added functions to get the fenerating fraction of a decimal number

ast.go

@@ -60,7 +60,7 @@ func (self *ast) addToken(tk *Token) (err error) {
 }
 
 func (self *ast) addToken2(tk *Token) (t *term, err error) {
-	if t = newTerm(tk, nil); t != nil {
+	if t = newTerm(tk); t != nil {
 		err = self.addTerm(t)
 	} else {
 		err = tk.Errorf("unexpected token %q", tk.String())

common-errors.go

@@ -18,6 +18,10 @@ func errExpectedGot(funcName string, kind string, value any) error {
 	return fmt.Errorf("%s() expected %s, got %T (%v)", funcName, kind, value, value)
 }
 
+func errDivisionByZero(funcName string) error {
+	return fmt.Errorf("%s() division by zero", funcName)
+}
+
 // --- Parameter errors
 
 func errOneParam(funcName string) error {

dict_test.go

@@ -23,22 +23,9 @@ func TestDictParser(t *testing.T) {
 	inputs := []inputType{
 		/*  1 */ {`{}`, map[any]any{}, nil},
 		/*  2 */ {`{123}`, nil, errors.New(`[1:6] expected ":", got "}"`)},
-		/*  3 */ {`{1:"one",2:"two",3:"three"}`, map[int64]any{int64(1):"one", int64(2):"two", int64(3):"three"}, nil},
+		/*  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},
-		// /*  3 */ {`[1,2,"hello"]`, []any{int64(1), int64(2), "hello"}, nil},
+		/*  5 */ {`#{1:"one",2:"two",3:"three"}`, int64(3), nil},
-		// /*  4 */ {`[1+2, not true, "hello"]`, []any{int64(3), false, "hello"}, nil},
-		// /*  5 */ {`[1,2]+[3]`, []any{int64(1), int64(2), int64(3)}, nil},
-		// /*  6 */ {`[1,4,3,2]-[3]`, []any{int64(1), int64(4), int64(2)}, nil},
-		// /*  7 */ {`add([1,4,3,2])`, int64(10), nil},
-		// /*  8 */ {`add([1,[2,2],3,2])`, int64(10), nil},
-		// /*  9 */ {`mul([1,4,3.0,2])`, float64(24.0), nil},
-		// /* 10 */ {`add([1,"hello"])`, nil, errors.New(`add(): param nr 2 (2 in 1) has wrong type string, number expected`)},
-		// /* 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},
 	}
 
 	succeeded := 0

doc/Expr.adoc

@@ -22,17 +22,23 @@ Expressions calculator
 
 toc::[]
 
-#TODO: Work in progress (last update on 2024/05/09, 07:17 am)#
+#TODO: Work in progress (last update on 2024/05/10, 06:52 a.m.)#
 
 == Expr
 _Expr_ is a GO package capable of analysing, interpreting and calculating expressions.
 
+=== Concepts and terminology
+#TODO#
+
+image::expression-diagram.png[]
+
 === `dev-expr` test tool
 `dev-expr` is a simple program that can be used to evaluate expressions interactively. As its name suggests, it was created for testing purpose. In fact, beyond in additon to the automatic test suite based on the Go test framework, `dev-expr` provides an important aid for quickly testing of new features during their development.
 
-It cat work as a REPL, *R*ead-*E*xecute-*P*rint-*L*oop, or it can process expression acquired from files or standard input.
+It cat work as a _REPL_, _**R**ead-**E**xecute-**P**rint-**L**oop_, or it can process expression acquired from files or standard input.
+
+The program can be downloaded from https://git.portale-stac.it/go-pkg/-/packages/generic/dev-expr/[dev-expr].
 
-The program in located in the _tools_ directory.
 Here are some examples of execution.
 
 .Run `dev-expr` in REPL mode and ask for help
@@ -103,11 +109,6 @@ Here are some examples of execution.
 <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.
 
-=== Concepts and terminology
-#TODO#
-
-image::expression-diagram.png[]
-
 == Data types
 _Expr_ supports numerical, string, relational, boolean expressions, and mixed-type lists.
 
@@ -193,6 +194,25 @@ Some arithmetic operators can also be used with strings.
 | [blue]`*` | _repeat_ | Make _n_ copy of a string  | [blue]`"one" * 2` _["oneone"]_
 |===
 
+The items of strings can be accessed using the dot `.` operator.
+
+.Item access syntax
+[source,bnf]
+----
+<item> ::= <string-expr>"."<index-expr>
+----
+
+.String examples
+`>>>` [blue]`s="abc"`  [gray]_assign the string to variable s_ +
+[green]`abc` +
+`>>>` [blue]`s.1`      [gray]_char at position 1 (starting from 0)_ +
+[green]`b` +
+`>>>` [blue]`s.(-1)`   [gray]_char at position -1, the rightmost one_ +
+[green]`c` +
+`>>>` [blue]`\#s`       [gray]_number of chars_ +
+[gren]`3` +
+`>>>` [blue]`#"abc"`   [gray]_number of chars_ +
+[green]`3` +
 
 === Boolean
 Boolean data type has two values only: _true_ and _false_. Relational and Boolean expressions produce Boolean values.
@@ -277,29 +297,27 @@ The items of array can be accessed using the dot `.` operator.
 ----
 
