemExpected {
 				prev := scanner.Previous()
 				err = prev.ErrorExpectedGot("list-item")
@@ -175,11 +194,10 @@ func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term
 		itemExpected = lastSym == SymComma
 	}
 	if err == nil {
-		// TODO Check arguments
 		if lastSym != SymClosedSquare {
 			err = scanner.Previous().ErrorExpectedGot("]")
 		} else {
-			subtree = newListTerm(args)
+			subtree = newListTerm(r, c, args)
 		}
 	}
 	return
@@ -277,6 +295,7 @@ func (self *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtree
 			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
 			subtree = newDictTerm(args)
+			// subtree = newMapTerm(args)
 		}
 	}
 	return
@@ -293,14 +312,14 @@ func (self *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defaul
 			err = tk.Errorf("case list in default clause")
 			return
 		}
-		if filterList, err = self.parseList(scanner, allowVarRef); err != nil {
+		if filterList, err = self.parseList(scanner, false, allowVarRef); err != nil {
 			return
 		}
 		tk = scanner.Next()
 		startRow = tk.row
 		startCol = tk.col
 	} else if !defaultCase {
-		filterList = newListTerm(make([]*term, 0))
+		filterList = newListTerm(startRow, startCol, make([]*term, 0))
 	}
 
 	if tk.Sym == SymOpenBrace {
@@ -351,6 +370,14 @@ func (self *parser) Parse(scanner *scanner, termSymbols ...Symbol) (tree *ast, e
 	return self.parseGeneral(scanner, true, false, termSymbols...)
 }
 
+func couldBeACollection(t *term) bool {
+	var sym = SymUnknown
+	if t != nil {
+		sym = t.symbol()
+	}
+	return sym == SymList || sym == SymString || sym == SymDict || sym == SymExpression || sym == SymVariable
+}
+
 func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef bool, termSymbols ...Symbol) (tree *ast, err error) {
 	var selectorTerm *term = nil
 	var currentTerm *term = nil
@@ -389,7 +416,7 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 			var subTree *ast
 			if subTree, err = self.parseGeneral(scanner, false, allowVarRef, SymClosedRound); err == nil {
 				subTree.root.priority = priValue
-				err = tree.addTerm(subTree.root)
+				err = tree.addTerm(newExprTerm(subTree.root))
 				currentTerm = subTree.root
 			}
 		case SymFuncCall:
@@ -400,16 +427,29 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 			}
 		case SymOpenSquare:
 			var listTerm *term
-			if listTerm, err = self.parseList(scanner, allowVarRef); err == nil {
+			parsingIndeces := couldBeACollection(currentTerm)
+			if listTerm, err = self.parseList(scanner, parsingIndeces, allowVarRef); err == nil {
+				if parsingIndeces {
+					indexTk := NewToken(listTerm.tk.row, listTerm.tk.col, SymIndex, listTerm.source())
+					indexTerm := newTerm(indexTk)
+					if err = tree.addTerm(indexTerm); err == nil {
 						err = tree.addTerm(listTerm)
+					}
+				} else {
+					err = tree.addTerm(listTerm)
+				}
 				currentTerm = listTerm
 			}
 		case SymOpenBrace:
+			if currentTerm != nil && currentTerm.symbol() == SymColon {
+				err = currentTerm.Errorf(`selector-case outside of a selector context`)
+			} else {
 				var mapTerm *term
 				if mapTerm, err = self.parseDictionary(scanner, allowVarRef); err == nil {
 					err = tree.addTerm(mapTerm)
 					currentTerm = mapTerm
 				}
+			}
 		case SymEqual:
 			if err = checkPrevSymbol(lastSym, SymIdentifier, tk); err == nil {
 				currentTerm, err = tree.addToken2(tk)
@@ -438,15 +478,17 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 			}
 		case SymColon, SymDoubleColon:
 			var caseTerm *term
-			if selectorTerm == nil {
+			if selectorTerm != nil {
-				err = tk.Errorf("selector-case outside of a selector context")
+				if caseTerm, err = self.parseSelectorCase(scanner, allowVarRef, tk.Sym == SymDoubleColon); err == nil {
-			} else if caseTerm, err = self.parseSelectorCase(scanner, allowVarRef, tk.Sym == SymDoubleColon); err == nil {
 					addSelectorCase(selectorTerm, caseTerm)
 					currentTerm = caseTerm
 					if tk.Sym == SymDoubleColon {
 						selectorTerm = nil
 					}
 				}
+			} else {
+				currentTerm, err = tree.addToken2(tk)
+			}
 		default:
 			currentTerm, err = tree.addToken2(tk)
 		}

scanner.go

@@ -74,6 +74,14 @@ func (self *scanner) unreadChar() (err error) {
 	return
 }
 
+func (self *scanner) lastPos() (r, c int) {
+	if self.prev != nil {
+		r = self.prev.row
+		c = self.prev.col
+	}
+	return
+}
+
 func (self *scanner) Previous() *Token {
 	return self.prev
 }
@@ -385,7 +393,8 @@ func (self *scanner) parseNumber(firstCh byte) (tk *Token) {
 				}
 			}
 		}
-		if err == nil && (ch == 'e' || ch == 'E') {
+		if err == nil {
+			if ch == 'e' || ch == 'E' {
 				sym = SymFloat
 				sb.WriteByte(ch)
 				if ch, err = self.readChar(); err == nil {
@@ -398,7 +407,23 @@ func (self *scanner) parseNumber(firstCh byte) (tk *Token) {
 							sb.WriteByte(ch)
 						}
 					} else {
-					err = errors.New("expected integer exponent")
+						err = fmt.Errorf("[%d:%d] expected integer exponent, got %c", self.row, self.column, ch)
+					}
+				}
+			} else if ch == '(' {
+				sym = SymFraction
+				sb.WriteByte(ch)
+				ch, err = self.readChar()
+				for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
+					sb.WriteByte(ch)
+				}
+				if err == nil {
+					if ch != ')' {
+						err = fmt.Errorf("[%d:%d] expected ')', got '%c'", self.row, self.column, ch)
+					} else {
+						sb.WriteByte(ch)
+						_, err = self.readChar()
+					}
 				}
 			}
 		}
@@ -412,6 +437,8 @@ func (self *scanner) parseNumber(firstCh byte) (tk *Token) {
 		txt := sb.String()
 		if sym == SymFloat {
 			value, err = strconv.ParseFloat(txt, 64)
+		} else if sym == SymFraction {
+			value, err = makeGeneratingFraction(txt)
 		} else {
 			value, err = strconv.ParseInt(txt, numBase, 64)
 		}

simple-func-store.go

@@ -1,142 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// simple-func-store.go
-package expr
-
-import (
-	"fmt"
-	"strings"
-)
-
-type SimpleFuncStore struct {
-	SimpleVarStore
-	funcStore map[string]*funcInfo
-}
-
-type funcInfo struct {
-	name    string
-	minArgs int
-	maxArgs int
-	functor Functor
-}
-
-func (info *funcInfo) ToString(opt FmtOpt) string {
-	var sb strings.Builder
-	var i int
-	sb.WriteString("func(")
-	for i = 0; i < info.minArgs; i++ {
-		if i > 0 {
-			sb.WriteString(", ")
-		}
-		sb.WriteString(fmt.Sprintf("arg%d", i+1))
-	}
-	for ; i < info.maxArgs; i++ {
-		sb.WriteString(fmt.Sprintf("arg%d", i+1))
-	}
-	if info.maxArgs < 0 {
-		if info.minArgs > 0 {
-			sb.WriteString(", ")
-		}
-		sb.WriteString("...")
-	}
-	sb.WriteString(") {...}")
-	return sb.String()
-}
-
-func (info *funcInfo) Name() string {
-	return info.name
-}
-
-func (info *funcInfo) MinArgs() int {
-	return info.minArgs
-}
-
-func (info *funcInfo) MaxArgs() int {
-	return info.maxArgs
-}
-
-func (info *funcInfo) Functor() Functor {
-	return info.functor
-}
-
-func NewSimpleFuncStore() *SimpleFuncStore {
-	ctx := &SimpleFuncStore{
-		SimpleVarStore: SimpleVarStore{varStore: make(map[string]any)},
-		funcStore:      make(map[string]*funcInfo),
-	}
-	ImportBuiltinsFuncs(ctx)
-	return ctx
-}
-
-func (ctx *SimpleFuncStore) Clone() ExprContext {
-	svs := ctx.SimpleVarStore
-	return &SimpleFuncStore{
-		// SimpleVarStore: SimpleVarStore{varStore: CloneMap(ctx.varStore)},
-		SimpleVarStore: SimpleVarStore{varStore: svs.cloneVars()},
-		funcStore:      CloneFilteredMap(ctx.funcStore, func(name string) bool { return name[0] != '@' }),
-	}
-}
-
-func funcsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
-	sb.WriteString("funcs: {\n")
-	first := true
-	for _, name := range ctx.EnumFuncs(func(name string) bool { return true }) {
-		if first {
-			first = false
-		} else {
-			sb.WriteByte(',')
-			sb.WriteByte('\n')
-		}
-		value, _ := ctx.GetFuncInfo(name)
-		sb.WriteString(strings.Repeat("\t", indent+1))
-		sb.WriteString(name)
-		sb.WriteString("=")
-		if formatter, ok := value.(Formatter); ok {
-			sb.WriteString(formatter.ToString(0))
-		} else {
-			sb.WriteString(fmt.Sprintf("%v", value))
-		}
-	}
-	sb.WriteString("\n}\n")
-}
-
-func (ctx *SimpleFuncStore) ToString(opt FmtOpt) string {
-	var sb strings.Builder
-	sb.WriteString(ctx.SimpleVarStore.ToString(opt))
-	funcsCtxToBuilder(&sb, ctx, 0)
-	return sb.String()
-}
-
-func (ctx *SimpleFuncStore) GetFuncInfo(name string) (info ExprFunc, exists bool) {
-	info, exists = ctx.funcStore[name]
-	return
-}
-
-func (ctx *SimpleFuncStore) RegisterFunc(name string, functor Functor, minArgs, maxArgs int) {
-	ctx.funcStore[name] = &funcInfo{name: name, minArgs: minArgs, maxArgs: maxArgs, functor: functor}
-}
-
-func (ctx *SimpleFuncStore) EnumFuncs(acceptor func(name string) (accept bool)) (funcNames []string) {
-	funcNames = make([]string, 0)
-	for name := range ctx.funcStore {
-		if acceptor != nil {
-			if acceptor(name) {
-				funcNames = append(funcNames, name)
-			}
-		} else {
-			funcNames = append(funcNames, name)
-		}
-	}
-	return
-}
-
-func (ctx *SimpleFuncStore) Call(name string, args []any) (result any, err error) {
-	if info, exists := ctx.funcStore[name]; exists {
-		functor := info.functor
-		result, err = functor.Invoke(ctx, name, args)
-	} else {
-		err = fmt.Errorf("unknown function %s()", name)
-	}
-	return
-}

