Doc: concepts

common-params.go

@@ -20,3 +20,8 @@ const (
 	ParamFilepath  = "filepath"
 	ParamDirpath   = "dirpath"
 )
+
+// to be moved in its own source file
+const (
+	ConstLastIndex = 0xFFFF_FFFF
+)

doc/Expr.adoc

@@ -22,18 +22,45 @@ Expressions calculator
 
 toc::[]
 
-#TODO: Work in progress (last update on 2024/06/02, 08:18 a.m.)#
+#TODO: Work in progress (last update on 2024/06/17, 16:31 a.m.)#
 
 == Expr
 _Expr_ is a GO package capable of analysing, interpreting and calculating expressions.
 
+
 === Concepts and terminology
-#TODO#
+
+Expressions are texts containing sequences of operations represented by a syntax very similar to that of most programming languages. _Expr_ package provides these macro functions:
+
+* *_Scanner_* -- Its input is a text. It scans expression text characters to produce a flow of logical symbol and related attributes, aka tokens.
+* *_Parser_* -- Parser input is the token flow coming from the scanner. It analyses the token flow verifyng if it complies with the _Expr_ syntax. If that is the case, the Parser generates the Abstract Syntax Tree (AST). This is tree data structure that represents the components of an expressions and how they are related one each other.
+* *_Calculator_*. Its input is the AST. It computes the parsed expression contained in the AST and returns the result or an error.
 
 image::expression-diagram.png[]
 
+==== Variables
+_Expr_ supports variables. The result of an expression can be stored in a variable and reused in other espressions simply specifying the name of the variable as an operand.
+
+==== Multi-expression
+An input text valid for _Expr_ can contain more than an expression. Expressions are separated by [blue]`;` (semicolon). When an input contains two or more expressions it is called _multi-expression_.
+
+_Expr_ parses and computes each expression of a multi-espression, from the left to the right. If all expressions are computed without errors, it only returns the value of the last, the right most.
+
+The result of each expression of a multi-expression is stored in an automatic variable named _last_. In this way, each expression can refer to the result of the previous one without the need to assign that value to a new dedicated variable.
+
+==== Calculation context
+All objects, such as variables and functions, created during the calculation of an expression are stored in a memory called _context_.
+
+The expression context is analogous to the stack-frame of other programming languages. When a function is called, a new context is allocated to store local definitions.
+
+Function contexts are created by cloning the calling context. More details on this topic are given later in this document.
+
+_Expr_ creates and keeps a inner _global context_ where it stores imported functions, either from builtin or plugin modules. To perform calculations, the calling program must provide its own context; this is the _main context_. All calculations take place in this context. As mentioned eralier, when a function is called, a new context is created by cloning the calling context. The createt context can be called _function context_.
+
+Imported functions are registerd in the _global context_. When an expression first calls an imported function, that function is linked to the current context; this can be the _main context_ or a _function context_.
+
 === `dev-expr` test tool
-`dev-expr` is a simple program that can be used to evaluate expressions interactively. As its name suggests, it was created for testing purpose.  In fact, in additon to the automatic verification test suite based on the Go test framework, `dev-expr` provides an important aid for quickly testing of new features during their development.
+`dev-expr` is a simple program that can be used to evaluate expressions interactively. As its name suggests, it was created for testing purpose.  In fact, in additon to the automatic verification test suite based on the Go test framework, `dev-expr` provided an important aid for quickly testing of new features during their development.
 
 `dev-expr` can work as a _REPL_, _**R**ead-**E**xecute-**P**rint-**L**oop_, or it can process expression acquired from files or standard input.
 
@@ -47,11 +74,10 @@ Here are some examples of execution.
 # Type 'exit' or Ctrl+D to quit the program.
 