 .Items of list
-[source,go]
+`>>>` [blue]`[1,2,3].1` +
-----
+[green]`2` +
-`>>>` [blue]`[1,2,3].1`
+`>>>` [blue]`list=[1,2,3]; list.1` +
-[green]`2`
+[green]`2` +
-`>>>` [blue]`list=[1,2,3]; list.1`
+`>>>` [blue]`["one","two","three"].1` +
-[green]`2`
+[green]`two` +
-`>>>` [blue]`["one","two","three"].1`
+`>>>` [blue]`list=["one","two","three"]; list.(2-1)` +
-[green]`two`
+[green]`two` +
-`>>>` [blue]`list=["one","two","three"]; list.(2-1)`
+`>>>` [blue]`list.(-1)` +
-[green]`two`
+[green]`three` +
-`>>>` [blue]`list.(-1)`
+`>>>` [blue]`list.(10)` +
-[green]`three`
+[red]`Eval Error: [1:9] index 10 out of bounds` +
-`>>>` [blue]`list.(-1)`
+`>>>` [blue]`#list` +
-[green]`three`
+[green]`3`
-`>>>` [blue]`list.(10)`
-----
 
 
 
 == Dictionaries
 The _dictionary_ data-type is set of pairs _key/value_. It is also known as _map_ or _associative array_. Dictionary literals are sequences of pairs separated by comma `,`; sequences are enclosed between brace brackets.
 
-.List examples
+.Dictionary examples
 [source,go]
 ----
 {1:"one", 2:"two"}
@@ -310,7 +328,7 @@ The _dictionary_ data-type is set of pairs _key/value_. It is also known as _map
 WARNING: Support for dictionaries is still ongoing.
 
 == Variables
-A variable is an identifier with an assigned value. Variables are stored in the object that implements the _ExprContext_ interface.
+A variable is an identifier with an assigned value. Variables are stored in the object that implements the Go _ExprContext_ interface, e.g. _SimpleVarStore_ or _SimpleFuncStore_.
 
 .Examples
 [source,go]
@@ -364,23 +382,30 @@ The _selector operator_ is very similar to the _switch/case/default_ statement a
 <multi-expression> ::= <expression> {";" <expression>}
 ----
 
-In other words, the selector operator evaluates the expression (`<select-expression>`) on the left-hand side of the `?` symbol; it then compares the result obtained with the values listed in the `<match-list>`'s. If the comparision find a match with a value in a match-list, the associated  `<case-multi-expression>` is evaluted, and its result will be the final result of the selection operation.
+In other words, the selector operator evaluates the expression (`<select-expression>`) on the left-hand side of the `?` symbol; it then compares the result obtained with the values listed in the `<match-list>`'s. If the comparision finds a match with a value in a match-list, the associated  `<case-multi-expression>` is evaluted, and its result will be the final result of the selection operation.
 
 The match lists are optional. In that case, the position, from left to right, of the `<selector-case>` is used as match-list. Of course, that only works if the select-expression results in an integer.
 
 The `:` symbol (colon) is the separator of the selector-cases. Note that if the value of the select-expression does not match any match-list, an error will be issued. Therefore, it is strongly recommended to provide a default (multi-)expression introduced by the `::` symbol (double-colon). Also note that the default expression has no match-list.
 
-
 .Examples
 [source,go]
 ----
-1 ? {"a"} : {"b"}                           // returns "b"
+`>>>` [blue]`1 ? {"a"} : {"b"}`
-10 ? {"a"} : {"b"} :: {"c"}                 // returns "c"
+[green]`b`
-10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}      // returns "b"
+`>>>` [blue]`10 ? {"a"} : {"b"} :: {"c"}`
-10 ? {"a"} :[true, 2+8] {"b"} ::[10] {"c"}  // error:  "... case list in default clause"
+[green]`c'
-10 ? {"a"} :[10] {x="b" but x} :: {"c"}     // returns "b"
+[green]`>>>` [blue]`10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}`
-10 ? {"a"} :[10] {x="b"; x} :: {"c"}        // returns "b"
+[green]`b`
-10 ? {"a"} : {"b"}                          // error:  "... no case catches the value (10) of the selection expression
+`>>>` [blue]`10 ? {"a"} :[true, 2+8] {"b"} ::[10] {"c"}`
+[red]`Parse Error: [1:34] case list in default clause`
+[green]`>>>` [blue]`10 ? {"a"} :[10] {x="b" but x} :: {"c"}`
+[green]`b`
+`>>>` [blue]`10 ? {"a"} :[10] {x="b"; x} :: {"c"}`
+[green]`b`
+`>>>` [blue]`10 ? {"a"} : {"b"}`
+[red]`Eval Error: [1:3] no case catches the value (10) of the selection expression`
+
 ----
 
