<article>
    <h2>Specification</h2>
    <nav>
        <ul>
            <li><a href="#syntax">Syntax</a>
                <ul>
                    <li><a href="#comments">Comments</a>
                    <li><a href="#integer-literals">Integer Literals</a></li>
                    <li><a href="#string-literals">String Literals</a></li>
                    <li><a href="#quotation-literals">Quotation Literals</a></li>
                    <li><a href="#symbol-identifiers">Symbol Identifiers</a></li>
                </ul>
            </li>
            <li><a href="#data-types">Data Types</a>
                <ul>
                    <li><a href="#integers">Integers</a></li>
                    <li><a href="#strings">Strings</a></li>
                    <li><a href="#quotations">Quotations</a></li>
                    <li><a href="#symbols">Symbols</a></li>
                </ul>
            </li>
            <li><a href="#stack">Stack</a>
                <ul>
                    <li><a href="#pushing-literals">Pushing Literals</a></li>
                    <li><a href="#pushing-symbols">Pushing Symbols</a></li>
                </ul>
            </li>
            <li><a href="#registry">Registry</a></li>
            <li><a href="#native-symbols">Native Symbol Reference</a>
                <ul>
                    <li><a href="#memory-management-symbols">Memory Management Symbols</a></li>
                    <li><a href="#control-flow-symbols">Control Flow Symbols</a></li>
                    <li><a href="#stack-management-symbols">Stack Management Symbols</a></li>
                    <li><a href="#evaluation-symbols">Evaluation Symbols</a></li>
                    <li><a href="#arithmetic-symbols">Arithmetic Symbols</a></li>
                    <li><a href="#bitwise-operations-symbols">Bitwise Operations Symbols</a></li>
                    <li><a href="#comparisons-symbols">Comparisons Symbols</a></li>
                    <li><a href="#boolean-logic-symbols">Boolean Logic Symbols</a></li>
                    <li><a href="#type-checking-and-conversion-symbols">Type Checking and Conversion Symbols</a></li>
                    <li><a href="#list-symbols">List (Strings and Quotations) Symbols</a></li>
                    <li><a href="#string-symbols">String Symbols</a></li>
                    <li><a href="#quotation-symbols">Quotation Symbols</a></li>
                    <li><a href="#input-output-symbols">Input/Output Symbols</a></li>
                    <li><a href="#file-symbols">File Symbols</a></li>
                    <li><a href="#shell-symbols">Shell Symbols</a></li>
                </ul>
            </li>
        </ul>
    </nav>


    <h3 id="introduction">Introduction<a href="#top"></a></h3>
    <p><strong>hex</strong> is a minimalist, concatenative, stack-based programming language designed for experimenting
        with the concatenative programming paradigm. It is inspired by the <a href="https://min-lang.org"
            target="_blank">min</a> programming language and aims to provide a small yet powerful language for creating
        short scripts and automating common tasks.</p>
    <p>hex supports 32-bit integers (written only in hexadecimal format), strings, and quotations (lists). It features
        a set of built-in symbols that implement arithmetic operations, boolean logic, bitwise operations, comparison of
        integers, I/O operations, file manipulation, external process execution, and stack manipulation. The language is
        fully homoiconic, meaning that everything in hex is data.</p>
    <p>hex was created with simplicity in mind, both in its implementation and usage. The language's design encourages a
        minimalist
        approach, focusing on essential features and avoiding unnecessary complexity.</p>
    <h3 id="syntax">Syntax<a href="#top"></a></h3>
    <p>The syntax of hex is designed to be simple and intuitive, following the principles of concatenative programming.
