Doc: closure example

doc/Expr.adoc

@@ -79,20 +79,20 @@ Here are some examples of execution.
 # Type 'exit' or Ctrl+D to quit the program.
 
 [user]$ ./dev-expr
-dev-expr -- Expressions calculator v1.10.0(build 14),2024/06/17 (celestino.amoroso@portale-stac.it)
+dev-expr -- Expressions calculator v1.12.0(build 1),2024/09/14 (celestino.amoroso@portale-stac.it)
-	Based on the Expr package v0.19.0
+	Based on the Expr package v0.26.0
 	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
       output -- Enable/Disable printing expression results. Options 'on', 'off', 'status'
+      source -- Load a file as input
+         tty -- Enable/Disable ansi output <1>
 
 --- Command line options:
     -b <builtin>       Import builtin modules.
@@ -155,9 +155,9 @@ _Expr_ supports three type of numbers:
 
 . [blue]#Integers#
 . [blue]#Floats#
-. [blue]#Factions#
+. [blue]#Fractions#
 
-In mixed operations involving integers, fractions and floats, automatic type promotion to the largest type take place.
+In mixed operations involving integers, fractions and floats, automatic type promotion to the largest type is performed.
 
 ==== Integers
 __Expr__'s integers are a subset of the integer set. Internally they are stored as Golang _int64_ values.
@@ -183,11 +183,11 @@ Value range: *-9223372036854775808* to *9223372036854775807*
 [cols="^1,^2,6,4"]
 |===
 | Symbol    | Operation     | Description               | Examples
-| [blue]`+` | _sum_         | Add two values            | [blue]`-1 + 2` -> 1
+| [blue]`+` | _Sum_         | Add two values            | [blue]`-1 + 2` -> _1_
-| [blue]`-` | _subtraction_ | Subtract the right value from the left one | [blue]`3 - 1` -> 2
+| [blue]`-` | _Subtraction_ | Subtract the right value from the left one | [blue]`3 - 1` -> _2_
-| [blue]`*` | _product_     | Multiply two values       | [blue]`-1 * 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]`/` | _Integer division_    | Divide the left value by the right one^(*)^ | [blue]`-11 / 2` -> _-5_
-| [blue]`%` | _Modulo_      | Remainder of the integer division | [blue]`5 % 2` -> 1
+| [blue]`%` | _Modulo_      | Remainder of the integer division | [blue]`5 % 2` -> _1_
 |===
 
 ^(*)^ See also the _float division_ [blue]`./` below.
@@ -228,11 +228,11 @@ _dec-seq_ = _see-integer-literal-syntax_
 [cols="^1,^2,6,4"]
 |===
 | Symbol    | Operation     | Description               | Examples
-| [blue]`+` | _sum_         | Add two values            | [blue]`4 + 0.5` -> 4.5
+| [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]`-` | _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]`*` | _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_    | 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
+| [blue]`./`| _Forced float division_ | Force float division   | [blue]`-1 ./ 2` -> -0.5
 |===
 
 ==== Fractions
@@ -308,7 +308,7 @@ Strings are character sequences enclosed between two double quote [blue]`"`.
 `>>>` [blue]`"123\tabc"` +
 [green]`123{nbsp}{nbsp}{nbsp}{nbsp}abc`
 
-Some arithmetic operators can also be used with strings.
+Some arithmetic operators also apply to strings.
 
 .String operators
 [cols="^1,^2,6,4"]
@@ -444,6 +444,7 @@ _non-empty-list_ = "**[**" _any-value_ {"**,**" _any-value_} "**]**" +
 | [blue]`[]` | _Item at index_ | 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_
+| [blue]`#` | _Size_ | Number of items in a list | [blue]`#[1,2,3]` -> _3_
 |===
 
 Array's items can be accessed using the index `[]` operator.
@@ -458,10 +459,16 @@ Array's items can be accessed using the index `[]` operator.
 *_slice_* = _string-expr_ "**[**" _integer-expr_ "**:**" _integer-expr_ "**]**"
 ====
 
-.Items of list
+.Examples: Getting items from lists
 `>>>` [blue]`[1,2,3][1]` +
 [green]`2`
 
+`>>>` [blue]`index=2; ["a", "b", "c", "d"][index]` +
+[green]`c`
+
+`>>>` [blue]`["a", "b", "c", "d"][2:]` +
+[green]`["c", "d"]`
+
 `>>>` [blue]`list=[1,2,3]; list[1]` +
 [green]`2`
 
@@ -471,25 +478,44 @@ Array's items can be accessed using the index `[]` operator.
 `>>>` [blue]`list=["one","two","three"]; list[2-1]` +
 [green]`two`
 
+`>>>` [blue]`list[1]="six"; list` +
+[green]`["one", "six", "three"]`
+
 `>>>` [blue]`list[-1]` +
 [green]`three`
 
 `>>>` [blue]`list[10]` +
 [red]`Eval Error: [1:9] index 10 out of bounds`
 
+.Example: Number of elements in a list
 `>>>` [blue]`#list` +
 [green]`3`
 
-`>>>` [blue]`index=2; ["a", "b", "c", "d"][index]` +
+.Examples: Element insertion
-[green]`c`
+`>>>` [blue]`"first" >> list` +
+[green]`["first", "one", "six", "three"]`
 
+`>>>` [blue]`list << "last"` +
+[green]`["first", "one", "six", "three", "last"]`
+
+.Examples: Element in list
+`>>>` [blue]`"six" in list` +
+[green]`true`
+
+`>>>` [blue]`"ten" in list` +
+[green]`false`
+
+.Examples: Concatenation and filtering
+`>>>` [blue]`[1,2,3] + ["one", "two", "three"]` +
+[green]`[1, 2, 3, "one", "two", "three"]`
+
+`>>>` [blue]`[1,2,3,4] - [2,4]` +
+[green]`[1, 3]`
 
-`>>>` [blue]`["a", "b", "c", "d"][2:]` +
-[green]`["c", "d"]`
 
 
 === Dictionaries
-The _dictionary_, or _dict_, data-type is set of pairs _key/value_. It is also known as _map_ or _associative array_.
+The _dictionary_, or _dict_, data-type represents sets  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.
 