 [user]$ ./dev-expr
-expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@portale-stac.it)
+dev-expr -- Expressions calculator v1.10.0(build 14),2024/06/17 (celestino.amoroso@portale-stac.it)
-	Based on the Expr package v0.10.0
+	Based on the Expr package v0.19.0
 	Type help to get the list of available commands
 	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
-
 >>> help
 --- REPL commands:
       source -- Load a file as input
@@ -61,6 +87,7 @@ expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@por
         help -- Show command list
           ml -- Enable/Disable multi-line output
         mods -- List builtin modules
+      output -- Enable/Disable printing expression results. Options 'on', 'off', 'status'
 
 --- Command line options:
     -b <builtin>       Import builtin modules.
@@ -70,9 +97,10 @@ expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@por
     -i                 Force REPL operation when all -e occurences have been processed
     -h, --help, help   Show this help menu
     -m, --modules      List all builtin modules
+    --noout            Disable printing of expression results
     -p                 Print prefix form
     -t                 Print tree form <2>
-
+    -v, --version      Show program version
 >>> 
 ----
 
@@ -83,8 +111,8 @@ expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@por
 [source,shell]
 ----
 [user]$ ./dev-expr
-expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@portale-stac.it)
+dev-expr -- Expressions calculator v1.10.0(build 14),2024/06/17 (celestino.amoroso@portale-stac.it)
-	Based on the Expr package v0.10.0
+	Based on the Expr package v0.19.0
 	Type help to get the list of available commands
 	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
 
@@ -101,21 +129,21 @@ expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@por
 7
 -
 6
->>> 1+2 but 5|2+0.5 <4>
+>>> 4+2 but 5|2+0.5 <4>
 3
->>> 1+2; 5|2+0.5 <5>
+>>> 4+2; 5|2+0.5 <5>
 3
 >>>
 ----
 
-<1> Number bases: 0x = hexadecimal, 0o = octal, 0b = binary.
+<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.
 
 == Data types
-_Expr_ supports numerical, string, relational, boolean expressions, and mixed-type lists.
+_Expr_ has its type system which is a subset of Golang's type system. It supports numerical, string, relational, boolean expressions, and mixed-type lists and maps.
 
 === Numbers
 _Expr_ supports three type of numbers:
@@ -272,25 +300,31 @@ 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.
+The items of strings can be accessed using the square `[]` operator.
 
 .Item access syntax
 ====
-_item_ = _string-expr_ "**.**" _integer-expr_
+_item_ = _string-expr_ "**[**" _integer-expr_ "**]**" 
+====
+
+.Sub string syntax
+====
+_sub-string_ = _string-expr_ "**[**" _integer-expr_ "**:**" _integer-expr_ "**]**" 
 ====
 
 .String examples
-`>>>` [blue]`s="abc"`  [gray]_// assign the string to variable s_ +
+`>>>` [blue]`s="abcd"`  [gray]_// assign the string to variable s_ +
-[green]`abc` +
+[green]`"abcd"` +
-`>>>` [blue]`s.1`      [gray]_// char at position 1 (starting from 0)_ +
+`>>>` [blue]`s[1]`      [gray]_// char at position 1 (starting from 0)_ +
-[green]`b` +
+[green]`"b"` +
-`>>>` [blue]`s.(-1)`   [gray]_// char at position -1, the rightmost one_ +
+`>>>` [blue]`s.[-1]`    [gray]_// char at position -1, the rightmost one_ +
-[green]`c` +
+[green]`"d"` +
 `>>>` [blue]`\#s`       [gray]_// number of chars_ +
-[gren]`3` +
+[gren]`4` +
 `>>>` [blue]`#"abc"`    [gray]_// number of chars_ +
-[green]`3`
+[green]`3` +
-
+`>>>` [blue]`s[1:3]`    [gray]_// chars from position 1 to position 3 excluded_ +
+[grean]`"bc"`
 
 === Booleans
 Boolean data type has two values only: [blue]_true_ and [blue]_false_. Relational and boolean expressions result in boolean values.