 == Priorities of operators

doc/Expr.html

@@ -535,8 +535,8 @@ pre.rouge .ss {
 <ul class="sectlevel1">
 <li><a href="#_expr">1. Expr</a>
 <ul class="sectlevel2">
-<li><a href="#_dev_expr_test_tool">1.1. <code>dev-expr</code> test tool</a></li>
+<li><a href="#_concepts_and_terminology">1.1. Concepts and terminology</a></li>
-<li><a href="#_concepts_and_terminology">1.2. Concepts and terminology</a></li>
+<li><a href="#_dev_expr_test_tool">1.2. <code>dev-expr</code> test tool</a></li>
 </ul>
 </li>
 <li><a href="#_data_types">2. Data types</a>
@@ -545,7 +545,7 @@ pre.rouge .ss {
 <li><a href="#_fractions">2.2. Fractions</a></li>
 <li><a href="#_strings">2.3. Strings</a></li>
 <li><a href="#_boolean">2.4. Boolean</a></li>
-<li><a href="#_list">2.5. List</a></li>
+<li><a href="#_lists">2.5. Lists</a></li>
 </ul>
 </li>
 <li><a href="#_dictionaries">3. Dictionaries</a></li>
@@ -579,7 +579,7 @@ pre.rouge .ss {
 <div class="sectionbody">
 <!-- toc disabled -->
 <div class="paragraph">
-<p><mark>TODO: Work in progress (last update on 2024/05/09, 07:17 am)</mark></p>
+<p><mark>TODO: Work in progress (last update on 2024/05/10, 06:52 a.m.)</mark></p>
 </div>
 </div>
 </div>
@@ -590,16 +590,29 @@ pre.rouge .ss {
 <p><em>Expr</em> is a GO package capable of analysing, interpreting and calculating expressions.</p>
 </div>
 <div class="sect2">
-<h3 id="_dev_expr_test_tool"><a class="anchor" href="#_dev_expr_test_tool"></a><a class="link" href="#_dev_expr_test_tool">1.1. <code>dev-expr</code> test tool</a></h3>
+<h3 id="_concepts_and_terminology"><a class="anchor" href="#_concepts_and_terminology"></a><a class="link" href="#_concepts_and_terminology">1.1. Concepts and terminology</a></h3>
+<div class="paragraph">
+<p><mark>TODO</mark></p>
+</div>
+<div class="imageblock">
+<div class="content">
+<img src="expression-diagram.png" alt="expression diagram">
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="_dev_expr_test_tool"><a class="anchor" href="#_dev_expr_test_tool"></a><a class="link" href="#_dev_expr_test_tool">1.2. <code>dev-expr</code> test tool</a></h3>
 <div class="paragraph">
 <p><code>dev-expr</code> is a simple program that can be used to evaluate expressions interactively. As its name suggests, it was created for testing purpose. In fact, beyond in additon to the automatic test suite based on the Go test framework, <code>dev-expr</code> provides an important aid for quickly testing of new features during their development.</p>
 </div>
 <div class="paragraph">
-<p>It cat work as a REPL, *R*ead-*E*xecute-*P*rint-*L*oop, or it can process expression acquired from files or standard input.</p>
+<p>It cat work as a <em>REPL</em>, <em><strong>R</strong>ead-<strong>E</strong>xecute-<strong>P</strong>rint-<strong>L</strong>oop</em>, or it can process expression acquired from files or standard input.</p>
 </div>
 <div class="paragraph">
-<p>The program in located in the <em>tools</em> directory.
+<p>The program can be downloaded from <a href="https://git.portale-stac.it/go-pkg/-/packages/generic/dev-expr/">dev-expr</a>.</p>
-Here are some examples of execution.</p>
+</div>
+<div class="paragraph">
+<p>Here are some examples of execution.</p>
 </div>
 <div class="listingblock">
 <div class="title">Run <code>dev-expr</code> in REPL mode and ask for help</div>
@@ -697,17 +710,6 @@ Here are some examples of execution.</p>
 </table>
 </div>
 </div>
-<div class="sect2">
-<h3 id="_concepts_and_terminology"><a class="anchor" href="#_concepts_and_terminology"></a><a class="link" href="#_concepts_and_terminology">1.2. Concepts and terminology</a></h3>
-<div class="paragraph">
-<p><mark>TODO</mark></p>
-</div>
-<div class="imageblock">
-<div class="content">
-<img src="expression-diagram.png" alt="expression diagram">
-</div>
-</div>
-</div>
 </div>
 </div>
 <div class="sect1">
@@ -791,14 +793,14 @@ Here are some examples of execution.</p>
 <div class="sect2">
 <h3 id="_fractions"><a class="anchor" href="#_fractions"></a><a class="link" href="#_fractions">2.2. Fractions</a></h3>
 <div class="paragraph">
-<p><em>Expr</em> also suports fractions. Fraction literals are made with tow 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 vertical bar <code>|</code>.</p>
 </div>
 <div class="paragraph">
 <div class="title">Examples</div>
 <p><code>&gt;&gt;&gt;</code> <code class="blue">1 | 2</code><br>
 <code class="green">1|2</code><br>
 <code>&gt;&gt;&gt;</code> <code class="blue">4|6</code><br>
-<code class="green">2|3</code> <em class="gray">Fractions are always reduced to theri lowest terms</em><br>
+<code class="green">2|3</code> <em class="gray">Fractions are always reduced to their lowest terms</em><br>
 <code>&gt;&gt;&gt;</code> <code class="blue">1|2 + 2|3</code><br>
 <code class="green">7|6</code><br>
 <code>&gt;&gt;&gt;</code> <code class="blue">1|2 * 2|3</code><br>
@@ -866,6 +868,28 @@ Here are some examples of execution.</p>
 </tr>
 </tbody>
 </table>
+<div class="paragraph">
+<p>The items of strings can be accessed using the dot <code>.</code> operator.</p>
+</div>
+<div class="listingblock">
+<div class="title">Item access syntax</div>
+<div class="content">
+<pre class="rouge highlight"><code data-lang="bnf">&lt;item&gt; ::= &lt;string-expr&gt;"."&lt;index-expr&gt;</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<div class="title">String examples</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">s="abc"</code>  <em class="gray">assign the string to variable s</em><br>
+<code class="green">abc</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">s.1</code>      <em class="gray">char at position 1 (starting from 0)</em><br>
+<code class="green">b</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">s.(-1)</code>   <em class="gray">char at position -1, the rightmost one</em><br>
+<code class="green">c</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">#s</code>       <em class="gray">number of chars</em><br>
+<code class="gren">3</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">#"abc"</code>   <em class="gray">number of chars</em><br>
+<code class="green">3</code><br></p>
+</div>
 </div>