@@ -515,6 +541,7 @@ _non-empty-dict_ = "**{**" _key-scalar_ "**:**" _any-value_ {"**,**" _key-scalar
 | [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_
+| [blue]`#` | _Size_ | Number of items in a dict | [blue]`#{1:"a",2:"b",3:"c"}` -> _3_
 |===
 
 .Examples
@@ -533,6 +560,9 @@ _non-empty-dict_ = "**{**" _key-scalar_ "**:**" _any-value_ {"**,**" _key-scalar
 `>>>` [blue]`d={"one":1, "two":2}; d["six"]=6; d` +
 [green]`{"two": 2, "one": 1, "six": 6}`
 
+`>>>` [blue]`#d` +
+[green]`3`
+
 
 == Variables
 _Expr_, like most programming languages, supports variables. A variable is an identifier with an assigned value. Variables are stored in _contexts_.
@@ -556,7 +586,7 @@ NOTE: The assign operator [blue]`=` returns the value assigned to the variable.
 `>>>` [blue]`a_b` +
 [green]`3`
 
-`>>>` [blue]`x = 5.2 * (9-3)`  [gray]_// The assigned value has the typical approximation error of the float data-type_ +
+`>>>` [blue]`x = 5.2 * (9-3)`  [gray]_// The assigned value here has the typical approximation error of the float data-type_ +
 [green]`31.200000000000003`
 
 `>>>` [blue]`x = 1; y = 2*x` +
@@ -664,8 +694,8 @@ The [blue]`:` symbol (colon) is the separator of the selector-cases. Note that i
 [red]`Eval Error: [1:3] no case catches the value (10) of the selection expression`
 
 
-=== Variable default value [blue]`??` and [blue]`?=`
+=== Variable default value [blue]`??`, [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 defined; otherwise they return the value of the right expression.
+The left operand of first two operators, [blue]`??` and [blue]`?=`, must be a variable. The right operator can be any expression. They return the value of the variable if this is defined; otherwise they return the value of the right expression.
 
 IMPORTANT: If the left variable is defined, the right expression is not evaluated at all.
 
@@ -673,6 +703,10 @@ The [blue]`??` operator do not change the status of the left variable.
 
 The [blue]`?=` assigns the calculated value of the right expression to the left variable.
 
+The third one, [blue]`?!`, is the alternate operator. If the variable on the left size is not defined, it returns [blue]_nil_. Otherwise it returns the result of the expressione on the right side.
+
+IMPORTANT: If the left variable is NOT defined, the right expression is not evaluated at all.
+
 .Examples
 `>>>` [blue]`var ?? (1+2)` +
 [green]`3`
@@ -686,6 +720,15 @@ The [blue]`?=` assigns the calculated value of the right expression to the left
 `>>>` [blue]`var` +
 [green]`3`
 
+`>>>` [blue]`x ?! 5` +
+[green]`nil`
+
+`>>>` [blue]`x=1; x ?! 5` +
+[green]`5`
+
+`>>>` [blue]`y ?! (c=5); c` +
+[red]`Eval Error: undefined variable or function "c"`
+
 NOTE: These operators have a high priority, in particular higher than the operator [blue]`=`.
 
 == Priorities of operators
@@ -700,9 +743,10 @@ The table below shows all supported operators by decreasing priorities.
 | [blue]`[`...`]` | _Postfix_ | _Dict item_ | _dict_ `[` _any_ `]` -> _any_
 .2+|*INC*| [blue]`++` | _Postfix_ | _Post increment_| _integer-variable_ `++` -> _integer_
 | [blue]`++` | _Postfix_ | _Next item_ | _iterator_ `++` -> _any_
-.2+|*DEFAULT*| [blue]`??` | _Infix_ | _Default value_| _variable_ `??` _any-expr_ -> _any_
+.3+|*DEFAULT*| [blue]`??` | _Infix_ | _Default value_| _variable_ `??` _any-expr_ -> _any_
 | [blue]`?=` | _Infix_ | _Default/assign value_| _variable_ `?=` _any-expr_ -> _any_
-.1+| *ITER*^1^| [blue]`()` | _Prefix_ | _Iterator value_ | `()` _iterator_ -> _any_
+| [blue]`?!` | _Infix_ | _Alternate value_| _variable_ `?!` _any-expr_ -> _any_
+//.1+| *ITER*^1^| [blue]`()` | _Prefix_ | _Iterator value_ | `()` _iterator_ -> _any_
 .1+|*FACT*| [blue]`!` | _Postfix_ | _Factorial_| _integer_ `!` -> _integer_
 .3+|*SIGN*| [blue]`+`, [blue]`-` | _Prefix_ | _Change-sign_| (`+`\|`-`) _number_ -> _number_
 | [blue]`#` | _Prefix_ | _Lenght-of_ | `#` _collection_ -> _integer_
@@ -741,7 +785,7 @@ The table below shows all supported operators by decreasing priorities.
 .1+|*RANGE*| [blue]`:` | _Infix_ | _Index-range_ | _integer_ `:` _integer_ -> _integer-pair_
 |===
 