        In hex, programs are composed of sequences of literals and symbols, which are evaluated from left to right.</p>
    <p>
        Literals push values onto the stack, while symbols manipulate the stack or perform operations. There are no
        explicit control structures; instead, hex relies on stack manipulation and quotations to achieve flow control
        and data management. Symbols in hex can be used to store values globally, providing a way to manage state across
        different parts of a program.</p>
    <p>hex programs are written as sequences of whitespace-separated tokens. Tokens can be literals, symbols, or
        comments.</p>
    <p>This is an example of a simple hex program:</p>
    <pre><code>    $; Filters a quotation to keep only the even numbers$$
    ($0x2$$ $0x3$$ $0x4$$ $0x5$$ $0x6$$) ($0x2$$ $:%$$ $0x0$$ $:==$$) $:filter$$</code></pre>
    <p>This example includes:</p>
    <ul>
        <li>One single-line comment: <code>$; Filters a quotation to keep only the even numbers$$</code></li>
        <li>Two quotations: <code>($0x2$$ $0x3$$ $0x4$$ $0x5$$ $0x6$$)</code> and
            <code>($0x2$$ $:%$$ $0x0$$ $:==$$)</code>
        </li>
        <li>Three symbols: <code>$:%$$</code>, <code>$:==$$</code>, and <code>$:filter$$</code></li>
    </ul>
    <h4 id="comments">Comments<a href="#top"></a></h4>

    <p>Comments in hex are used to annotate code and are ignored during execution. There are two types of comments:
        single-line comments and multi-line comments.</p>

    <h5 id="single-line-comments">Single-line Comments<a href="#top"></a></h5>
    <p>Single-line comments start with a semicolon (<code>;</code>) and continue until the end of the line. Everything
        after the semicolon is ignored.</p>
    <p>Example:</p>
    <pre><code>    $; This is a single-line comment$$
    $0x2$$ $0x3$$ $:+$$ $; This adds 0x2 and 0x3$</code></pre>

    <h5 id="multi-line-comments">Multi-line Comments<a href="#top"></a></h5>
    <p>Multi-line comments start with <code>#|</code> and end with <code>|#</code>. Everything between these markers is
        ignored, allowing comments to span multiple lines.</p>
    <p>Example:</p>
    <pre><code>    $#|
      This is a multi-line comment
      It can span multiple lines
    |#$
    $0x2$$ $0x3$$ $:+$$ $#| This adds 0x2 and 0x3 |#$</code></pre>
    <h4 id="integer-literals">Integer Literals<a href="#top"></a></h4>
    <p>Integer literals in hex are always written in hexadecimal form, prefixed with <code>0x</code>. They can contain
        up to 8 hexadecimal digits, representing 32-bit integers. Hexadecimal digits include the numbers
        <code>0-9</code> and the letters <code>>a-f</code> (or <code>A-F</code>), which correspond to the decimal values
        10-15.
    </p>
    <p>Integers in hex can be positive or negative, and are implemented using <a
            href="https://en.wikipedia.org/wiki/Two%27s_complement" target="_blank">two's complement</a> representation.
        For more information on two's complement, see .</p>
    <p>Examples:</p>
    <ul>
        <li><code>$0x1$$</code> represents the decimal value 1.</li>
        <li><code>$0xa$$</code> represents the decimal value 10.</li>
        <li><code>$0x1f$$</code> represents the decimal value 31.</li>
        <li><code>$0xffffffff$$</code> represents the decimal value -1 (in two's complement).</li>
    </ul>
    <p>Integers are case-insensitive; typically, lowercase letters are preferred but not mandatory.</p>
    <h4 id="string-literals">String Literals<a href="#top"></a></h4>
    <p>String literals in hex are delimited by double quotes (<code>"</code>). They can contain any character except for
        a newline, meaning that strings must be on a single line. To include special characters within a string, hex
        supports the following escape codes:</p>
    <ul>
        <li><code>&#92;n</code> - Newline</li>
        <li><code>&#92;t</code> - Tab</li>
        <li><code>&#92;r</code> - Carriage return</li>
        <li><code>&#92;b</code> - Backspace</li>
        <li><code>&#92;f</code> - Form feed</li>
        <li><code>&#92;v</code> - Vertical tab</li>
        <li><code>&#92;&#92;</code> - Backslash</li>
        <li><code>&#92;"</code> - Double quote</li>
    </ul>
    <p>Example:</p>
    <pre><code>$"Hello, World!&bsol;nThis is a new line."$$</code></pre>
    <h4 id="quotation-literals">Quotation Literals<a href="#top"></a></h4>
    <p>Quotations in hex are delimited by parentheses (they must start with <code>(</code> and end with <code>)</code>).