doc/Expr.html

@@ -535,7 +535,13 @@ pre.rouge .ss {
 <ul class="sectlevel1">
 <li><a href="#_expr">1. Expr</a>
 <ul class="sectlevel2">
-<li><a href="#_concepts_and_terminology">1.1. Concepts and terminology</a></li>
+<li><a href="#_concepts_and_terminology">1.1. Concepts and terminology</a>
+<ul class="sectlevel3">
+<li><a href="#_variables">1.1.1. Variables</a></li>
+<li><a href="#_multi_expression">1.1.2. Multi-expression</a></li>
+<li><a href="#_calculation_context">1.1.3. Calculation context</a></li>
+</ul>
+</li>
 <li><a href="#_dev_expr_test_tool">1.2. <code>dev-expr</code> test tool</a></li>
 </ul>
 </li>
@@ -554,7 +560,7 @@ pre.rouge .ss {
 <li><a href="#_dictionaries">2.5. Dictionaries</a></li>
 </ul>
 </li>
-<li><a href="#_variables">3. Variables</a></li>
+<li><a href="#_variables_2">3. Variables</a></li>
 <li><a href="#_other_operations">4. Other operations</a>
 <ul class="sectlevel2">
 <li><a href="#_operator">4.1. <code class="blue">;</code> operator</a></li>
@@ -585,7 +591,7 @@ pre.rouge .ss {
 <div class="sectionbody">
 <!-- toc disabled -->
 <div class="paragraph">
-<p><mark>TODO: Work in progress (last update on 2024/06/02, 08:18 a.m.)</mark></p>
+<p><mark>TODO: Work in progress (last update on 2024/06/17, 16:31 a.m.)</mark></p>
 </div>
 </div>
 </div>
@@ -598,18 +604,67 @@ pre.rouge .ss {
 <div class="sect2">
 <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>
+<p>Expressions are texts containing sequences of operations represented by a syntax very similar to that of most programming languages. <em>Expr</em> package provides these macro functions:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p><strong><em>Scanner</em></strong>&#8201;&#8212;&#8201;Its input is a text. It scans expression text characters to produce a flow of logical symbol and related attributes, aka tokens.</p>
+</li>
+<li>
+<p><strong><em>Parser</em></strong>&#8201;&#8212;&#8201;Parser input is the token flow coming from the scanner. It analyses the token flow verifyng if it complies with the <em>Expr</em> syntax. If that is the case, the Parser generates the Abstract Syntax Tree (AST). This is tree data structure that represents the components of an expressions and how they are related one each other.</p>
+</li>
+<li>
+<p><strong><em>Calculator</em></strong>. Its input is the AST. It computes the parsed expression contained in the AST and returns the result or an error.</p>
+</li>
+</ul>
 </div>
 <div class="imageblock">
 <div class="content">
 <img src="expression-diagram.png" alt="expression diagram">
 </div>
 </div>
+<div class="sect3">
+<h4 id="_variables"><a class="anchor" href="#_variables"></a><a class="link" href="#_variables">1.1.1. Variables</a></h4>
+<div class="paragraph">
+<p><em>Expr</em> supports variables. The result of an expression can be stored in a variable and reused in other espressions simply specifying the name of the variable as an operand.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="_multi_expression"><a class="anchor" href="#_multi_expression"></a><a class="link" href="#_multi_expression">1.1.2. Multi-expression</a></h4>
+<div class="paragraph">
+<p>An input text valid for <em>Expr</em> can contain more than an expression. Expressions are separated by <code class="blue">;</code> (semicolon). When an input contains two or more expressions it is called <em>multi-expression</em>.</p>
+</div>
+<div class="paragraph">
+<p><em>Expr</em> parses and computes each expression of a multi-espression, from the left to the right. If all expressions are computed without errors, it only returns the value of the last, the right most.</p>
+</div>
+<div class="paragraph">
+<p>The result of each expression of a multi-expression is stored in an automatic variable named <em>last</em>. In this way, each expression can refer to the result of the previous one without the need to assign that value to a new dedicated variable.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="_calculation_context"><a class="anchor" href="#_calculation_context"></a><a class="link" href="#_calculation_context">1.1.3. Calculation context</a></h4>
+<div class="paragraph">
+<p>All objects, such as variables and functions, created during the calculation of an expression are stored in a memory called <em>context</em>.</p>
+</div>
+<div class="paragraph">
+<p>The expression context is analogous to the stack-frame of other programming languages. When a function is called, a new context is allocated to store local definitions.</p>
+</div>
+<div class="paragraph">
+<p>Function contexts are created by cloning the calling context. More details on this topic are given later in this document.</p>
+</div>
+<div class="paragraph">
+<p><em>Expr</em> creates and keeps a inner <em>global context</em> where it stores imported functions, either from builtin or plugin modules. To perform calculations, the calling program must provide its own context; this is the <em>main context</em>. All calculations take place in this context. As mentioned eralier, when a function is called, a new context is created by cloning the calling context. The createt context can be called <em>function context</em>.</p>
+</div>
+<div class="paragraph">
+<p>Imported functions are registerd in the <em>global context</em>. When an expression first calls an imported function, that function is linked to the current context; this can be the <em>main context</em> or a <em>function context</em>.</p>
+</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, in additon to the automatic verification 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>
+<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, in additon to the automatic verification test suite based on the Go test framework, <code>dev-expr</code> provided an important aid for quickly testing of new features during their development.</p>
 </div>
 <div class="paragraph">
 <p><code>dev-expr</code> can 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>
@@ -626,11 +681,10 @@ pre.rouge .ss {
 <pre class="rouge highlight"><code data-lang="shell"><span class="c"># Type 'exit' or Ctrl+D to quit the program.</span>
 
