solved a number of problems highlighted by the syntax analyzer

Also, fixed and improved some parsing sections concerning collection indeces and ranges

builtin-base.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"math"
 	"strconv"
+	"strings"
 )
 
 const (
@@ -188,6 +189,30 @@ func fractFunc(ctx ExprContext, name string, args map[string]any) (result any, e
 // 	return
 // }
 
+func evalFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+	if source, ok := args[ParamSource].(string); ok {
+		var expr Expr
+
+		parser := NewParser()
+		if ctx == nil {
+			ctx = NewSimpleStore()
+		}
+
+		r := strings.NewReader(source)
+		scanner := NewScanner(r, DefaultTranslations())
+
+		if expr, err = parser.Parse(scanner); err == nil {
+			CtrlEnable(ctx, control_export_all)
+			result, err = expr.Eval(ctx)
+		}
+	} else {
+		err = ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+	}
+	return
+}
+
+//// import
+
 func ImportBuiltinsFuncs(ctx ExprContext) {
 	anyParams := []ExprFuncParam{
 		NewFuncParam(ParamValue),
@@ -211,6 +236,10 @@ func ImportBuiltinsFuncs(ctx ExprContext) {
 		NewFuncParam(ParamValue),
 		NewFuncParamFlagDef(ParamDenominator, PfDefault, int64(1)),
 	})
+
+	ctx.RegisterFunc("eval", NewGolangFunctor(evalFunc), TypeAny, []ExprFuncParam{
+		NewFuncParam(ParamSource),
+	})
 }
 
 func init() {

builtin-import.go

@@ -44,7 +44,7 @@ func doImport(ctx ExprContext, name string, dirList []string, it Iterator) (resu
 			var expr *ast
 			scanner := NewScanner(file, DefaultTranslations())
 			parser := NewParser()
-			if expr, err = parser.parseGeneral(scanner, true, true); err == nil {
+			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, SymEos); err == nil {
 				result, err = expr.Eval(ctx)
 			}
 			if err != nil {

common-errors.go

@@ -55,8 +55,25 @@ func ErrInvalidParameterValue(funcName, paramName string, paramValue any) error
 	return fmt.Errorf("%s(): invalid value %s (%v) for parameter %q", funcName, TypeName(paramValue), paramValue, paramName)
 }
 
+func undefArticle(s string) (article string) {
+	if len(s) > 0 && strings.Contains("aeiou", s[0:1]) {
+		article = "an"
+	} else {
+		article = "a"
+	}
+	return
+}
+
+func prependUndefArticle(s string) (result string) {
+	return undefArticle(s) + " " + s
+}
+
 func ErrWrongParamType(funcName, paramName, paramType string, paramValue any) error {
-	return fmt.Errorf("%s(): the %q parameter must be a %s, got a %s (%v)", funcName, paramName, paramType, TypeName(paramValue), paramValue)
+	var artWantType, artGotType string
+	gotType := TypeName(paramValue)
+	artGotType = prependUndefArticle(gotType)
+	artWantType = prependUndefArticle(paramType)
+	return fmt.Errorf("%s(): the %q parameter must be %s, got %s (%v)", funcName, paramName, artWantType, artGotType, paramValue)
 }
 
 func ErrUnknownParam(funcName, paramName string) error {

context-helpers.go

@@ -29,7 +29,7 @@ func exportObjects(destCtx, sourceCtx ExprContext) {
 	exportAll := CtrlIsEnabled(sourceCtx, control_export_all)
 	// fmt.Printf("Exporting from sourceCtx [%p] to destCtx [%p] -- exportAll=%t\n", sourceCtx, destCtx, exportAll)
 	// Export variables
-	for _, refName := range sourceCtx.EnumVars(func(name string) bool { return exportAll || name[0] == '@' }) {
+	for _, refName := range sourceCtx.EnumVars(func(name string) bool { return (exportAll || name[0] == '@') && !(name[0] == '_') }) {
 		// fmt.Printf("\tExporting %q\n", refName)
 		refValue, _ := sourceCtx.GetVar(refName)
 		exportVar(destCtx, refName, refValue)

doc/Expr.adoc

@@ -127,22 +127,22 @@ dev-expr -- Expressions calculator v1.10.0(build 14),2024/06/17 (celestino.amoro
 9.5
 >>> 0xFD + 0b1 + 0o1 <1>
 255
->>> 1|2 + 2|3 <2>
+>>> 1:2 + 2:3 <2>
-7|6
+7:6
 >>> ml <3>
->>> 1|2 + 2|3
+>>> 1:2 + 2:3
 7
 -
 6
->>> 4+2 but 5|2+0.5 <4>
+>>> 4+2 but 5:2+0.5 <4>
 3
->>> 4+2; 5|2+0.5 <5>
+>>> 4+2; 5:2+0.5 <5>
 3
 >>>
 ----
 
 <1> Number bases: 0x = _hexadecimal_, 0o = _octal_, 0b = _binary_.
-<2> Fractions: _numerator_ | _denominator_.
+<2> Fractions: _numerator_ : _denominator_.
 <3> Activate multi-line output of fractions.
 <4> But operator, see <<_but_operator>>.
 <5> Multi-expression: the same result of the previous single expression but this it is obtained with two separated calculations.
@@ -236,11 +236,11 @@ _dec-seq_ = _see-integer-literal-syntax_
 |===
 
 ==== Fractions
-_Expr_ also supports fractions. Fraction literals are made with two integers separated by a vertical bar `|`.
+_Expr_ also supports fractions. Fraction literals are made with two integers separated by a colon character `:`.
 
 .Fraction literal syntax
 ====
-*_fraction_* = [__sign__] (_num-den-spec_ | _float-spec_) +
+*_fraction_* = [__sign__] (_num-den-spec_ "**:**" _float-spec_) +
 _sign_ = "**+**" | "**-**" +
 _num-den-spec_ = _digit-seq_ "**|**" _digit-seq_ +
 _float-spec_ = _dec-seq_ "**.**" [_dec-seq_] "**(**" _dec-seq_ "**)**" +
@@ -249,44 +249,44 @@ _digit-seq_ = _see-integer-literal-syntax_
 ====
 
 .Examples
-`>>>` [blue]`1 | 2` +
+`>>>` [blue]`1 : 2` +
-[green]`1|2`
+[green]`1:2`
 
-`>>>` [blue]`4|6`  [gray]_// Fractions are always reduced to their lowest terms_ +
+`>>>` [blue]`4:6`  [gray]_// Fractions are always reduced to their lowest terms_ +
-[green]`2|3`
+[green]`2:3`
 
-`>>>` [blue]`1|2 + 2|3` +
+`>>>` [blue]`1:2 + 2:3` +
-[green]`7|6`
+[green]`7:6`
 
-`>>>` [blue]`1|2 * 2|3` +
+`>>>` [blue]`1:2 * 2:3` +
-[green]`1|3`
+[green]`1:3`
 
-`>>>` [blue]`1|2 / 1|3` +
+`>>>` [blue]`1:2 / 1:3` +
-[green]`3|2`
+[green]`3:2`
 
-`>>>` [blue]`1|2 ./ 1|3` [gray]_// Force decimal division_ +
+`>>>` [blue]`1:2 ./ 1:3` [gray]_// Force decimal division_ +
 [green]`1.5`
 
-`>>>` [blue]`-1|2` +
+`>>>` [blue]`-1:2` +
-[green]`-1|2`
+[green]`-1:2`
 
-`>>>` [blue]`1|-2` [gray]_// Invalid sign specification_ +
+`>>>` [blue]`1:-2` [gray]_// Invalid sign specification_ +
-[red]_Eval Error: [1:3] infix operator "|" requires two non-nil operands, got 1_
+[red]_Eval Error: [1:3] infix operator ":" requires two non-nil operands, got 1_
 
-`>>>` [blue]`1|(-2)` +
+`>>>` [blue]`1:(-2)` +
-[green]`-1|2`
+[green]`-1:2`
 
 
 Fractions can be used together with integers and floats in expressions.
 
 .Examples
-`>>>` [blue]`1|2 + 5` +
+`>>>` [blue]`1:2 + 5` +
-[green]`11|2`
+[green]`11:2`
 
-`>>>` [blue]`4 - 1|2` +
+`>>>` [blue]`4 - 1:2` +
-[green]`7|2`
+[green]`7:2`
 
-`>>>` [blue]`1.0 + 1|2` +
+`>>>` [blue]`1.0 + 1:2` +
 [green]`1.5`
 
 
@@ -753,7 +753,7 @@ The table below shows all supported operators by decreasing priorities.
 | [blue]`#` | _Prefix_ | _Size-of_ | `#` _iterator_ -> _integer_
 .2+|*SELECT*| [blue]`? : ::` | _Multi-Infix_ | _Case-Selector_ | _any-expr_ `?` _case-list_ _case-expr_ `:` _case-list_ _case-expr_ ... `::` _default-expr_ -> _any_
 | [blue]`? : ::` | _Multi-Infix_ | _Index-Selector_ | _int-expr_ `?` _case-expr_ `:` _case-expr_ ... `::` _default-expr_ -> _any_
-.1+|*FRACT*| [blue]`\|` | _Infix_ | _Fraction_ | _integer_ `\|` _integer_ -> _fraction_
+.1+|*FRACT*| [blue]`:` | _Infix_ | _Fraction_ | _integer_ `:` _integer_ -> _fraction_
 .5+|*PROD*| [blue]`*` | _Infix_ | _Product_ | _number_ `*` _number_ -> _number_
 | [blue]`*` | _Infix_ | _String-repeat_ | _string_ `*` _integer_ -> _string_
 | [blue]`/` | _Infix_ | _Division_ | _number_ `/` _number_ -> _number_
@@ -765,6 +765,9 @@ The table below shows all supported operators by decreasing priorities.
 | [blue]`+` | _Infix_ |  _Dict-join_ | _dict_ `+` _dict_ -> _dict_
 | [blue]`-` | _Infix_ | _Subtraction_ | _number_ `-` _number_ -> _number_
 | [blue]`-` | _Infix_ | _List-difference_ | _list_ `-` _list_ -> _list_
+.3+|*BINARY*| [blue]`&` | _Infix_ | _Binary And_ | _number_ `&` _number_ -> _number_
+| [blue]`\|` | _Infix_ | _Binary Or_ | _number_ `\|` _number_ -> _number_
+| [blue]`~` | _Prefix_ | _Binary Not_ | `~` _number_ -> _number_
 .8+|*RELATION*| [blue]`<` | _Infix_ | _Less_ | _comparable_ `<` _comparable_ -> _boolean_
 | [blue]`\<=` | _Infix_ |  _less-equal_ | _comparable_ `\<=` _comparable_ -> _boolean_
 | [blue]`>` | _Infix_ |  _Greater_ | _comparable_ `>` _comparable_ -> _boolean_