 <div class="sect2">
 <h3 id="_boolean"><a class="anchor" href="#_boolean"></a><a class="link" href="#_boolean">2.4. Boolean</a></h3>
@@ -1003,7 +1027,7 @@ Here are some examples of execution.</p>
 </div>
 </div>
 <div class="sect2">
-<h3 id="_list"><a class="anchor" href="#_list"></a><a class="link" href="#_list">2.5. List</a></h3>
+<h3 id="_lists"><a class="anchor" href="#_lists"></a><a class="link" href="#_lists">2.5. Lists</a></h3>
 <div class="paragraph">
 <p><em>Expr</em> supports list of mixed-type values, also specified by normal expressions.</p>
 </div>
@@ -1048,6 +1072,32 @@ Here are some examples of execution.</p>
 </tr>
 </tbody>
 </table>
+<div class="paragraph">
+<p>The items of array can be accessed using the dot <code>.</code> operator.</p>
+</div>
+<div class="listingblock">
+<div class="title">Item access syntax</div>
+<div class="content">
+<pre class="rouge highlight"><code data-lang="bnf">&lt;item&gt; ::= &lt;list-expr&gt;"."&lt;index-expr&gt;</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<div class="title">Items of list</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">[1,2,3].1</code><br>
+<code class="green">2</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">list=[1,2,3]; list.1</code><br>
+<code class="green">2</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">["one","two","three"].1</code><br>
+<code class="green">two</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">list=["one","two","three"]; list.(2-1)</code><br>
+<code class="green">two</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">list.(-1)</code><br>
+<code class="green">three</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">list.(10)</code><br>
+<code class="red">Eval Error: [1:9] index 10 out of bounds</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">#list</code><br>
+<code class="green">3</code></p>
+</div>
 </div>
 </div>
 </div>
@@ -1058,7 +1108,7 @@ Here are some examples of execution.</p>
 <p>The <em>dictionary</em> data-type is set of pairs <em>key/value</em>. It is also known as <em>map</em> or <em>associative array</em>. Dictionary literals are sequences of pairs separated by comma <code>,</code>; sequences are enclosed between brace brackets.</p>
 </div>
 <div class="listingblock">
-<div class="title">List examples</div>
+<div class="title">Dictionary examples</div>
 <div class="content">
 <pre class="rouge highlight"><code data-lang="go"><span class="p">{</span><span class="m">1</span><span class="o">:</span><span class="s">"one"</span><span class="p">,</span> <span class="m">2</span><span class="o">:</span><span class="s">"two"</span><span class="p">}</span>
 <span class="p">{</span><span class="s">"one"</span><span class="o">:</span><span class="m">1</span><span class="p">,</span> <span class="s">"two"</span><span class="o">:</span> <span class="m">2</span><span class="p">}</span>
@@ -1083,7 +1133,7 @@ Support for dictionaries is still ongoing.
 <h2 id="_variables"><a class="anchor" href="#_variables"></a><a class="link" href="#_variables">4. Variables</a></h2>
 <div class="sectionbody">
 <div class="paragraph">
-<p>A variable is an identifier with an assigned value. Variables are stored in the object that implements the <em>ExprContext</em> interface.</p>
+<p>A variable is an identifier with an assigned value. Variables are stored in the object that implements the Go <em>ExprContext</em> interface, e.g. <em>SimpleVarStore</em> or <em>SimpleFuncStore</em>.</p>
 </div>
 <div class="listingblock">
 <div class="title">Examples</div>
@@ -1173,7 +1223,7 @@ The value on the left side of <code class="blue">=</code> must be an identifier.
 </div>
 </div>
 <div class="paragraph">
-<p>In other words, the selector operator evaluates the expression (<code>&lt;select-expression&gt;</code>) on the left-hand side of the <code>?</code> symbol; it then compares the result obtained with the values listed in the <code>&lt;match-list&gt;&#8217;s. If the comparision find a match with a value in a match-list, the associated  `&lt;case-multi-expression&gt;</code> is evaluted, and its result will be the final result of the selection operation.</p>
+<p>In other words, the selector operator evaluates the expression (<code>&lt;select-expression&gt;</code>) on the left-hand side of the <code>?</code> symbol; it then compares the result obtained with the values listed in the <code>&lt;match-list&gt;&#8217;s. If the comparision finds a match with a value in a match-list, the associated  `&lt;case-multi-expression&gt;</code> is evaluted, and its result will be the final result of the selection operation.</p>
 </div>
 <div class="paragraph">
 <p>The match lists are optional. In that case, the position, from left to right, of the <code>&lt;selector-case&gt;</code> is used as match-list. Of course, that only works if the select-expression results in an integer.</p>
@@ -1184,13 +1234,21 @@ The value on the left side of <code class="blue">=</code> must be an identifier.
 <div class="listingblock">
 <div class="title">Examples</div>
 <div class="content">
-<pre class="rouge highlight"><code data-lang="go"><span class="m">1</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span> <span class="p">{</span><span class="s">"b"</span><span class="p">}</span>                           <span class="c">// returns "b"</span>
+<pre class="rouge highlight"><code data-lang="go"><span class="s">`&gt;&gt;&gt;`</span> <span class="p">[</span><span class="n">blue</span><span class="p">]</span><span class="s">`1 ? {"a"} : {"b"}`</span>
-<span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span> <span class="p">{</span><span class="s">"b"</span><span class="p">}</span> <span class="o">::</span> <span class="p">{</span><span class="s">"c"</span><span class="p">}</span>                 <span class="c">// returns "c"</span>
+<span class="p">[</span><span class="n">green</span><span class="p">]</span><span class="s">`b`</span>