simple-func-store.go.bak

@@ -0,0 +1,244 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// simple-func-store.go
+package expr
+
+import (
+	"fmt"
+	"slices"
+	"strings"
+)
+
+type SimpleFuncStore struct {
+	SimpleVarStore
+	funcStore map[string]*funcInfo
+}
+
+type paramFlags uint16
+
+const (
+	pfOptional paramFlags = 1 << iota
+	pfRepeat
+)
+
+type funcParamInfo struct {
+	name         string
+	flags        paramFlags
+	defaultValue any
+}
+
+func newFuncParam(name string) *funcParamInfo {
+	return &funcParamInfo{name: name}
+}
+
+func newFuncParamFlag(name string, flags paramFlags) *funcParamInfo {
+	return &funcParamInfo{name: name, flags: flags}
+}
+
+func newFuncParamFlagDef(name string, flags paramFlags, defValue any) *funcParamInfo {
+	return &funcParamInfo{name: name, flags: flags, defaultValue: defValue}
+}
+
+func (param *funcParamInfo) Name() string {
+	return param.name
+}
+
+func (param *funcParamInfo) Type() string {
+	return "any"
+}
+
+func (param *funcParamInfo) IsOptional() bool {
+	return (param.flags & pfOptional) != 0
+}
+
+func (param *funcParamInfo) IsRepeat() bool {
+	return (param.flags & pfRepeat) != 0
+}
+
+func (param *funcParamInfo) DefaultValue() any {
+	return param.defaultValue
+}
+
+type funcInfo struct {
+	name       string
+	minArgs    int
+	maxArgs    int
+	functor    Functor
+	params     []ExprFuncParam
+	returnType string
+}
+
+func (info *funcInfo) Params() []ExprFuncParam {
+	return info.params
+}
+
+func (info *funcInfo) ReturnType() string {
+	return info.returnType
+}
+
+func (info *funcInfo) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	sb.WriteByte('(')
+	if info.params != nil {
+		for i, p := range info.params {
+			if i > 0 {
+				sb.WriteString(", ")
+			}
+			sb.WriteString(p.Name())
+			if p.IsOptional() {
+				sb.WriteByte('=')
+				if s, ok := p.DefaultValue().(string); ok {
+					sb.WriteByte('"')
+					sb.WriteString(s)
+					sb.WriteByte('"')
+				} else {
+					sb.WriteString(fmt.Sprintf("%v", p.DefaultValue()))
+				}
+			}
+		}
+	}
+	if info.maxArgs < 0 {
+		sb.WriteString(" ...")
+	}
+	sb.WriteString(") -> ")
+	if len(info.returnType) > 0 {
+		sb.WriteString(info.returnType)
+	} else {
+		sb.WriteString(typeAny)
+	}
+	return sb.String()
+}
+
+func (info *funcInfo) Name() string {
+	return info.name
+}
+
+func (info *funcInfo) MinArgs() int {
+	return info.minArgs
+}
+
+func (info *funcInfo) MaxArgs() int {
+	return info.maxArgs
+}
+
+func (info *funcInfo) Functor() Functor {
+	return info.functor
+}
+
+func NewSimpleFuncStore() *SimpleFuncStore {
+	ctx := &SimpleFuncStore{
+		SimpleVarStore: SimpleVarStore{varStore: make(map[string]any)},
+		funcStore:      make(map[string]*funcInfo),
+	}
+	//ImportBuiltinsFuncs(ctx)
+	return ctx
+}
+
+func (ctx *SimpleFuncStore) Clone() ExprContext {
+	svs := ctx.SimpleVarStore
+	return &SimpleFuncStore{
+		// SimpleVarStore: SimpleVarStore{varStore: CloneMap(ctx.varStore)},
+		SimpleVarStore: SimpleVarStore{varStore: svs.cloneVars()},
+		funcStore:      CloneFilteredMap(ctx.funcStore, func(name string) bool { return name[0] != '@' }),
+	}
+}
+
+func funcsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
+	sb.WriteString("funcs: {\n")
+	first := true
+	names := ctx.EnumFuncs(func(name string) bool { return true })
+	slices.Sort(names)
+	for _, name := range names {
+		if first {
+			first = false
+		} else {
+			sb.WriteByte(',')
+			sb.WriteByte('\n')
+		}
+		value, _ := ctx.GetFuncInfo(name)
+		sb.WriteString(strings.Repeat("\t", indent+1))
+		sb.WriteString(name)
+		//sb.WriteString("=")
+		if formatter, ok := value.(Formatter); ok {
+			sb.WriteString(formatter.ToString(0))
+		} else {
+			sb.WriteString(fmt.Sprintf("%v", value))
+		}
+	}
+	sb.WriteString("\n}\n")
+}
+
+func (ctx *SimpleFuncStore) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	sb.WriteString(ctx.SimpleVarStore.ToString(opt))
+	funcsCtxToBuilder(&sb, ctx, 0)
+	return sb.String()
+}
+
+func (ctx *SimpleFuncStore) GetFuncInfo(name string) (info ExprFunc, exists bool) {
+	info, exists = ctx.funcStore[name]
+	return
+}
+
+// func (ctx *SimpleFuncStore) RegisterFunc(name string, functor Functor, minArgs, maxArgs int) {
+// 	ctx.funcStore[name] = &funcInfo{name: name, minArgs: minArgs, maxArgs: maxArgs, functor: functor}
+// }
+
+func (ctx *SimpleFuncStore) RegisterFuncInfo(info ExprFunc) {
+	ctx.funcStore[info.Name()], _ = info.(*funcInfo)
+}
+
+func (ctx *SimpleFuncStore) RegisterFunc2(name string, functor Functor, returnType string, params []ExprFuncParam) error {
+	var minArgs = 0
+	var maxArgs = 0
+	if params != nil {
+		for _, p := range params {
+			if maxArgs == -1 {
+				return fmt.Errorf("no more params can be specified after the ellipsis symbol: %q", p.Name())
+				// } else if p.IsRepeat() {
+				// 	maxArgs = -1
+				// 	continue
+			}
+			if p.IsOptional() {
+				maxArgs++
+			} else if maxArgs == minArgs {
+				minArgs++
+				maxArgs++
+			} else {
+				return fmt.Errorf("can't specify non-optional param after optional ones: %q", p.Name())
+			}
+			if p.IsRepeat() {
+				maxArgs = -1
+			}
+		}
+	}
+	ctx.funcStore[name] = &funcInfo{
+		name: name, minArgs: minArgs, maxArgs: maxArgs, functor: functor, returnType: returnType, params: params,
+	}
+	return nil
+}
+
+func (ctx *SimpleFuncStore) EnumFuncs(acceptor func(name string) (accept bool)) (funcNames []string) {
+	funcNames = make([]string, 0)
+	for name := range ctx.funcStore {
+		if acceptor != nil {
+			if acceptor(name) {
+				funcNames = append(funcNames, name)
+			}
+		} else {
+			funcNames = append(funcNames, name)
+		}
+	}
+	return
+}
+
+func (ctx *SimpleFuncStore) Call(name string, args []any) (result any, err error) {
+	if info, exists := ctx.funcStore[name]; exists {
+		functor := info.functor
+		result, err = functor.Invoke(ctx, name, args)
+	} else {
+		err = fmt.Errorf("unknown function %s()", name)
+	}
+	return
+}

