commented code removed

- 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)

common-type-names.go

@@ -13,5 +13,6 @@ const (
 	typeInt      = "integer"
 	typeItem     = "item"
 	typeNumber   = "number"
+	typePair     = "pair"
 	typeString   = "string"
 )

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

@@ -58,7 +58,7 @@ func boolFunc(ctx ExprContext, name string, args []any) (result any, err error)
 	switch v := args[0].(type) {
 	case int64:
 		result = (v != 0)
-	case *fraction:
+	case *FractionType:
 		result = v.num != 0
 	case float64:
 		result = v != 0.0
@@ -112,7 +112,7 @@ func decFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 		if f, err = strconv.ParseFloat(v, 64); err == nil {
 			result = f
 		}
-	case *fraction:
+	case *FractionType:
 		result = v.toFloat()
 	default:
 		err = errCantConvert(name, v, "float")
@@ -145,7 +145,7 @@ func fractFunc(ctx ExprContext, name string, args []any) (result any, err error)
 		}
 	case string:
 		result, err = makeGeneratingFraction(v)
-	case *fraction:
+	case *FractionType:
 		result = v
 	default:
 		err = errCantConvert(name, v, "float")

func-math.go

@@ -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++
@@ -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++
@@ -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)
 			}

list-type.go

@@ -0,0 +1,102 @@
+// 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.indexDeepCmp(item) >= 0; !answer {
+				break
+			}
+		}
+	}
+	return
+}
+
+// func equal(a,b *ListType) (eq bool) {
+// 	if len(*a) == len(*b) {
+// 		eq = true
+// 		for i, v := range
+// 	}
+// 	return
+// }

operand-list.go

@@ -4,91 +4,14 @@
 // operand-list.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
-}
-
 // -------- 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,

operator-dot.go

@@ -4,8 +4,6 @@
 // operator-dot.go
 package expr
 
-import "fmt"
-
 // -------- dot term
 func newDotTerm(tk *Token) (inst *term) {
 	return &term{
@@ -17,24 +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 {
-				v = maxValue + v
-			}
-			if v >= 0 && v < maxValue {
-				index = 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
 
@@ -48,27 +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 = string(unboxedValue[index])
-		}
-	case *DictType:
-		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 ExtIterator:
-		if indexTerm.symbol() == SymVariable {
+		if indexTerm.symbol() == SymVariable /*|| indexTerm.symbol() == SymString */ {
 			opName := indexTerm.source()
 			if unboxedValue.HasOperation(opName) {
 				v, err = unboxedValue.CallOperation(opName, []any{})
@@ -76,10 +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-fraction.go

@@ -9,205 +9,8 @@ package expr
 import (
 	"errors"
 	"fmt"
-	"math"
-	"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 float64ToFraction(f float64) (fract *fraction, 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 *fraction, 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 *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()
-}
-
-func (f *fraction) TypeName() string {
-	return "fraction"
-}
-
 // -------- fraction term
 func newFractionTerm(tk *Token) *term {
 	return &term{
@@ -252,168 +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-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-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 +18,29 @@ func newEqualTerm(tk *Token) (inst *term) {
 	}
 }
 
+func equals(a, b any) (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 {
+		eq = reflect.DeepEqual(a, b)
+	}
+
+	return
+}
+
 func evalEqual(ctx ExprContext, self *term) (v any, err error) {
 	var leftValue, rightValue any
 
@@ -25,21 +48,7 @@ func evalEqual(ctx ExprContext, self *term) (v any, err error) {
 		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)
-	}
+	v, err = equals(leftValue, rightValue)
 	return
 }
 
@@ -48,8 +57,6 @@ 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 +72,11 @@ 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 +84,52 @@ 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)
+		if isLess {
+			for _, item := range *aList {
+				if bList.indexDeepCmp(item) < 0 {
+					isLess = false
+					break
+				}
+			}
+		}
+	} 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
 	}
-
-	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)
-	}
+	v, err = lessThan(self, leftValue, rightValue)
 	return
 }
 
@@ -141,6 +145,33 @@ func newLessEqualTerm(tk *Token) (inst *term) {
 	}
 }
 
+func sameContent(a, b any) (same bool, err error) {
+	la, _ := a.(*ListType)
+	lb, _ := b.(*ListType)
+	if len(*la) == len(*lb) {
+		same = true
+		for i, item := range *la {
+			if same, err = equals(item, (*lb)[i]); err != nil || !same {
+				break
+			}
+		}
+	}
+	return
+}
+
+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)
+			}
+		}
+	}
+	return
+}
+
 func evalLessEqual(ctx ExprContext, self *term) (v any, err error) {
 	var leftValue, rightValue any
 