 <span class="o">[</span>user]<span class="nv">$ </span>./dev-expr
-<span class="nb">expr</span> <span class="nt">--</span> Expressions calculator v1.7.1<span class="o">(</span>build 2<span class="o">)</span>,2024/05/16 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
+dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o">(</span>build 14<span class="o">)</span>,2024/06/17 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
-	Based on the Expr package v0.10.0
+	Based on the Expr package v0.19.0
 	Type <span class="nb">help </span>to get the list of available commands
 	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
-
 <span class="o">&gt;&gt;&gt;</span> <span class="nb">help</span>
 <span class="nt">---</span> REPL commands:
       <span class="nb">source</span> <span class="nt">--</span> Load a file as input
@@ -640,6 +694,7 @@ pre.rouge .ss {
         <span class="nb">help</span> <span class="nt">--</span> Show <span class="nb">command </span>list
           ml <span class="nt">--</span> Enable/Disable multi-line output
         mods <span class="nt">--</span> List <span class="nb">builtin </span>modules
+      output <span class="nt">--</span> Enable/Disable printing expression results. Options <span class="s1">'on'</span>, <span class="s1">'off'</span>, <span class="s1">'status'</span>
 
 <span class="nt">---</span> Command line options:
     <span class="nt">-b</span> &lt;<span class="nb">builtin</span><span class="o">&gt;</span>       Import <span class="nb">builtin </span>modules.
@@ -649,9 +704,10 @@ pre.rouge .ss {
     <span class="nt">-i</span>                 Force REPL operation when all <span class="nt">-e</span> occurences have been processed
     <span class="nt">-h</span>, <span class="nt">--help</span>, <span class="nb">help   </span>Show this <span class="nb">help </span>menu
     <span class="nt">-m</span>, <span class="nt">--modules</span>      List all <span class="nb">builtin </span>modules
+    <span class="nt">--noout</span>            Disable printing of expression results
     <span class="nt">-p</span>                 Print prefix form
     <span class="nt">-t</span>                 Print tree form <i class="conum" data-value="2"></i><b>(2)</b>
-
+    <span class="nt">-v</span>, <span class="nt">--version</span>      Show program version
 <span class="o">&gt;&gt;&gt;</span></code></pre>
 </div>
 </div>
@@ -671,8 +727,8 @@ pre.rouge .ss {
 <div class="title">REPL examples</div>
 <div class="content">
 <pre class="rouge highlight"><code data-lang="shell"><span class="o">[</span>user]<span class="nv">$ </span>./dev-expr
-<span class="nb">expr</span> <span class="nt">--</span> Expressions calculator v1.7.1<span class="o">(</span>build 2<span class="o">)</span>,2024/05/16 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
+dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o">(</span>build 14<span class="o">)</span>,2024/06/17 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
-	Based on the Expr package v0.10.0
+	Based on the Expr package v0.19.0
 	Type <span class="nb">help </span>to get the list of available commands
 	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
 