doc/Expr.html

@@ -474,6 +474,16 @@ pre.rouge .gh {
   color: #b8bb26;
   font-weight: bold;
 }
+pre.rouge .ge {
+  font-style: italic;
+}
+pre.rouge .ges {
+  font-weight: bold;
+  font-style: italic;
+}
+pre.rouge .gs {
+  font-weight: bold;
+}
 pre.rouge .k, pre.rouge .kn, pre.rouge .kp, pre.rouge .kr, pre.rouge .kv {
   color: #fb4934;
 }
@@ -745,16 +755,16 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 9.5
 <span class="o">&gt;&gt;&gt;</span> 0xFD + 0b1 + 0o1 <i class="conum" data-value="1"></i><b>(1)</b>
 255
-<span class="o">&gt;&gt;&gt;</span> 1|2 + 2|3 <i class="conum" data-value="2"></i><b>(2)</b>
+<span class="o">&gt;&gt;&gt;</span> 1:2 + 2:3 <i class="conum" data-value="2"></i><b>(2)</b>
-7|6
+7:6
 <span class="o">&gt;&gt;&gt;</span> ml <i class="conum" data-value="3"></i><b>(3)</b>
-<span class="o">&gt;&gt;&gt;</span> 1|2 + 2|3
+<span class="o">&gt;&gt;&gt;</span> 1:2 + 2:3
 7
 -
 6
-<span class="o">&gt;&gt;&gt;</span> 4+2 but 5|2+0.5 <i class="conum" data-value="4"></i><b>(4)</b>
+<span class="o">&gt;&gt;&gt;</span> 4+2 but 5:2+0.5 <i class="conum" data-value="4"></i><b>(4)</b>
 3
-<span class="o">&gt;&gt;&gt;</span> 4+2<span class="p">;</span> 5|2+0.5 <i class="conum" data-value="5"></i><b>(5)</b>
+<span class="o">&gt;&gt;&gt;</span> 4+2<span class="p">;</span> 5:2+0.5 <i class="conum" data-value="5"></i><b>(5)</b>
 3
 <span class="o">&gt;&gt;&gt;</span></code></pre>
 </div>
@@ -767,7 +777,7 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 </tr>
 <tr>
 <td><i class="conum" data-value="2"></i><b>2</b></td>
-<td>Fractions: <em>numerator</em> | <em>denominator</em>.</td>
+<td>Fractions: <em>numerator</em> : <em>denominator</em>.</td>
 </tr>
 <tr>
 <td><i class="conum" data-value="3"></i><b>3</b></td>
@@ -981,13 +991,13 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 <div class="sect3">
 <h4 id="_fractions"><a class="anchor" href="#_fractions"></a><a class="link" href="#_fractions">2.1.3. Fractions</a></h4>
 <div class="paragraph">
-<p><em>Expr</em> also supports fractions. Fraction literals are made with two integers separated by a vertical bar <code>|</code>.</p>
+<p><em>Expr</em> also supports fractions. Fraction literals are made with two integers separated by a colon character <code>:</code>.</p>
 </div>
 <div class="exampleblock">
 <div class="title">Example 3. Fraction literal syntax</div>
 <div class="content">
 <div class="paragraph">
-<p><strong><em>fraction</em></strong> = [<em>sign</em>] (<em>num-den-spec</em> | <em>float-spec</em>)<br>
+<p><strong><em>fraction</em></strong> = [<em>sign</em>] (<em>num-den-spec</em> "<strong>:</strong>" <em>float-spec</em>)<br>
 <em>sign</em> = "<strong>+</strong>" | "<strong>-</strong>"<br>
 <em>num-den-spec</em> = <em>digit-seq</em> "<strong>|</strong>" <em>digit-seq</em><br>
 <em>float-spec</em> = <em>dec-seq</em> "<strong>.</strong>" [<em>dec-seq</em>] "<strong>(</strong>" <em>dec-seq</em> "<strong>)</strong>"<br>
@@ -998,55 +1008,55 @@ dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o
 </div>
 <div class="paragraph">
 <div class="title">Examples</div>
-<p><code>&gt;&gt;&gt;</code> <code class="blue">1 | 2</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">1 : 2</code><br>
-<code class="green">1|2</code></p>
+<code class="green">1:2</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">4|6</code>  <em class="gray">// Fractions are always reduced to their lowest terms</em><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">4:6</code>  <em class="gray">// Fractions are always reduced to their lowest terms</em><br>
-<code class="green">2|3</code></p>
+<code class="green">2:3</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">1|2 + 2|3</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">1:2 + 2:3</code><br>
-<code class="green">7|6</code></p>
+<code class="green">7:6</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">1|2 * 2|3</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">1:2 * 2:3</code><br>
-<code class="green">1|3</code></p>
+<code class="green">1:3</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">1|2 / 1|3</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">1:2 / 1:3</code><br>
-<code class="green">3|2</code></p>
+<code class="green">3:2</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">1|2 ./ 1|3</code> <em class="gray">// Force decimal division</em><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">1:2 ./ 1:3</code> <em class="gray">// Force decimal division</em><br>
 <code class="green">1.5</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">-1|2</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">-1:2</code><br>
-<code class="green">-1|2</code></p>
+<code class="green">-1:2</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">1|-2</code> <em class="gray">// Invalid sign specification</em><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">1:-2</code> <em class="gray">// Invalid sign specification</em><br>
-<em class="red">Eval Error: [1:3] infix operator "|" requires two non-nil operands, got 1</em></p>
+<em class="red">Eval Error: [1:3] infix operator ":" requires two non-nil operands, got 1</em></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">1|(-2)</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">1:(-2)</code><br>
-<code class="green">-1|2</code></p>
+<code class="green">-1:2</code></p>
 </div>
 <div class="paragraph">
 <p>Fractions can be used together with integers and floats in expressions.</p>
 </div>
 <div class="paragraph">
 <div class="title">Examples</div>
-<p><code>&gt;&gt;&gt;</code> <code class="blue">1|2 + 5</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">1:2 + 5</code><br>
-<code class="green">11|2</code></p>
+<code class="green">11:2</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">4 - 1|2</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">4 - 1:2</code><br>
-<code class="green">7|2</code></p>
+<code class="green">7:2</code></p>
 </div>
 <div class="paragraph">
-<p><code>&gt;&gt;&gt;</code> <code class="blue">1.0 + 1|2</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">1.0 + 1:2</code><br>
 <code class="green">1.5</code></p>
 </div>
 </div>
@@ -1992,10 +2002,10 @@ These operators have a high priority, in particular higher than the operator <co
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><strong>FRACT</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"><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>Fraction</em></p></td>
-<td class="tableblock halign-center valign-top"><p class="tableblock"><em>integer</em> <code>|</code> <em>integer</em> &#8594; <em>fraction</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>integer</em> <code>:</code> <em>integer</em> &#8594; <em>fraction</em></p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top" rowspan="5"><p class="tableblock"><strong>PROD</strong></p></td>
@@ -2066,6 +2076,25 @@ These operators have a high priority, in particular higher than the operator <co
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>list</em> <code>-</code> <em>list</em> &#8594; <em>list</em></p></td>
 </tr>
 <tr>
+<td class="tableblock halign-center valign-top" rowspan="3"><p class="tableblock"><strong>BINARY</strong></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">&amp;</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>Binary And</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>number</em> <code>&amp;</code> <em>number</em> &#8594; <em>number</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>Infix</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Binary Or</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>number</em> <code>|</code> <em>number</em> &#8594; <em>number</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>Prefix</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Binary Not</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code>~</code> <em>number</em> &#8594; <em>number</em></p></td>
+</tr>
+<tr>
 <td class="tableblock halign-center valign-top" rowspan="8"><p class="tableblock"><strong>RELATION</strong></p></td>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">&lt;</code></p></td>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>Infix</em></p></td>
@@ -2432,7 +2461,7 @@ g(@p):any{}`
 </div>
 <div id="footer">
 <div id="footer-text">
-Last updated 2024-09-30 07:29:03 +0200
+Last updated 2024-12-23 07:20:48 +0100
 </div>
 </div>
 </body>

fraction-type.go

@@ -50,9 +50,9 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 	} else if s[0] == '+' {
 		s = s[1:]
 	}
-//	if strings.HasSuffix(s, "()") {
+	//	if strings.HasSuffix(s, "()") {
-//		s = s[0 : len(s)-2]
+	//		s = s[0 : len(s)-2]
-//	}
+	//	}
 	s = strings.TrimSuffix(s, "()")
 	parts = strings.SplitN(s, ".", 2)
 	if num, err = strconv.ParseInt(parts[0], 10, 64); err != nil {
@@ -124,36 +124,38 @@ func (f *FractionType) String() string {
 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))
+		sb.WriteString(fmt.Sprintf("%d:%d", f.num, f.den))
 	} else {
-		var s, num string
+		var sign, num string
 		if f.num < 0 && opt&TTY == 0 {
 			num = strconv.FormatInt(-f.num, 10)
-			s = "-"
+			sign = "-"
 		} 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)))
+			sNum := fmt.Sprintf("\x1b[4m%[1]*s\x1b[0m\n", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, sign+num))
+			sb.WriteString(sNum)
 		} else {
-			if len(s) > 0 {
+			if len(sign) > 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 {
+			if len(sign) > 0 {
-				sb.WriteString(s)
+				sb.WriteString(sign)
 				sb.WriteByte(' ')
 			}
 			sb.WriteString(strings.Repeat("-", size))
 			sb.WriteByte('\n')
-			if len(s) > 0 {
+			if len(sign) > 0 {
 				sb.WriteString("  ")
 			}
 		}
-		sb.WriteString(fmt.Sprintf("%[1]*s", -size, fmt.Sprintf("%[1]*s", (size+len(den))/2, den)))
+		sDen := fmt.Sprintf("%[1]*s", size, fmt.Sprintf("%[1]*s", (size+len(den))/2, den))
+		sb.WriteString(sDen)
 	}
 
 	return sb.String()

go.mod

@@ -1,3 +1,7 @@
 module git.portale-stac.it/go-pkg/expr
 
-go 1.21.6
+go 1.22.0
+
+toolchain go1.23.3
+
+require golang.org/x/exp v0.0.0-20241204233417-43b7b7cde48d

go.sum

@@ -0,0 +1,4 @@
+github.com/yqylovy/goimportdot v0.0.0-20170519021755-eb181a7eeabe h1:bWYrKmmfv37uNgXTdwkLSKYiYPJ1yfWmjBnvtMyAYzk=
+github.com/yqylovy/goimportdot v0.0.0-20170519021755-eb181a7eeabe/go.mod h1:alTKUpAJ/zbp17qvZwcFNwzufrb5DljMDY4mgJlIHao=
+golang.org/x/exp v0.0.0-20241204233417-43b7b7cde48d h1:0olWaB5pg3+oychR51GUVCEsGkeCU/2JxjBgIo4f3M0=
+golang.org/x/exp v0.0.0-20241204233417-43b7b7cde48d/go.mod h1:qj5a5QZpwLU2NLQudwIN5koi3beDhSAlJwa67PuM98c=

iterator.go

@@ -5,7 +5,7 @@
 package expr
 
 import (
-	"errors"
+	// "errors"
 	"fmt"
 )
 
@@ -43,6 +43,6 @@ func errNoOperation(name string) error {
 	return fmt.Errorf("no %s() function defined in the data-source", name)
 }
 
-func errInvalidDataSource() error {
+// func errInvalidDataSource() error {
-	return errors.New("invalid data-source")
+// 	return errors.New("invalid data-source")
-}
+// }

operator-assign.go

@@ -99,7 +99,106 @@ func evalAssign(ctx ExprContext, opTerm *term) (v any, err error) {
 	return
 }
 