simple-store.go

@@ -0,0 +1,184 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// simple-store.go
+package expr
+
+import (
+	"fmt"
+	"slices"
+	"strings"
+)
+
+type SimpleStore struct {
+	varStore  map[string]any
+	funcStore map[string]ExprFunc
+}
+
+func NewSimpleStore() *SimpleStore {
+	ctx := &SimpleStore{
+		varStore:  make(map[string]any),
+		funcStore: make(map[string]ExprFunc),
+	}
+	return ctx
+}
+
+func filterRefName(name string) bool  { return name[0] != '@' }
+func filterPrivName(name string) bool { return name[0] != '_' }
+
+func (ctx *SimpleStore) Clone() ExprContext {
+	return &SimpleStore{
+		varStore:  CloneFilteredMap(ctx.varStore, filterRefName),
+		funcStore: CloneFilteredMap(ctx.funcStore, filterRefName),
+	}
+}
+
+func (ctx *SimpleStore) Merge(src ExprContext) {
+	for _, name := range src.EnumVars(filterRefName) {
+		ctx.varStore[name], _ = src.GetVar(name)
+	}
+	for _, name := range src.EnumFuncs(filterRefName) {
+		ctx.funcStore[name], _ = src.GetFuncInfo(name)
+	}
+}
+
+func varsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
+	sb.WriteString("vars: {\n")
+	first := true
+	for _, name := range ctx.EnumVars(filterPrivName) {
+		if first {
+			first = false
+		} else {
+			sb.WriteByte(',')
+			sb.WriteByte('\n')
+		}
+
+		value, _ := ctx.GetVar(name)
+		sb.WriteString(strings.Repeat("\t", indent+1))
+		sb.WriteString(name)
+		sb.WriteString(": ")
+		if f, ok := value.(Formatter); ok {
+			sb.WriteString(f.ToString(0))
+		} else if _, ok = value.(Functor); ok {
+			sb.WriteString("func(){}")
+			// } else if _, ok = value.(map[any]any); ok {
+			// 	sb.WriteString("dict{}")
+		} else {
+			sb.WriteString(fmt.Sprintf("%v", value))
+		}
+	}
+	sb.WriteString(strings.Repeat("\t", indent))
+	sb.WriteString("\n}\n")
+}
+
+func varsCtxToString(ctx ExprContext, indent int) string {
+	var sb strings.Builder
+	varsCtxToBuilder(&sb, ctx, indent)
+	return sb.String()
+}
+
+func funcsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
+	sb.WriteString("funcs: {\n")
+	first := true
+	names := ctx.EnumFuncs(func(name string) bool { return true })
+	slices.Sort(names)
+	for _, name := range names {
+		if first {
+			first = false
+		} else {
+			sb.WriteByte(',')
+			sb.WriteByte('\n')
+		}
+		value, _ := ctx.GetFuncInfo(name)
+		sb.WriteString(strings.Repeat("\t", indent+1))
+		sb.WriteString(name)
+		//sb.WriteString("=")
+		if formatter, ok := value.(Formatter); ok {
+			sb.WriteString(formatter.ToString(0))
+		} else {
+			sb.WriteString(fmt.Sprintf("%v", value))
+		}
+	}
+	sb.WriteString("\n}\n")
+}
+
+func (ctx *SimpleStore) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	varsCtxToBuilder(&sb, ctx, 0)
+	funcsCtxToBuilder(&sb, ctx, 0)
+	return sb.String()
+}
+
+func (ctx *SimpleStore) GetVar(varName string) (v any, exists bool) {
+	v, exists = ctx.varStore[varName]
+	return
+}
+
+func (ctx *SimpleStore) UnsafeSetVar(varName string, value any) {
+	// fmt.Printf("[%p] setVar(%v, %v)\n", ctx, varName, value)
+	ctx.varStore[varName] = value
+}
+
+func (ctx *SimpleStore) SetVar(varName string, value any) {
+	// fmt.Printf("[%p] SetVar(%v, %v)\n", ctx, varName, value)
+	if allowedValue, ok := fromGenericAny(value); ok {
+		ctx.varStore[varName] = allowedValue
+	} else {
+		panic(fmt.Errorf("unsupported type %T of value %v", value, value))
+	}
+}
+
+func (ctx *SimpleStore) EnumVars(acceptor func(name string) (accept bool)) (varNames []string) {
+	varNames = make([]string, 0)
+	for name := range ctx.varStore {
+		if acceptor != nil {
+			if acceptor(name) {
+				varNames = append(varNames, name)
+			}
+		} else {
+			varNames = append(varNames, name)
+		}
+	}
+	return
+}
+
+func (ctx *SimpleStore) GetFuncInfo(name string) (info ExprFunc, exists bool) {
+	info, exists = ctx.funcStore[name]
+	return
+}
+
+func (ctx *SimpleStore) RegisterFuncInfo(info ExprFunc) {
+	ctx.funcStore[info.Name()], _ = info.(*funcInfo)
+}
+
+func (ctx *SimpleStore) RegisterFunc(name string, functor Functor, returnType string, params []ExprFuncParam) (err error) {
+	var info *funcInfo
+	if info, err = newFuncInfo(name, functor, returnType, params); err == nil {
+		ctx.funcStore[name] = info
+	}
+	return
+}
+
+func (ctx *SimpleStore) EnumFuncs(acceptor func(name string) (accept bool)) (funcNames []string) {
+	funcNames = make([]string, 0)
+	for name := range ctx.funcStore {
+		if acceptor != nil {
+			if acceptor(name) {
+				funcNames = append(funcNames, name)
+			}
+		} else {
+			funcNames = append(funcNames, name)
+		}
+	}
+	return
+}
+
+func (ctx *SimpleStore) Call(name string, args []any) (result any, err error) {
+	if info, exists := ctx.funcStore[name]; exists {
+		functor := info.Functor()
+		result, err = functor.Invoke(ctx, name, args)
+	} else {
+		err = fmt.Errorf("unknown function %s()", name)
+	}
+	return
+}

simple-var-store.go.bak

@@ -36,7 +36,7 @@ func (ctx *SimpleVarStore) GetVar(varName string) (v any, exists bool) {
 	return
 }
 
-func (ctx *SimpleVarStore) setVar(varName string, value any) {
+func (ctx *SimpleVarStore) UnsafeSetVar(varName string, value any) {
 	// fmt.Printf("[%p] setVar(%v, %v)\n", ctx, varName, value)
 	ctx.varStore[varName] = value
 }
@@ -72,7 +72,12 @@ func (ctx *SimpleVarStore) Call(name string, args []any) (result any, err error)
 	return
 }
 
-func (ctx *SimpleVarStore) RegisterFunc(name string, functor Functor, minArgs, maxArgs int) {
+// func (ctx *SimpleVarStore) RegisterFunc(name string, functor Functor, minArgs, maxArgs int) {
+// }
+func (ctx *SimpleVarStore) RegisterFuncInfo(info ExprFunc) {
+}
+func (ctx *SimpleVarStore) RegisterFunc2(name string, f Functor, returnType string, param []ExprFuncParam) error {
+	return nil
 }
 
 func (ctx *SimpleVarStore) EnumFuncs(acceptor func(name string) (accept bool)) (funcNames []string) {
@@ -98,8 +103,8 @@ func varsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
 			sb.WriteString(f.ToString(0))
 		} else if _, ok = value.(Functor); ok {
 			sb.WriteString("func(){}")
-		} else if _, ok = value.(map[any]any); ok {
+			// } else if _, ok = value.(map[any]any); ok {
-			sb.WriteString("dict{}")
+			// 	sb.WriteString("dict{}")
 		} else {
 			sb.WriteString(fmt.Sprintf("%v", value))
 		}

symbol.go

@@ -72,7 +72,9 @@ const (
 	SymIdentifier
 	SymBool
 	SymInteger
+	SymVariable
 	SymFloat
+	SymFraction
 	SymString
 	SymIterator
 	SymOr
@@ -83,6 +85,7 @@ const (
 	SymFuncDef
 	SymList
 	SymDict
+	SymIndex
 	SymExpression
 	SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
 	SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"
@@ -98,6 +101,7 @@ const (
 	SymKwBut
 	SymKwFunc
 	SymKwBuiltin
+	SymKwIn
 	SymKwInclude
 	SymKwNil
 )
@@ -111,6 +115,7 @@ func init() {
 		"BUILTIN": SymKwBuiltin,
 		"BUT":     SymKwBut,
 		"FUNC":    SymKwFunc,
+		"IN":      SymKwIn,
 		"INCLUDE": SymKwInclude,
 		"NOT":     SymKwNot,
 		"OR":      SymKwOr,