-^1^ Experimental
+//^1^ Experimental
 
 
 == Functions
@@ -752,25 +796,122 @@ Functions in _Expr_ are very similar to functions available in many programming
 
 
 === _Expr_ function definition
-A function is identified and referenced by its name. It can have zero or more parameter. _Expr_ functions also support optional parameters.
+A function is identified and referenced by its name. It can have zero or more parameter. _Expr_ functions also support optional parameters and passing paramters by name.
 
 .Expr's function definition syntax
 ====
-*_function-definition_* = _identifier_ "**=**"  "**func(**" [_param-list_] "**)**"  "**{**" _multi-expression_ "**}**" +
+*_function-definition_* = _identifier_ "**=**"  "**func(**" [_formal-param-list_] "**)**"  "**{**" _multi-expression_ "**}**" +
-_param_list_ = _required-param-list_ [ "**,**" _optional-param-list_ ] +
+_formal-param_list_ = _required-param-list_ [ "**,**" _optional-param-list_ ] +
 _required-param-list_ = _identifier_ { "**,**" _identifier_ } +
 _optional-param-list_ = _optional-parm_ { "**,**" _optional-param_ } +
-_optional-param_ = _identifier_ "**=**" _any-expr_
+_optional-param_ = _param-name_ "**=**" _any-expr_ +
+_param-name_ = _identifier_
 ====
 
 .Examples
-#TODO#
+`>>>` [gray]_// A simple function: it takes two parameters and returns their "sum"_**^(*)^** +
+`>>>` [blue]`sum = func(a, b){ a + b }` +
+[green]`sum(a, b):any{}`
+
+^(\*)^ Since the plus, *+*, operator is defined for multiple data-types, the _sum()_ function can be used for any pair of that types.
+
+`>>>` [gray]_// A more complex example: recursive calculation of the n-th value of Fibonacci's sequence_ +
+`>>>` [blue]`fib = func(n){ n ? [0] {0}: [1] {1} :: {fib(n-1)+fib(n-2)} }` +
+[green]`fib(n):any{}`
+
+
+`>>>` [gray]_// Same function fib() but entered by splitting it over mulple text lines_ +
+`>>>` [blue]`fib = func(n){ \` +
+`\...` [blue]`{nbsp}{nbsp}n ? \` +
+`\...` [blue]`{nbsp}{nbsp}{nbsp}{nbsp}[0] {0} : \` +
+`\...` [blue]`{nbsp}{nbsp}{nbsp}{nbsp}[1] {1} :: \` +
+`\...` [blue]`{nbsp}{nbsp}{nbsp}{nbsp}{ \` +
+`\...` [blue]`{nbsp}{nbsp}{nbsp}{nbsp}{nbsp}{nbsp}fib(n-1) + fib(n-2) \` +
+`\...` [blue]`{nbsp}{nbsp}{nbsp}{nbsp}} \` +
+`\...` [blue]`}` +
+[green]`fib(n):any{}`
+
+`>>>` [gray]_// Required and optional parameters_ +
+`>>>` [blue]`measure = func(value, unit="meter"){ value + " " + unit + (value > 1) ? [true] {"s"} :: {""}}` +
+[green]`measure(value, unit="meter"):any{}`
+
 
 === _Golang_ function definition
 Description of how to define Golan functions and how to bind them to _Expr_ are topics treated in another document that I'll write, one day, maybe.
 
