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Revised^6 Report on the Algorithmic Language Scheme
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<a name="node_chap_B"></a>
<h1 class=chapter>
<div class=chapterheading><a href="r6rs-Z-H-2.html#node_toc_node_chap_B">Appendix B</a></div><br>
<a href="r6rs-Z-H-2.html#node_toc_node_chap_B">Sample definitions for derived forms</a></h1>
<p></p>
<p>
This appendix contains sample definitions for some of the keywords
described in this report in terms of simpler forms:</p>
<p>
</p>
<a name="node_sec_Temp_36"></a>
<h4 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_Temp_36"><tt>cond</tt></a></h4>
<p>The <tt>cond</tt> keyword (section&nbsp;<a href="r6rs-Z-H-14.html#node_sec_11.4.5">11.4.5</a>)
could be defined in terms of <tt>if</tt>, <tt>let</tt> and <tt>begin</tt> using <tt>syntax-rules</tt> as follows:</p>
<p>
</p>
<tt>(define-syntax&nbsp;<tt>cond</tt>
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;(else&nbsp;=&gt;)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((cond&nbsp;(else&nbsp;result1&nbsp;result2&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(begin&nbsp;result1&nbsp;result2&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((cond&nbsp;(test&nbsp;=&gt;&nbsp;result))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((temp&nbsp;test))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(if&nbsp;temp&nbsp;(result&nbsp;temp))))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((cond&nbsp;(test&nbsp;=&gt;&nbsp;result)&nbsp;clause1&nbsp;clause2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((temp&nbsp;test))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(if&nbsp;temp</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(result&nbsp;temp)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(cond&nbsp;clause1&nbsp;clause2&nbsp;...))))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((cond&nbsp;(test))&nbsp;test)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((cond&nbsp;(test)&nbsp;clause1&nbsp;clause2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((temp&nbsp;test))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(if&nbsp;temp</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;temp</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(cond&nbsp;clause1&nbsp;clause2&nbsp;...))))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((cond&nbsp;(test&nbsp;result1&nbsp;result2&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(if&nbsp;test&nbsp;(begin&nbsp;result1&nbsp;result2&nbsp;...)))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((cond&nbsp;(test&nbsp;result1&nbsp;result2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;clause1&nbsp;clause2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(if&nbsp;test</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(begin&nbsp;result1&nbsp;result2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(cond&nbsp;clause1&nbsp;clause2&nbsp;...)))))</p>
<p></tt>
</p>
<a name="node_sec_Temp_37"></a>
<h4 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_Temp_37"><tt>case</tt></a></h4>
<p>The <tt>case</tt> keyword (section&nbsp;<a href="r6rs-Z-H-14.html#node_sec_11.4.5">11.4.5</a>) could be defined in terms of <tt>let</tt>, <tt>cond</tt>, and
<tt>memv</tt> (see library chapter&nbsp;on &ldquo;List utilities&rdquo;) using <tt>syntax-rules</tt> as follows:</p>
<p>
</p>
<tt>(define-syntax&nbsp;<tt>case</tt>
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;(else)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((case&nbsp;expr0</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((key&nbsp;...)&nbsp;res1&nbsp;res2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(else&nbsp;else-res1&nbsp;else-res2&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((tmp&nbsp;expr0))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(cond</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((memv&nbsp;tmp&nbsp;'(key&nbsp;...))&nbsp;res1&nbsp;res2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(else&nbsp;else-res1&nbsp;else-res2&nbsp;...))))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((case&nbsp;expr0</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((keya&nbsp;...)&nbsp;res1a&nbsp;res2a&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((keyb&nbsp;...)&nbsp;res1b&nbsp;res2b&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((tmp&nbsp;expr0))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(cond</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((memv&nbsp;tmp&nbsp;'(keya&nbsp;...))&nbsp;res1a&nbsp;res2a&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((memv&nbsp;tmp&nbsp;'(keyb&nbsp;...))&nbsp;res1b&nbsp;res2b&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...)))))</p>
<p></tt></p>
<p>
</p>
<a name="node_sec_Temp_38"></a>
<h4 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_Temp_38"><tt>let*</tt></a></h4>
<p>The <tt>let*</tt> keyword (section&nbsp;<a href="r6rs-Z-H-14.html#node_sec_11.4.6">11.4.6</a>)
could be defined in terms of <tt>let</tt>
using <tt>syntax-rules</tt> as follows:</p>
<p>
</p>
<tt>(define-syntax&nbsp;<tt>let*</tt>