t_ast_test.go

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// ast_test.go
+// t_ast_test.go
 package expr
 
 import (

t_dict_test.go

@@ -0,0 +1,150 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_dict_test.go
+package expr
+
+import (
+	"errors"
+
+	"strings"
+	"testing"
+)
+
+func TestDictParser(t *testing.T) {
+	section := "Dict"
+
+	type inputType struct {
+		source     string
+		wantResult any
+		wantErr    error
+	}
+
+	inputs := []inputType{
+		/*  1 */ {`{}`, map[any]any{}, nil},
+		/*  2 */ {`{123}`, nil, errors.New(`[1:6] expected ":", got "}"`)},
+		/*  3 */ {`{1:"one",2:"two",3:"three"}`, map[int64]any{int64(1): "one", int64(2): "two", int64(3): "three"}, nil},
+		/*  4 */ {`{1:"one",2:"two",3:"three"}[3]`, "three", nil},
+		/*  5 */ {`#{1:"one",2:"two",3:"three"}`, int64(3), nil},
+		/*  6 */ {`{1:"one"} + {2:"two"}`, map[any]any{1: "one", 2: "two"}, nil},
+		/*  7 */ {`2 in {1:"one", 2:"two"}`, true, nil},
+	}
+
+	succeeded := 0
+	failed := 0
+
+	// inputs1 := []inputType{
+	// 	/*  7 */ {`add([1,4,3,2])`, int64(10), nil},
+	// }
+
+	for i, input := range inputs {
+		var expr *ast
+		var gotResult any
+		var gotErr error
+
+		ctx := NewSimpleStore()
+		ctx.SetVar("var1", int64(123))
+		ctx.SetVar("var2", "abc")
+		ImportMathFuncs(ctx)
+		parser := NewParser(ctx)
+
+		logTest(t, i+1, "Dict", input.source, input.wantResult, input.wantErr)
+
+		r := strings.NewReader(input.source)
+		scanner := NewScanner(r, DefaultTranslations())
+
+		good := true
+		if expr, gotErr = parser.Parse(scanner); gotErr == nil {
+			gotResult, gotErr = expr.Eval(ctx)
+		}
+
+		if (gotResult == nil && input.wantResult != nil) || (gotResult != nil && input.wantResult == nil) {
+			t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
+			good = false
+		}
+
+		if gotList, okGot := gotResult.([]any); okGot {
+			if wantList, okWant := input.wantResult.([]any); okWant {
+				if (gotList == nil && wantList != nil) || (gotList != nil && wantList == nil) {
+					t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
+					good = false
+				} else {
+					equal := len(gotList) == len(wantList)
+					if equal {
+						for i, gotItem := range gotList {
+							wantItem := wantList[i]
+							equal = gotItem == wantItem
+							if !equal {
+								break
+							}
+						}
+					}
+					if !equal {
+						t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
+						good = false
+					}
+				}
+			}
+		}
+
+		if gotErr != input.wantErr {
+			if input.wantErr == nil || gotErr == nil || (gotErr.Error() != input.wantErr.Error()) {
+				t.Errorf("%d: %q  -> err = <%v>, want <%v>", i+1, input.source, gotErr, input.wantErr)
+				good = false
+			}
+		}
+
+		if good {
+			succeeded++
+		} else {
+			failed++
+		}
+	}
+	t.Logf("%s -- test count: %d, succeeded: %d, failed: %d", section, len(inputs), succeeded, failed)
+}
+
+func TestDictToStringMultiLine(t *testing.T) {
+	var good bool
+	section := "dict-ToString-ML"
+	want := `{
+	"first": 1
+}`
+	args := map[any]*term{
+		"first": newLiteralTerm(NewValueToken(0, 0, SymInteger, "1", 1)),
+	}
+	dict := newDict(args)
+	got := dict.ToString(MultiLine)
+	// fmt.Printf("got=%q\n", got)
+
+	if good = got == want; !good {
+		t.Errorf("ToString(MultiLine): got = %q, want %q", got, want)
+	}
+
+	if good {
+		t.Logf("%s -- succeeded", section)
+	} else {
+		t.Logf("%s -- failed", section)
+	}
+}
+
+func TestDictToString(t *testing.T) {
+	var good bool
+	section := "dict-ToString-SL"
+	want := `{"first": 1}`
+	args := map[any]*term{
+		"first": newLiteralTerm(NewValueToken(0, 0, SymInteger, "1", 1)),
+	}
+	dict := newDict(args)
+	got := dict.ToString(0)
+	// fmt.Printf("got=%q\n", got)
+
+	if good = got == want; !good {
+		t.Errorf("ToString(0): got = %q, want %q", got, want)
+	}
+
+	if good {
+		t.Logf("%s -- succeeded", section)
+	} else {
+		t.Logf("%s -- failed", section)
+	}
+}

t_expr_test.go

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// expr_test.go
+// t_expr_test.go
 package expr
 
 import (
@@ -21,13 +21,8 @@ func TestExpr(t *testing.T) {
 		/*   2 */ {`fact=func(n){(n)?{1}::{n*fact(n-1)}}; fact(5)`, int64(120), nil},
 		/*   3 */ {`f=openFile("test-file.txt"); line=readFile(f); closeFile(f); line`, "uno", nil},
 		/*   4 */ {`mynot=func(v){int(v)?{true}::{false}}; mynot(0)`, true, nil},
-	}
+		/*   5 */ {`1 ? {1} : [1+0] {3*(1+1)}`, int64(6), nil},
-
+		/*   6 */ {`
-	succeeded := 0
-	failed := 0
-
-	inputs1 := []inputType{
-		/*   1 */ {`
 		ds={
 			"init":func(end){@end=end; @current=0 but true},
 			"current":func(){current},
@@ -41,12 +36,15 @@ func TestExpr(t *testing.T) {
 `, int64(1), nil},
 	}
 
-	for i, input := range inputs1 {
+	succeeded := 0
+	failed := 0
+
+	for i, input := range inputs {
 		var expr Expr
 		var gotResult any
 		var gotErr error
 
-		ctx := NewSimpleFuncStore()
+		ctx := NewSimpleStore()
 		// ImportMathFuncs(ctx)
 		// ImportImportFunc(ctx)
 		ImportOsFuncs(ctx)