 === Function calls
-#TODO: function calls operations#
+To call a function, either Expr or Golang type, it is necessary to specify its name and, at least, its required parameters.
+
+.Function invocation syntax
+====
+*_function-call_* = _identifier_ "**(**" _actual-param-list_ "**)**" +
+_actual-param-list_ = [_positional-params_] [_named-parameters_] +
+_positional-params_ = _any-value_ { "*,*" _any-value_ } +
+_named-params_ = _param-name_ "**=**" _any-value_ { "*,*" _param-name_ "**=**" _any-value_ } +
+_param-name_ = _identifier_
+====
+
+.Examples of calling the `sum()` functions defined above
+`>>>` [gray]_// sum of two integers_ +
+`>>>` [blue]`sum(-6, 2)` +
+[green]`-4` +
+`>>>` [gray]_// same as above but passing the parameters by name_ +
+`>>>` [blue]`sum(a=-6, b=2)` +
+[green]`-4` +
+`>>>` [gray]_// again, but swapping parameter positions (see the diff() examples below)_ +
+`>>>` [blue]`sum(b=2, a=-6)` +
+[green]`-4` +
+`>>>` [gray]_// sum of a fraction and an integer_ +
+`>>>` [blue]`sum(3|2, 2)` +
+[green]`7|2` +
+`>>>` [gray]_// sum of two strings_ +
+`>>>` [blue]`sum("bye", "-bye")` +
+[green]`"bye-bye"` +
+`>>>` [gray]_// sum of two lists_ +
+`>>>` [blue]`sum(["one", 1], ["two", 2])` +
+[green]`["one", 1, "two", 2]`
+
+.Examples of calling a function with parameters passed by name
+`>>>` [gray]_// diff(a,b) calculates a-b_ +
+`>>>` [blue]`diff = func(a,b){a-b}` +
+[green]`diff(a, b):any{}` +
+`>>>` [gray]_// simple invocation_ +
+`>>>` [blue]`diff(10,8)` +
+[green]`2` +
+`>>>` [gray]_// swapped parameters passed by name_ +
+`>>>` [blue]`diff(b=8,a=10)` +
+[green]`2`
+
+.Examples of calling the `fib()` function defined above
+`>>>` [gray]_// Fibonacci sequence: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ..._ +
+`>>>` [blue]`fib(6)` +
+[green]`8` +
+`>>>` [blue]`fib(9)` +
+[green]`34`
+
+.Examples of calling the `measure()` functions defined above
+`>>>` [gray]_// simple call_ +
+`>>>` [blue]`measure(10,"litre")` +
+[green]`"10 litres"` +
+`>>>` [gray]_// accept the default unit_ +
+`>>>` [blue]`measure(8)` +
+[green]`"8 meters"` +
+`>>>` [gray]_// without the required parameter 'value'_ +
+`>>>` [blue]`measure(unit="degrees"))` +
+[red]`Eval Error: measure(): missing params -- value`
+
+.Examples of context binding (closures)
+`>>>` [blue]`factory = func(n=2){ func(x){x*n} }` +
+[green]`factory(n=2):any{}` +
+`>>>` [blue]`double = factory()` +
+[green]`double(x):any{}` +
+`>>>` [blue]`triple = factory(3)` +
+[green]`triple(x):any{}` +
+`>>>` [blue]`double(5)` +
+[green]`10` +
+`>>>` [blue]`triple(5)` +
+[green]`15`
+
 
 Functions compute values in a local context (scope) that do not make effects on the calling context. This is the normal behavior. Using the reference operator [blue]`@` it is possibile to export local definition to the calling context.
 

doc/Expr.html

@@ -567,7 +567,7 @@ pre.rouge .ss {
 <li><a href="#_but_operator">4.2. <code class="blue">but</code> operator</a></li>
 <li><a href="#_assignment_operator">4.3. Assignment operator <code class="blue">=</code></a></li>
 <li><a href="#_selector_operator">4.4. Selector operator <code class="blue">? : ::</code></a></li>
-<li><a href="#_variable_default_value_and">4.5. Variable default value <code class="blue">??</code> and <code class="blue">?=</code></a></li>
+<li><a href="#_variable_default_value_and">4.5. Variable default value <code class="blue">??</code>, <code class="blue">?=</code>, and <code class="blue">?!</code></a></li>
 </ul>
 </li>
 <li><a href="#_priorities_of_operators">5. Priorities of operators</a></li>
@@ -687,20 +687,20 @@ pre.rouge .ss {
 <pre class="rouge highlight"><code data-lang="shell"><span class="c"># Type 'exit' or Ctrl+D to quit the program.</span>
 
 <span class="o">[</span>user]<span class="nv">$ </span>./dev-expr
-dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o">(</span>build 14<span class="o">)</span>,2024/06/17 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
+dev-expr <span class="nt">--</span> Expressions calculator v1.12.0<span class="o">(</span>build 1<span class="o">)</span>,2024/09/14 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
-	Based on the Expr package v0.19.0
+	Based on the Expr package v0.26.0
 	Type <span class="nb">help </span>to get the list of available commands
 	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
 <span class="o">&gt;&gt;&gt;</span> <span class="nb">help</span>
 <span class="nt">---</span> REPL commands:
-      <span class="nb">source</span> <span class="nt">--</span> Load a file as input
-         <span class="nb">tty</span> <span class="nt">--</span> Enable/Disable ansi output <i class="conum" data-value="1"></i><b>(1)</b>
         base <span class="nt">--</span> Set the integer output base: 2, 8, 10, or 16
         <span class="nb">exit</span> <span class="nt">--</span> Exit the program
         <span class="nb">help</span> <span class="nt">--</span> Show <span class="nb">command </span>list
           ml <span class="nt">--</span> Enable/Disable multi-line output
         mods <span class="nt">--</span> List <span class="nb">builtin </span>modules
       output <span class="nt">--</span> Enable/Disable printing expression results. Options <span class="s1">'on'</span>, <span class="s1">'off'</span>, <span class="s1">'status'</span>
+      <span class="nb">source</span> <span class="nt">--</span> Load a file as input
+         <span class="nb">tty</span> <span class="nt">--</span> Enable/Disable ansi output <i class="conum" data-value="1"></i><b>(1)</b>
 