+//-------- assign term
+
+func newOpAssignTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priAssign,
+		evalFunc: evalOpAssign,
+	}
+}
+
+func getCollectionItemValue(ctx ExprContext, collectionTerm, keyListTerm *term) (value any, err error) {
+	var collectionValue, keyListValue, keyValue any
+	var keyList *ListType
+	var ok bool
+
+	if collectionValue, err = collectionTerm.compute(ctx); err != nil {
+		return
+	}
+
+	if keyListValue, err = keyListTerm.compute(ctx); err != nil {
+		return
+	} else if keyList, ok = keyListValue.(*ListType); !ok || len(*keyList) != 1 {
+		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, TypeName(keyListValue))
+		return
+	}
+	if keyValue = (*keyList)[0]; keyValue == nil {
+		err = keyListTerm.Errorf("index/key is nil")
+		return
+	}
+
+	switch collection := collectionValue.(type) {
+	case *ListType:
+		if index, ok := keyValue.(int64); ok {
+			value = (*collection)[index]
+		} else {
+			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, TypeName(keyValue))
+		}
+	case *DictType:
+		value = (*collection)[keyValue]
+	default:
+		err = collectionTerm.Errorf("collection expected")
+	}
+	return
+}
+
+func getAssignValue(ctx ExprContext, leftTerm *term) (value any, err error) {
+	if leftTerm.symbol() == SymIndex {
+		value, err = getCollectionItemValue(ctx, leftTerm.children[0], leftTerm.children[1])
+	} else {
+		value, _ = ctx.GetVar(leftTerm.source())
+	}
+	return
+}
+
+func evalOpAssign(ctx ExprContext, opTerm *term) (v any, err error) {
+	var rightValue, leftValue any
+	if err = opTerm.checkOperands(); err != nil {
+		return
+	}
+
+	leftTerm := opTerm.children[0]
+	leftSym := leftTerm.symbol()
+	if leftSym != SymVariable && leftSym != SymIndex {
+		err = leftTerm.tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.tk.source)
+		return
+	}
+
+	rightChild := opTerm.children[1]
+
+	if rightValue, err = rightChild.compute(ctx); err == nil {
+		if leftValue, err = getAssignValue(ctx, leftTerm); err == nil {
+			switch opTerm.symbol() {
+			case SymPlusEqual:
+				v, err = sumValues(opTerm, leftValue, rightValue)
+			case SymMinusEqual:
+				v, err = diffValues(opTerm, leftValue, rightValue)
+			case SymStarEqual:
+				v, err = mulValues(opTerm, leftValue, rightValue)
+			case SymSlashEqual:
+				v, err = divValues(opTerm, leftValue, rightValue)
+			case SymPercEqual:
+				v, err = remainderValues(opTerm, leftValue, rightValue)
+			default:
+				err = opTerm.Errorf("unsupported assign operator %q", opTerm.source())
+			}
+			if err == nil {
+				err = assignValue(ctx, leftTerm, v)
+			}
+		}
+	}
+	return
+}
+
 // init
 func init() {
 	registerTermConstructor(SymEqual, newAssignTerm)
+	registerTermConstructor(SymPlusEqual, newOpAssignTerm)
+	registerTermConstructor(SymMinusEqual, newOpAssignTerm)
+	registerTermConstructor(SymStarEqual, newOpAssignTerm)
+	registerTermConstructor(SymSlashEqual, newOpAssignTerm)
 }

operator-binary.go

@@ -0,0 +1,104 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-binary.go
+package expr
+
+//-------- NOT term
+
+func newBinNotTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priBinary,
+		evalFunc: evalBinaryNot,
+	}
+}
+
+func evalBinaryNot(ctx ExprContext, opTerm *term) (v any, err error) {
+	var value any
+
+	if value, err = opTerm.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	if IsInteger(value) {
+		i, _ := value.(int64)
+		v = ^i
+	} else {
+		err = opTerm.errIncompatibleType(value)
+	}
+	return
+}
+
+//-------- Binary AND term
+
+func newBinAndTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priBinary,
+		evalFunc: evalBinaryAnd,
+	}
+}
+
+func evalBinaryAnd(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+	var leftInt, rightInt int64
+	var lok, rok bool
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+
+	leftInt, lok = leftValue.(int64)
+	rightInt, rok = rightValue.(int64)
+
+	if lok && rok {
+		v = leftInt & rightInt
+	} else {
+		err = self.errIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+//-------- Binary OR term
+
+func newBinOrTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priBinary,
+		evalFunc: evalBinaryOr,
+	}
+}
+
+func evalBinaryOr(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+	var leftInt, rightInt int64
+	var lok, rok bool
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+
+	leftInt, lok = leftValue.(int64)
+	rightInt, rok = rightValue.(int64)
+
+	if lok && rok {
+		v = leftInt | rightInt
+	} else {
+		err = self.errIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymTilde, newBinNotTerm)
+	registerTermConstructor(SymAmpersand, newBinAndTerm)
+	registerTermConstructor(SymVertBar, newBinOrTerm)
+}

operator-context.go

@@ -20,7 +20,7 @@ func evalContextValue(ctx ExprContext, opTerm *term) (v any, err error) {
 	var childValue any
 
 	var sourceCtx ExprContext
-	if opTerm.children == nil || len(opTerm.children) == 0 {
+	if len(opTerm.children) == 0 {
 		sourceCtx = ctx
 	} else if opTerm.children[0].symbol() == SymVariable && opTerm.children[0].source() == "global" {
 		sourceCtx = globalCtx

operator-fraction.go

@@ -49,18 +49,23 @@ func evalFraction(ctx ExprContext, opTerm *term) (v any, err error) {
 		den = -den
 		num = -num
 	}
-	g := gcd(num, den)
+	if num != 0 {
-	num = num / g
+		g := gcd(num, den)
-	den = den / g
+		num = num / g
-	if den == 1 {
+		den = den / g
-		v = num
+		if den == 1 {
+			v = num
+		} else {
+			v = &FractionType{num, den}
+		}
 	} else {
-		v = &FractionType{num, den}
+		v = &FractionType{0, den}
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymVertBar, newFractionTerm)
+	// registerTermConstructor(SymVertBar, newFractionTerm)
+	registerTermConstructor(SymColon, newFractionTerm)
 }

operator-index.go

@@ -113,6 +113,9 @@ func evalIndex(ctx ExprContext, opTerm *term) (v any, err error) {
 	} else if IsDict(leftValue) {
 		d := leftValue.(*DictType)
 		v, err = getDictItem(d, indexTerm, indexList, rightValue)
+	} else {
+		rightChild := opTerm.children[1]
+		err = rightChild.Errorf("invalid index type: %v", (*indexList)[0])
 	}
 	return
 }

operator-insert.go

@@ -40,6 +40,10 @@ func evalInsert(ctx ExprContext, opTerm *term) (v any, err error) {
 		if opTerm.children[1].symbol() == SymVariable {
 			ctx.UnsafeSetVar(opTerm.children[1].source(), v)
 		}
+	} else if IsInteger(leftValue) && IsInteger(rightValue) {
+		leftInt := leftValue.(int64)
+		rightInt := rightValue.(int64)
+		v = leftInt >> rightInt
 	} else {
 		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
 	}
@@ -60,6 +64,10 @@ func evalAppend(ctx ExprContext, opTerm *term) (v any, err error) {
 		if opTerm.children[0].symbol() == SymVariable {
 			ctx.UnsafeSetVar(opTerm.children[0].source(), v)
 		}
+	} else if IsInteger(leftValue) && IsInteger(rightValue) {
+		leftInt := leftValue.(int64)
+		rightInt := rightValue.(int64)
+		v = leftInt << rightInt
 	} else {
 		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
 	}

operator-prod.go

@@ -13,7 +13,7 @@ import (
 
 func newMultiplyTerm(tk *Token) (inst *term) {
 	return &term{
-		tk: *tk,
+		tk:       *tk,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priProduct,
@@ -21,13 +21,7 @@ func newMultiplyTerm(tk *Token) (inst *term) {
 	}
 }
 
-func evalMultiply(ctx ExprContext, prodTerm *term) (v any, err error) {
+func mulValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = prodTerm.evalInfix(ctx); err != nil {
-		return
-	}
-
 	if IsString(leftValue) && IsInteger(rightValue) {
 		s, _ := leftValue.(string)
 		n, _ := rightValue.(int64)
@@ -43,16 +37,26 @@ func evalMultiply(ctx ExprContext, prodTerm *term) (v any, err error) {
 			v = leftInt * rightInt
 		}
 	} else {
-		err = prodTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
+func evalMultiply(ctx ExprContext, prodTerm *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = prodTerm.evalInfix(ctx); err != nil {
+		return
+	}
+
+	return mulValues(prodTerm, leftValue, rightValue)
+}
+
 //-------- divide term
 
 func newDivideTerm(tk *Token) (inst *term) {
 	return &term{
-		tk: *tk,
+		tk:       *tk,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priProduct,
@@ -60,13 +64,7 @@ func newDivideTerm(tk *Token) (inst *term) {
 	}
 }
 
-func evalDivide(ctx ExprContext, opTerm *term) (v any, err error) {
+func divValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
-		return
-	}
-
 	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
 		if IsFloat(leftValue) || IsFloat(rightValue) {
 			d := numAsFloat(rightValue)
@@ -91,6 +89,16 @@ func evalDivide(ctx ExprContext, opTerm *term) (v any, err error) {
 	return
 }
 
+func evalDivide(ctx ExprContext, opTerm *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+		return
+	}
+
+	return divValues(opTerm, leftValue, rightValue)
+}
+
 //-------- divide as float term
 
 func newDivideAsFloatTerm(tk *Token) (inst *term) {
@@ -127,21 +135,14 @@ func evalDivideAsFloat(ctx ExprContext, floatDivTerm *term) (v any, err error) {
 
 func newRemainderTerm(tk *Token) (inst *term) {
 	return &term{
-		tk: *tk,
+		tk:       *tk,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priProduct,
-		evalFunc: evalReminder,
+		evalFunc: evalRemainder,
 	}
 }
-
+func remainderValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
-func evalReminder(ctx ExprContext, ramainderTerm *term) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = ramainderTerm.evalInfix(ctx); err != nil {
-		return
-	}
-
 	if IsInteger(leftValue) && IsInteger(rightValue) {
 		rightInt, _ := rightValue.(int64)
 		if rightInt == 0 {
@@ -151,11 +152,21 @@ func evalReminder(ctx ExprContext, ramainderTerm *term) (v any, err error) {
 			v = leftInt % rightInt
 		}
 	} else {
-		err = ramainderTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
+func evalRemainder(ctx ExprContext, remainderTerm *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = remainderTerm.evalInfix(ctx); err != nil {
+		return
+	}
+
+	return remainderValues(remainderTerm, leftValue, rightValue)
+}
+
 // init
 func init() {
 	registerTermConstructor(SymStar, newMultiplyTerm)

operator-range.go

@@ -34,12 +34,16 @@ func newRangeTerm(tk *Token) (inst *term) {
 	}
 }
 
+func changeColonToRange(t *term) {
+	if t.tk.IsSymbol(SymColon) {
+		t.tk.Sym = SymRange
+		t.evalFunc = evalRange
+	}
+}
+
 func evalRange(ctx ExprContext, opTerm *term) (v any, err error) {
 	var leftValue, rightValue any
 