        They can contain integers, strings, symbols, and
        even other quotations, allowing for nested structures.</p>
    <p>Examples:</p>
    <ul>
        <li><code>($0x1$$ $0x2$$ $0x3$$)</code> - A quotation containing three integer literals.</li>
        <li><code>($0x1$$ $"hello"$$ ($0x2$$ $0x3$$))</code> - A nested quotation containing an integer, a string, and
            another
            quotation.</li>
    </ul>
    <p>Unlike string literals, quotations can span multiple lines, making them suitable for representing complex data
        structures and control flow mechanisms.</p>
    <h4 id="symbol-identifiers">Symbol Identifiers<a href="#top"></a></h4>
    <p>Symbol identifiers in hex are used to represent built-in native symbols and user-defined symbols.</p>
    <p>There are 0x40 (64) <a href="#native-symbols">native symbols</a> in hex, and some of them contain special
        characters like <code>==</code> or <code>.</code></p>
    <p>Instead, user-defined symbols:</p>
    <ul>
        <li>must start with a letter (<code>a-z</code> or <code>A-Z</code>) or an underscore (<code>_</code>)</li>
        <li>can contain additional letters (<code>a-z</code> or <code>A-Z</code>), digits (<code>0-9</code>), dashes
            (<code>-</code>) and underscores (<code>_</code>)</li>
    </ul>
    <p>Symbols are case-sensitive.</p>
    <h3 id="data-types">Data Types<a href="#top"></a></h3>
    <p>hex supports the following data types:</p>
    <ul>
        <li><a href="#integers">Integers</a> &mdash; 32-bit signed integers represented in hexadecimal form.</li>
        <li><a href="#strings">Strings</a> &mdash; Sequences of characters delimited by double quotes.</li>
        <li><a href="#quotations">Quotations</a> &mdash; Lists of literals, symbols, and other quotations delimited by
            parentheses.</li>
        <li><a href="#symbols">Symbols</a> &mdash; Identifiers representing native or user-defined symbols.</li>
    </ul>
    <h4 id="integers">Integers<a href="#top"></a></h4>
    <p>Integers in hex are 32-bit signed values represented in hexadecimal form. They can be positive or negative (using
        two's complement), and range from <code>-2,147,483,647</code> (<code>-2<sup>31</sup></code>) and
        <code>2,147,483,647</code> (<code>2<sup>31</sup> - 1</code>)
    </p>
    <p>Integers are written using the prefix <code>$0x$$</code> followed by up to 8 hexadecimal digits.</p>
    <p>hex integers are case-insensitive, meaning that <code>$0x1f$$</code> and
        <code><span class="hex-integer">0X1F</span></code> are equivalent
        (however, lowercase letters are preferred).
    </p>
    computations.</p>
    <p>Because hex has no boolean data type, $0x0$$ is assumed to be false, and any other integer value is assumed to be
        true.</p>
    <p>Examples:</p>
    <ul>
        <li><code>$0x1$$</code> &mdash; Represents the decimal value 1.</li>
        <li><code>$0xffffffff$$</code> &mdash; Represents the decimal value -1.</li>
        <li><code>$0x10$$</code> &mdash; Represents the decimal value 16.</li>
    </ul>
    <h4 id="strings">Strings<a href="#top"></a></h4>
    <p>Strings in hex are sequences of characters delimited by double quotes (<code>"</code>). They can contain any
        character except for a newline character, and special characters can be escaped using backslashes.</p>
    <p>Strings are used to represent textual data and can be manipulated using various string manipulation symbols in
        hex.</p>
    <p>Examples:</p>
    <ul>
        <li><code>$"Hello, World!"$$</code> &mdash; Represents the string <code>Hello, World!</code>.</li>
        <li><code>$"This is a string with a newline:&bsol;nSecond line."$$</code> &mdash; Represents a string with a
            newline character.</li>
    </ul>
    <h4 id="quotations">Quotations<a href="#top"></a></h4>
    <p>Quotations in hex are lists of literals (including other quotations) and symbols delimited by parentheses
        (<code>(</code>
        and <code>)</code>). They are used to represent structured data and are a fundamental part of the language's
        syntax.</p>
    <p>An important thing to remember about quotations is that any symbol contained in them will not be executed, and
        this is a fundamental property of hex and other concatenative programming languages, because it means that
        quotation effectively acts as code blocks, holding code that can be executed later on using appropriate
        dequoting symbols.</p>
    <p>Consider the following example:</p>
    <pre><code>    $0x0$$ $"t-count"$$ $::$$
    ($:t-count$$ $0xa$$ $:&lt;$$)
        (
            $:t-count$$ $:puts$$
            $:t-count$$ $0x1$$ $:+$$ $"t-count"$$ $::$$
        )
    $:while$$
    $"t-count"$$ $:#$$</code></pre>
    <p>This example defines a symbol <code>$:t-count$$</code> that counts from 0 to 9 and prints each number to the
        standard
        output. The quotation <code>($:t-count$$ $0xa$$ $:&lt;$$)</code> is used to check if the count is less than 10,
        and the
        <code>$:while$$</code> symbol repeats the process until the condition is no longer met.
