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<tr><td align="center" bgcolor="#8381de"><div class="skribetitle"><strong><big><big><big>R5Rs<br/>Scheme Revised(5) Report on the Algorithmic Language Scheme -- Notes</big></big></big></strong></div><center>
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<tr><td valign="top" align="left"></td><td colspan="4" width="100%"><a href="r5rs-1.html#Summary">Summary</a></td></tr>
<tr><td valign="top" align="left"></td><td colspan="4" width="100%"><a href="r5rs-2.html#Introduction">Introduction</a></td></tr>
<tr><td valign="top" align="left"></td><td colspan="4" width="100%"><a href="r5rs-3.html#Table-of-contents">Table of contents</a></td></tr>
<tr><td valign="top" align="left">1</td><td colspan="4" width="100%"><a href="r5rs-4.html#Overview-of-Scheme">Overview of Scheme</a></td></tr>
<tr><td valign="top" align="left">2</td><td colspan="4" width="100%"><a href="r5rs-5.html#Lexical-conventions">Lexical conventions</a></td></tr>
<tr><td valign="top" align="left">3</td><td colspan="4" width="100%"><a href="r5rs-6.html#Basic-concepts">Basic concepts</a></td></tr>
<tr><td valign="top" align="left">4</td><td colspan="4" width="100%"><a href="r5rs-7.html#Expressions">Expressions</a></td></tr>
<tr><td valign="top" align="left">5</td><td colspan="4" width="100%"><a href="r5rs-8.html#Program-structure">Program structure</a></td></tr>
<tr><td valign="top" align="left">6</td><td colspan="4" width="100%"><a href="r5rs-9.html#Standard-procedures">Standard procedures</a></td></tr>
<tr><td valign="top" align="left">7</td><td colspan="4" width="100%"><a href="r5rs-10.html#Formal-syntax-and-semantics">Formal syntax and semantics</a></td></tr>
<tr><td valign="top" align="left">8</td><td colspan="4" width="100%"><a href="r5rs-11.html#Concepts">Concepts</a></td></tr>
<tr><td valign="top" align="left">9</td><td colspan="4" width="100%"><a href="r5rs-12.html#Variables-and-Procedures">Variables and Procedures</a></td></tr>
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<div class="section-atitle"><table width="100%"><tr><td bgcolor="#dedeff"><h3><font color="black">Language changes</font>
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<a name="Language-changes" class="mark"></a>
This section enumerates the changes that have been made to Scheme since
the ``Revised^4 report'' [R4RS] was published.<br/><br/><ul class="itemize" id='itemize7051'
><li>The report is now a superset of the IEEE standard for Scheme
[IEEEScheme]: implementations that conform to the report will
also conform to the standard. This required the following changes:<br/><br/><ul class="itemize" id='itemize7031'
><li>The empty list is now required to count as true.<br/><br/></li>
<li>The classification of features as essential or inessential has been
removed. There are now three classes of built-in procedures: primitive,
library, and optional. The optional procedures are <samp id='samp7019'
>load</samp>,
<samp id='samp7020'
>with-input-from-file</samp>, <samp id='samp7021'
>with-output-to-file</samp>,
<samp id='samp7022'
>transcript-on</samp>, <samp id='samp7023'
>transcript-off</samp>, and
<samp id='samp7024'
>interaction-environment</samp>,
and <samp id='samp7025'
>-</samp> and <samp id='samp7026'
>/</samp> with more than two arguments.
None of these are in the IEEE standard.<br/><br/></li>
<li>Programs are allowed to redefine built-in procedures. Doing so
will not change the behavior of other built-in procedures.<br/><br/></li>
</ul>
</li>
<li><em id='emph7033'
>Port</em> has been added to the list of disjoint types.<br/><br/></li>
<li>The macro appendix has been removed. High-level macros are now part
of the main body of the report. The rewrite rules for derived expressions
have been replaced with macro definitions. There are no reserved identifiers.<br/><br/></li>
<li><samp id='samp7038'
>Syntax-rules</samp> now allows vector patterns.<br/><br/></li>
<li>Multiple-value returns, <samp id='samp7041'
>eval</samp>, and <samp id='samp7042'
>dynamic-wind</samp> have
been added.<br/><br/></li>
<li>The calls that are required to be implemented in a properly tail-recursive
fashion are defined explicitly.<br/><br/></li>
<li>`<samp id='samp7047'
>@</samp>' can be used within identifiers. `<samp id='samp7048'
>|</samp>' is reserved
for possible future extensions.<br/><br/></li>
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