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let*&nbsp;()&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;()&nbsp;body1&nbsp;body2&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let*&nbsp;((name1&nbsp;expr1)&nbsp;(name2&nbsp;expr2)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((name1&nbsp;expr1))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let*&nbsp;((name2&nbsp;expr2)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)))))</p>
<p></tt></p>
<p>
</p>
<a name="node_sec_Temp_39"></a>
<h4 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_Temp_39"><tt>letrec</tt></a></h4>
<p>The <tt>letrec</tt> keyword (section&nbsp;<a href="r6rs-Z-H-14.html#node_sec_11.4.6">11.4.6</a>)
could be defined approximately in terms of <tt>let</tt>
and <tt>set!</tt> using <tt>syntax-rules</tt>, using a helper
to generate the temporary variables
needed to hold the values before the assignments are made,
as follows:</p>
<p>
</p>
<tt>(define-syntax&nbsp;<tt>letrec</tt>
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((letrec&nbsp;()&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;()&nbsp;body1&nbsp;body2&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((letrec&nbsp;((var&nbsp;init)&nbsp;...)&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(letrec-helper</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(var&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((var&nbsp;init)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...))))</p>
<p class=nopadding></p>
<p class=nopadding>(define-syntax&nbsp;letrec-helper</p>
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((letrec-helper</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(temp&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((var&nbsp;init)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((var&nbsp;&lt;undefined&gt;)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((temp&nbsp;init)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(set!&nbsp;var&nbsp;temp)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;()&nbsp;body1&nbsp;body2&nbsp;...)))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((letrec-helper</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(x&nbsp;y&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(temp&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((var&nbsp;init)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(letrec-helper</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(y&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(newtemp&nbsp;temp&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((var&nbsp;init)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...))))</p>
<p></tt></p>
<p>
The syntax <tt>&lt;undefined&gt;</tt> represents an expression that
returns something that, when stored in a location, causes an exception
with condition type <tt>&amp;assertion</tt> to
be raised if an attempt to read from or write to the location occurs before the
assignments generated by the <tt>letrec</tt> transformation take place.
(No such expression is defined in Scheme.)</p>
<p>
A simpler definition using <tt>syntax-case</tt> and <tt>generate-temporaries</tt> is given in library
chapter&nbsp;on &ldquo;<tt>syntax-case</tt>&rdquo;.</p>
<p>
</p>
<a name="node_sec_Temp_40"></a>
<h4 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_Temp_40"><tt>letrec*</tt></a></h4>
<p>The <tt>letrec*</tt> keyword could be defined approximately in terms of
<tt>let</tt> and <tt>set!</tt> using <tt>syntax-rules</tt> as follows:</p>
<p>
</p>
<tt>(define-syntax&nbsp;<tt>letrec*</tt>
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((letrec*&nbsp;((var1&nbsp;init1)&nbsp;...)&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((var1&nbsp;&lt;undefined&gt;)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(set!&nbsp;var1&nbsp;init1)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;()&nbsp;body1&nbsp;body2&nbsp;...)))))</p>
<p></tt></p>
<p>
The syntax <tt>&lt;undefined&gt;</tt> is as in the definition of <tt>letrec</tt> above.</p>
<p>
</p>
<a name="node_sec_Temp_41"></a>
<h4 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_Temp_41"><tt>let-values</tt></a></h4>
<p>The following definition of <tt>let-values</tt> (section&nbsp;<a href="r6rs-Z-H-14.html#node_sec_11.4.6">11.4.6</a>)
using <tt>syntax-rules</tt>
employs a pair of helpers to
create temporary names for the formals.</p>
<p>
</p>
<tt>(define-syntax&nbsp;let-values
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let-values&nbsp;(binding&nbsp;...)&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let-values-helper1</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(binding&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...))))</p>
<p class=nopadding></p>
<p class=nopadding>(define-syntax&nbsp;let-values-helper1</p>
<p class=nopadding>&nbsp;&nbsp;;;&nbsp;map&nbsp;over&nbsp;the&nbsp;bindings</p>