t_funcs_test.go

@@ -0,0 +1,116 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_funcs_test.go
+package expr
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestFuncs(t *testing.T) {
+	inputs := []inputType{
+		/*   1 */ {`isNil(nil)`, true, nil},
+		/*   2 */ {`v=nil; isNil(v)`, true, nil},
+		/*   3 */ {`v=5; isNil(v)`, false, nil},
+		/*   4 */ {`int(true)`, int64(1), nil},
+		/*   5 */ {`int(false)`, int64(0), nil},
+		/*   6 */ {`int(3.1)`, int64(3), nil},
+		/*   7 */ {`int(3.9)`, int64(3), nil},
+		/*   8 */ {`int("432")`, int64(432), nil},
+		/*   9 */ {`int("1.5")`, nil, errors.New(`strconv.Atoi: parsing "1.5": invalid syntax`)},
+		/*  10 */ {`int("432", 4)`, nil, errors.New(`too much params -- expected 1, got 2`)},
+		/*  11 */ {`int(nil)`, nil, errors.New(`int() can't convert <nil> to int`)},
+		/*  12 */ {`two=func(){2}; two()`, int64(2), nil},
+		/*  13 */ {`double=func(x) {2*x}; (double(3))`, int64(6), nil},
+		/*  14 */ {`double=func(x){2*x}; double(3)`, int64(6), nil},
+		/*  15 */ {`double=func(x){2*x}; a=5; double(3+a) + 1`, int64(17), nil},
+		/*  16 */ {`double=func(x){2*x}; a=5; two=func() {2}; (double(3+a) + 1) * two()`, int64(34), nil},
+		/*  17 */ {`builtin "import"; import("./test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
+		/*  18 */ {`builtin "import"; import("test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
+		/*  19 */ {`@x="hello"; @x`, nil, errors.New(`[1:3] variable references are not allowed in top level expressions: "@x"`)},
+		/*  20 */ {`f=func(){@x="hello"}; f(); x`, "hello", nil},
+		/*  21 */ {`f=func(@y){@y=@y+1}; f(2); y`, int64(3), nil},
+		/*  22 */ {`f=func(@y){g=func(){@x=5}; @y=@y+g()}; f(2); y+x`, nil, errors.New(`undefined variable or function "x"`)},
+		/*  23 */ {`f=func(@y){g=func(){@x=5}; @z=g(); @y=@y+@z}; f(2); y+z`, int64(12), nil},
+		/*  24 */ {`f=func(@y){g=func(){@x=5}; g(); @z=x; @y=@y+@z}; f(2); y+z`, int64(12), nil},
+		/*  25 */ {`f=func(@y){g=func(){@x=5}; g(); @z=x; @x=@y+@z}; f(2); y+x`, int64(9), nil},
+		/*  26 */ {`builtin "import"; importAll("./test-funcs.expr"); six()`, int64(6), nil},
+		/*  27 */ {`builtin "import"; import("./sample-export-all.expr"); six()`, int64(6), nil},
+		/*  28 */ {`builtin "string"; joinStr("-", "one", "two", "three")`, "one-two-three", nil},
+		/*  29 */ {`builtin "string"; joinStr("-", ["one", "two", "three"])`, "one-two-three", nil},
+		/*  30 */ {`builtin "string"; ls= ["one", "two", "three"]; joinStr("-", ls)`, "one-two-three", nil},
+		/*  31 */ {`builtin "string"; ls= ["one", "two", "three"]; joinStr(1, ls)`, nil, errors.New(`joinStr() the "separator" parameter must be a string, got a int64 (1)`)},
+		/*  32 */ {`builtin "string"; ls= ["one", 2, "three"]; joinStr("-", ls)`, nil, errors.New(`joinStr() expected string, got int64 (2)`)},
+		/*  33 */ {`builtin "string"; "<"+trimStr("  bye bye  ")+">"`, "<bye bye>", nil},
+		/*  34 */ {`builtin "string"; subStr("0123456789", 1,2)`, "12", nil},
+		/*  35 */ {`builtin "string"; subStr("0123456789", -3,2)`, "78", nil},
+		/*  36 */ {`builtin "string"; subStr("0123456789", -3)`, "789", nil},
+		/*  37 */ {`builtin "string"; subStr("0123456789")`, "0123456789", nil},
+		/*  38 */ {`builtin "string"; startsWithStr("0123456789", "xyz", "012")`, true, nil},
+		/*  39 */ {`builtin "string"; startsWithStr("0123456789", "xyz", "0125")`, false, nil},
+		/*  40 */ {`builtin "string"; startsWithStr("0123456789")`, nil, errors.New(`too few params -- expected 2 or more, got 1`)},
+		/*  41 */ {`builtin "string"; endsWithStr("0123456789", "xyz", "789")`, true, nil},
+		/*  42 */ {`builtin "string"; endsWithStr("0123456789", "xyz", "0125")`, false, nil},
+		/*  43 */ {`builtin "string"; endsWithStr("0123456789")`, nil, errors.New(`too few params -- expected 2 or more, got 1`)},
+		/*  44 */ {`builtin "string"; splitStr("one-two-three", "-", )`, newListA("one", "two", "three"), nil},
+		/*  45 */ {`isInt(2+1)`, true, nil},
+		/*  46 */ {`isInt(3.1)`, false, nil},
+		/*  47 */ {`isFloat(3.1)`, true, nil},
+		/*  48 */ {`isString("3.1")`, true, nil},
+		/*  49 */ {`isString("3" + 1)`, true, nil},
+		/*  50 */ {`isList(["3",  1])`, true, nil},
+		/*  51 */ {`isDict({"a":"3",  "b":1})`, true, nil},
+		/*  52 */ {`isFract(1|3)`, true, nil},
+		/*  53 */ {`isFract(3|1)`, false, nil},
+		/*  54 */ {`isRational(3|1)`, true, nil},
+		/*  55 */ {`builtin "math.arith"; add(1,2)`, int64(3), nil},
+		/*  56 */ {`fract("2.2(3)")`, newFraction(67, 30), nil},
+		/*  57 */ {`fract("1.21(3)")`, newFraction(91, 75), nil},
+		/*  58 */ {`fract(1.21(3))`, newFraction(91, 75), nil},
+		/*  59 */ {`fract(1.21)`, newFraction(121, 100), nil},
+		/*  60 */ {`dec(2)`, float64(2), nil},
+		/*  61 */ {`dec(2.0)`, float64(2), nil},
+		/*  62 */ {`dec("2.0")`, float64(2), nil},
+		/*  63 */ {`dec(true)`, float64(1), nil},
+		/*  64 */ {`dec(true")`, nil, errors.New("[1:11] missing string termination \"")},
+		/*  65 */ {`builtin "string"; joinStr("-", [1, "two", "three"])`, nil, errors.New(`joinStr() expected string, got int64 (1)`)},
+		/*  66 */ {`dec()`, nil, errors.New(`too few params -- expected 1, got 0`)},
+		/*  67 */ {`dec(1,2,3)`, nil, errors.New(`too much params -- expected 1, got 3`)},
+		/*  68 */ {`builtin "string"; joinStr()`, nil, errors.New(`too few params -- expected 1 or more, got 0`)},
+		/*  69 */ /*{`builtin "string"; $$global`, `vars: {
+
+		}
+		funcs: {
+		    	add(any=0 ...) -> number,
+		    	dec(any) -> decimal,
+		    	endsWithStr(source, suffix) -> boolean,
+		    	fract(any, denominator=1) -> fraction,
+		    	import( ...) -> any,
+		    	importAll( ...) -> any,
+		    	int(any) -> integer,
+		    	isBool(any) -> boolean,
+		    	isDec(any) -> boolean,
+		    	isDict(any) -> boolean,
+		    	isFloat(any) -> boolean,
+		    	isFract(any) -> boolean,
+		    	isInt(any) -> boolean,
+		    	isList(any) -> boolean,
+		    	isNil(any) -> boolean,
+		    	isString(any) -> boolean,
+		    	joinStr(separator, item="" ...) -> string,
+		    	mul(any=1 ...) -> number,
+		    	splitStr(source, separator="", count=-1) -> list of string,
+		    	startsWithStr(source, prefix) -> boolean,
+		    	subStr(source, start=0, count=-1) -> string,
+		    	trimStr(source) -> string
+		}
+		`, nil},*/
+	}
+
+	t.Setenv("EXPR_PATH", ".")
+
+	// parserTestSpec(t, "Func", inputs, 69)
+	parserTest(t, "Func", inputs)
+}

t_graph_test.go

@@ -1,10 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// t_graph_test.go
-// All rights reserved.
-
-// graph_test.go
 package expr
 
 import (

t_helpers_test.go

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// helpers_test.go
+// t_helpers_test.go
 package expr
 
 import (
@@ -52,7 +52,7 @@ func TestEvalStringA(t *testing.T) {
 
 func TestEvalString(t *testing.T) {
 
-	ctx := NewSimpleVarStore()
+	ctx := NewSimpleStore()
 	ctx.SetVar("a", uint8(1))
 	ctx.SetVar("b", int8(2))
 	ctx.SetVar("f", 2.0)

t_index_test.go

@@ -0,0 +1,27 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_index_test.go
+package expr
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestCollections(t *testing.T) {
+	section := "Collection"
+	inputs := []inputType{
+		/*   1 */ {`"abcdef"[1:3]`, "bc", nil},
+		/*   2 */ {`"abcdef"[:3]`, "abc", nil},
+		/*   3 */ {`"abcdef"[1:]`, "bcdef", nil},
+		/*   4 */ {`"abcdef"[:]`, "abcdef", nil},
+		// /*   5 */ {`[0,1,2,3,4][:]`, ListType{int64(0), int64(1), int64(2), int64(3), int64(4)}, nil},
+		/*   5 */ {`"abcdef"[1:2:3]`, nil, errors.New(`[1:14] left operand '(1, 2)' [pair] and right operand '3' [integer] are not compatible with operator ":"`)},
+	}
+
+	t.Setenv("EXPR_PATH", ".")
+
+	// parserTestSpec(t, section, inputs, 5)
+	parserTest(t, section, inputs)
+}

t_iterator_test.go

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// iterator_test.go
+// t_iterator_test.go
 package expr
 
 import "testing"

t_list_test.go

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// list_test.go
+// t_list_test.go
 package expr
 
 import (
@@ -33,6 +33,19 @@ func TestListParser(t *testing.T) {
 		/*  11 */ {`[a=1,b=2,c=3] but a+b+c`, int64(6), nil},
 		/*  12 */ {`[1,2,3] << 2+2`, []any{int64(1), int64(2), int64(3), int64(4)}, nil},
 		/*  13 */ {`2-1 >> [2,3]`, []any{int64(1), int64(2), int64(3)}, nil},
+		/*  14 */ {`[1,2,3][1]`, int64(2), nil},
+		/*  15 */ {`ls=[1,2,3] but ls[1]`, int64(2), nil},
+		/*  16 */ {`ls=[1,2,3] but ls[-1]`, int64(3), nil},
+		/*  17 */ {`list=["one","two","three"]; list[10]`, nil, errors.New(`[1:34] index 10 out of bounds`)},
+		/*  18 */ {`["a", "b", "c"]`, newListA("a", "b", "c"), nil},
+		/*  19 */ {`["a", "b", "c"]`, newList([]any{"a", "b", "c"}), nil},
+		/*  20 */ {`#["a", "b", "c"]`, int64(3), nil},
+		/*  21 */ {`"b" in ["a", "b", "c"]`, true, nil},
+		/*  22 */ {`a=[1,2]; (a)<<3`, []any{1, 2, 3}, nil},
+		/*  23 */ {`a=[1,2]; (a)<<3; 1`, []any{1, 2}, nil},
+		/*  24 */ {`["a","b","c","d"][1]`, "b", nil},
+		/*  25 */ {`["a","b","c","d"][1,1]`, nil, errors.New(`[1:19] one index only is allowed`)},
+		/*  26 */ {`[0,1,2,3,4][:]`, ListType{int64(0), int64(1), int64(2), int64(3), int64(4)}, nil},
 
