171 lines
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171 lines
12 KiB
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>Function Prologue Instructions (Guile Reference Manual)</title>
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Instruction-Set.html" rel="up" title="Instruction Set">
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<link href="Shuffling-Instructions.html" rel="next" title="Shuffling Instructions">
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</head>
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<body lang="en">
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<div class="subsubsection-level-extent" id="Function-Prologue-Instructions">
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<div class="nav-panel">
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<p>
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Next: <a href="Shuffling-Instructions.html" accesskey="n" rel="next">Shuffling Instructions</a>, Previous: <a href="Call-and-Return-Instructions.html" accesskey="p" rel="prev">Call and Return Instructions</a>, Up: <a href="Instruction-Set.html" accesskey="u" rel="up">Instruction Set</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsubsection" id="Function-Prologue-Instructions-1"><span>9.3.7.2 Function Prologue Instructions<a class="copiable-link" href="#Function-Prologue-Instructions-1"> ¶</a></span></h4>
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<p>A function call in Guile is very cheap: the VM simply hands control to
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the procedure. The procedure itself is responsible for asserting that it
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has been passed an appropriate number of arguments. This strategy allows
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arbitrarily complex argument parsing idioms to be developed, without
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harming the common case.
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</p>
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<p>For example, only calls to keyword-argument procedures “pay” for the
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cost of parsing keyword arguments. (At the time of this writing, calling
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procedures with keyword arguments is typically two to four times as
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costly as calling procedures with a fixed set of arguments.)
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</p>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-assert_002dnargs_002dee"><span class="category-def">Instruction: </span><span><strong class="def-name">assert-nargs-ee</strong> <code class="def-code-arguments">c24:<var class="var">expected</var></code><a class="copiable-link" href="#index-assert_002dnargs_002dee"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-assert_002dnargs_002dge"><span class="category-def">Instruction: </span><span><strong class="def-name">assert-nargs-ge</strong> <code class="def-code-arguments">c24:<var class="var">expected</var></code><a class="copiable-link" href="#index-assert_002dnargs_002dge"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-assert_002dnargs_002dle"><span class="category-def">Instruction: </span><span><strong class="def-name">assert-nargs-le</strong> <code class="def-code-arguments">c24:<var class="var">expected</var></code><a class="copiable-link" href="#index-assert_002dnargs_002dle"> ¶</a></span></dt>
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<dd><p>If the number of actual arguments is not <code class="code">==</code>, <code class="code">>=</code>, or
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<code class="code"><=</code> <var class="var">expected</var>, respectively, signal an error.
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</p>
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<p>The number of arguments is determined by subtracting the stack pointer
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from the frame pointer (<code class="code">fp - sp</code>). See <a class="xref" href="Stack-Layout.html">Stack Layout</a>, for more
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details on stack frames. Note that <var class="var">expected</var> includes the
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procedure itself.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-arguments_003c_003d_003f"><span class="category-def">Instruction: </span><span><strong class="def-name">arguments<=?</strong> <code class="def-code-arguments">c24:<var class="var">expected</var></code><a class="copiable-link" href="#index-arguments_003c_003d_003f"> ¶</a></span></dt>
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<dd><p>Set the <code class="code">LESS_THAN</code>, <code class="code">EQUAL</code>, or <code class="code">NONE</code> comparison result
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values if the number of arguments is respectively less than, equal to,
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or greater than <var class="var">expected</var>.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-positional_002darguments_003c_003d_003f"><span class="category-def">Instruction: </span><span><strong class="def-name">positional-arguments<=?</strong> <code class="def-code-arguments">c24:<var class="var">nreq</var> x8:<var class="var">_</var> c24:<var class="var">expected</var></code><a class="copiable-link" href="#index-positional_002darguments_003c_003d_003f"> ¶</a></span></dt>
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<dd><p>Set the <code class="code">LESS_THAN</code>, <code class="code">EQUAL</code>, or <code class="code">NONE</code> comparison result
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values if the number of positional arguments is respectively less than,
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equal to, or greater than <var class="var">expected</var>. The first <var class="var">nreq</var>
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arguments are positional arguments, as are the subsequent arguments that
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are not keywords.
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</p></dd></dl>
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<p>The <code class="code">arguments<=?</code> and <code class="code">positional-arguments<=?</code> instructions
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are used to implement multiple arities, as in <code class="code">case-lambda</code>.
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See <a class="xref" href="Case_002dlambda.html">Case-lambda</a>, for more information. See <a class="xref" href="Branch-Instructions.html">Branch Instructions</a>,
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for more on comparison results.