-<span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span><span class="p">[</span><span class="no">true</span><span class="p">,</span> <span class="m">2</span><span class="o">+</span><span class="m">8</span><span class="p">]</span> <span class="p">{</span><span class="s">"b"</span><span class="p">}</span> <span class="o">::</span> <span class="p">{</span><span class="s">"c"</span><span class="p">}</span>      <span class="c">// returns "b"</span>
+<span class="s">`&gt;&gt;&gt;`</span> <span class="p">[</span><span class="n">blue</span><span class="p">]</span><span class="s">`10 ? {"a"} : {"b"} :: {"c"}`</span>
-<span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span><span class="p">[</span><span class="no">true</span><span class="p">,</span> <span class="m">2</span><span class="o">+</span><span class="m">8</span><span class="p">]</span> <span class="p">{</span><span class="s">"b"</span><span class="p">}</span> <span class="o">::</span><span class="p">[</span><span class="m">10</span><span class="p">]</span> <span class="p">{</span><span class="s">"c"</span><span class="p">}</span>  <span class="c">// error:  "... case list in default clause"</span>
+<span class="p">[</span><span class="n">green</span><span class="p">]</span><span class="s">`c'
-<span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span><span class="p">[</span><span class="m">10</span><span class="p">]</span> <span class="p">{</span><span class="n">x</span><span class="o">=</span><span class="s">"b"</span> <span class="n">but</span> <span class="n">x</span><span class="p">}</span> <span class="o">::</span> <span class="p">{</span><span class="s">"c"</span><span class="p">}</span>     <span class="c">// returns "b"</span>
+[green]`</span><span class="o">&gt;&gt;&gt;</span><span class="s">` [blue]`</span><span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span><span class="p">[</span><span class="no">true</span><span class="p">,</span> <span class="m">2</span><span class="o">+</span><span class="m">8</span><span class="p">]</span> <span class="p">{</span><span class="s">"b"</span><span class="p">}</span> <span class="o">::</span> <span class="p">{</span><span class="s">"c"</span><span class="p">}</span><span class="s">`
-<span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span><span class="p">[</span><span class="m">10</span><span class="p">]</span> <span class="p">{</span><span class="n">x</span><span class="o">=</span><span class="s">"b"</span><span class="p">;</span> <span class="n">x</span><span class="p">}</span> <span class="o">::</span> <span class="p">{</span><span class="s">"c"</span><span class="p">}</span>        <span class="c">// returns "b"</span>
+[green]`</span><span class="n">b</span><span class="s">`
-<span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span> <span class="p">{</span><span class="s">"b"</span><span class="p">}</span>                          <span class="c">// error:  "... no case catches the value (10) of the selection expression</span></code></pre>
+`</span><span class="o">&gt;&gt;&gt;</span><span class="s">` [blue]`</span><span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span><span class="p">[</span><span class="no">true</span><span class="p">,</span> <span class="m">2</span><span class="o">+</span><span class="m">8</span><span class="p">]</span> <span class="p">{</span><span class="s">"b"</span><span class="p">}</span> <span class="o">::</span><span class="p">[</span><span class="m">10</span><span class="p">]</span> <span class="p">{</span><span class="s">"c"</span><span class="p">}</span><span class="s">`
+[red]`</span><span class="n">Parse</span> <span class="n">Error</span><span class="o">:</span> <span class="p">[</span><span class="m">1</span><span class="o">:</span><span class="m">34</span><span class="p">]</span> <span class="k">case</span> <span class="n">list</span> <span class="n">in</span> <span class="k">default</span> <span class="n">clause</span><span class="s">`
+[green]`</span><span class="o">&gt;&gt;&gt;</span><span class="s">` [blue]`</span><span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span><span class="p">[</span><span class="m">10</span><span class="p">]</span> <span class="p">{</span><span class="n">x</span><span class="o">=</span><span class="s">"b"</span> <span class="n">but</span> <span class="n">x</span><span class="p">}</span> <span class="o">::</span> <span class="p">{</span><span class="s">"c"</span><span class="p">}</span><span class="s">`
+[green]`</span><span class="n">b</span><span class="s">`
+`</span><span class="o">&gt;&gt;&gt;</span><span class="s">` [blue]`</span><span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span><span class="p">[</span><span class="m">10</span><span class="p">]</span> <span class="p">{</span><span class="n">x</span><span class="o">=</span><span class="s">"b"</span><span class="p">;</span> <span class="n">x</span><span class="p">}</span> <span class="o">::</span> <span class="p">{</span><span class="s">"c"</span><span class="p">}</span><span class="s">`
+[green]`</span><span class="n">b</span><span class="s">`
+`</span><span class="o">&gt;&gt;&gt;</span><span class="s">` [blue]`</span><span class="m">10</span> <span class="err">?</span> <span class="p">{</span><span class="s">"a"</span><span class="p">}</span> <span class="o">:</span> <span class="p">{</span><span class="s">"b"</span><span class="p">}</span><span class="s">`
+[red]`</span><span class="n">Eval</span> <span class="n">Error</span><span class="o">:</span> <span class="p">[</span><span class="m">1</span><span class="o">:</span><span class="m">3</span><span class="p">]</span> <span class="n">no</span> <span class="k">case</span> <span class="n">catches</span> <span class="n">the</span> <span class="n">value</span> <span class="p">(</span><span class="m">10</span><span class="p">)</span> <span class="n">of</span> <span class="n">the</span> <span class="n">selection</span> <span class="n">expression</span><span class="s">`
+</span></code></pre>
 </div>
 </div>
 </div>
@@ -1461,7 +1519,7 @@ The value on the left side of <code class="blue">=</code> must be an identifier.
 </div>
 <div id="footer">
 <div id="footer-text">
-Last updated 2024-05-09 07:18:01 +0200
+Last updated 2024-05-11 20:13:17 +0200
 </div>
 </div>
 </body>