-	// if err = self.checkOperands(); err != nil {
-	// 	return
-	// }
 	if len(opTerm.children) == 0 {
 		leftValue = int64(0)
 		rightValue = int64(-1)
@@ -52,7 +56,8 @@ func evalRange(ctx ExprContext, opTerm *term) (v any, err error) {
 		return
 	}
 	if !(IsInteger(leftValue) && IsInteger(rightValue)) {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		// err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = errRangeInvalidSpecification(opTerm)
 		return
 	}
 
@@ -63,7 +68,15 @@ func evalRange(ctx ExprContext, opTerm *term) (v any, err error) {
 	return
 }
 
+func errRangeInvalidSpecification(t *term) error {
+	return t.Errorf("invalid range specification")
+}
+
+func errRangeUnexpectedExpression(t *term) error {
+	return t.Errorf("unexpected range expression")
+}
+
 // init
 func init() {
-	registerTermConstructor(SymColon, newRangeTerm)
+	registerTermConstructor(SymRange, newRangeTerm)
 }

operator-sum.go

@@ -21,13 +21,7 @@ func newPlusTerm(tk *Token) (inst *term) {
 	}
 }
 
-func evalPlus(ctx ExprContext, plusTerm *term) (v any, err error) {
+func sumValues(plusTerm *term, leftValue, rightValue any) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = plusTerm.evalInfix(ctx); err != nil {
-		return
-	}
-
 	if (IsString(leftValue) && isNumberString(rightValue)) || (IsString(rightValue) && isNumberString(leftValue)) {
 		v = fmt.Sprintf("%v%v", leftValue, rightValue)
 	} else if IsNumber(leftValue) && IsNumber(rightValue) {
@@ -59,10 +53,22 @@ func evalPlus(ctx ExprContext, plusTerm *term) (v any, err error) {
 		c := leftDict.clone()
 		c.merge(rightDict)
 		v = c
+	} else if isFraction(leftValue) && isFraction(rightValue) {
+		v, err = sumAnyFract(leftValue, rightValue)
 	} else {
 		err = plusTerm.errIncompatibleTypes(leftValue, rightValue)
 	}
-	return
+	return v, err
+}
+
+func evalPlus(ctx ExprContext, plusTerm *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = plusTerm.evalInfix(ctx); err != nil {
+		return
+	}
+
+	return sumValues(plusTerm, leftValue, rightValue)
 }
 
 //-------- minus term
@@ -77,13 +83,7 @@ func newMinusTerm(tk *Token) (inst *term) {
 	}
 }
 
-func evalMinus(ctx ExprContext, minusTerm *term) (v any, err error) {
+func diffValues(minusTerm *term, leftValue, rightValue any) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = minusTerm.evalInfix(ctx); err != nil {
-		return
-	}
-
 	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
 		if IsFloat(leftValue) || IsFloat(rightValue) {
 			v = numAsFloat(leftValue) - numAsFloat(rightValue)
@@ -110,6 +110,16 @@ func evalMinus(ctx ExprContext, minusTerm *term) (v any, err error) {
 	return
 }
 
+func evalMinus(ctx ExprContext, minusTerm *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = minusTerm.evalInfix(ctx); err != nil {
+		return
+	}
+
+	return diffValues(minusTerm, leftValue, rightValue)
+}
+
 // init
 func init() {
 	registerTermConstructor(SymPlus, newPlusTerm)

parser.go

@@ -6,10 +6,46 @@ package expr
 
 import (
 	"errors"
+
+	"golang.org/x/exp/constraints"
 )
 
 //-------- parser
 
+type parserContext uint16
+
+const (
+	parserNoFlags                = 0
+	allowMultiExpr parserContext = 1 << iota
+	allowVarRef
+	selectorContext
+	listContext                                // squareContext for list
+	indexContext                               // squareContext for index
+	allowIndex                                 // allow index in squareContext
+	squareContext = listContext | indexContext // Square parenthesis for list or index
+)
+
+func hasFlag[T constraints.Unsigned](set T, singleFlag T) bool {
+	return (set & singleFlag) != 0
+}
+
+func addFlags[T constraints.Unsigned](set T, flags T) T {
+	return set | flags
+}
+
+func addFlagsCond[T constraints.Unsigned](set T, flags T, cond bool) (newSet T) {
+	if cond {
+		newSet = set | flags
+	} else {
+		newSet = set
+	}
+	return
+}
+
+func remFlags[T constraints.Unsigned](set T, flags T) T {
+	return set & (^flags)
+}
+
 type parser struct {
 }
 
@@ -24,13 +60,13 @@ func (parser *parser) Next(scanner *scanner) (tk *Token) {
 	return
 }
 
-func (parser *parser) parseFuncCall(scanner *scanner, allowVarRef bool, tk *Token) (tree *term, err error) {
+func (parser *parser) parseFuncCall(scanner *scanner, ctx parserContext, tk *Token) (tree *term, err error) {
 	args := make([]*term, 0, 10)
 	itemExpected := false
 	lastSym := SymUnknown
 	for lastSym != SymClosedRound && lastSym != SymEos {
 		var subTree *ast
-		if subTree, err = parser.parseItem(scanner, allowVarRef, SymComma, SymClosedRound); err != nil {
+		if subTree, err = parser.parseItem(scanner, ctx, SymComma, SymClosedRound); err != nil {
 			break
 		}
 		prev := scanner.Previous()
@@ -77,7 +113,7 @@ func (parser *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 			if tk.Sym == SymEqual {
 				var paramExpr *ast
 				defaultParamsStarted = true
-				if paramExpr, err = parser.parseItem(scanner, false, SymComma, SymClosedRound); err != nil {
+				if paramExpr, err = parser.parseItem(scanner, parserNoFlags, SymComma, SymClosedRound); err != nil {
 					break
 				}
 				param.forceChild(paramExpr.root)
@@ -100,7 +136,7 @@ func (parser *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 	if err == nil {
 		tk = parser.Next(scanner)
 		if tk.IsSymbol(SymOpenBrace) {
-			body, err = parser.parseGeneral(scanner, true, true, SymClosedBrace)
+			body, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, SymClosedBrace)
 		} else {
 			err = tk.ErrorExpectedGot("{")
 		}
@@ -126,27 +162,33 @@ func paramAlreadyDefined(args []*term, param *term) (position int) {
 	return
 }
 
-func (parser *parser) parseList(scanner *scanner, parsingIndeces bool, allowVarRef bool) (subtree *term, err error) {
+func (parser *parser) parseList(scanner *scanner, ctx parserContext) (listTerm *term, err error) {
 	r, c := scanner.lastPos()
 	args := make([]*term, 0)
 	lastSym := SymUnknown
 	itemExpected := false
+	itemCtx := remFlags(ctx, allowIndex)
 	for lastSym != SymClosedSquare && lastSym != SymEos {
-		var subTree *ast
 		zeroRequired := scanner.current.Sym == SymColon
-		if subTree, err = parser.parseItem(scanner, allowVarRef, SymComma, SymClosedSquare); err == nil {
+		var itemTree *ast
-			root := subTree.root
+		if itemTree, err = parser.parseItem(scanner, itemCtx, SymComma, SymClosedSquare); err == nil {
+			root := itemTree.root
 			if root != nil {
-				if !parsingIndeces && root.symbol() == SymColon {
+				if hasFlag(ctx, allowIndex) && root.symbol() == SymColon {
-					err = root.Errorf("unexpected range expression")
+					changeColonToRange(root)
+				}
+				if !hasFlag(ctx, allowIndex) && root.symbol() == SymRange {
+					// err = root.Errorf("unexpected range expression")
+					err = errRangeUnexpectedExpression(root)
 					break
 				}
 				args = append(args, root)
-				if parsingIndeces && root.symbol() == SymColon && zeroRequired { //len(root.children) == 0 {
+				if hasFlag(ctx, allowIndex) && root.symbol() == SymRange && 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")
+						// err = root.Errorf("invalid range specification")
+						err = errRangeInvalidSpecification(root)
 						break
 					}
 					zeroTk := NewValueToken(root.tk.row, root.tk.col, SymInteger, "0", int64(0))
@@ -163,26 +205,28 @@ func (parser *parser) parseList(scanner *scanner, parsingIndeces bool, allowVarR
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == SymComma
+		if itemExpected = lastSym == SymComma; itemExpected {
+			remFlags(ctx, allowIndex)
+		}
 	}
 	if err == nil {
 		if lastSym != SymClosedSquare {
 			err = scanner.Previous().ErrorExpectedGot("]")
 		} else {
-			subtree = newListTerm(r, c, args)
+			listTerm = newListTerm(r, c, args)
 		}
 	}
 	return
 }
 
-func (parser *parser) parseIterDef(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
+func (parser *parser) parseIterDef(scanner *scanner, ctx parserContext) (subtree *term, err error) {
 	tk := scanner.Previous()
 	args := make([]*term, 0)
 	lastSym := SymUnknown
 	itemExpected := false
 	for lastSym != SymClosedRound && lastSym != SymEos {
 		var subTree *ast
-		if subTree, err = parser.parseItem(scanner, allowVarRef, SymComma, SymClosedRound); err == nil {
+		if subTree, err = parser.parseItem(scanner, ctx, SymComma, SymClosedRound); err == nil {
 			if subTree.root != nil {
 				args = append(args, subTree.root)
 			} else if itemExpected {
@@ -228,7 +272,7 @@ func (parser *parser) parseDictKey(scanner *scanner) (key any, err error) {
 	return
 }
 
-func (parser *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
+func (parser *parser) parseDictionary(scanner *scanner, ctx parserContext) (subtree *term, err error) {
 	args := make(map[any]*term, 0)
 	lastSym := SymUnknown
 	itemExpected := false
@@ -245,7 +289,7 @@ func (parser *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtr
 			}
 			break
 		}
-		if subTree, err = parser.parseItem(scanner, allowVarRef, SymComma, SymClosedBrace); err == nil {
+		if subTree, err = parser.parseItem(scanner, ctx, SymComma, SymClosedBrace); err == nil {
 			if subTree.root != nil {
 				args[key] = subTree.root
 			} else /*if key != nil*/ {
@@ -264,15 +308,15 @@ func (parser *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtr
 			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
 			subtree = newDictTerm(args)
-			// subtree = newMapTerm(args)
 		}
 	}
 	return
 }
 