@@ -689,9 +745,9 @@ pre.rouge .ss {
 7
 -
 6
-<span class="o">&gt;&gt;&gt;</span> 1+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> 1+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>
@@ -700,11 +756,11 @@ pre.rouge .ss {
 <table>
 <tr>
 <td><i class="conum" data-value="1"></i><b>1</b></td>
-<td>Number bases: 0x = hexadecimal, 0o = octal, 0b = binary.</td>
+<td>Number bases: 0x = <em>hexadecimal</em>, 0o = <em>octal</em>, 0b = <em>binary</em>.</td>
 </tr>
 <tr>
 <td><i class="conum" data-value="2"></i><b>2</b></td>
-<td>Fractions: numerator | denominator.</td>
+<td>Fractions: <em>numerator</em> | <em>denominator</em>.</td>
 </tr>
 <tr>
 <td><i class="conum" data-value="3"></i><b>3</b></td>
@@ -727,7 +783,7 @@ pre.rouge .ss {
 <h2 id="_data_types"><a class="anchor" href="#_data_types"></a><a class="link" href="#_data_types">2. Data types</a></h2>
 <div class="sectionbody">
 <div class="paragraph">
-<p><em>Expr</em> supports numerical, string, relational, boolean expressions, and mixed-type lists.</p>
+<p><em>Expr</em> has its type system which is a subset of Golang&#8217;s type system. It supports numerical, string, relational, boolean expressions, and mixed-type lists and maps.</p>
 </div>
 <div class="sect2">
 <h3 id="_numbers"><a class="anchor" href="#_numbers"></a><a class="link" href="#_numbers">2.1. Numbers</a></h3>
@@ -1011,28 +1067,38 @@ pre.rouge .ss {
 </tbody>
 </table>
 <div class="paragraph">
-<p>The items of strings can be accessed using the dot <code>.</code> operator.</p>
+<p>The items of strings can be accessed using the square <code>[]</code> operator.</p>
 </div>
 <div class="exampleblock">
 <div class="title">Example 4. Item access syntax</div>
 <div class="content">
 <div class="paragraph">
-<p><em>item</em> = <em>string-expr</em> "<strong>.</strong>" <em>integer-expr</em></p>
+<p><em>item</em> = <em>string-expr</em> "<strong>[</strong>" <em>integer-expr</em> "<strong>]</strong>"</p>
+</div>
+</div>
+</div>
+<div class="exampleblock">
+<div class="title">Example 5. Sub string syntax</div>
+<div class="content">
+<div class="paragraph">
+<p><em>sub-string</em> = <em>string-expr</em> "<strong>[</strong>" <em>integer-expr</em> "<strong>:</strong>" <em>integer-expr</em> "<strong>]</strong>"</p>
 </div>
 </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>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">s="abcd"</code>  <em class="gray">// assign the string to variable s</em><br>
-<code class="green">abc</code><br>
+<code class="green">"abcd"</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>&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 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>&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 class="green">"d"</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 class="gren">4</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></p>
+<code class="green">3</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">s[1:3]</code>    <em class="gray">// chars from position 1 to position 3 excluded</em><br>
+<code class="grean">"bc"</code></p>