func-base.go

@@ -43,6 +43,11 @@ func isFractionFunc(ctx ExprContext, name string, args []any) (result any, err e
 	return
 }
 
+func isRationalFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsRational(args[0])
+	return
+}
+
 func isListFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	result = IsList(args[0])
 	return
@@ -53,9 +58,7 @@ func isDictionaryFunc(ctx ExprContext, name string, args []any) (result any, err
 	return
 }
 
-
 func intFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	if len(args) == 1 {
 	switch v := args[0].(type) {
 	case int64:
 		result = v
@@ -75,8 +78,77 @@ func intFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	default:
 		err = errCantConvert(name, v, "int")
 	}
+	return
+}
+
+func decFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	switch v := args[0].(type) {
+	case int64:
+		result = float64(v)
+	case float64:
+		result = v
+	case bool:
+		if v {
+			result = float64(1)
 		} else {
-		err = errOneParam(name)
+			result = float64(0)
+		}
+	case string:
+		var f float64
+		if f, err = strconv.ParseFloat(v, 64); err == nil {
+			result = f
+		}
+	case *fraction:
+		result = v.toFloat()
+	default:
+		err = errCantConvert(name, v, "float")
+	}
+	return
+}
+
+func fractFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	switch v := args[0].(type) {
+	case int64:
+		var den int64 = 1
+		if len(args) > 1 {
+			var ok bool
+			if den, ok = args[1].(int64); !ok {
+				err = errExpectedGot(name, "integer", args[1])
+			} else if den == 0 {
+				err = errDivisionByZero(name)
+			}
+		}
+		if err == nil {
+			result = newFraction(v, den)
+		}
+	case float64:
+		result, err = float64ToFraction(v)
+		// var n, d int64
+		// if n, d, err = float64ToFraction(v); err == nil {
+		//	result = newFraction(n, d)
+		// }
+	case bool:
+		if v {
+			result = newFraction(1, 1)
+		} else {
+			result = newFraction(0, 1)
+		}
+	case string:
+		result, err = makeGeneratingFraction(v)
+		// var f float64
+		// // TODO temporary implementation
+		// if f, err = strconv.ParseFloat(v, 64); err == nil {
+		// 	var n, d int64
+		// 	if n, d, err = float64ToFraction(f); err == nil {
+		// 		result = newFraction(n, d)
+		// 	}
+		// } else {
+		// 	errors.New("convertion from string to float is ongoing")
+		// }
+	case *fraction:
+		result = v
+	default:
+		err = errCantConvert(name, v, "float")
 	}
 	return
 }
@@ -93,10 +165,13 @@ func ImportBuiltinsFuncs(ctx ExprContext) {
 	ctx.RegisterFunc("isString", &simpleFunctor{f: isStringFunc}, 1, 1)
 	ctx.RegisterFunc("isFraction", &simpleFunctor{f: isFractionFunc}, 1, 1)
 	ctx.RegisterFunc("isFract", &simpleFunctor{f: isFractionFunc}, 1, 1)
+	ctx.RegisterFunc("isRational", &simpleFunctor{f: isRationalFunc}, 1, 1)
 	ctx.RegisterFunc("isList", &simpleFunctor{f: isListFunc}, 1, 1)
 	ctx.RegisterFunc("isDictionary", &simpleFunctor{f: isDictionaryFunc}, 1, 1)
 	ctx.RegisterFunc("isDict", &simpleFunctor{f: isDictionaryFunc}, 1, 1)
 	ctx.RegisterFunc("int", &simpleFunctor{f: intFunc}, 1, 1)
+	ctx.RegisterFunc("dec", &simpleFunctor{f: decFunc}, 1, 1)
+	ctx.RegisterFunc("fract", &simpleFunctor{f: fractFunc}, 1, 2)
 }
 