 		// /*  8 */ {`[int(x)|x=csv("test.csv",1,all(),1)]`, []any{int64(10), int64(40), int64(20)}, nil},
 		// /*  9 */ {`sum(@[int(x)|x=csv("test.csv",1,all(),1)])`, []any{int64(10), int64(40), int64(20)}, nil},
@@ -50,9 +63,7 @@ func TestListParser(t *testing.T) {
 		var gotResult any
 		var gotErr error
 
-		ctx := NewSimpleFuncStore()
+		ctx := NewSimpleStore()
-		ctx.SetVar("var1", int64(123))
-		ctx.SetVar("var2", "abc")
 		ImportMathFuncs(ctx)
 		parser := NewParser(ctx)
 

t_parser_test.go

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// parser_test.go
+// t_parser_test.go
 package expr
 
 import (
@@ -11,6 +11,12 @@ import (
 	"testing"
 )
 
+type inputType struct {
+	source     string
+	wantResult any
+	wantErr    error
+}
+
 func TestGeneralParser(t *testing.T) {
 	inputs := []inputType{
 		/*   1 */ {`1+/*5*/2`, int64(3), nil},
@@ -29,10 +35,10 @@ func TestGeneralParser(t *testing.T) {
 		/*  14 */ {`not true`, false, nil},
 		/*  15 */ {`true and false`, false, nil},
 		/*  16 */ {`true or false`, true, nil},
-		/*  17 */ {`"uno" + "due"`, `unodue`, nil},
+		/*  *17 */ {`"uno" + "due"`, `unodue`, nil},
-		/*  18 */ {`"uno" + 2`, `uno2`, nil},
+		/*  *18 */ {`"uno" + 2`, `uno2`, nil},
-		/*  19 */ {`"uno" + (2+1)`, `uno3`, nil},
+		/*  *19 */ {`"uno" + (2+1)`, `uno3`, nil},
-		/*  20 */ {`"uno" * (2+1)`, `unounouno`, nil},
+		/*  *20 */ {`"uno" * (2+1)`, `unounouno`, nil},
 		/*  21 */ {"1", int64(1), nil},
 		/*  22 */ {"1.5", float64(1.5), nil},
 		/*  23 */ {"1.5*2", float64(3.0), nil},
@@ -92,7 +98,7 @@ func TestGeneralParser(t *testing.T) {
 		/*  77 */ {`5 % 2`, int64(1), nil},
 		/*  78 */ {`5 % (-2)`, int64(1), nil},
 		/*  79 */ {`-5 % 2`, int64(-1), nil},
-		/*  80 */ {`5 % 2.0`, nil, errors.New(`[1:4] left operand '5' [int64] and right operand '2' [float64] are not compatible with operator "%"`)},
+		/*  80 */ {`5 % 2.0`, nil, errors.New(`[1:4] left operand '5' [integer] and right operand '2' [float] are not compatible with operator "%"`)},
 		/*  81 */ {`"a" < "b" AND NOT (2 < 1)`, true, nil},
 		/*  82 */ {`"a" < "b" AND NOT (2 == 1)`, true, nil},
 		/*  83 */ {`"a" < "b" AND ~ 2 == 1`, true, nil},
@@ -131,7 +137,7 @@ func TestGeneralParser(t *testing.T) {
 		/* 116 */ {`null`, nil, errors.New(`undefined variable or function "null"`)},
 		/* 117 */ {`{"key"}`, nil, errors.New(`[1:8] expected ":", got "}"`)},
 		/* 118 */ {`{"key":}`, nil, errors.New(`[1:9] expected "dictionary-value", got "}"`)},
-		/* 119 */ {`{}`, map[any]any{}, nil},
+		/* 119 */ {`{}`, &DictType{}, nil},
 		/* 120 */ {`1|2`, newFraction(1, 2), nil},
 		/* 121 */ {`1|2 + 1`, newFraction(3, 2), nil},
 		/* 122 */ {`1|2 - 1`, newFraction(-1, 2), nil},
@@ -150,68 +156,30 @@ func TestGeneralParser(t *testing.T) {
 		/* 135 */ {`builtin "math.arith"; mul(1|2, 2|3)`, newFraction(2, 6), nil},
 		/* 136 */ {`builtin "math.arith"; mul(1|2, 1.0, 2)`, float64(1.0), nil},
 		/* 137 */ {`builtin "os.file"`, int64(1), nil},
+		/* 138 */ {`v=10; v++; v`, int64(11), nil},
+		/* 139 */ {`1+1|2+0.5`, float64(2), nil},
+		/* 140 */ {`1.2()`, newFraction(6, 5), nil},
+		/* 141 */ {`1|(2-2)`, nil, errors.New(`division by zero`)},
 	}
-	check_env_expr_path := 113
 
+	// t.Setenv("EXPR_PATH", ".")
+	// parserTestSpec(t, "General", inputs, 102)
+	parserTest(t, "General", inputs)
+}
+
+func parserTestSpec(t *testing.T, section string, inputs []inputType, spec ...int) {
 	succeeded := 0
 	failed := 0
-
+	for _, count := range spec {
-	// inputs1 := []inputType{
+		good := doTest(t, section, &inputs[count-1], count)
-	// 	/* 159 */ {`include "file-reader.expr"; it=$(ds,"int.list"); mul(it)`, int64(12000), nil},
-	// }
-
-	for i, input := range inputs {
-		var expr Expr
-		var gotResult any
-		var gotErr error
-
-		ctx := NewSimpleFuncStore()
-		// ctx.SetVar("var1", int64(123))
-		// ctx.SetVar("var2", "abc")
-		// ImportMathFuncs(ctx)
-		// ImportImportFuncs(ctx)
-		parser := NewParser(ctx)
-
-		logTest(t, i+1, "General", input.source, input.wantResult, input.wantErr)
-
-		r := strings.NewReader(input.source)
-		scanner := NewScanner(r, DefaultTranslations())
-
-		good := true
-		if expr, gotErr = parser.Parse(scanner); gotErr == nil {
-			gotResult, gotErr = expr.Eval(ctx)
-		}
-
-		eq := reflect.DeepEqual(gotResult, input.wantResult)
-
-		if !eq /*gotResult != input.wantResult*/ {
-			t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
-			good = false
-		}
-
-		if gotErr != input.wantErr {
-			if input.wantErr == nil || gotErr == nil || (gotErr.Error() != input.wantErr.Error()) {
-				t.Errorf("%d: %q -> err = <%v>, want <%v>", i+1, input.source, gotErr, input.wantErr)
-				good = false
-			}
-		}
 
 		if good {
 			succeeded++
 		} else {
 			failed++
-			if i+1 == check_env_expr_path {
-				t.Logf(`NOTICE: Test nr %d requires EXPR_PATH="."`, check_env_expr_path)
 		}
 	}
-	}
+	t.Logf("%s -- test count: %d, succeeded: %d, failed: %d", section, len(spec), succeeded, failed)
-	t.Logf("test count: %d, succeeded count: %d, failed count: %d", len(inputs), succeeded, failed)
-}
-
-type inputType struct {
-	source     string
-	wantResult any
-	wantErr    error
 }
 
 func parserTest(t *testing.T, section string, inputs []inputType) {
@@ -219,46 +187,8 @@ func parserTest(t *testing.T, section string, inputs []inputType) {
 	succeeded := 0
 	failed := 0
 
-	// inputs1 := []inputType{
-	// 	/* 159 */ {`include "file-reader.expr"; it=$(ds,"int.list"); mul(it)`, int64(12000), nil},
-	// }
-
 	for i, input := range inputs {
-		var expr Expr
+		good := doTest(t, section, &input, i+1)
-		var gotResult any
-		var gotErr error
-
-		ctx := NewSimpleFuncStore()
-		// ctx.SetVar("var1", int64(123))
-		// ctx.SetVar("var2", "abc")
-		// ImportMathFuncs(ctx)
-		// ImportImportFuncs(ctx)
-		parser := NewParser(ctx)
-
-		logTest(t, i+1, "Iterator", input.source, input.wantResult, input.wantErr)
-
-		r := strings.NewReader(input.source)
-		scanner := NewScanner(r, DefaultTranslations())
-
-		good := true
-		if expr, gotErr = parser.Parse(scanner); gotErr == nil {
-			gotResult, gotErr = expr.Eval(ctx)
-		}
-
-		eq := reflect.DeepEqual(gotResult, input.wantResult)
-
-		if !eq /*gotResult != input.wantResult*/ {
-			t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
-			good = false
-		}
-
-		if gotErr != input.wantErr {
-			if input.wantErr == nil || gotErr == nil || (gotErr.Error() != input.wantErr.Error()) {
-				t.Errorf("%d: %q -> err = <%v>, want <%v>", i+1, input.source, gotErr, input.wantErr)
-				good = false
-			}
-		}
-
 		if good {
 			succeeded++
 		} else {
@@ -268,6 +198,40 @@ func parserTest(t *testing.T, section string, inputs []inputType) {
 	t.Logf("%s -- test count: %d, succeeded: %d, failed: %d", section, len(inputs), succeeded, failed)
 }
 