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</p>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-bind_002dkwargs"><span class="category-def">Instruction: </span><span><strong class="def-name">bind-kwargs</strong> <code class="def-code-arguments">c24:<var class="var">nreq</var> c8:<var class="var">flags</var> c24:<var class="var">nreq-and-opt</var> x8:<var class="var">_</var> c24:<var class="var">ntotal</var> n32:<var class="var">kw-offset</var></code><a class="copiable-link" href="#index-bind_002dkwargs"> ¶</a></span></dt>
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<dd><p><var class="var">flags</var> is a bitfield, whose lowest bit is <var class="var">allow-other-keys</var>,
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second bit is <var class="var">has-rest</var>, and whose following six bits are unused.
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</p>
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<p>Find the last positional argument, and shuffle all the rest above
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<var class="var">ntotal</var>. Initialize the intervening locals to
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<code class="code">SCM_UNDEFINED</code>. Then load the constant at <var class="var">kw-offset</var> words
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from the current <var class="var">ip</var>, and use it and the <var class="var">allow-other-keys</var>
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flag to bind keyword arguments. If <var class="var">has-rest</var>, collect all shuffled
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arguments into a list, and store it in <var class="var">nreq-and-opt</var>. Finally,
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clear the arguments that we shuffled up.
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</p>
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<p>The parsing is driven by a keyword arguments association list, looked up
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using <var class="var">kw-offset</var>. The alist is a list of pairs of the form
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<code class="code">(<var class="var">kw</var> . <var class="var">index</var>)</code>, mapping keyword arguments to their
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local slot indices. Unless <code class="code">allow-other-keys</code> is set, the parser
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will signal an error if an unknown key is found.
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</p>
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<p>A macro-mega-instruction.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-bind_002doptionals"><span class="category-def">Instruction: </span><span><strong class="def-name">bind-optionals</strong> <code class="def-code-arguments">f24:<var class="var">nlocals</var></code><a class="copiable-link" href="#index-bind_002doptionals"> ¶</a></span></dt>
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<dd><p>Expand the current frame to have at least <var class="var">nlocals</var> locals, filling
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in any fresh values with <code class="code">SCM_UNDEFINED</code>. If the frame has more
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than <var class="var">nlocals</var> locals, it is left as it is.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-bind_002drest"><span class="category-def">Instruction: </span><span><strong class="def-name">bind-rest</strong> <code class="def-code-arguments">f24:<var class="var">dst</var></code><a class="copiable-link" href="#index-bind_002drest"> ¶</a></span></dt>
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<dd><p>Collect any arguments at or above <var class="var">dst</var> into a list, and store that
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list at <var class="var">dst</var>.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-alloc_002dframe"><span class="category-def">Instruction: </span><span><strong class="def-name">alloc-frame</strong> <code class="def-code-arguments">c24:<var class="var">nlocals</var></code><a class="copiable-link" href="#index-alloc_002dframe"> ¶</a></span></dt>
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<dd><p>Ensure that there is space on the stack for <var class="var">nlocals</var> local
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variables. The value of any new local is undefined.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-reset_002dframe"><span class="category-def">Instruction: </span><span><strong class="def-name">reset-frame</strong> <code class="def-code-arguments">c24:<var class="var">nlocals</var></code><a class="copiable-link" href="#index-reset_002dframe"> ¶</a></span></dt>
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<dd><p>Like <code class="code">alloc-frame</code>, but doesn’t check that the stack is big enough,
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and doesn’t initialize values to <code class="code">SCM_UNDEFINED</code>. Used to reset
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the frame size to something less than the size that was previously set
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via alloc-frame.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-assert_002dnargs_002dee_002flocals"><span class="category-def">Instruction: </span><span><strong class="def-name">assert-nargs-ee/locals</strong> <code class="def-code-arguments">c12:<var class="var">expected</var> c12:<var class="var">nlocals</var></code><a class="copiable-link" href="#index-assert_002dnargs_002dee_002flocals"> ¶</a></span></dt>
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<dd><p>Equivalent to a sequence of <code class="code">assert-nargs-ee</code> and
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<code class="code">allocate-frame</code>. The number of locals reserved is <var class="var">expected</var>
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+ <var class="var">nlocals</var>.
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</p></dd></dl>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="Shuffling-Instructions.html">Shuffling Instructions</a>, Previous: <a href="Call-and-Return-Instructions.html">Call and Return Instructions</a>, Up: <a href="Instruction-Set.html">Instruction Set</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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