    </p>
    <p>In this case, the first two quotations are first pushed on the stack, and the the <code>$:while$$</code> symbols
        perform the dequoting necessary to implement the expected control flow.</p>
    <h4 id="symbols">Symbols<a href="#top"></a></h4>
    <p>In hex there native symbols and user-defined symbols. Native symbols are
        built-in functions that perform specific operations, while user-defined symbols are created by the user to store
        values or define custom behavior.</p>
    <p>hex provides 64 ($0x40$$) native symbols that cover a wide range of functionality, including arithmetic
        operations, control flow, I/O operations, file manipulation, and stack manipulation.</p>
    <p>You can think of symbols as both functions that manipulate the <a href="#stack">stack</a>, or
        variables that can be used to store literal values.</p>
    <p>While native symbol identifiers sometimes are comprised of special characters, like {{sym-==}}, user-defined
        symbol identifier must adhere to
        <a href="symbol-identifiers">specific rules</a>.
    </p>
    <p>All symbols are stored in a single <a href="#registry">registry</a>, implemented as a simple dictionary.
        Therefore, all symbols in hex are global, and not lexically scoped. The main driver for this is to keep the
        language as simple as possible.</p>
    <p>You can define your own symbols and delete them using the <a href="#memory-management-symbols">memory management
            symbols</a> provided natively. However, native symbols <em>cannot</em> be deleted.</p>
    <h3 id="stack">Stack<a href="#top"></a></h3>
    <p>The stack is a fundamental data structure in hex that holds values and controls the flow of execution. hex is a
        stack-based language, meaning that all operations are performed on a stack of values. The order according to
        which items are added (pushed) to or removed (popped) from the stack is <abbr
            title="Last In, First Out">LIFO</abbr>.</p>
    <p>In the canonical implementation, the hex stack can contain up to 256 items. If you try to push more items on the
        stack, a stack overflow error will be raised and the program will terminate. While this may seem a relatively
        low number, it is important to note that typically there will not be more than 5-10 items on the stack at any
        time, because typically symbols are used to frequently pop them out of the stacks.</p>
    <h4 id="pushing-literals">Pushing Literals<a href="#top"></a></h4>
    <p>Literals are values that are directly pushed onto the stack. In hex, literals can be integers, strings, or
        quotations. When a literal is encountered in a hex program, it is pushed onto the stack for further processing.
    </p>
    <p>Examples:</p>
    <ul>
        <li><code>$0x1$$</code> &mdash; Pushes the integer 1 onto the stack.</li>
        <li><code>$"Hello, World!"$$</code> &mdash; Pushes the string <code>Hello, World!</code> onto the stack.</li>
        <li><code>($0x1$$ $0x2$$ $0x3$$)</code> &mdash; Pushes the quotation <code>($0x1$$ $0x2$$ $0x3$$)</code> onto
            the stack.
        </li>
    </ul>
    <h4 id="pushing-symbols">Pushing Symbols<a href="#top"></a></h4>
    <p>Symbols in hex are used to represent native or user-defined functions and values. When a symbol is encountered in
        a hex program, it is looked up in the registry, and its associated value or function is pushed onto the stack.
    </p>
    <p>Native symbols can perform manipulations on the stack; they can pop values from the stack and push values back
        in.</p>
    <p>By contrast, you can only define literals as user-defined symbols, but you can define a quotation which can then
        be <em>dequoted</em> through symbols like {{sym-.}}, which pushes all the items in a quotations
        on the stack, one by one.</p>
    <p>Consider the following example hex program:</p>
    <pre><code>    ($:dup$$ $:*$$ $:*$$) $"square"$$ $::$$
    $0x3$$ $:square$$ $:.$$ $:puts$$ $; prints 9$$</code></pre>
    <p>This program defines a symbol $:square$$ that can be used to calculate the square value of an integer, using the
        symbol {{sym-:}}. From then on, if $:square$$ is found anywhere in the same hex program, it
        will be substituted with <code>($:*$$ $:*$$)</code>. However, this is not enough to calculate the square value,
        because the logic to do so is in a quotation. To "execute" (dequote) a quotation, you must use the {{sym-.}}
        symbol, which pushes all the items in the quotation on the stack, which is equivalent
        to the following program:</p>
    <pre><code>    $0x3$$ $:dup$$ $:*$$ $:*$$ $:puts$$ $; prints 9$$</code></pre>
    <h3 id="registry">Registry<a href="#top"></a></h3>