 <span class="nt">---</span> Command line options:
     <span class="nt">-b</span> &lt;<span class="nb">builtin</span><span class="o">&gt;</span>       Import <span class="nb">builtin </span>modules.
@@ -805,12 +805,12 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 <p><span class="blue">Floats</span></p>
 </li>
 <li>
-<p><span class="blue">Factions</span></p>
+<p><span class="blue">Fractions</span></p>
 </li>
 </ol>
 </div>
 <div class="paragraph">
-<p>In mixed operations involving integers, fractions and floats, automatic type promotion to the largest type take place.</p>
+<p>In mixed operations involving integers, fractions and floats, automatic type promotion to the largest type is performed.</p>
 </div>
 <div class="sect3">
 <h4 id="_integers"><a class="anchor" href="#_integers"></a><a class="link" href="#_integers">2.1.1. Integers</a></h4>
@@ -855,33 +855,33 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">+</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>sum</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Sum</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Add two values</p></td>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">-1 + 2</code> &#8594; 1</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">-1 + 2</code> &#8594; <em>1</em></p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">-</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>subtraction</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Subtraction</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Subtract the right value from the left one</p></td>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">3 - 1</code> &#8594; 2</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">3 - 1</code> &#8594; <em>2</em></p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">*</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>product</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Product</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Multiply two values</p></td>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">-1 * 2</code> &#8594; -2</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">-1 * 2</code> &#8594; <em>-2</em></p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">/</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Division</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Integer division</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Divide the left value by the right one<sup>(*)</sup></p></td>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">-10 / 2</code> &#8594; 5</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">-11 / 2</code> &#8594; <em>-5</em></p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">%</code></p></td>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>Modulo</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Remainder of the integer division</p></td>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">5 % 2</code> &#8594; 1</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">5 % 2</code> &#8594; <em>1</em></p></td>
 </tr>
 </tbody>
 </table>
@@ -946,31 +946,31 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">+</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>sum</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Sum</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Add two values</p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">4 + 0.5</code> &#8594; 4.5</p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">-</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>subtraction</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Subtraction</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Subtract the right value from the left one</p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">4 - 0.5</code> &#8594; 3.5</p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">*</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>product</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Product</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Multiply two values</p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">4 * 0.5</code> &#8594; 2.0</p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">/</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Division</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Float division</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Divide the left value by the right one</p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">1.0 / 2</code> &#8594; 0.5</p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">./</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Float division</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Forced float division</em></p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">Force float division</p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">-1 ./ 2</code> &#8594; -0.5</p></td>
 </tr>
@@ -1074,7 +1074,7 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 <code class="green">123&#160;&#160;&#160;&#160;abc</code></p>
 </div>
 <div class="paragraph">
-<p>Some arithmetic operators can also be used with strings.</p>
+<p>Some arithmetic operators also apply to strings.</p>
 </div>
 <table class="tableblock frame-all grid-all stretch">
 <caption class="title">Table 3. String operators</caption>
@@ -1393,6 +1393,12 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 <td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">2 in [1,2,3]</code> &#8594; <em>true</em><br>
 <code class="blue">6 in [1,2,3]</code> &#8594; <em>false</em></p></td>
 </tr>
+<tr>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">#</code></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Size</em></p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">Number of items in a list</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">#[1,2,3]</code> &#8594; <em>3</em></p></td>
+</tr>
 </tbody>
 </table>
 <div class="paragraph">
@@ -1415,11 +1421,19 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 </div>
 </div>
 <div class="paragraph">
-<div class="title">Items of list</div>
+<div class="title">Examples: Getting items from lists</div>
 <p><code>&gt;&gt;&gt;</code> <code class="blue">[1,2,3][1]</code><br>
 <code class="green">2</code></p>
 </div>
 <div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">index=2; ["a", "b", "c", "d"][index]</code><br>
+<code class="green">c</code></p>
+</div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">["a", "b", "c", "d"][2:]</code><br>
+<code class="green">["c", "d"]</code></p>
+</div>
+<div class="paragraph">