+func doTest(t *testing.T, section string, input *inputType, count int) (good bool) {
+	var expr Expr
+	var gotResult any
+	var gotErr error
+
+	ctx := NewSimpleStore()
+	parser := NewParser(ctx)
+
+	logTest(t, count, section, input.source, input.wantResult, input.wantErr)
+
+	r := strings.NewReader(input.source)
+	scanner := NewScanner(r, DefaultTranslations())
+
+	good = true
+	if expr, gotErr = parser.Parse(scanner); gotErr == nil {
+		gotResult, gotErr = expr.Eval(ctx)
+	}
+
+	eq := reflect.DeepEqual(gotResult, input.wantResult)
+
+	if !eq /*gotResult != input.wantResult*/ {
+		t.Errorf("%d: %q -> result = %v [%T], want = %v [%T]", count, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
+		good = false
+	}
+
+	if gotErr != input.wantErr {
+		if input.wantErr == nil || gotErr == nil || (gotErr.Error() != input.wantErr.Error()) {
+			t.Errorf("%d: %q -> got-err = <%v>, expected-err = <%v>", count, input.source, gotErr, input.wantErr)
+			good = false
+		}
+	}
+	return
+}
+
 func logTest(t *testing.T, n int, section, source string, wantResult any, wantErr error) {
 	if wantErr == nil {
 		t.Logf("[+]%s nr %3d -- %q  --> %v", section, n, source, wantResult)

t_relational_test.go

@@ -0,0 +1,52 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_template_test.go
+package expr
+
+import (
+	"testing"
+)
+
+func TestRelational(t *testing.T) {
+	section := "Relational"
+	inputs := []inputType{
+		/*   1 */ {`1 == 3-2`, true, nil},
+		/*   2 */ {`"a" == "a"`, true, nil},
+		/*   3 */ {`true == false`, false, nil},
+		/*   4 */ {`1.0 == 3.0-2`, true, nil},
+		/*   5 */ {`[1,2] == [2,1]`, false, nil},
+		/*   6 */ {`1 != 3-2`, false, nil},
+		/*   7 */ {`"a" != "a"`, false, nil},
+		/*   8 */ {`true != false`, true, nil},
+		/*   9 */ {`1.0 != 3.0-2`, false, nil},
+		/*  10 */ {`[1,2] != [2,1]`, true, nil},
+		/*  11 */ {`1|2 == 1|3`, false, nil},
+		/*  12 */ {`1|2 != 1|3`, true, nil},
+		/*  13 */ {`1|2 == 4|8`, true, nil},
+		/*  14 */ {`1 < 8`, true, nil},
+		/*  15 */ {`1 <= 8`, true, nil},
+		/*  16 */ {`"a" < "b"`, true, nil},
+		/*  17 */ {`"a" <= "b"`, true, nil},
+		/*  18 */ {`1.0 < 8`, true, nil},
+		/*  19 */ {`1.0 <= 8`, true, nil},
+		/*  20 */ {`1.0 <= 1.0`, true, nil},
+		/*  21 */ {`1.0 == 1`, true, nil},
+		/*  22 */ {`1|2 < 1|3`, false, nil},
+		/*  23 */ {`1|2 <= 1|3`, false, nil},
+		/*  24 */ {`1|2 > 1|3`, true, nil},
+		/*  25 */ {`1|2 >= 1|3`, true, nil},
+		/*  26 */ {`[1,2,3] > [2]`, true, nil},
+		/*  27 */ {`[1,2,3] > [9]`, false, nil},
+		/*  28 */ {`[1,2,3] >= [6]`, false, nil},
+		/*  29 */ {`[1,2,3] >= [2,6]`, false, nil},
+		/*  30 */ {`[1,[2,3],4] > [[3,2]]`, true, nil},
+		/*  31 */ {`[1,[2,[3,4]],5] > [[[4,3],2]]`, true, nil},
+		/*  32 */ {`[[4,3],2] IN [1,[2,[3,4]],5]`, true, nil},
+	}
+
+	// t.Setenv("EXPR_PATH", ".")
+
+	// parserTestSpec(t, section, inputs, 31)
+	parserTest(t, section, inputs)
+}

t_scanner_test.go

@@ -1,12 +1,13 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// scanner_test.go
+// t_scanner_test.go
 package expr
 
 import (
 	"errors"
 	"fmt"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -55,15 +56,18 @@ func TestScanner(t *testing.T) {
 		/* 33 */ {`(`, SymOpenRound, nil, nil},
 		/* 34 */ {`)`, SymClosedRound, nil, nil},
 		/* 35 */ {`1E+2`, SymFloat, float64(100), nil},
-		/* 36 */ {`1E+x`, SymError, errors.New("expected integer exponent"), nil},
+		/* 36 */ {`1E+x`, SymError, errors.New("[1:5] expected integer exponent, got x"), nil},
 		/* 37 */ {`$`, SymDollar, nil, nil},
 		/* 38 */ {`\`, SymError, errors.New("incomplete escape sequence"), nil},
 		/* 39 */ {`"string"`, SymString, "string", nil},
-		/* 39 */ {`identifier`, SymIdentifier, "identifier", nil},
+		/* 40 */ {`identifier`, SymIdentifier, "identifier", nil},
+		/* 41 */ {`1.2(3)`, SymFraction, newFraction(37, 30), nil},
 	}
 
 	for i, input := range inputs {
-
+		// if i != 40 {
+		// 	continue
+		// }
 		if input.wantErr == nil {
 			t.Log(fmt.Sprintf("[+]Test nr %2d -- %q", i+1, input.source))
 		} else {
@@ -75,7 +79,8 @@ func TestScanner(t *testing.T) {
 
 		if tk := scanner.Next(); tk == nil {
 			t.Errorf("%d: %q -> got = (nil), want %v (value %v [%T])", i+1, input.source, input.wantSym, input.wantValue, input.wantValue)
-		} else if tk.Sym != input.wantSym || tk.Value != input.wantValue {
+			// } else if tk.Sym != input.wantSym || tk.Value != input.wantValue {
+		} else if tk.Sym != input.wantSym || !reflect.DeepEqual(tk.Value, input.wantValue) {
 			if tk.Sym == SymError && input.wantSym == tk.Sym {
 				if tkErr, tkOk := tk.Value.(error); tkOk {
 					if inputErr, inputOk := input.wantValue.(error); inputOk {
@@ -86,7 +91,7 @@ func TestScanner(t *testing.T) {
 					}
 				}
 			} else {
-				t.Errorf("%d: %q -> got = %v (value=%v [%T), want %v (value=%v [%T)", i+1,
+				t.Errorf("%d: %q -> got = %v (value=%v [%T]), want %v (value=%v [%T])", i+1,
 					input.source, tk.Sym, tk.Value, tk.Value, input.wantSym, input.wantValue, input.wantValue)
 			}
 		}

t_strings_test.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_strings_test.go
+package expr
+
+import (
+	"testing"
+)
+
+func TestStringsParser(t *testing.T) {
+	inputs := []inputType{
+		/*  1 */ {`"uno" + "due"`, `unodue`, nil},
+		/*  2 */ {`"uno" + 2`, `uno2`, nil},
+		/*  3 */ {`"uno" + (2+1)`, `uno3`, nil},
+		/*  4 */ {`"uno" * (2+1)`, `unounouno`, nil},
+		/*  5 */ {`"abc"[1]`, `b`, nil},
+		/*  6 */ {`#"abc"`, int64(3), nil},
+	}
+	parserTest(t, "String", inputs)
+}

t_template_test.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_template_test.go
+package expr
+
+import (
+	"testing"
+)
+
+func TestSomething(t *testing.T) {
+	section := "Something"
+	inputs := []inputType{
+		/*   1 */ {`1`, int64(1), nil},
+	}
+
+	// t.Setenv("EXPR_PATH", ".")
+
+	// parserTestSpec(t, section, inputs, 1)
+	parserTest(t, section, inputs)
+}

t_term_test.go

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// term_test.go
+// t_term_test.go
 package expr
 