-func (parser *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defaultCase bool) (caseTerm *term, err error) {
+func (parser *parser) parseSelectorCase(scanner *scanner, ctx parserContext, defaultCase bool) (caseTerm *term, err error) {
 	var filterList *term
 	var caseExpr *ast
+	ctx = remFlags(ctx, allowIndex)
 	tk := parser.Next(scanner)
 	startRow := tk.row
 	startCol := tk.col
@@ -281,7 +325,7 @@ func (parser *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defa
 			err = tk.Errorf("case list in default clause")
 			return
 		}
-		if filterList, err = parser.parseList(scanner, false, allowVarRef); err != nil {
+		if filterList, err = parser.parseList(scanner, remFlags(ctx, allowIndex)); err != nil {
 			return
 		}
 		tk = parser.Next(scanner)
@@ -292,7 +336,7 @@ func (parser *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defa
 	}
 
 	if tk.Sym == SymOpenBrace {
-		if caseExpr, err = parser.parseGeneral(scanner, true, allowVarRef, SymClosedBrace); err != nil {
+		if caseExpr, err = parser.parseGeneral(scanner, ctx|allowMultiExpr, SymClosedBrace); err != nil {
 			return
 		}
 	} else {
@@ -318,25 +362,28 @@ func addSelectorCase(selectorTerm, caseTerm *term) {
 	caseTerm.parent = selectorTerm
 }
 
-func (parser *parser) parseSelector(scanner *scanner, tree *ast, allowVarRef bool) (selectorTerm *term, err error) {
+func (parser *parser) parseSelector(scanner *scanner, tree *ast, ctx parserContext) (selectorTerm *term, err error) {
 	var caseTerm *term
+
+	ctx = remFlags(ctx, allowIndex)
 	tk := scanner.makeToken(SymSelector, '?')
 	if selectorTerm, err = tree.addToken(tk); err != nil {
 		return
 	}
 
-	if caseTerm, err = parser.parseSelectorCase(scanner, allowVarRef, false); err == nil {
+	if caseTerm, err = parser.parseSelectorCase(scanner, ctx|allowVarRef, false); err == nil {
 		addSelectorCase(selectorTerm, caseTerm)
 	}
 	return
 }
 
-func (parser *parser) parseItem(scanner *scanner, allowVarRef bool, termSymbols ...Symbol) (tree *ast, err error) {
+func (parser *parser) parseItem(scanner *scanner, ctx parserContext, termSymbols ...Symbol) (tree *ast, err error) {
-	return parser.parseGeneral(scanner, false, allowVarRef, termSymbols...)
+	return parser.parseGeneral(scanner, ctx|allowVarRef, termSymbols...)
 }
 
 func (parser *parser) Parse(scanner *scanner, termSymbols ...Symbol) (tree *ast, err error) {
-	return parser.parseGeneral(scanner, true, false, termSymbols...)
+	termSymbols = append(termSymbols, SymEos)
+	return parser.parseGeneral(scanner, allowMultiExpr, termSymbols...)
 }
 
 func couldBeACollection(t *term) bool {
@@ -347,15 +394,22 @@ func couldBeACollection(t *term) bool {
 	return sym == SymList || sym == SymString || sym == SymDict || sym == SymExpression || sym == SymVariable
 }
 
-// func areSymbolsOutOfCtx(tk *Token, ctxTerm *term, syms ...Symbol) bool {
+func listSubTree(tree *ast, listTerm *term, allowIndeces bool) (root *term, err error) {
-// 	var areOut = false
+	var tk *Token
-// 	if ctxTerm != nil {
+	if allowIndeces {
-// 		areOut = tk.IsOneOf(syms)
+		tk = NewToken(listTerm.tk.row, listTerm.tk.col, SymIndex, listTerm.source())
-// 	}
+		root = newTerm(tk)
-// 	return areOut
+		if err = tree.addTerm(root); err == nil {
-// }
+			err = tree.addTerm(listTerm)
+		}
+	} else {
+		root = listTerm
+		err = tree.addTerm(listTerm)
+	}
+	return
+}
 
-func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef bool, termSymbols ...Symbol) (tree *ast, err error) {
+func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymbols ...Symbol) (tree *ast, err error) {
 	var selectorTerm *term = nil
 	var currentTerm *term = nil
 	var tk *Token
@@ -369,7 +423,7 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 		// }
 
 		if tk.Sym == SymSemiColon {
-			if allowForest {
+			if hasFlag(ctx, allowMultiExpr) {
 				tree.ToForest()
 				firstToken = true
 				currentTerm = nil
@@ -387,6 +441,9 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 				tk.Sym = SymChangeSign
 			} else if tk.Sym == SymPlus {
 				tk.Sym = SymUnchangeSign
+			} else if tk.IsSymbol(SymExclamation) {
+				err = tk.Errorf("postfix opertor %q requires an operand on its left", tk)
+				break
 			}
 			firstToken = false
 		}
@@ -394,47 +451,36 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 		switch tk.Sym {
 		case SymOpenRound:
 			var subTree *ast
-			if subTree, err = parser.parseGeneral(scanner, false, allowVarRef, SymClosedRound); err == nil {
+			if subTree, err = parser.parseGeneral(scanner, ctx, SymClosedRound); err == nil {
 				subTree.root.priority = priValue
 				err = tree.addTerm(newExprTerm(subTree.root))
 				currentTerm = subTree.root
 			}
 		case SymFuncCall:
 			var funcCallTerm *term
-			if funcCallTerm, err = parser.parseFuncCall(scanner, allowVarRef, tk); err == nil {
+			if funcCallTerm, err = parser.parseFuncCall(scanner, ctx, tk); err == nil {
 				err = tree.addTerm(funcCallTerm)
 				currentTerm = funcCallTerm
 			}
 		case SymOpenSquare:
 			var listTerm *term
-			parsingIndeces := couldBeACollection(currentTerm)
+			newCtx := addFlagsCond(addFlags(ctx, squareContext), allowIndex, couldBeACollection(currentTerm))
-			if listTerm, err = parser.parseList(scanner, parsingIndeces, allowVarRef); err == nil {
+			if listTerm, err = parser.parseList(scanner, newCtx); err == nil {
-				if parsingIndeces {
+				currentTerm, err = listSubTree(tree, listTerm, hasFlag(newCtx, allowIndex))
-					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 = parser.parseDictionary(scanner, allowVarRef); err == nil {
+				if mapTerm, err = parser.parseDictionary(scanner, ctx); err == nil {
 					err = tree.addTerm(mapTerm)
 					currentTerm = mapTerm
 				}
 			}
-		case SymEqual:
+		case SymEqual, SymPlusEqual, SymMinusEqual, SymStarEqual, SymSlashEqual, SymPercEqual:
-			// if err = checkPrevSymbol(lastSym, SymIdentifier, tk); err == nil {
 			currentTerm, err = tree.addToken(tk)
 			firstToken = true
-			// }
 		case SymFuncDef:
 			var funcDefTerm *term
 			if funcDefTerm, err = parser.parseFuncDef(scanner); err == nil {
@@ -443,24 +489,25 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 			}
 		case SymDollarRound:
 			var iterDefTerm *term
-			if iterDefTerm, err = parser.parseIterDef(scanner, allowVarRef); err == nil {
+			if iterDefTerm, err = parser.parseIterDef(scanner, ctx); err == nil {
 				err = tree.addTerm(iterDefTerm)
 				currentTerm = iterDefTerm
 			}
 		case SymIdentifier:
-			if tk.source[0] == '@' && !allowVarRef {
+			if tk.source[0] == '@' && !hasFlag(ctx, allowVarRef) {
 				err = tk.Errorf("variable references are not allowed in top level expressions: %q", tk.source)
 			} else {
 				currentTerm, err = tree.addToken(tk)
 			}
 		case SymQuestion:
-			if selectorTerm, err = parser.parseSelector(scanner, tree, allowVarRef); err == nil {
+			if selectorTerm, err = parser.parseSelector(scanner, tree, ctx); err == nil {
 				currentTerm = selectorTerm
+				addFlags(ctx, selectorContext)
 			}
 		case SymColon, SymDoubleColon:
 			var caseTerm *term
 			if selectorTerm != nil {
-				if caseTerm, err = parser.parseSelectorCase(scanner, allowVarRef, tk.Sym == SymDoubleColon); err == nil {
+				if caseTerm, err = parser.parseSelectorCase(scanner, ctx, tk.Sym == SymDoubleColon); err == nil {
 					addSelectorCase(selectorTerm, caseTerm)
 					currentTerm = caseTerm
 					if tk.Sym == SymDoubleColon {
@@ -468,80 +515,38 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 					}
 				}
 			} else {
+				// if hasFlag(ctx, allowIndex) {
+				// 	tk.Sym = SymRange
+				// }
 				currentTerm, err = tree.addToken(tk)
 			}
-			if tk.IsSymbol(SymColon) {
+			if tk.IsOneOfA(SymColon, SymRange) {
 				// Colon outside a selector term acts like a separator
 				firstToken = true
 			}
-		case SymPlusEqual, SymMinusEqual, SymStarEqual:
-			currentTerm, err = parser.expandOpAssign(scanner, tree, tk, allowVarRef)
 		default:
 			currentTerm, err = tree.addToken(tk)
 		}
 
 		if currentTerm != nil && currentTerm.tk.Sym != SymSelector && currentTerm.parent != nil && currentTerm.parent.tk.Sym != SymSelector {
 			selectorTerm = nil
-
+			remFlags(ctx, selectorContext)
 		}
 		// lastSym = tk.Sym
 	}
 
 	if err == nil {
-		err = tk.Error()
+		if !tk.IsOneOf(termSymbols) {
-	}
+			var symDesc string
-	return
+			if tk.IsSymbol(SymError) {
-}
+				symDesc = tk.ErrorText()
-
+			} else {
-// func checkPrevSymbol(lastSym, wantedSym Symbol, tk *Token) (err error) {
+				symDesc = SymToString(tk.Sym)
-// 	if lastSym != wantedSym {
-// 		err = fmt.Errorf(`assign operator (%q) must be preceded by a variable`, tk.source)
-// 	}
-// 	return
-// }
-
-func (parser *parser) expandOpAssign(scanner *scanner, tree *ast, tk *Token, allowVarRef bool) (t *term, err error) {
-	var opSym Symbol
-	var opString string
-
-	if tree.root != nil {
-		switch tk.Sym {
-		case SymPlusEqual:
-			opString = "+"
-			opSym = SymPlus
-		case SymMinusEqual:
-			opString = "-"
-			opSym = SymMinus
-		case SymStarEqual:
-			opString = "*"
-			opSym = SymStar
-		default:
-			err = tk.Errorf("unsopported operator %q", tk.source)
-			return
-		}
-		leftExpr := tree.root.Clone()
-		leftExpr.setParent(nil)
-		if t, err = tree.addToken(NewToken(tk.row, tk.col, SymEqual, "=")); err == nil {
-			t = leftExpr
-			if err = tree.addTerm(leftExpr); err == nil {
-				if t, err = tree.addToken(NewToken(tk.row, tk.col, opSym, opString)); err == nil {
-
-					var subTree *ast
-					if subTree, err = parser.parseGeneral(scanner, false, allowVarRef, SymSemiColon, SymClosedRound, SymClosedBrace, SymClosedSquare); err == nil {
-						if scanner.Previous().IsOneOfA(SymSemiColon, SymClosedRound, SymClosedBrace, SymClosedSquare) {
-							if err = scanner.UnreadToken(); err != nil {
-								return
-							}
-						}
-						subTree.root.priority = priValue
-						err = tree.addTerm(newExprTerm(subTree.root))
-						t = subTree.root
-					}
-				}
 			}
+			err = tk.ErrorExpectedGotStringWithPrefix("expected one of", SymListToString(termSymbols, true), symDesc)
+		} else {
+			err = tk.Error()
 		}
-	} else {
-		err = tk.Errorf("left operand of %q must be a variable or a variable expression", tk)
 	}
 	return
 }

scanner.go

@@ -40,9 +40,9 @@ func DefaultTranslations() map[Symbol]Symbol {
 		SymKwAnd:           SymAnd,
 		SymDoubleVertBar:   SymOr,
 		SymKwOr:            SymOr,
-		SymTilde:           SymNot,
+		// SymTilde:           SymNot,
-		SymKwNot:           SymNot,
+		SymKwNot:       SymNot,
-		SymLessGreater:     SymNotEqual,
+		SymLessGreater: SymNotEqual,
 	}
 }
 