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let-values</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((id&nbsp;temp)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;((id&nbsp;temp)&nbsp;...)&nbsp;body1&nbsp;body2&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let-values</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;assocs</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((formals1&nbsp;expr1)&nbsp;(formals2&nbsp;expr2)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let-values-helper2</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;formals1</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;expr1</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;assocs</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((formals2&nbsp;expr2)&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...))))</p>
<p class=nopadding></p>
<p class=nopadding>(define-syntax&nbsp;let-values-helper2</p>
<p class=nopadding>&nbsp;&nbsp;;;&nbsp;create&nbsp;temporaries&nbsp;for&nbsp;the&nbsp;formals</p>
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let-values-helper2</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;temp-formals</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;expr1</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;assocs</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;bindings</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(call-with-values</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(lambda&nbsp;()&nbsp;expr1)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(lambda&nbsp;temp-formals</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let-values-helper1</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;assocs</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;bindings</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...))))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let-values-helper2</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(first&nbsp;.&nbsp;rest)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(temp&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;expr1</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(assoc&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;bindings</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let-values-helper2</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rest</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(temp&nbsp;...&nbsp;newtemp)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;expr1</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(assoc&nbsp;...&nbsp;(first&nbsp;newtemp))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;bindings</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let-values-helper2</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rest-formal</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(temp&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;expr1</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(assoc&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;bindings</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(call-with-values</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(lambda&nbsp;()&nbsp;expr1)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(lambda&nbsp;(temp&nbsp;...&nbsp;.&nbsp;newtemp)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let-values-helper1</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(assoc&nbsp;...&nbsp;(rest-formal&nbsp;newtemp))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;bindings</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...))))))</p>
<p></tt></p>
<p>
</p>
<a name="node_sec_Temp_42"></a>
<h4 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_Temp_42"><tt>let*-values</tt></a></h4>
<p>The following macro defines <tt>let*-values</tt> in terms of <tt>let</tt>
and <tt>let-values</tt> using <tt>syntax-rules</tt>:</p>
<p>
</p>
<tt>(define-syntax&nbsp;let*-values
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let*-values&nbsp;()&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let&nbsp;()&nbsp;body1&nbsp;body2&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let*-values&nbsp;(binding1&nbsp;binding2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let-values&nbsp;(binding1)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(let*-values&nbsp;(binding2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)))))</p>
<p></tt></p>
<p>
</p>
<a name="node_sec_Temp_43"></a>
<h4 class=section><a href="r6rs-Z-H-2.html#node_toc_node_sec_Temp_43"><tt>let</tt></a></h4>
<p>The <tt>let</tt> keyword could be defined in terms of <tt>lambda</tt> and <tt>letrec</tt>
using <tt>syntax-rules</tt> as
follows:</p>
<p>
</p>
<tt>(define-syntax&nbsp;<tt>let</tt>
<p class=nopadding>&nbsp;&nbsp;(syntax-rules&nbsp;()</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let&nbsp;((name&nbsp;val)&nbsp;...)&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((lambda&nbsp;(name&nbsp;...)&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;val&nbsp;...))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;((let&nbsp;tag&nbsp;((name&nbsp;val)&nbsp;...)&nbsp;body1&nbsp;body2&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((letrec&nbsp;((tag&nbsp;(lambda&nbsp;(name&nbsp;...)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;body1&nbsp;body2&nbsp;...)))</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;tag)</p>
<p class=nopadding>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;val&nbsp;...))))</p>
<p></tt></p>
<p>
</p>
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