 <p><code>&gt;&gt;&gt;</code> <code class="blue">list=[1,2,3]; list[1]</code><br>
 <code class="green">2</code></p>
 </div>
@@ -1432,6 +1446,10 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 <code class="green">two</code></p>
 </div>
 <div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">list[1]="six"; list</code><br>
+<code class="green">["one", "six", "three"]</code></p>
+</div>
+<div class="paragraph">
 <p><code>&gt;&gt;&gt;</code> <code class="blue">list[-1]</code><br>
 <code class="green">three</code></p>
 </div>
@@ -1440,22 +1458,42 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 <code class="red">Eval Error: [1:9] index 10 out of bounds</code></p>
 </div>
 <div class="paragraph">
+<div class="title">Example: Number of elements in a list</div>
 <p><code>&gt;&gt;&gt;</code> <code class="blue">#list</code><br>
 <code class="green">3</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">index=2; ["a", "b", "c", "d"][index]</code><br>
+<div class="title">Examples: Element insertion</div>
-<code class="green">c</code></p>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">"first" &gt;&gt; list</code><br>
+<code class="green">["first", "one", "six", "three"]</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">["a", "b", "c", "d"][2:]</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">list &lt;&lt; "last"</code><br>
-<code class="green">["c", "d"]</code></p>
+<code class="green">["first", "one", "six", "three", "last"]</code></p>
+</div>
+<div class="paragraph">
+<div class="title">Examples: Element in list</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">"six" in list</code><br>
+<code class="green">true</code></p>
+</div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">"ten" in list</code><br>
+<code class="green">false</code></p>
+</div>
+<div class="paragraph">
+<div class="title">Examples: Concatenation and filtering</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">[1,2,3] + ["one", "two", "three"]</code><br>
+<code class="green">[1, 2, 3, "one", "two", "three"]</code></p>
+</div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">[1,2,3,4] - [2,4]</code><br>
+<code class="green">[1, 3]</code></p>
 </div>
 </div>
 <div class="sect2">
 <h3 id="_dictionaries"><a class="anchor" href="#_dictionaries"></a><a class="link" href="#_dictionaries">2.5. Dictionaries</a></h3>
 <div class="paragraph">
-<p>The <em>dictionary</em>, or <em>dict</em>, data-type is set of pairs <em>key/value</em>. It is also known as <em>map</em> or <em>associative array</em>.</p>
+<p>The <em>dictionary</em>, or <em>dict</em>, data-type represents sets  of pairs <em>key/value</em>. It is also known as <em>map</em> or <em>associative array</em>.</p>
 </div>
 <div class="paragraph">
 <p>Dictionary literals are sequences of pairs separated by comma <code class="blue">,</code> enclosed between brace brackets.</p>
@@ -1514,6 +1552,12 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 <td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">"one" in {"one":1, "two":2}</code> &#8594; <em>true</em><br>
 <code class="blue">"six" in {"one":1, "two":2}</code> &#8594; <em>false</em></p></td>
 </tr>
+<tr>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">#</code></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Size</em></p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">Number of items in a dict</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code class="blue">#{1:"a",2:"b",3:"c"}</code> &#8594; <em>3</em></p></td>
+</tr>
 </tbody>
 </table>
 <div class="paragraph">
@@ -1537,6 +1581,10 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 <p><code>&gt;&gt;&gt;</code> <code class="blue">d={"one":1, "two":2}; d["six"]=6; d</code><br>
 <code class="green">{"two": 2, "one": 1, "six": 6}</code></p>
 </div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">#d</code><br>
+<code class="green">3</code></p>
+</div>
 </div>
 </div>
 </div>
@@ -1582,7 +1630,7 @@ The assign operator <code class="blue">=</code> returns the value assigned to th
 <code class="green">3</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">x = 5.2 * (9-3)</code>  <em class="gray">// The assigned value has the typical approximation error of the float data-type</em><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">x = 5.2 * (9-3)</code>  <em class="gray">// The assigned value here has the typical approximation error of the float data-type</em><br>
 <code class="green">31.200000000000003</code></p>
 </div>
 <div class="paragraph">
@@ -1751,9 +1799,9 @@ Technically <code class="blue">;</code> is not treated as a real operator. It ac
 </div>
 </div>
 <div class="sect2">
-<h3 id="_variable_default_value_and"><a class="anchor" href="#_variable_default_value_and"></a><a class="link" href="#_variable_default_value_and">4.5. Variable default value <code class="blue">??</code> and <code class="blue">?=</code></a></h3>
+<h3 id="_variable_default_value_and"><a class="anchor" href="#_variable_default_value_and"></a><a class="link" href="#_variable_default_value_and">4.5. Variable default value <code class="blue">??</code>, <code class="blue">?=</code>, and <code class="blue">?!</code></a></h3>
 <div class="paragraph">
-<p>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 defined; otherwise they return the value of the right expression.</p>
+<p>The left operand of first two operators, <code class="blue">??</code> and <code class="blue">?=</code>, must be a variable. The right operator can be any expression. They return the value of the variable if this is defined; otherwise they return the value of the right expression.</p>
 </div>
 <div class="admonitionblock important">
 <table>
@@ -1774,6 +1822,21 @@ If the left variable is defined, the right expression is not evaluated at all.
 <p>The <code class="blue">?=</code> assigns the calculated value of the right expression to the left variable.</p>
 </div>
 <div class="paragraph">
+<p>The third one, <code class="blue">?!</code>, is the alternate operator. If the variable on the left size is not defined, it returns <em class="blue">nil</em>. Otherwise it returns the result of the expressione on the right side.</p>
+</div>
+<div class="admonitionblock important">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-important" title="Important"></i>
+</td>
+<td class="content">
+If the left variable is NOT defined, the right expression is not evaluated at all.
+</td>
+</tr>
+</table>
+</div>
+<div class="paragraph">
 <div class="title">Examples</div>
 <p><code>&gt;&gt;&gt;</code> <code class="blue">var ?? (1+2)</code><br>