    <p>The registry in hex is a simple dictionary that stores symbols and their associated values or functions. The
        registry is used to look up symbols when they are encountered in a hex program and to store user-defined symbols
        and their values.</p>
    <p>When a symbol is pushed onto the stack, hex looks up the symbol in the registry and pushes its associated value
        or function onto the stack. If the symbol is not found in the registry, an error is raised.</p>
    <p>The registry is implemented as a simple key-value store, where the keys are symbol identifiers and the values are
        the associated values or functions. The registry is global and shared across the entire hex program.</p>
    <p>hex provides a set of <a href="#native-symbols">native symbols</a> that are pre-defined in the registry and
        cannot be deleted or modified. These symbols provide basic functionality for arithmetic operations, control
        flow,
        I/O operations, file manipulation, and stack manipulation.</p>
    <p>hex also allows users to define their own symbols and store values in the registry. User-defined symbols can be
        created, modified, and deleted using the <a href="#memory-management-symbols">memory management symbols</a>
        provided natively.</p>
    <p>It is important to note that the registry is a global store, meaning that symbols are not lexically scoped and
        can be accessed from anywhere in the program. This design choice was made to keep the language simple and
        straightforward.</p>
    <p>In the canonical hex implementation, the registry can hold up to 1024 symbols (960 of which can be user-defined
        symbols).</p>
    <h3 id="native-symbols">Native Symbol Reference<a href="#top"></a></h3>
    <p>hex provides a set of 64 ($0x40$$) native symbols that are built-in and pre-defined in the registry. The
        following section provides details on each of these symbols, including a signature illustrating how each symbol
        manipulates the stack.</p>
    <p>The notation used to specify the signature of a symbol is as follows:</p>
    <pre><code>    <mark>in1 in2 ... inN &rarr; out1 out2 ... outM</mark></code></pre>
    <p>Where <code>in1</code>, <code>in2</code>, ..., <code>inN</code> are the items consumed from the stack,
        and <code>out1</code>, <code>out2</code>, ..., <code>outM</code> are the items pushed back onto the
        stack.</p>
    <p> Note that the <code>&rarr;</code> character represents the symbol being described, and: </p>
    <ul>
        <li><code>inN</code> is the first element on the stack <em>before</em> the symbol is pushed on the stack.
        </li>
        <li><code>outM</code> is the first element on the stack <em>after</em> the symbol is pushed on the stack.
        </li>
    </ul>
    <p>The following abbreviations are used to represent different types of literals (and each can have a numerical
        suffix for differentiation within the signature):</p>
    <ul>
        <li><code>a</code> &mdash; Any literal value</li>
        <li><code>s</code> &mdash; String</li>
        <li><code>q</code> &mdash; Quotation</li>
        <li><code>i</code> &mdash; Integer</li>
    </ul>
    <p>Additionally, <code>*</code> is used to represent zero or more literals of any type.</p>
    <p>Consider, for example, the following signature for the {{sym-swap}} symbol:</p>
    <p><mark> a1 a2 &rarr; a2 a1</mark></p>
    <p>This signature indicates that the symbol {{sym-swap}} pops two items from the stack (<code>a1</code> and
        <code>a2</code>), and then pushes them back onto the stack in reverse order (<code>a2</code> and
        <code>a1</code>).
    </p>
    <h4 id="memory-management-symbols">Memory Management Symbols<a href="#top"></a></h4>
    <h5 id="store-symbol"><code>$::$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>a s &rarr;</mark></p>
    <p>Stores the literal <code>a</code> in the registry as the symbol <code>s</code>.</p>
    <h5 id="free-symbol"><code>$:#$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>s &rarr;</mark></p>
    <p>Frees the symbol <code>s</code> from the registry.</p>
    <h4 id="control-flow-symbols">Control Flow Symbols<a href="#top"></a></h4>
    <h5 id="if-symbol"><code>$:if$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>q1 q2 q3 &rarr; *</mark></p>
    <p>Dequotes quotation <code>q1</code>, if it pushes a positive integer on the stack it dequotes <code>q2</code>,
        otherwise
        dequotes <code>q3</code>.</p>
    <h5 id="when-symbol"><code>$:when$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>q1 q2 &rarr; *</mark></p>
    <p>Dequotes quotation <code>q1</code>, if it pushes a positive integer on the stack it dequotes <code>q2</code>.