@@ -149,6 +149,8 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			if next, _ := scanner.peek(); next == '*' {
 				scanner.readChar()
 				tk = scanner.fetchBlockComment()
+			} else if next, _ = scanner.peek(); next == '=' {
+				tk = scanner.moveOn(SymSlashEqual, ch, next)
 			} else if next == '/' {
 				scanner.readChar()
 				tk = scanner.fetchOnLineComment()
@@ -458,7 +460,7 @@ func (scanner *scanner) parseNumber(firstCh byte) (tk *Token) {
 		tk = scanner.makeErrorToken(err)
 	} else {
 		var value any
-		err = scanner.sync(err) // TODO: Check this function
+		_ = scanner.sync(err) // TODO: Check this function
 		txt := sb.String()
 		if sym == SymFloat {
 			value, err = strconv.ParseFloat(txt, 64)
@@ -590,7 +592,7 @@ func (scanner *scanner) fetchString(termCh byte) (tk *Token) {
 	}
 	if err != nil {
 		if err == io.EOF {
-			tk = scanner.makeErrorToken(errors.New("missing string termination \""))
+			tk = scanner.makeErrorToken(errors.New(string(termCh)))
 		} else {
 			tk = scanner.makeErrorToken(err)
 		}

symbol-map.go

@@ -0,0 +1,181 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// Symbol.go
+package expr
+
+import (
+	"strings"
+)
+
+var symbolMap map[Symbol]symbolSpec
+
+type symbolClass int16
+
+const (
+	symClassOperator symbolClass = iota
+	symClassPostOp
+	symClassIdentifier
+	symClassDelimiter
+	symClassParenthesis
+	symClassDeclaration
+	symClassValue
+	symClassOther
+)
+
+type symbolSpec struct {
+	repr string
+	kind symbolClass
+}
+
+func init() {
+
+	symbolMap = map[Symbol]symbolSpec{
+		SymUnknown:         {"<unknown>", symClassOther}, //  -1: Unknown symbol
+		SymNone:            {"<null>", symClassOther},    //   0: Null value for variable of type symbol
+		SymError:           {"<error>", symClassOther},   //   1: Error reading from stream
+		SymEos:             {"<eos>", symClassOther},     //   2: End of stream
+		SymMinus:           {"-", symClassOperator},      //   3: '-'
+		SymMinusEqual:      {"-=", symClassOperator},     //   4: '-='
+		SymDoubleMinus:     {"--", symClassOperator},     //   5: '--'
+		SymPlus:            {"+", symClassOperator},      //   6: '+'
+		SymPlusEqual:       {"+=", symClassOperator},     //   7: '+='
+		SymDoublePlus:      {"++", symClassOperator},     //   8: '++'
+		SymStar:            {"*", symClassOperator},      //   9: '*'
+		SymDoubleStar:      {"**", symClassOperator},     //  10: '**'
+		SymSlash:           {"/", symClassOperator},      //  11: '/'
+		SymBackSlash:       {"\\", symClassOperator},     //  12: '\'
+		SymVertBar:         {"|", symClassOperator},      //  13: '|'
+		SymDoubleVertBar:   {"||", symClassOperator},     //  14: '||'
+		SymComma:           {",", symClassOperator},      //  15: ','
+		SymColon:           {":", symClassOperator},      //  16: ':'
+		SymSemiColon:       {";", symClassOperator},      //  17: ';'
+		SymDot:             {".", symClassOperator},      //  18: '.'
+		SymDotSlash:        {"./", symClassOperator},     //  19: './'
+		SymQuote:           {"'", symClassDelimiter},     //  20: '\''
+		SymDoubleQuote:     {"\"", symClassDelimiter},    //  21: '"'
+		SymBackTick:        {"`", symClassOperator},      //  22: '`'
+		SymExclamation:     {"!", symClassPostOp},        //  23: '!'
+		SymQuestion:        {"?", symClassOperator},      //  24: '?'
+		SymAmpersand:       {"&", symClassOperator},      //  25: '&'
+		SymDoubleAmpersand: {"&&", symClassOperator},     //  26: '&&'
+		SymPercent:         {"%", symClassOperator},      //  27: '%'
+		SymAt:              {"@", symClassOperator},      //  28: '@'
+		SymUndescore:       {"_", symClassOperator},      //  29: '_'
+		SymEqual:           {"=", symClassOperator},      //  30: '='
+		SymDoubleEqual:     {"==", symClassOperator},     //  31: '=='
+		SymLess:            {"<", symClassOperator},      //  32: '<'
+		SymLessOrEqual:     {"<=", symClassOperator},     //  33: '<='
+		SymGreater:         {">", symClassOperator},      //  34: '>'
+		SymGreaterOrEqual:  {">=", symClassOperator},     //  35: '>='
+		SymLessGreater:     {"<>", symClassOperator},     //  36: '<>'
+		SymNotEqual:        {"!=", symClassOperator},     //  37: '!='
+		SymDollar:          {"$", symClassOperator},      //  38: '$'
+		SymHash:            {"#", symClassOperator},      //  39: '#'
+		SymOpenRound:       {"(", symClassParenthesis},   //  40: '('
+		SymClosedRound:     {")", symClassParenthesis},   //  41: ')'
+		SymOpenSquare:      {"[", symClassParenthesis},   //  42: '['
+		SymClosedSquare:    {"]", symClassParenthesis},   //  43: ']'
+		SymOpenBrace:       {"{", symClassParenthesis},   //  44: '{'
+		SymClosedBrace:     {"}", symClassParenthesis},   //  45: '}'
+		SymTilde:           {"~", symClassOperator},      //  46: '~'
+		SymDoubleQuestion:  {"??", symClassOperator},     //  47: '??'
+		SymQuestionEqual:   {"?=", symClassOperator},     //  48: '?='
+		SymQuestionExclam:  {"?!", symClassOperator},     //  49: '?!'
+		SymDoubleAt:        {"@@", symClassOperator},     //  50: '@@'
+		SymDoubleColon:     {"::", symClassOperator},     //  51: '::'
+		SymInsert:          {">>", symClassOperator},     //  52: '>>'
+		SymAppend:          {"<<", symClassOperator},     //  53: '<<'
+		SymCaret:           {"^", symClassOperator},      //  54: '^'
+		SymDollarRound:     {"$(", symClassOperator},     //  55: '$('
+		SymOpenClosedRound: {"()", symClassPostOp},       //  56: '()'
+		SymDoubleDollar:    {"$$", symClassOperator},     //  57: '$$'
+		SymDoubleDot:       {"..", symClassOperator},     //  58: '..'
+		SymTripleDot:       {"...", symClassOperator},    //  59: '...'
+		SymStarEqual:       {"*=", symClassOperator},     //  60: '*='
+		SymSlashEqual:      {"/=", symClassOperator},     //  61: '/='
+		SymPercEqual:       {"%=", symClassOperator},     //  62: '%='
+		// SymChangeSign
+		// SymUnchangeSign
+		// SymIdentifier
+		// SymBool
+		// SymInteger
+		// SymVariable
+		// SymFloat
+		// SymFraction
+		// SymString
+		// SymIterator
+		// SymOr:  "or",
+		// SymAnd: "and",
+		// SymNot: "not",
+		// SymComment
+		// SymFuncCall
+		// SymFuncDef
+		// SymList
+		// SymDict
+		// SymIndex
+		// SymExpression
+		// SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
+		// SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"
+		// // SymOpenComment                       //   0: '/*'
+		// // SymClosedComment                     //   0: '*/'
+		// // SymOneLineComment                    //   0: '//'
+		// keywordBase
+		SymKwAnd:     {"and", symClassOperator},
+		SymKwNot:     {"not", symClassOperator},
+		SymKwOr:      {"or", symClassOperator},
+		SymKwBut:     {"but", symClassOperator},
+		SymKwFunc:    {"func(", symClassDeclaration},
+		SymKwBuiltin: {"builtin", symClassOperator},
+		SymKwPlugin:  {"plugin", symClassOperator},
+		SymKwIn:      {"in", symClassOperator},
+		SymKwInclude: {"include", symClassOperator},
+		SymKwNil:     {"nil", symClassValue},
+		SymKwUnset:   {"unset", symClassOperator},
+	}
+}
+
+func SymToString(sym Symbol) string {
+	if s, ok := symbolMap[sym]; ok {
+		return s.repr
+	}
+	return ""
+}
+
+func SymListToString(symList []Symbol, quote bool) string {
+	var sb strings.Builder
+	if len(symList) == 0 {
+		sb.WriteString("<nothing>")
+	} else {
+		for _, sym := range symList {
+			if sb.Len() > 0 {
+				sb.WriteByte(',')
+				sb.WriteByte(' ')
+			}
+			if quote {
+				sb.WriteByte('`')
+			}
+			sb.WriteString(SymToString(sym))
+			if quote {
+				sb.WriteByte('`')
+			}
+		}
+	}
+	return sb.String()
+}
+
+func StringEndsWithOperator(s string) bool {
+	return endingOperator(s) != SymNone
+}
+
+func endingOperator(s string) (sym Symbol) {
+	sym = SymNone
+	lower := strings.ToLower(s)
+	for symbol, spec := range symbolMap {
+		if spec.kind == symClassOperator && strings.HasSuffix(lower, spec.repr) {
+			sym = symbol
+			break
+		}
+	}
+	return
+}

symbol.go

@@ -69,6 +69,8 @@ const (
 	SymDoubleDot                         //  58: '..'
 	SymTripleDot                         //  59: '...'
 	SymStarEqual                         //  60: '*='
+	SymSlashEqual                        //  61: '/='
+	SymPercEqual                         //  62: '%='
 	SymChangeSign
 	SymUnchangeSign
 	SymIdentifier
@@ -88,6 +90,7 @@ const (
 	SymList
 	SymDict
 	SymIndex
+	SymRange // [index : index]
 	SymExpression
 	SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
 	SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"