 <code class="green">3</code></p>
@@ -1790,6 +1853,18 @@ If the left variable is defined, the right expression is not evaluated at all.
 <p><code>&gt;&gt;&gt;</code> <code class="blue">var</code><br>
 <code class="green">3</code></p>
 </div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">x ?! 5</code><br>
+<code class="green">nil</code></p>
+</div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">x=1; x ?! 5</code><br>
+<code class="green">5</code></p>
+</div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">y ?! (c=5); c</code><br>
+<code class="red">Eval Error: undefined variable or function "c"</code></p>
+</div>
 <div class="admonitionblock note">
 <table>
 <tr>
@@ -1857,7 +1932,7 @@ These operators have a high priority, in particular higher than the operator <co
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>iterator</em> <code>++</code> &#8594; <em>any</em></p></td>
 </tr>
 <tr>
-<td class="tableblock halign-center valign-top" rowspan="2"><p class="tableblock"><strong>DEFAULT</strong></p></td>
+<td class="tableblock halign-center valign-top" rowspan="3"><p class="tableblock"><strong>DEFAULT</strong></p></td>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">??</code></p></td>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>Infix</em></p></td>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>Default value</em></p></td>
@@ -1870,11 +1945,10 @@ These operators have a high priority, in particular higher than the operator <co
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>variable</em> <code>?=</code> <em>any-expr</em> &#8594; <em>any</em></p></td>
 </tr>
 <tr>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><strong>ITER</strong><sup>1</sup></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">?!</code></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">()</code></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Infix</em></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Prefix</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Alternate value</em></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Iterator value</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>variable</em> <code>?!</code> <em>any-expr</em> &#8594; <em>any</em></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><code>()</code> <em>iterator</em> &#8594; <em>any</em></p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><strong>FACT</strong></p></td>
@@ -2107,9 +2181,6 @@ These operators have a high priority, in particular higher than the operator <co
 </tr>
 </tbody>
 </table>
-<div class="paragraph">
-<p><sup>1</sup> Experimental</p>
-</div>
 </div>
 </div>
 <div class="sect1">
@@ -2131,23 +2202,51 @@ These operators have a high priority, in particular higher than the operator <co
 <div class="sect2">
 <h3 id="_expr_function_definition"><a class="anchor" href="#_expr_function_definition"></a><a class="link" href="#_expr_function_definition">6.1. <em>Expr</em> function definition</a></h3>
 <div class="paragraph">
-<p>A function is identified and referenced by its name. It can have zero or more parameter. <em>Expr</em> functions also support optional parameters.</p>
+<p>A function is identified and referenced by its name. It can have zero or more parameter. <em>Expr</em> functions also support optional parameters and passing paramters by name.</p>
 </div>
 <div class="exampleblock">
 <div class="title">Example 14. Expr&#8217;s function definition syntax</div>
 <div class="content">
 <div class="paragraph">
-<p><strong><em>function-definition</em></strong> = <em>identifier</em> "<strong>=</strong>"  "<strong>func(</strong>" [<em>param-list</em>] "<strong>)</strong>"  "<strong>{</strong>" <em>multi-expression</em> "<strong>}</strong>"<br>
+<p><strong><em>function-definition</em></strong> = <em>identifier</em> "<strong>=</strong>"  "<strong>func(</strong>" [<em>formal-param-list</em>] "<strong>)</strong>"  "<strong>{</strong>" <em>multi-expression</em> "<strong>}</strong>"<br>
-<em>param_list</em> = <em>required-param-list</em> [ "<strong>,</strong>" <em>optional-param-list</em> ]<br>
+<em>formal-param_list</em> = <em>required-param-list</em> [ "<strong>,</strong>" <em>optional-param-list</em> ]<br>
 <em>required-param-list</em> = <em>identifier</em> { "<strong>,</strong>" <em>identifier</em> }<br>
 <em>optional-param-list</em> = <em>optional-parm</em> { "<strong>,</strong>" <em>optional-param</em> }<br>
-<em>optional-param</em> = <em>identifier</em> "<strong>=</strong>" <em>any-expr</em></p>
+<em>optional-param</em> = <em>param-name</em> "<strong>=</strong>" <em>any-expr</em><br>
+<em>param-name</em> = <em>identifier</em></p>
 </div>
 </div>
 </div>
 <div class="paragraph">
 <div class="title">Examples</div>
-<p><mark>TODO</mark></p>
+<p><code>&gt;&gt;&gt;</code> <em class="gray">// A simple function: it takes two parameters and returns their "sum"</em><strong><sup>(*)</sup></strong><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">sum = func(a, b){ a + b }</code><br>
+<code class="green">sum(a, b):any{}</code></p>
+</div>
+<div class="paragraph">
+<p><sup>(*)</sup> Since the plus, *+*, operator is defined for multiple data-types, the <em>sum()</em> function can be used for any pair of that types.</p>
+</div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <em class="gray">// A more complex example: recursive calculation of the n-th value of Fibonacci&#8217;s sequence</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">fib = func(n){ n ? [0] {0}: [1] {1} :: {fib(n-1)+fib(n-2)} }</code><br>
+<code class="green">fib(n):any{}</code></p>
+</div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <em class="gray">// Same function fib() but entered by splitting it over mulple text lines</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">fib = func(n){ \</code><br>
+<code>...</code> <code class="blue">&#160;&#160;n ? \</code><br>
+<code>...</code> <code class="blue">&#160;&#160;&#160;&#160;[0] {0} : \</code><br>
+<code>...</code> <code class="blue">&#160;&#160;&#160;&#160;[1] {1} :: \</code><br>
+<code>...</code> <code class="blue">&#160;&#160;&#160;&#160;{ \</code><br>
+<code>...</code> <code class="blue">&#160;&#160;&#160;&#160;&#160;&#160;fib(n-1) + fib(n-2) \</code><br>
+<code>...</code> <code class="blue">&#160;&#160;&#160;&#160;} \</code><br>
+<code>...</code> <code class="blue">}</code><br>
+<code class="green">fib(n):any{}</code></p>
+</div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <em class="gray">// Required and optional parameters</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">measure = func(value, unit="meter"){ value + " " + unit + (value &gt; 1) ? [true] {"s"} :: {""}}</code><br>