 func init() {

funcs_test.go

@@ -57,16 +57,21 @@ func TestFuncs(t *testing.T) {
 		/*  44 */ {`builtin "string"; splitStr("one-two-three", "-", )`, newListA("one", "two", "three"), nil},
 		/*  45 */ {`isInt(2+1)`, true, nil},
 		/*  46 */ {`isInt(3.1)`, false, nil},
-		/*  46 */ {`isFloat(3.1)`, true, nil},
+		/*  47 */ {`isFloat(3.1)`, true, nil},
-		/*  47 */ {`isString("3.1")`, true, nil},
+		/*  48 */ {`isString("3.1")`, true, nil},
-		/*  48 */ {`isString("3" + 1)`, true, nil},
+		/*  49 */ {`isString("3" + 1)`, true, nil},
-		/*  49 */ {`isList(["3",  1])`, true, nil},
+		/*  50 */ {`isList(["3",  1])`, true, nil},
-		/*  50 */ {`isDict({"a":"3",  "b":1})`, true, nil},
+		/*  51 */ {`isDict({"a":"3",  "b":1})`, true, nil},
-		/*  51 */ {`isFract(3|1)`, true, nil},
+		/*  52 */ {`isFract(1|3)`, true, nil},
+		/*  53 */ {`isFract(3|1)`, false, nil},
+		/*  54 */ {`isRational(3|1)`, true, nil},
+		/*  55 */ {`builtin "math.arith"; add(1,2)`, int64(3), nil},
+		/*  56 */ {`fract("2.2(3)")`, newFraction(67, 30), nil},
+		/*  57 */ {`fract("1.21(3)")`, newFraction(91, 75), nil},
 	}
 
 	t.Setenv("EXPR_PATH", ".")
 
-	// parserTest(t, "Func", inputs[25:26])
+	//parserTest(t, "Func", inputs[54:55])
 	parserTest(t, "Func", inputs)
 }

global-context.go

@@ -0,0 +1,54 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// global-context.go
+package expr
+
+import "path/filepath"
+
+var globalCtx *SimpleFuncStore
+
+func ImportInContext(name string) (exists bool) {
+	var mod *module
+	if mod, exists = moduleRegister[name]; exists {
+		mod.importFunc(globalCtx)
+		mod.imported = true
+	}
+	return
+}
+
+func ImportInContextByGlobPattern(pattern string) (count int, err error) {
+	var matched bool
+	for name, mod := range moduleRegister {
+		if matched, err = filepath.Match(pattern, name); err == nil {
+			if matched {
+				count++
+				mod.importFunc(globalCtx)
+				mod.imported = true
+			}
+		} else {
+			break
+		}
+	}
+	return
+}
+
+func GetVar(ctx ExprContext, name string) (value any, exists bool) {
+	if value, exists = ctx.GetVar(name); !exists {
+		value, exists = globalCtx.GetVar(name)
+	}
+	return
+}
+
+func GetFuncInfo(ctx ExprContext, name string) (item ExprFunc, exists bool, ownerCtx ExprContext) {
+	if item, exists = ctx.GetFuncInfo(name); exists {
+		ownerCtx = ctx
+	} else if item, exists = globalCtx.GetFuncInfo(name); exists {
+		ownerCtx = globalCtx
+	}
+	return
+}
+
+func init() {
+	globalCtx = NewSimpleFuncStore()
+}

list_test.go

@@ -39,6 +39,7 @@ func TestListParser(t *testing.T) {
 		/*  17 */ {`list=["one","two","three"]; list.10`, nil, errors.New(`[1:36] 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},
 
 		// /*  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},

module-register.go

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

operand-func.go

@@ -23,7 +23,7 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 
 // -------- eval func call
 func checkFunctionCall(ctx ExprContext, name string, params []any) (err error) {
-	if info, exists := ctx.GetFuncInfo(name); exists {
+	if info, exists, owner := GetFuncInfo(ctx, name); exists {
 		if info.MinArgs() > len(params) {
 			if info.MaxArgs() < 0 {
 				err = fmt.Errorf("too few params -- expected %d or more, got %d", info.MinArgs(), len(params))
@@ -31,9 +31,12 @@ func checkFunctionCall(ctx ExprContext, name string, params []any) (err error) {
 				err = fmt.Errorf("too few params -- expected %d, got %d", info.MinArgs(), len(params))
 			}
 		}
-		if info.MaxArgs() >= 0 && info.MaxArgs() < len(params) {
+		if err == nil && info.MaxArgs() >= 0 && info.MaxArgs() < len(params) {
 			err = fmt.Errorf("too much params -- expected %d, got %d", info.MaxArgs(), len(params))
 		}
+		if err == nil && owner != ctx {
+			ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
+		}
 	} else {
 		err = fmt.Errorf("unknown function %s()", name)
 	}