    </p>
    <h5 id="while-symbol"><code>$:while$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>q1 q2 &rarr; *</mark></p>
    <p>Dequotes quotation <code>q1</code>, if it pushes a positive integer on the stack it dequotes <code>q2</code>
        and
        repeats the process.</p>
    <h5 id="error-symbol"><code>$:error$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>&rarr; s</mark></p>
    <p>Pushes the last error message to the stack.</p>
    <h5 id="try-symbol"><code>$:try$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>q1 q2 &rarr; *</mark></p>
    <p>Dequotes quotation <code>q1</code>, if it throws an error it dequotes <code>q2</code>.</p>
    <h4 id="stack-management-symbols">Stack Management Symbol<a href="#top"></a></h4>
    <h5 id="dup-symbol"><code>$:dup$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> a &rarr; a a</mark></p>
    <p>Duplicates literal <code>a</code> and pushes it on the stack.</p>
    <h5 id="stack-symbol"><code>$:stack$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> &rarr; q</mark></p>
    <p>Pushes the items currently on the stack as a quotation on the stack.</p>
    <h5 id="clear-symbol"><code>$:clear$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> &rarr;</mark></p>
    <p>Clears the stack.</p>
    <h5 id="pop-symbol"><code>$:pop$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> a &rarr;</mark></p>
    <p>Removes the top item from the stack.</p>
    <h5 id="swap-symbol"><code>$:swap$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> a1 a2 &rarr; a2 a1</mark></p>
    <p>Swaps the top two items on the stack.</p>
    <h4 id="evaluation-symbols">Evaluation Symbols<a href="#top"></a></h4>
    <h5 id="i-symbol"><code>$:.$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>q &rarr; *</mark></p>
    <p>Dequotes quotation <code>q</code>.</p>
    <h5 id="eval-symbol"><code>$:!$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>(s|q) &rarr; *</mark></p>
    <p>Evaluates the string <code>s</code> as an hex program, or the array of integers to be interpreted as hex bytecode
        (HBX format).</p>
    <h5 id="quote-symbol"><code>$:&#39;$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>a &rarr; q</mark></p>
    <p>Pushes the literal <code>a</code> wrapped in a quotation on the stack.</p>
    <h4 id="arithmetic-symbols">Arithmetic Symbols<a href="#top"></a></h4>
    <h5 id="add-symbol"><code>$:+$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 i2 &rarr; i</mark></p>
    <p>Pushes the result of the sum of <code>i1</code> and <code>i2</code> on the stack.</p>
    <h5 id="subtract-symbol"><code>$:-$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes the result of the subtraction of <code>12</code> from <code>i1</code> on the stack.</p>
    <h5 id="multiply-symbol"><code>$:*$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes the result of the multiplication of <code>i1</code> and <code>12</code> on the stack.</p>
    <h5 id="divide-symbol"><code>$:/$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes the result of the division of <code>i1</code> by <code>12</code> on the stack.</p>
    <h5 id="modulo-symbol"><code>$:%$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes the result of the modulo of <code>i1</code> by <code>12</code> on the stack.</p>
    <h4 id="bitwise-operations-symbols">Bitwise Operations Symbols<a href="#top"></a></h4>
    <h5 id="bitwise-and-symbol"><code>$:&amp;$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes the result of a bitwise and of <code>i1</code> and <code>i2</code> on the stack.</p>
    <h5 id="bitwise-or-symbol"><code>$:|$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes the result of a bitwise or of <code>i1</code> and <code>i2</code> on the stack.</p>
    <h5 id="bitwise-xor-symbol"><code>$:^$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes the result of a bitwise xor of <code>i1</code> and <code>i2</code> on the stack.</p>
    <h5 id="bitwise-not-symbol"><code>$:~$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i &rarr; i</mark></p>
    <p>Pushes the result of a bitwise not of <code>i</code> on the stack.</p>
    <h5 id="bitwise-leftshift-symbol"><code>$:&lt;&lt;$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes the result of shifting <code>i1</code> by <code>i2</code> bits to the left.</p>
    <h5 id="bitwise-rightshift-symbol"><code>$:&gt;&gt;$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes the result of shifting <code>i1</code> by <code>i2</code> bits to the right.</p>
    <h4 id="comparisons-symbols">Comparisons Symbols<a href="#top"></a></h4>
    <h5 id="equal-symbol"><code>$:==$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> a1 a2 &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>a1</code> and <code>a2</code> are equal, or <code>0x0</code>
        otherwise.</p>
    <h5 id="notequal-symbol"><code>$:!=$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>a1</code> and <code>a2</code> are not equal, or
        <code>0x0</code>
        otherwise.