+<code class="green">measure(value, unit="meter"):any{}</code></p>
 </div>
 </div>
 <div class="sect2">
@@ -2159,7 +2258,85 @@ These operators have a high priority, in particular higher than the operator <co
 <div class="sect2">
 <h3 id="_function_calls"><a class="anchor" href="#_function_calls"></a><a class="link" href="#_function_calls">6.3. Function calls</a></h3>
 <div class="paragraph">
-<p><mark>TODO: function calls operations</mark></p>
+<p>To call a function, either Expr or Golang type, it is necessary to specify its name and, at least, its required parameters.</p>
+</div>
+<div class="exampleblock">
+<div class="title">Example 15. Function invocation syntax</div>
+<div class="content">
+<div class="paragraph">
+<p><strong><em>function-call</em></strong> = <em>identifier</em> "<strong>(</strong>" <em>actual-param-list</em> "<strong>)</strong>"<br>
+<em>actual-param-list</em> = [<em>positional-params</em>] [<em>named-parameters</em>]<br>
+<em>positional-params</em> = <em>any-value</em> { "<strong>,</strong>" <em>any-value</em> }<br>
+<em>named-params</em> = <em>param-name</em> "<strong>=</strong>" <em>any-value</em> { "<strong>,</strong>" <em>param-name</em> "<strong>=</strong>" <em>any-value</em> }<br>
+<em>param-name</em> = <em>identifier</em></p>
+</div>
+</div>
+</div>
+<div class="paragraph">
+<div class="title">Examples of calling the <code>sum()</code> functions defined above</div>
+<p><code>&gt;&gt;&gt;</code> <em class="gray">// sum of two integers</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">sum(-6, 2)</code><br>
+<code class="green">-4</code><br>
+<code>&gt;&gt;&gt;</code> <em class="gray">// same as above but passing the parameters by name</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">sum(a=-6, b=2)</code><br>
+<code class="green">-4</code><br>
+<code>&gt;&gt;&gt;</code> <em class="gray">// again, but swapping parameter positions (see the diff() examples below)</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">sum(b=2, a=-6)</code><br>
+<code class="green">-4</code><br>
+<code>&gt;&gt;&gt;</code> <em class="gray">// sum of a fraction and an integer</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">sum(3|2, 2)</code><br>
+<code class="green">7|2</code><br>
+<code>&gt;&gt;&gt;</code> <em class="gray">// sum of two strings</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">sum("bye", "-bye")</code><br>
+<code class="green">"bye-bye"</code><br>
+<code>&gt;&gt;&gt;</code> <em class="gray">// sum of two lists</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">sum(["one", 1], ["two", 2])</code><br>
+<code class="green">["one", 1, "two", 2]</code></p>
+</div>
+<div class="paragraph">
+<div class="title">Examples of calling a function with parameters passed by name</div>
+<p><code>&gt;&gt;&gt;</code> <em class="gray">// diff(a,b) calculates a-b</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">diff = func(a,b){a-b}</code><br>
+<code class="green">diff(a, b):any{}</code><br>
+<code>&gt;&gt;&gt;</code> <em class="gray">// simple invocation</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">diff(10,8)</code><br>
+<code class="green">2</code><br>
+<code>&gt;&gt;&gt;</code> <em class="gray">// swapped parameters passed by name</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">diff(b=8,a=10)</code><br>
+<code class="green">2</code></p>
+</div>
+<div class="paragraph">
+<div class="title">Examples of calling the <code>fib()</code> function defined above</div>
+<p><code>&gt;&gt;&gt;</code> <em class="gray">// Fibonacci sequence: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, &#8230;&#8203;</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">fib(6)</code><br>
+<code class="green">8</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">fib(9)</code><br>
+<code class="green">34</code></p>
+</div>
+<div class="paragraph">
+<div class="title">Examples of calling the <code>measure()</code> functions defined above</div>
+<p><code>&gt;&gt;&gt;</code> <em class="gray">// simple call</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">measure(10,"litre")</code><br>
+<code class="green">"10 litres"</code><br>
+<code>&gt;&gt;&gt;</code> <em class="gray">// accept the default unit</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">measure(8)</code><br>
+<code class="green">"8 meters"</code><br>
+<code>&gt;&gt;&gt;</code> <em class="gray">// without the required parameter 'value'</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">measure(unit="degrees"))</code><br>
+<code class="red">Eval Error: measure(): missing params&#8201;&#8212;&#8201;value</code></p>
+</div>
+<div class="paragraph">
+<div class="title">Examples of context binding (closures)</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">factory = func(n=2){ func(x){x*n} }</code><br>
+<code class="green">factory(n=2):any{}</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">double = factory()</code><br>
+<code class="green">double(x):any{}</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">triple = factory(3)</code><br>
+<code class="green">triple(x):any{}</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">double(5)</code><br>
+<code class="green">10</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">triple(5)</code><br>
+<code class="green">15</code></p>
 </div>
 <div class="paragraph">
 <p>Functions compute values in a local context (scope) that do not make effects on the calling context. This is the normal behavior. Using the reference operator <code class="blue">@</code> it is possibile to export local definition to the calling context.</p>
@@ -2204,7 +2381,7 @@ These operators have a high priority, in particular higher than the operator <co
 </div>
 <div id="footer">
 <div id="footer-text">
-Last updated 2024-09-12 06:56:30 +0200
+Last updated 2024-09-18 20:46:46 +0200
 </div>
 </div>
 </body>

parser.go

@@ -417,6 +417,7 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 		case SymEqual:
 			// if err = checkPrevSymbol(lastSym, SymIdentifier, tk); err == nil {
 			currentTerm, err = tree.addToken(tk)
+			firstToken = true
 			// }
 		case SymFuncDef:
 			var funcDefTerm *term
@@ -483,7 +484,7 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 // 	return
 // }
 
-func (parser *parser) expandOpAssign(scanner * scanner, tree *ast, tk *Token, allowVarRef bool) (t *term, err error) {
+func (parser *parser) expandOpAssign(scanner *scanner, tree *ast, tk *Token, allowVarRef bool) (t *term, err error) {
 	var opSym Symbol
 	var opString string