108 lines
4.8 KiB
HTML
108 lines
4.8 KiB
HTML
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<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!--
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Generated from r6rs.tex by tex2page, v 20100828
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(running on MzScheme 4.2.4, :unix),
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(c) Dorai Sitaram,
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http://evalwhen.com/tex2page/index.html
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-->
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>
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Revised^6 Report on the Algorithmic Language Scheme
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</title>
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<link rel="stylesheet" type="text/css" href="r6rs-Z-S.css" title=default>
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<meta name=robots content="index,follow">
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</head>
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<body>
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<div id=slidecontent>
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<div align=right class=navigation>[Go to <span><a href="r6rs.html">first</a>, <a href="r6rs-Z-H-10.html">previous</a></span><span>, <a href="r6rs-Z-H-12.html">next</a></span> page<span>; </span><span><a href="r6rs-Z-H-2.html#node_toc_start">contents</a></span><span><span>; </span><a href="r6rs-Z-H-21.html#node_index_start">index</a></span>]</div>
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<p></p>
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<a name="node_chap_8"></a>
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<h1 class=chapter>
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<div class=chapterheading><a href="r6rs-Z-H-2.html#node_toc_node_chap_8">Chapter 8</a></div><br>
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<a href="r6rs-Z-H-2.html#node_toc_node_chap_8">Top-level programs</a></h1>
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<p></p>
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<p>
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A <a name="node_idx_290"></a><em>top-level program</em> specifies an entry point for defining and running
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a Scheme program. A top-level program specifies a set of libraries to import and
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code to run. Through the imported libraries, whether directly or through the
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transitive closure of importing, a top-level program defines a complete Scheme
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program.</p>
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<p>
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</p>
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<a name="node_sec_8.1"></a>
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<h2 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_8.1">8.1 Top-level program syntax</a></h2>
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<p></p>
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<p>
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A top-level program is a delimited piece of text, typically a file, that
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has the following form:
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</p>
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<tt><import form> <top-level body><p></tt>
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An <import form> has the following form:
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</p>
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<tt>(import <import spec> <tt>...</tt>)<p></tt>
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A <top-level body> has the following form:
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</p>
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<tt><top-level body form> <tt>...</tt><p></tt>
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A <top-level body form> is either a <definition> or an
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<expression>.</p>
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<p>
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The <import form> is identical to the import clause in
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libraries (see section <a href="r6rs-Z-H-10.html#node_sec_7.1">7.1</a>),
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and specifies a set of libraries to import. A <top-level
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body> is like a <library body> (see
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section <a href="r6rs-Z-H-10.html#node_sec_7.1">7.1</a>), except that
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definitions and expressions may occur in any order. Thus, the syntax
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specified by <top-level body form> refers to the result of macro
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expansion.</p>
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<p>
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When uses of <tt>begin</tt>, <tt>let-syntax</tt>, or <tt>letrec-syntax</tt>
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from the <tt>(rnrs base (6))</tt> library
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occur in a top-level body prior to the first
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expression, they are spliced into the body; see section <a href="r6rs-Z-H-14.html#node_sec_11.4.7">11.4.7</a>.
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Some or all of the body, including portions wrapped in <tt>begin</tt>,
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<tt>let-syntax</tt>, or <tt>letrec-syntax</tt>
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forms, may be specified by a syntactic abstraction
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(see section <a href="r6rs-Z-H-12.html#node_sec_9.2">9.2</a>).</p>
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<p>
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</p>
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<a name="node_sec_8.2"></a>
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<h2 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_8.2">8.2 Top-level program semantics</a></h2>
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<p>A top-level program is executed by treating the program similarly to a library, and
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evaluating its definitions and expressions.
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The semantics of a top-level body may be roughly explained by
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a simple translation into a library body:
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Each <expression> that appears before a
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definition in
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the top-level body is converted into a dummy definition
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</p>
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<tt>(define <variable> (begin <expression> <unspecified>))<p></tt>
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where <variable> is a fresh identifier and <unspecified>
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is a side-effect-free expression returning an unspecified value.
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(It is generally impossible to determine which forms are
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definitions and expressions without concurrently expanding the body, so
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the actual translation is somewhat more complicated; see
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chapter <a href="r6rs-Z-H-13.html#node_chap_10">10</a>.)</p>
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<p>
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On platforms that support it, a top-level program may access its command line
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by calling the <tt>command-line</tt> procedure (see library
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section on “Command-line access and exit values”).</p>
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<p>
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</p>
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<p></p>
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<div class=smallskip></div>
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<p style="margin-top: 0pt; margin-bottom: 0pt">
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<div align=right class=navigation>[Go to <span><a href="r6rs.html">first</a>, <a href="r6rs-Z-H-10.html">previous</a></span><span>, <a href="r6rs-Z-H-12.html">next</a></span> page<span>; </span><span><a href="r6rs-Z-H-2.html#node_toc_start">contents</a></span><span><span>; </span><a href="r6rs-Z-H-21.html#node_index_start">index</a></span>]</div>
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</p>
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<p></p>
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</div>
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</body>
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</html>
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