    </p>
    <h5 id="greaterthan-symbol"><code>$:&gt;$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>i1</code> is greater than <code>i2</code>, or <code>0x0</code>
        otherwise.</p>
    <h5 id="lessthan-symbol"><code>$:&lt;$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>i1</code> is less than <code>i2</code>, or <code>0x0</code>
        otherwise.</p>
    <h5 id="greaterthanequal-symbol"><code>$:&gt;=$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 12 &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>i1</code> is greater than or equal to <code>i2</code>, or
        <code>0x0</code> otherwise.
    </p>
    <h5 id="lessthanequal-symbol"><code>$:&lt;=$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 i2 &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>i1</code> is less than or equal to <code>i2</code>, or
        <code>0x0</code> otherwise.
    </p>
    <h4 id="boolean-logic-symbols">Boolean Logic Symbols<a href="#top"></a></h4>
    <h5 id="and-symbol"><code>$:and$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 i2 &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>i1</code> and <code>i2</code> are non-zero integers, or
        <code>0x0</code> otherwise.
    </p>
    <h5 id="or-symbol"><code>$:or$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 i2 &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>i1</code> or <code>i2</code> are non-zero integers, or
        <code>0x0</code> otherwise.
    </p>
    <h5 id="not-symbol"><code>$:not$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>i</code> is zero, or <code>0x0</code> otherwise.</p>
    <h5 id="xor-symbol"><code>$:xor$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i1 i2 &rarr; i</mark></p>
    <p>Pushes <code>0x1</code> on the stack if <code>i1</code> and <code>i2</code> are different, or
        <code>0x0</code>
        otherwise.
    </p>
    <h4 id="type-checking-and-conversion-symbols">Type Checking and Conversion Symbols<a href="#top"></a></h4>
    <h5 id="int-symbol"><code>$:int$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>s &rarr; i</mark></p>
    <p>Converts the string <code>s</code> representing a hexadecimal integer to an integer value and pushes it on
        the
        stack.</p>
    <h5 id="str-symbol"><code>$:str$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i &rarr; s</mark></p>
    <p>Converts the integer <code>i</code> to a string representing a hexadecimal integer and pushes it on the
        stack.
    </p>
    <h5 id="dec-symbol"><code>$:dec$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i &rarr; s</mark></p>
    <p>Converts the integer <code>i</code> to a string representing a decimal integer and pushes it on the stack.
    </p>
    <h5 id="hex-symbol"><code>$:hex$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> s &rarr; i</mark></p>
    <p>Converts the string <code>s</code> representing a decimal integer to an integer value and pushes it on the
        stack.
    </p>
    <h5 id="ord-symbol"><code>$:ord$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> s &rarr; i</mark></p>
    <p>Pushes the ASCII value of the string <code>s</code> on the stack.</p>
    <p>If <code>s</code> is longer than 1 character or if it is not representable using an ASCII code between $0x0$$
        and
        $0x7f$$, <code>$0xffffffff$$</code> is pushed on the stack.</p>
    <h5 id="chr-symbol"><code>$:chr$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i &rarr; s</mark></p>
    <p>Pushes the ASCII character represented by the integer <code>i</code> on the stack.</p>
    <p>If <code>i</code> is not between $0x0$$ and $0x7f$$, an empty string is pushed on the stack.</p>
    <h5 id="type-symbol"><code>$:type$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> a &rarr; s</mark></p>
    <p>Pushes the type of the literal <code>a</code> on the stack (<code>integer</code>, <code>string</code>,
        <code>quotation</code>, <code>native-symbol</code>, <code>user-symbol</code>, <code>invalid</code>, or
        <code>unknown</code>).
    </p>
    <h4 id="list-symbols">List (Strings and Quotations) Symbols<a href="#top"></a></h4>
    <h5 id="cat-symbol"><code>$:cat$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> (s1 s2|q1 q2) &rarr; (s|q)</mark></p>
    <p>Pushes the result of the concatenation of two strings or two quotations on the stack.</p>
    <h5 id="len-symbol"><code>$:len$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> (s|q) &rarr; i</mark></p>
    <p>Pushes the length of a string or a quotation on the stack.</p>
    <h5 id="get-symbol"><code>$:get$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> (s|q) i &rarr; a</mark></p>
    <p>Pushes the <code>i</code>th item of a string or a quotation on the stack.</p>
    <h5 id="index-symbol"><code>$:index$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> (s a|q a) &rarr; i</mark></p>
    <p>Pushes the index of the first occurrence of the literal <code>a</code> in a string or a quotation on the
        stack.