 </div>
 </div>
 <div class="sect2">
@@ -1179,7 +1245,7 @@ pre.rouge .ss {
 <p><em>Expr</em> supports list of mixed-type values, also specified by normal expressions. Internally, <em>Expr</em>'s lists are Go arrays.</p>
 </div>
 <div class="exampleblock">
-<div class="title">Example 5. List literal syntax</div>
+<div class="title">Example 6. List literal syntax</div>
 <div class="content">
 <div class="paragraph">
 <p><strong><em>list</em></strong> = <em>empty-list</em> | <em>non-empty-list</em><br>
@@ -1261,7 +1327,7 @@ pre.rouge .ss {
 <p>The items of array can be accessed using the dot <code>.</code> operator.</p>
 </div>
 <div class="exampleblock">
-<div class="title">Example 6. Item access syntax</div>
+<div class="title">Example 7. Item access syntax</div>
 <div class="content">
 <div class="paragraph">
 <p><em>item</em> = <em>list-expr</em> "<strong>.</strong>" <em>integer-expr</em></p>
@@ -1297,7 +1363,7 @@ pre.rouge .ss {
 <p>Dictionary literals are sequences of pairs separated by comma <code class="blue">,</code> enclosed between brace brackets.</p>
 </div>
 <div class="exampleblock">
-<div class="title">Example 7. Dict literal syntax</div>
+<div class="title">Example 8. Dict literal syntax</div>
 <div class="content">
 <div class="paragraph">
 <p><strong><em>dict</em></strong> = <em>empty-dict</em> | <em>non-empty-dict</em><br>
@@ -1357,13 +1423,13 @@ pre.rouge .ss {
 </div>
 </div>
 <div class="sect1">
-<h2 id="_variables"><a class="anchor" href="#_variables"></a><a class="link" href="#_variables">3. Variables</a></h2>
+<h2 id="_variables_2"><a class="anchor" href="#_variables_2"></a><a class="link" href="#_variables_2">3. Variables</a></h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p><em>Expr</em>, like most programming languages, supports variables. A variable is an identifier with an assigned value. Variables are stored in <em>contexts</em>.</p>
 </div>
 <div class="exampleblock">
-<div class="title">Example 8. Variable literal syntax</div>
+<div class="title">Example 9. Variable literal syntax</div>
 <div class="content">
 <div class="paragraph">
 <p><strong><em>variable</em></strong> = <em>identifier</em> "<strong>=</strong>" <em>any-value</em><br>
@@ -1884,7 +1950,7 @@ These operators have a high priority, in particular higher than the operator <co
 </div>
 <div id="footer">
 <div id="footer-text">
-Last updated 2024-06-03 06:26:03 +0200
+Last updated 2024-06-19 09:33:41 +0200
 </div>
 </div>
 </body>

operator-index.go

@@ -40,11 +40,14 @@ func verifyRange(indexTerm *term, indexList *ListType, maxValue int) (startIndex
 	v, _ := ((*indexList)[0]).(*intPair)
 	startIndex = v.a
 	endIndex = v.b
+	if endIndex == ConstLastIndex {
+		endIndex = maxValue
+	}
 	if startIndex < 0 && startIndex >= -maxValue {
 		startIndex = maxValue + startIndex
 	}
 	if endIndex < 0 && endIndex >= -maxValue {
-		endIndex = maxValue + endIndex + 1
+		endIndex = maxValue + endIndex
 	}
 	if startIndex < 0 || startIndex > maxValue {
 		err = indexTerm.Errorf("range start-index %d is out of bounds", startIndex)