t_builtin-base_test.go

@@ -30,9 +30,9 @@ func TestFuncBase(t *testing.T) {
 		/*  16 */ {`isString("3" + 1)`, true, nil},
 		/*  17 */ {`isList(["3",  1])`, true, nil},
 		/*  18 */ {`isDict({"a":"3",  "b":1})`, true, nil},
-		/*  19 */ {`isFract(1|3)`, true, nil},
+		/*  19 */ {`isFract(1:3)`, true, nil},
-		/*  20 */ {`isFract(3|1)`, false, nil},
+		/*  20 */ {`isFract(3:1)`, false, nil},
-		/*  21 */ {`isRational(3|1)`, true, nil},
+		/*  21 */ {`isRational(3:1)`, true, nil},
 		/*  22 */ {`fract("2.2(3)")`, newFraction(67, 30), nil},
 		/*  23 */ {`fract("1.21(3)")`, newFraction(91, 75), nil},
 		/*  24 */ {`fract(1.21(3))`, newFraction(91, 75), nil},
@@ -41,26 +41,27 @@ func TestFuncBase(t *testing.T) {
 		/*  27 */ {`dec(2.0)`, float64(2), nil},
 		/*  28 */ {`dec("2.0")`, float64(2), nil},
 		/*  29 */ {`dec(true)`, float64(1), nil},
-		/*  30 */ {`dec(true")`, nil, `[1:11] missing string termination "`},
+		/*  30 */ {`dec(true")`, nil, "[1:11] expected one of `,`, `)`, got `\"`"},
 		/*  31 */ {`dec()`, nil, `dec(): too few params -- expected 1, got 0`},
 		/*  32 */ {`dec(1,2,3)`, nil, `dec(): too many params -- expected 1, got 3`},
 		/*  33 */ {`isBool(false)`, true, nil},
-		/*  34 */ {`fract(1|2)`, newFraction(1, 2), nil},
+		/*  34 */ {`fract(1:2)`, newFraction(1, 2), nil},
 		/*  35 */ {`fract(12,2)`, newFraction(6, 1), nil},
 		/*  36 */ {`bool(2)`, true, nil},
-		/*  37 */ {`bool(1|2)`, true, nil},
+		/*  37 */ {`bool(1:2)`, true, nil},
 		/*  38 */ {`bool(1.0)`, true, nil},
 		/*  39 */ {`bool("1")`, true, nil},
 		/*  40 */ {`bool(false)`, false, nil},
 		/*  41 */ {`bool([1])`, nil, `bool(): can't convert list to bool`},
 		/*  42 */ {`dec(false)`, float64(0), nil},
-		/*  43 */ {`dec(1|2)`, float64(0.5), nil},
+		/*  43 */ {`dec(1:2)`, float64(0.5), nil},
 		/*  44 */ {`dec([1])`, nil, `dec(): can't convert list to float`},
+		/*  45 */ {`eval("a=3"); a`, int64(3), nil},
 		// /*  45 */ {`string([1])`, nil, `string(): can't convert list to string`},
 	}
 
 	t.Setenv("EXPR_PATH", ".")
 
-	//runTestSuiteSpec(t, section, inputs, 10)
+	// runTestSuiteSpec(t, section, inputs, 45)
 	runTestSuite(t, section, inputs)
 }

t_builtin-string_test.go

@@ -15,7 +15,7 @@ func TestFuncString(t *testing.T) {
 		/*   1 */ {`builtin "string"; strJoin("-", "one", "two", "three")`, "one-two-three", nil},
 		/*   2 */ {`builtin "string"; strJoin("-", ["one", "two", "three"])`, "one-two-three", nil},
 		/*   3 */ {`builtin "string"; ls= ["one", "two", "three"]; strJoin("-", ls)`, "one-two-three", nil},
-		/*   4 */ {`builtin "string"; ls= ["one", "two", "three"]; strJoin(1, ls)`, nil, `strJoin(): the "separator" parameter must be a string, got a integer (1)`},
+		/*   4 */ {`builtin "string"; ls= ["one", "two", "three"]; strJoin(1, ls)`, nil, `strJoin(): the "separator" parameter must be a string, got an integer (1)`},
 		/*   5 */ {`builtin "string"; ls= ["one", 2, "three"]; strJoin("-", ls)`, nil, `strJoin(): expected string, got integer (2)`},
 		/*   6 */ {`builtin "string"; "<"+strTrim("  bye bye  ")+">"`, "<bye bye>", nil},
 		/*   7 */ {`builtin "string"; strSub("0123456789", 1,2)`, "12", nil},

t_expr_test.go

@@ -17,13 +17,13 @@ func TestExpr(t *testing.T) {
 		/*   3 */ {`builtin "os.file"; f=fileOpen("test-file.txt"); line=fileReadText(f); fileClose(f); line`, "uno", nil},
 		/*   4 */ {`mynot=func(v){int(v)?{true}::{false}}; mynot(0)`, true, nil},
 		/*   5 */ {`1 ? {1} : [1+0] {3*(1+1)}`, int64(6), nil},
-		/*   6 */ {`a=3; a+=1`, int64(4), nil},
+		/*   6 */ {`a=3; a+=1; a`, int64(4), nil},
-		/*   7 */ {`a=3; a-=1`, int64(2), nil},
+		/*   7 */ {`a=3; a-=1; a`, int64(2), nil},
-		/*   8 */ {`a=3; a*=2`, int64(6), nil},
+		/*   8 */ {`a=3; a*=2; a`, int64(6), nil},
 		/*   9 */ {`v=[10,20,30]; v[0]+=1; v[0]`, int64(11), nil},
 		/*  10 */ {`r={"a":10}; r["a"]+=1; r["a"]`, int64(11), nil},
-		/*  11 */ {`a=3; a/=2`, nil, `[1:8] left operand of "=" must be a variable or a collection's item`},
+		/*  11 */ {`a=3; a/=2`, int64(1), nil},
-		/*  12 */ {`*=2`, nil, `[1:2] left operand of "*=" must be a variable or a variable expression`},
+		/*  12 */ {`*=2`, nil, `[1:2] infix operator "*=" requires two non-nil operands, got 1`},
 		/*  13 */ {`a=3; a*=2+1; a`, int64(9), nil},
 		/*  14 */ {`a=3; (a*=2)+1; a`, int64(6), nil},
 		/*  15 */ {`a=3; a*=2)+1; a`, nil, `[1:11] unexpected token ")"`},
@@ -44,6 +44,6 @@ func TestExpr(t *testing.T) {
 	}
 	// t.Setenv("EXPR_PATH", ".")
 
-	// runTestSuiteSpec(t, section, inputs, 17)
+	// runTestSuiteSpec(t, section, inputs, 6, 7, 8, 9)
 	runTestSuite(t, section, inputs)
 }

t_fractions_test.go

@@ -11,35 +11,39 @@ import (
 func TestFractionsParser(t *testing.T) {
 	section := "Fraction"
 	inputs := []inputType{
-		/*   1 */ {`1|2`, newFraction(1, 2), nil},
+		/*   1 */ {`1:2`, newFraction(1, 2), nil},
-		/*   2 */ {`1|2 + 1`, newFraction(3, 2), nil},
+		/*   2 */ {`1:2 + 1`, newFraction(3, 2), nil},
-		/*   3 */ {`1|2 - 1`, newFraction(-1, 2), nil},
+		/*   3 */ {`1:2 - 1`, newFraction(-1, 2), nil},
-		/*   4 */ {`1|2 * 1`, newFraction(1, 2), nil},
+		/*   4 */ {`1:2 * 1`, newFraction(1, 2), nil},
-		/*   5 */ {`1|2 * 2|3`, newFraction(2, 6), nil},
+		/*   5 */ {`1:2 * 2:3`, newFraction(2, 6), nil},
-		/*   6 */ {`1|2 / 2|3`, newFraction(3, 4), nil},
+		/*   6 */ {`1:2 / 2:3`, newFraction(3, 4), nil},
-		/*   7 */ {`1|"5"`, nil, `denominator must be integer, got string (5)`},
+		/*   7 */ {`1:"5"`, nil, `denominator must be integer, got string (5)`},
-		/*   8 */ {`"1"|5`, nil, `numerator must be integer, got string (1)`},
+		/*   8 */ {`"1":5`, nil, `numerator must be integer, got string (1)`},
-		/*   9 */ {`1|+5`, nil, `[1:3] infix operator "|" requires two non-nil operands, got 1`},
+		/*   9 */ {`1:+5`, newFraction(1, 5), nil},
-		/*  10 */ {`1|(-2)`, newFraction(-1, 2), nil},
+		/*  10 */ {`1:(-2)`, newFraction(-1, 2), nil},
-		/*  11 */ {`builtin "math.arith"; add(1|2, 2|3)`, newFraction(7, 6), nil},
+		/*  11 */ {`builtin "math.arith"; add(1:2, 2:3)`, newFraction(7, 6), nil},
-		/*  12 */ {`builtin "math.arith"; add(1|2, 1.0, 2)`, float64(3.5), nil},
+		/*  12 */ {`builtin "math.arith"; add(1:2, 1.0, 2)`, float64(3.5), nil},
-		/*  13 */ {`builtin "math.arith"; mul(1|2, 2|3)`, newFraction(2, 6), nil},
+		/*  13 */ {`builtin "math.arith"; mul(1:2, 2:3)`, newFraction(2, 6), nil},
-		/*  14 */ {`builtin "math.arith"; mul(1|2, 1.0, 2)`, float64(1.0), nil},
+		/*  14 */ {`builtin "math.arith"; mul(1:2, 1.0, 2)`, float64(1.0), nil},
-		/*  15 */ {`1|0`, nil, `division by zero`},
+		/*  15 */ {`1:0`, nil, `division by zero`},
 		/*  16 */ {`fract(-0.5)`, newFraction(-1, 2), nil},
 		/*  17 */ {`fract("")`, (*FractionType)(nil), `bad syntax`},
 		/*  18 */ {`fract("-1")`, newFraction(-1, 1), nil},
 		/*  19 */ {`fract("+1")`, newFraction(1, 1), nil},
 		/*  20 */ {`fract("1a")`, (*FractionType)(nil), `strconv.ParseInt: parsing "1a": invalid syntax`},
 		/*  21 */ {`fract(1,0)`, nil, `fract(): division by zero`},
-		/*  22 */ {`string(1|2)`, "1|2", nil},
+		/*  22 */ {`string(1:2)`, "1:2", nil},
+		/*  23 */ {`1+1:2+0.5`, float64(2), nil},
+		/*  24 */ {`1:(2-2)`, nil, `division by zero`},
+		/*  25 */ {`[0,1][1-1]:1`, newFraction(0, 1), nil},
 	}
+	// runTestSuiteSpec(t, section, inputs, 25)
 	runTestSuite(t, section, inputs)
 }
 
 func TestFractionToStringSimple(t *testing.T) {
 	source := newFraction(1, 2)
-	want := "1|2"
+	want := "1:2"
 	got := source.ToString(0)
 	if got != want {
 		t.Errorf(`(1,2) -> result = %v [%T], want = %v [%T]`, got, got, want, want)
@@ -55,10 +59,9 @@ func TestFractionToStringMultiline(t *testing.T) {
 	}
 }
 
-// TODO Check this test: the output string ends with a space
+func TestToStringMultilineTty(t *testing.T) {
-func _TestToStringMultilineTty(t *testing.T) {
 	source := newFraction(-1, 2)
-	want := "\x1b[4m-1\x1b[0m\n2"
+	want := "\x1b[4m-1\x1b[0m\n 2"
 	got := source.ToString(MultiLine | TTY)
 	if got != want {
 		t.Errorf(`(1,2) -> result = %#v [%T], want = %#v [%T]`, got, got, want, want)

t_index_test.go

@@ -16,11 +16,13 @@ func TestCollections(t *testing.T) {
 		/*   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, `[1:14] left operand '(1, 2)' [pair] and right operand '3' [integer] are not compatible with operator ":"`},
+		/*   5 */ {`"abcdef"[1:2:3]`, nil, `[1:14] invalid range specification`},
+		/*   6 */ {`"abcdef"[((1>0)?{1}:{0}):3]`, "bc", nil},
+		/*   7 */ {`"abcdef"[[0,1][0]:1]`, "a", nil},
 	}
 
 	t.Setenv("EXPR_PATH", ".")
 