        If <code>a</code> is not found, <code>$0xffffffff$$</code> is pushed on the stack.</p>
    <h5 id="join-symbol"><code>$:join$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> q s1 &rarr; s2</mark></p>
    <p>Assuming that <code>q</code> is a quotation containing only strings, pushes the string <code>s2</code>
        obtained
        by joining each element of <code>q</code> together using <code>s1</code> as a delimiter. </p>
    <h4 id="string-symbols">String Symbols<a href="#top"></a></h4>
    <h5 id="split-symbol"><code>$:split$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> s1 s2 &rarr; q</mark></p>
    <p>Pushes a quotation <code>q</code> containing the strings obtained by splitting <code>s1</code> using
        <code>s2</code> as a delimiter.
    </p>
    <h5 id="replace-symbol"><code>$:replace$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> s1 s2 s3 &rarr; s4</mark></p>
    <p>Pushes the string <code>s4</code> obtained by replacing the first occurrence of <code>s2</code> in
        <code>s1</code> by
        <code>s3</code>.
    </p>
    <h4 id="quotation-symbols">Quotation Symbols<a href="#top"></a></h4>
    <h5 id="each-symbol"><code>$:each$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> q1 q2 &rarr; *</mark></p>
    <p>Dequotes quotation <code>q1</code> and applies it to each item of quotation <code>q2</code>.</p>
    <h5 id="map-symbol"><code>$:map$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> q1 q2 &rarr; q3</mark></p>
    <p>Dequotes quotation <code>q1</code> and applies it to each item of quotation <code>q2</code> to obtain a new
        quotation <code>q3</code>.
    <h5 id="filter-symbol"><code>$:filter$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> q1 q2 &rarr; q</mark></p>
    <p>Dequotes quotation <code>q1</code> and applies it to each item of quotation <code>q2</code> to obtain a new
        quotation <code>q</code> containing only the items that returned a positive integer.</p>
    <h4 id="input-output-symbols">Input/Output Symbols<a href="#top"></a></h4>
    <h5 id="puts-symbol"><code>$:puts$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> a &rarr;</mark></p>
    <p>Prints <code>a</code> to standard output, followed by a new line.</p>
    <h5 id="warn-symbol"><code>$:warn$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> a &rarr;</mark></p>
    <p>Prints <code>a</code> to standard error, followed by a new line.</p>
    <h5 id="print-symbol"><code>$:print$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> a &rarr;</mark></p>
    <p>Prints <code>a</code> to standard output.</p>
    <h5 id="gets-symbol"><code>$:gets$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> &rarr; s</mark></p>
    <p>Reads a line from standard input and pushes it on the stack as a string.</p>
    <h4 id="file-symbols">File Symbols<a href="#top"></a></h4>
    <h5 id="read-symbol"><code>$:read$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>s1 &rarr; (s2|q)</mark></p>
    <p>Reads the content of the file <code>s1</code> and pushes it on the stack as a string, if the file is in textual
        format, or as a quotation of integers representing bytes, if the file is in binary format.</p>
    <h5 id="write-symbol"><code>$:write$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>(s1|q) s2 &rarr;</mark></p>
    <p>Writes the string <code>s1</code> or the array of integers representing bytes <code>q</code> to the file
        <code>s2</code>.
    <h5 id="append-symbol"><code>$:append$$</code> Symbol<a href="#top"></a></h5>
    <p><mark>(s1|q) s2 &rarr;</mark></p>
    <p>Appends the string <code>s1</code> or the array of integers representing bytes <code>q</code> to the file
        <code>s2</code>.
    </p>
    <h4 id="shell-symbols">Shell Symbols<a href="#top"></a></h4>
    <h5 id="args-symbol"><code>$:args$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> &rarr; q</mark></p>
    <p>Pushes the command line arguments as a quotation on the stack.</p>
    <h5 id="exit-symbol"><code>$:exit$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> i &rarr;</mark></p>
    <p>Exits the program with the exit code <code>i</code>.</p>
    <h5 id="exec-symbol"><code>$:exec$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> s &rarr; i</mark></p>
    <p>Executes the string <code>s</code> as a shell command, and pushes the command return code on the stack.</p>
    <h5 id="run-symbol"><code>$:run$$</code> Symbol<a href="#top"></a></h5>
    <p><mark> s &rarr; q</mark></p>
    <p>Executes the string <code>s</code> as a shell command, capturing its output and errors. It pushes a quotation
        on
        the stack containing the following items:
    </p>
    <ul>
        <li>the exit code of the command as an integer</li>
        <li>the standard output of the command as a string</li>
        <li>the standard error of the command as a string</li>
    </ul>
</article>