operator-range.go

@@ -29,7 +29,7 @@ func newRangeTerm(tk *Token) (inst *term) {
 		tk:       *tk,
 		children: make([]*term, 0, 2),
 		position: posInfix,
-		priority: priDot,
+		priority: priRange,
 		evalFunc: evalRange,
 	}
 }
@@ -47,7 +47,7 @@ func evalRange(ctx ExprContext, self *term) (v any, err error) {
 		if leftValue, err = self.children[0].compute(ctx); err != nil {
 			return
 		}
-		rightValue = int64(-1)
+		rightValue = int64(ConstLastIndex)
 	} else if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
 		return
 	}

parser.go

@@ -325,6 +325,14 @@ 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 {
+// 	var areOut = false
+// 	if ctxTerm != nil {
+// 		areOut = tk.IsOneOf(syms)
+// 	}
+// 	return areOut
+// }
+
 func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef bool, termSymbols ...Symbol) (tree *ast, err error) {
 	var selectorTerm *term = nil
 	var currentTerm *term = nil
@@ -332,7 +340,7 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 	tree = NewAst()
 	firstToken := true
 	// lastSym := SymUnknown
-	for tk = scanner.Next(); err == nil && tk != nil && !tk.IsTerm(termSymbols); tk = scanner.Next() {
+	for tk = scanner.Next(); err == nil && tk != nil && !tk.IsTerm(termSymbols); /*&& !areSymbolsOutOfCtx(tk, selectorTerm, SymColon, SymDoubleColon)*/ tk = scanner.Next() {
 		if tk.Sym == SymComment {
 			continue
 		}
@@ -438,6 +446,10 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 			} else {
 				currentTerm, err = tree.addToken2(tk)
 			}
+			if tk.IsSymbol(SymColon) {
+				// Colon outside a selector term acts like a separator
+				firstToken = true
+			}
 		default:
 			currentTerm, err = tree.addToken2(tk)
 		}

t_list_test.go

@@ -49,8 +49,10 @@ func TestListParser(t *testing.T) {
 		/*  35 */ {`L=[1,2]; L[5]=9; L`, nil, errors.New(`index 5 out of bounds (0, 1)`)},
 		/*  36 */ {`L=[1,2]; L[]=9; L`, nil, errors.New(`[1:12] index/key specification expected, got [] [list]`)},
 		/*  37 */ {`L=[1,2]; L[nil]=9;`, nil, errors.New(`[1:12] index/key is nil`)},
-		// /*  8 */ {`[int(x)|x=csv("test.csv",1,all(),1)]`, []any{int64(10), int64(40), int64(20)}, nil},
+		/*  38 */ {`[0,1,2,3,4][2:3]`, newListA(int64(2)), nil},
-		// /*  9 */ {`sum(@[int(x)|x=csv("test.csv",1,all(),1)])`, []any{int64(10), int64(40), int64(20)}, nil},
+		/*  39 */ {`[0,1,2,3,4][3:-1]`, newListA(int64(3)), nil},
+		/*  40 */ {`[0,1,2,3,4][-3:-1]`, newListA(int64(2), int64(3)), nil},
+		/*  41 */ {`[0,1,2,3,4][0:]`, newListA(int64(0), int64(1), int64(2), int64(3), int64(4)), nil},
 	}
 
 	// t.Setenv("EXPR_PATH", ".")

token.go

@@ -60,7 +60,11 @@ func (tk *Token) IsError() bool {
 }
 
 func (tk *Token) IsTerm(termSymbols []Symbol) bool {
-	return tk.IsEos() || tk.IsError() || (termSymbols != nil && slices.Index(termSymbols, tk.Sym) >= 0)
+	return tk.IsEos() || tk.IsError() || tk.IsOneOf(termSymbols)
+}
+
+func (tk *Token) IsOneOf(termSymbols []Symbol) bool {
+	return termSymbols != nil && slices.Index(termSymbols, tk.Sym) >= 0
 }
 
 func (tk *Token) IsSymbol(sym Symbol) bool {