@@ -148,21 +179,8 @@ func evalLessEqual(ctx ExprContext, self *term) (v any, err error) {
 		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)
-	}
+	v, err = lessThanOrEqual(self, leftValue, rightValue)
+
 	return
 }
 
@@ -171,8 +189,6 @@ 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 +197,13 @@ func newGreaterTerm(tk *Token) (inst *term) {
 }
 
 func evalGreater(ctx ExprContext, self *term) (v any, err error) {
-	if v, err = evalLessEqual(ctx, self); err == nil {
-		b, _ := toBool(v)
-		v = !b
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
 	}
+
+	v, err = lessThan(self, rightValue, leftValue)
 	return
 }
 
@@ -193,8 +212,6 @@ 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 +220,13 @@ func newGreaterEqualTerm(tk *Token) (inst *term) {
 }
 
 func evalGreaterEqual(ctx ExprContext, self *term) (v any, err error) {
-	if v, err = evalLess(ctx, self); err == nil {
-		b, _ := toBool(v)
-		v = !b
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
 	}
+
+	v, err = lessThanOrEqual(self, rightValue, leftValue)
 	return
 }
 

operator-sum.go

@@ -38,23 +38,6 @@ func evalPlus(ctx ExprContext, self *term) (v any, err error) {
 			rightInt, _ := rightValue.(int64)
 			v = leftInt + rightInt
 		}
-		// } else if IsList(leftValue) || IsList(rightValue) {
-		// 	var leftList, rightList *ListType
-		// 	var ok bool
-		// 	if leftList, ok = leftValue.(*ListType); !ok {
-		// 		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)
-		// 	}
-		// 	for _, item := range *rightList {
-		// 		sumList = append(sumList, item)
-		// 	}
-		// 	v = &sumList
 	} else if IsList(leftValue) && IsList(rightValue) {
 		var leftList, rightList *ListType
 		leftList, _ = leftValue.(*ListType)

parser.go

@@ -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 {
-				args = append(args, subTree.root)
+			root := 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
@@ -294,14 +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 {
@@ -352,6 +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
@@ -401,16 +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)
@@ -439,15 +478,17 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 			}
 		case SymColon, SymDoubleColon:
 			var caseTerm *term
-			if selectorTerm == nil {
-				err = tk.Errorf("selector-case outside of a selector context")
-			} else if caseTerm, err = self.parseSelectorCase(scanner, allowVarRef, tk.Sym == SymDoubleColon); err == nil {
+			if selectorTerm != nil {
+				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
 }

symbol.go

@@ -85,6 +85,7 @@ const (
 	SymFuncDef
 	SymList
 	SymDict
+	SymIndex
 	SymExpression
 	SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
 	SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"

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

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// dict_test.go
+// t_dict_test.go
 package expr
 
 import (
@@ -24,7 +24,7 @@ func TestDictParser(t *testing.T) {
 		/*  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"}.2`, "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},

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 (

t_funcs_test.go

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

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).
-// All rights reserved.
-
-// graph_test.go
+// t_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 (

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 (
@@ -33,16 +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(`[1:36] index 10 out of bounds`)},
+		/*  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},
@@ -61,8 +64,6 @@ func TestListParser(t *testing.T) {
 		var gotErr error
 
 		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 (

t_relational_test.go

@@ -0,0 +1,49 @@
+// 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},
+	}
+
+	// t.Setenv("EXPR_PATH", ".")
+
+	// parserTestSpec(t, section, inputs, 27)
+	parserTest(t, section, inputs)
+}

t_scanner_test.go

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

t_strings_test.go

@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// strings_test.go
+// t_strings_test.go
 package expr
 
 import (
@@ -14,8 +14,8 @@ func TestStringsParser(t *testing.T) {
 		/*  2 */ {`"uno" + 2`, `uno2`, nil},
 		/*  3 */ {`"uno" + (2+1)`, `uno3`, nil},
 		/*  4 */ {`"uno" * (2+1)`, `unounouno`, nil},
-		/*  5 */ {`"abc".1`, `b`, nil},
-		/*  5 */ {`#"abc"`, int64(3), 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 (

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

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

term.go

@@ -12,6 +12,7 @@ type termPriority uint32
 
 const (
 	priNone termPriority = iota
+	priRange
 	priBut
 	priAssign
 	priOr

utils.go

@@ -40,12 +40,12 @@ func IsDict(v any) (ok bool) {
 }
 
 func IsFract(v any) (ok bool) {
-	_, ok = v.(*fraction)
+	_, ok = v.(*FractionType)
 	return ok
 }
 
 func IsRational(v any) (ok bool) {
-	if _, ok = v.(*fraction); !ok {
+	if _, ok = v.(*FractionType); !ok {
 		_, ok = v.(int64)
 	}
 	return ok
@@ -76,7 +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)