-	// parserTestSpec(t, section, inputs, 5)
+	// runTestSuiteSpec(t, section, inputs, 5)
 	runTestSuite(t, section, inputs)
 }

t_list_test.go

@@ -39,9 +39,9 @@ func TestListParser(t *testing.T) {
 		/*  25 */ {`["a","b","c","d"][1,1]`, nil, `[1:19] one index only is allowed`},
 		/*  26 */ {`[0,1,2,3,4][:]`, newListA(int64(0), int64(1), int64(2), int64(3), int64(4)), nil},
 		/*  27 */ {`["a", "b", "c"] << ;`, nil, `[1:18] infix operator "<<" requires two non-nil operands, got 1`},
-		/*  28 */ {`2 << 3;`, nil, `[1:4] left operand '2' [integer] and right operand '3' [integer] are not compatible with operator "<<"`},
+		/*  28 */ {`2 << 3;`, int64(16), nil},
 		/*  29 */ {`but >> ["a", "b", "c"]`, nil, `[1:6] infix operator ">>" requires two non-nil operands, got 0`},
-		/*  30 */ {`2 >> 3;`, nil, `[1:4] left operand '2' [integer] and right operand '3' [integer] are not compatible with operator ">>"`},
+		/*  30 */ {`2 >> 3;`, int64(0), nil},
 		/*  31 */ {`a=[1,2]; a<<3`, newListA(int64(1), int64(2), int64(3)), nil},
 		/*  33 */ {`a=[1,2]; 5>>a`, newListA(int64(5), int64(1), int64(2)), nil},
 		/*  34 */ {`L=[1,2]; L[0]=9; L`, newListA(int64(9), int64(2)), nil},

t_parser_test.go

@@ -77,7 +77,7 @@ func TestGeneralParser(t *testing.T) {
 		/*  63 */ {`"1.5" == `, nil, `[1:8] infix operator "==" requires two non-nil operands, got 1`},
 		/*  64 */ {`"1.5" != `, nil, `[1:8] infix operator "!=" requires two non-nil operands, got 1`},
 		/*  65 */ {"+1.5", float64(1.5), nil},
-		/*  66 */ {"+", nil, `[1:2] prefix operator "+" requires one not nil operand`},
+		/*  66 */ {"+", nil, `[1:2] prefix operator "+" requires one non-nil operand`},
 		/*  67 */ {"4 / 0", nil, `division by zero`},
 		/*  68 */ {"4.0 / 0", nil, `division by zero`},
 		/*  69 */ {"4.0 / \n2", float64(2.0), nil},
@@ -94,10 +94,10 @@ func TestGeneralParser(t *testing.T) {
 		/*  80 */ {`5 % 2.0`, nil, `[1:4] left operand '5' [integer] and right operand '2' [float] are not compatible with operator "%"`},
 		/*  81 */ {`"a" < "b" AND NOT (2 < 1)`, true, nil},
 		/*  82 */ {`"a" < "b" AND NOT (2 == 1)`, true, nil},
-		/*  83 */ {`"a" < "b" AND ~ 2 == 1`, true, nil},
+		/*  83 */ {`"a" < "b" AND NOT 2 == 1`, true, nil},
-		/*  84 */ {`~ 2 > 1`, false, nil},
+		/*  84 */ {`NOT 2 > 1`, false, nil},
-		/*  85 */ {`~ true && true`, false, nil},
+		/*  85 */ {`nOT true && true`, false, nil},
-		/*  86 */ {`~ false || true`, true, nil},
+		/*  86 */ {`NOT false || true`, true, nil},
 		/*  87 */ {`false but true`, true, nil},
 		/*  88 */ {`2+3 but 5*2`, int64(10), nil},
 		/*  89 */ {`x=2`, int64(2), nil},
@@ -132,15 +132,13 @@ func TestGeneralParser(t *testing.T) {
 		/* 118 */ {`{"key":}`, nil, "[1:9] expected `dictionary-value`, got `}`"},
 		/* 119 */ {`{}`, &DictType{}, nil},
 		/* 120 */ {`v=10; v++; v`, int64(11), nil},
-		/* 121 */ {`1+1|2+0.5`, float64(2), nil},
+		/* 121 */ {`1.2()`, newFraction(6, 5), nil},
-		/* 122 */ {`1.2()`, newFraction(6, 5), nil},
+		/* 122 */ {`x="abc"; x ?! #x`, int64(3), nil},
-		/* 123 */ {`1|(2-2)`, nil, `division by zero`},
+		/* 123 */ {`x ?! #x`, nil, `[1:7] prefix/postfix operator "#" do not support operand '<nil>' [nil]`},
-		/* 124 */ {`x="abc"; x ?! #x`, int64(3), nil},
+		/* 124 */ {`x ?! (x+1)`, nil, nil},
-		/* 125 */ {`x ?! #x`, nil, `[1:7] prefix/postfix operator "#" do not support operand '<nil>' [nil]`},
+		/* 125 */ {`"abx" ?! (x+1)`, nil, `[1:6] left operand of "?!" must be a variable`},
-		/* 126 */ {`x ?! (x+1)`, nil, nil},
+		/* 126 */ {`"abx" ?? "pqr"`, nil, `[1:6] left operand of "??" must be a variable`},
-		/* 127 */ {`"abx" ?! (x+1)`, nil, `[1:6] left operand of "?!" must be a variable`},
+		/* 127 */ {`"abx" ?= "pqr"`, nil, `[1:6] left operand of "?=" must be a variable`},
-		/* 128 */ {`"abx" ?? "pqr"`, nil, `[1:6] left operand of "??" must be a variable`},
-		/* 129 */ {`"abx" ?= "pqr"`, nil, `[1:6] left operand of "?=" must be a variable`},
 	}
 
 	// t.Setenv("EXPR_PATH", ".")

t_plugin_test.go

@@ -8,18 +8,18 @@ import (
 	"testing"
 )
 
-func _TestImportPlugin(t *testing.T) {
+// func TestImportPlugin(t *testing.T) {
-	t.Setenv("PLUGINS", "${HOME}/go/src/git.portale-stac.it/go")
+// 	t.Setenv("PLUGINS", "${HOME}/go/src/git.portale-stac.it/go")
-	t.Setenv("EXPR_PLUGIN_PATH","${PLUGINS}/expr-json-plugin:${PLUGINS}/expr-csv-plugin")
+// 	t.Setenv("EXPR_PLUGIN_PATH","${PLUGINS}/expr-json-plugin:${PLUGINS}/expr-csv-plugin")
 
-	gotCount, gotErr := importPluginFromSearchPath("json")
+// 	gotCount, gotErr := importPluginFromSearchPath("json")
-	if gotCount != 1 {
+// 	if gotCount != 1 {
-		t.Errorf("Import count: got=%d, want=1", gotCount)
+// 		t.Errorf("Import count: got=%d, want=1", gotCount)
-	}
+// 	}
-	if gotErr != nil {
+// 	if gotErr != nil {
-		t.Errorf("importPlugin() failed: %v", gotErr)
+// 		t.Errorf("importPlugin() failed: %v", gotErr)
-	}
+// 	}
-}
+// }
 
 func TestPluginExists(t *testing.T) {
 	name := "json"

t_relational_test.go

@@ -21,9 +21,9 @@ func TestRelational(t *testing.T) {
 		/*   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},
+		/*  11 */ {`1:2 == 1:3`, false, nil},
-		/*  12 */ {`1|2 != 1|3`, true, nil},
+		/*  12 */ {`1:2 != 1:3`, true, nil},
-		/*  13 */ {`1|2 == 4|8`, true, nil},
+		/*  13 */ {`1:2 == 4:8`, true, nil},
 		/*  14 */ {`1 < 8`, true, nil},
 		/*  15 */ {`1 <= 8`, true, nil},
 		/*  16 */ {`"a" < "b"`, true, nil},
@@ -32,10 +32,10 @@ func TestRelational(t *testing.T) {
 		/*  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},
+		/*  22 */ {`1:2 < 1:3`, false, nil},
-		/*  23 */ {`1|2 <= 1|3`, false, nil},
+		/*  23 */ {`1:2 <= 1:3`, false, nil},
-		/*  24 */ {`1|2 > 1|3`, true, nil},
+		/*  24 */ {`1:2 > 1:3`, true, nil},
-		/*  25 */ {`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},

term.go

@@ -19,6 +19,7 @@ const (
 	priAnd
 	priNot
 	priRelational
+	priBinary
 	priSum
 	priProduct
 	priFraction
@@ -62,8 +63,8 @@ func (s *term) Clone() (d *term) {
 		}
 	}
 	d = &term{
-		tk: *s.tk.Clone(),
+		tk:       *s.tk.Clone(),
-		parent: s.parent,
+		parent:   s.parent,
 		children: children,
 		position: s.position,
 		priority: s.priority,
@@ -211,11 +212,11 @@ func (term *term) checkOperands() (err error) {
 		}
 	case posPrefix:
 		if term.children == nil || len(term.children) != 1 || term.children[0] == nil {
-			err = term.tk.Errorf("prefix operator %q requires one not nil operand", term.tk.String())
+			err = term.tk.Errorf("prefix operator %q requires one non-nil operand", term.tk.String())
 		}
 	case posPostfix:
 		if term.children == nil || len(term.children) != 1 || term.anyChildrenNil() {
-			err = term.tk.Errorf("postfix operator %q requires one not nil operand", term.tk.String())
+			err = term.tk.Errorf("postfix operator %q requires one non-nil operand", term.tk.String())
 		}
 	case posMultifix:
 		if term.children == nil || len(term.children) < 3 || term.anyChildrenNil() {

token.go

@@ -93,6 +93,15 @@ func (tk *Token) Error() (err error) {
 	return
 }
 
+func (tk *Token) ErrorText() (err string) {
+	if tk.Sym == SymError {
+		if msg, ok := tk.Value.(error); ok {
+			err = msg.Error()
+		}
+	}
+	return
+}
+
 func (tk *Token) Errors(msg string) (err error) {
 	err = fmt.Errorf("[%d:%d] %v", tk.row, tk.col, msg)
 	return
@@ -104,6 +113,10 @@ func (tk *Token) ErrorExpectedGot(symbol string) (err error) {
 }
 
 func (tk *Token) ErrorExpectedGotString(symbol, got string) (err error) {
-	err = fmt.Errorf("[%d:%d] expected `%s`, got `%s`", tk.row, tk.col, symbol, got)
+	return tk.ErrorExpectedGotStringWithPrefix("expected", symbol, got)
+}
+
+func (tk *Token) ErrorExpectedGotStringWithPrefix(prefix, symbol, got string) (err error) {
+	err = fmt.Errorf("[%d:%d] %s %s, got `%s`", tk.row, tk.col, prefix, symbol, got)
 	return
 }