operand-var.go

@@ -24,8 +24,8 @@ func newVarTerm(tk *Token) *term {
 func evalVar(ctx ExprContext, self *term) (v any, err error) {
 	var exists bool
 	name := self.source()
-	if v, exists = ctx.GetVar(name); !exists {
+	if v, exists = GetVar(ctx, name); !exists {
-		if info, exists := ctx.GetFuncInfo(name); exists {
+		if info, exists, _ := GetFuncInfo(ctx, name); exists {
 			v = info.Functor()
 		} else {
 			err = fmt.Errorf("undefined variable or function %q", name)

operator-builtin.go

@@ -28,13 +28,13 @@ func evalBuiltin(ctx ExprContext, self *term) (v any, err error) {
 	count := 0
 	if IsString(childValue) {
 		module, _ := childValue.(string)
-		count, err = ImportInContextByGlobPattern(ctx, module)
+		count, err = ImportInContextByGlobPattern(module)
 	} else {
 		var moduleSpec any
 		it := NewAnyIterator(childValue)
 		for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {
 			if module, ok := moduleSpec.(string); ok {
-				if ImportInContext(ctx, module) {
+				if ImportInContext(module) {
 					count++
 				} else {
 					err = self.Errorf("unknown module %q", module)

operator-dot.go

@@ -57,7 +57,7 @@ func evalDot(ctx ExprContext, self *term) (v any, err error) {
 	case string:
 		var index int
 		if index, err = verifyIndex(ctx, indexTerm, len(unboxedValue)); err == nil {
-			v = unboxedValue[index]
+			v = string(unboxedValue[index])
 		}
 	case map[any]any:
 		var ok bool

operator-fraction.go

@@ -7,6 +7,7 @@ package expr
 import (
 	"errors"
 	"fmt"
+	"math"
 	"strconv"
 	"strings"
 )
@@ -24,6 +25,134 @@ func newFraction(num, den int64) *fraction {
 	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:]
+	}
+	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)
 }
@@ -146,12 +275,12 @@ func lcm(a, b int64) (l int64) {
 
 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)
+	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)
+	prod = newFraction(f1.num*f2.num, f1.den*f2.den)
 	return
 }
 

operator-length.go

@@ -24,11 +24,14 @@ func evalLength(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	if IsList(childValue) {
-		list, _ := childValue.([]any)
+		ls, _ := childValue.(*ListType)
-		v = int64(len(list))
+		v = int64(len(*ls))
 	} else if IsString(childValue) {
 		s, _ := childValue.(string)
 		v = int64(len(s))
+	} else if IsDict(childValue) {
+		m, _ := childValue.(map[any]any)
+		v = int64(len(m))
 	} else if it, ok := childValue.(Iterator); ok {
 		if extIt, ok := childValue.(ExtIterator); ok && extIt.HasOperation(countName) {
 			count, _ := extIt.CallOperation(countName, nil)

parser.go

@@ -119,7 +119,7 @@ func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 	for lastSym != SymClosedRound && lastSym != SymEos {
 		tk = scanner.Next()
 		if tk.IsSymbol(SymIdentifier) {
-			param := newTerm(tk, nil)
+			param := newTerm(tk)
 			args = append(args, param)
 			tk = scanner.Next()
 		} else if itemExpected {

parser_test.go

@@ -35,10 +35,10 @@ func TestGeneralParser(t *testing.T) {
 		/*  14 */ {`not true`, false, nil},
 		/*  15 */ {`true and false`, false, nil},
 		/*  16 */ {`true or false`, true, nil},
-		/*  17 */ {`"uno" + "due"`, `unodue`, nil},
+		/*  *17 */ {`"uno" + "due"`, `unodue`, nil},
-		/*  18 */ {`"uno" + 2`, `uno2`, nil},
+		/*  *18 */ {`"uno" + 2`, `uno2`, nil},
-		/*  19 */ {`"uno" + (2+1)`, `uno3`, nil},
+		/*  *19 */ {`"uno" + (2+1)`, `uno3`, nil},
-		/*  20 */ {`"uno" * (2+1)`, `unounouno`, nil},
+		/*  *20 */ {`"uno" * (2+1)`, `unounouno`, nil},
 		/*  21 */ {"1", int64(1), nil},
 		/*  22 */ {"1.5", float64(1.5), nil},
 		/*  23 */ {"1.5*2", float64(3.0), nil},

strings_test.go

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

term-constuctor-registry.go

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

utils.go

@@ -44,6 +44,13 @@ func IsFract(v any) (ok bool) {
 	return ok
 }
 
+func IsRational(v any) (ok bool) {
+	if _, ok = v.(*fraction); !ok {
+		_, ok = v.(int64)
+	}
+	return ok
+}
+
 func IsNumber(v any) (ok bool) {
 	return IsFloat(v) || IsInteger(v)
 }