 import (
@@ -31,6 +31,7 @@ func TestGetRoom(t *testing.T) {
 		t.Errorf("err: got <%v>, want <nil>", gotErr)
 	}
 }
+
 func TestGetChildrenCount(t *testing.T) {
 	tk1 := NewValueToken(0, 0, SymInteger, "100", 100)
 

t_token_test.go

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// token_test.go
+// t_token_test.go
 package expr
 
 import (

t_utils_test.go

@@ -0,0 +1,139 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_utils_test.go
+package expr
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestIsString(t *testing.T) {
+	count := 0
+	succeeded := 0
+	failed := 0
+
+	count++
+	if !IsBool(true) {
+		t.Errorf("%d: IsBool(true) -> result = false, want true", count)
+		failed++
+	} else {
+		succeeded++
+	}
+
+	count++
+	if !IsString("abc") {
+		t.Errorf("%d: IsString(\"abc\") -> result = false, want true", count)
+		failed++
+	} else {
+		succeeded++
+	}
+
+	count++
+	if !IsInteger(int64(123)) {
+		t.Errorf("%d: IsInteger(123) -> result = false, want true", count)
+		failed++
+	} else {
+		succeeded++
+	}
+
+	count++
+	if !IsFloat(1.23) {
+		t.Errorf("%d: IsFloat(1.23) -> result = false, want true", count)
+		failed++
+	} else {
+		succeeded++
+	}
+
+	count++
+	if !IsFloat(numAsFloat(123)) {
+		t.Errorf("%d: IsFloat(numAsFloat(123)) -> result = false, want true", count)
+		failed++
+	} else {
+		succeeded++
+	}
+
+	count++
+	b, ok := toBool(true)
+	if !(ok && b) {
+		t.Errorf("%d: toBool(true) b=%v, ok=%v -> result = false, want true", count, b, ok)
+		failed++
+	} else {
+		succeeded++
+	}
+
+	count++
+	b, ok = toBool("abc")
+	if !(ok && b) {
+		t.Errorf("%d: toBool(\"abc\") b=%v, ok=%v -> result = false, want true", count, b, ok)
+		failed++
+	} else {
+		succeeded++
+	}
+
+	t.Logf("test count: %d, succeeded count: %d, failed count: %d", count, succeeded, failed)
+}
+
+func TestToIntOk(t *testing.T) {
+	source := int64(64)
+	wantValue := int(64)
+	wantErr := error(nil)
+
+	gotValue, gotErr := toInt(source, "test")
+
+	if gotErr != nil || gotValue != wantValue {
+		t.Errorf("toInt(%v, \"test\") gotValue=%v, gotErr=%v -> wantValue=%v, wantErr=%v",
+			source, gotValue, gotErr, wantValue, wantErr)
+	}
+}
+
+func TestToIntErr(t *testing.T) {
+	source := uint64(64)
+	wantValue := 0
+	wantErr := errors.New(`test expected integer, got uint64 (64)`)
+
+	gotValue, gotErr := toInt(source, "test")
+
+	if gotErr.Error() != wantErr.Error() || gotValue != wantValue {
+		t.Errorf("toInt(%v, \"test\") gotValue=%v, gotErr=%v -> wantValue=%v, wantErr=%v",
+			source, gotValue, gotErr, wantValue, wantErr)
+	}
+}
+
+func TestAnyInteger(t *testing.T) {
+	type inputType struct {
+		source    any
+		wantValue int64
+		wantOk    bool
+	}
+	section := "utils.anyInteger"
+
+	inputs := []inputType{
+		/*  1 */ {int8(-8), int64(-8), true},
+		/*  2 */ {int16(-16), int64(-16), true},
+		/*  3 */ {int32(-32), int64(-32), true},
+		/*  4 */ {int64(-64), int64(-64), true},
+		/*  5 */ {uint8(8), int64(8), true},
+		/*  6 */ {uint16(16), int64(16), true},
+		/*  7 */ {uint32(32), int64(32), true},
+		/*  8 */ {uint64(64), int64(64), true},
+		/*  9 */ {int(-1), int64(-1), true},
+		/* 10 */ {true, 0, false},
+	}
+
+	succeeded := 0
+	failed := 0
+
+	for i, input := range inputs {
+		gotValue, gotOk := anyInteger(input.source)
+		if gotOk != input.wantOk || gotValue != input.wantValue {
+			t.Errorf("%d: anyInteger(%v) -> gotOk = %t, wantOk = %t; gotValue = %v, wantValue = %v",
+				i+1, input.source, gotOk, input.wantOk, gotValue, input.wantValue)
+			failed++
+		} else {
+			succeeded++
+		}
+	}
+	t.Logf("%s -- test count: %d, succeeded: %d, failed: %d", section, len(inputs), succeeded, failed)
+}

term-constuctor-registry.go

@@ -17,11 +17,10 @@ func registerTermConstructor(sym Symbol, constructor termContructor) {
 	constructorRegistry[sym] = constructor
 }
 
-func newTerm(tk *Token, parent *term) (inst *term) {
+func newTerm(tk *Token) (inst *term) {
 	if constructorRegistry != nil {
 		if construct, exists := constructorRegistry[tk.Sym]; exists {
 			inst = construct(tk)
-			inst.setParent(parent)
 		}
 	}
 	return

term.go

@@ -12,6 +12,7 @@ type termPriority uint32
 
 const (
 	priNone termPriority = iota
+	priRange
 	priBut
 	priAssign
 	priOr
@@ -161,10 +162,14 @@ func (self *term) toInt(computedValue any, valueDescription string) (i int, err
 }
 
 func (self *term) errIncompatibleTypes(leftValue, rightValue any) error {
+	leftType := getTypeName(leftValue)
+	leftText := getFormatted(leftValue, Truncate)
+	rightType := getTypeName(rightValue)
+	rightText := getFormatted(rightValue, Truncate)
 	return self.tk.Errorf(
-		"left operand '%v' [%T] and right operand '%v' [%T] are not compatible with operator %q",
+		"left operand '%s' [%s] and right operand '%s' [%s] are not compatible with operator %q",
-		leftValue, leftValue,
+		leftText, leftType,
-		rightValue, rightValue,
+		rightText, rightType,
 		self.source())
 }
 

utils.go

@@ -9,37 +9,58 @@ import (
 	"reflect"
 )
 
-func isString(v any) (ok bool) {
+func IsString(v any) (ok bool) {
 	_, ok = v.(string)
 	return ok
 }
 
-func isInteger(v any) (ok bool) {
+func IsInteger(v any) (ok bool) {
 	_, ok = v.(int64)
 	return ok
 }
 
-func isFloat(v any) (ok bool) {
+func IsFloat(v any) (ok bool) {
 	_, ok = v.(float64)
 	return ok
 }
 
-func isList(v any) (ok bool) {
+func IsBool(v any) (ok bool) {
+	_, ok = v.(bool)
+	return ok
+}
+
+func IsList(v any) (ok bool) {
 	_, ok = v.(*ListType)
 	return ok
 }
 
-func isDict(v any) (ok bool) {
+func IsDict(v any) (ok bool) {
-	_, ok = v.(map[any]any)
+	_, ok = v.(*DictType)
 	return ok
 }
 
-func isNumber(v any) (ok bool) {
+func IsFract(v any) (ok bool) {
-	return isFloat(v) || isInteger(v)
+	_, ok = v.(*FractionType)
+	return ok
+}
+
+func IsRational(v any) (ok bool) {
+	if _, ok = v.(*FractionType); !ok {
+		_, ok = v.(int64)
+	}
+	return ok
+}
+
+func IsNumber(v any) (ok bool) {
+	return IsFloat(v) || IsInteger(v)
+}
+
+func isNumOrFract(v any) (ok bool) {
+	return IsFloat(v) || IsInteger(v) || isFraction(v)
 }
 
 func isNumberString(v any) (ok bool) {
-	return isString(v) || isNumber(v)
+	return IsString(v) || IsNumber(v)
 }
 
 func isFunctor(v any) (ok bool) {
@@ -55,7 +76,7 @@ func isIterator(v any) (ok bool) {
 func numAsFloat(v any) (f float64) {
 	var ok bool
 	if f, ok = v.(float64); !ok {
-		if fract, ok := v.(*fraction); ok {
+		if fract, ok := v.(*FractionType); ok {
 			f = fract.toFloat()
 		} else {
 			i, _ := v.(int64)
@@ -126,6 +147,12 @@ func fromGenericAny(v any) (exprAny any, ok bool) {
 	if exprAny, ok = anyFloat(v); ok {
 		return
 	}
+	if exprAny, ok = v.(*DictType); ok {
+		return
+	}
+	if exprAny, ok = v.(*ListType); ok {
+		return
+	}
 	return
 }
 
@@ -182,3 +209,11 @@ func toInt(value any, description string) (i int, err error) {
 	}
 	return
 }
+
+func ForAll[T, V any](ts []T, fn func(T) V) []V {
+	result := make([]V, len(ts))
+	for i, t := range ts {
+		result[i] = fn(t)
+	}
+	return result
+}