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<title>Defunctorize - MLton Standard ML Compiler (SML Compiler)</title>
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      Defunctorize
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Defunctorize is a translation pass from the <a href="CoreML">CoreML</a> <a href="IntermediateLanguage">IntermediateLanguage</a> to the <a href="XML">XML</a> <a href="IntermediateLanguage">IntermediateLanguage</a>. <h2 id="head-55f8ebc805e65b5b71ddafdae390e3be2bcd69af">Description</h2>
<p>
This pass converts a <a href="CoreML">CoreML</a> program to an <a href="XML">XML</a> program by performing: 
</p>

    <ul>

    <li>
<p>
 linearization 
</p>
</li>
    <li>
<p>
 <a href="MatchCompile">MatchCompile</a> 
</p>
</li>
    <li>
<p>
 polymorphic <tt>val</tt> dec expansion 
</p>
</li>
    <li>
<p>
 <tt>datatype</tt> lifting (to the top-level) 
</p>
</li>

    </ul>


<h2 id="head-8781d615fd77be9578225c40ac67b9471394cced">Implementation</h2>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/defunctorize/defunctorize.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">defunctorize.sig</a> <a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/defunctorize/defunctorize.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">defunctorize.fun</a> <h2 id="head-35ec00231a68203708e39f0e2cc10b50c6bf62de">Details and Notes</h2>
<p>
This pass is grossly misnamed and does not perform defunctorization. 
</p>
<h4 id="head-98226d2b13506c91181c040abfc6bb115b088746">Datatype Lifting</h4>
<p>
This pass moves all <tt>datatype</tt> declarations to the top level. 
</p>
<p>
<a href="StandardML">Standard ML</a> <tt>datatype</tt> declarations can contain type variables that are not bound in the declaration itself.  For example, the following program is valid. 
<pre class=code>
<B><FONT COLOR="#A020F0">fun</FONT></B> <B><FONT COLOR="#228B22">'a</FONT></B> f (x: 'a) =
   <B><FONT COLOR="#A020F0">let</FONT></B>
      <B><FONT COLOR="#A020F0">datatype</FONT></B><B><FONT COLOR="#228B22"> 'b t </FONT></B>=<B><FONT COLOR="#228B22"> <FONT COLOR="#B8860B">T</FONT> <B><FONT COLOR="#A020F0">of</FONT></B> 'a * 'b
      </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> y: int t = T (x, <B><FONT COLOR="#5F9EA0">1</FONT></B>)
   <B><FONT COLOR="#A020F0">in</FONT></B> 
      <B><FONT COLOR="#5F9EA0">13</FONT></B>
   <B><FONT COLOR="#A020F0">end</FONT></B>
</PRE>
 
</p>
<p>
Unfortunately, the <tt>datatype</tt> declaration can not be immediately moved to the top level, because that would leave <tt>'a</tt> free. 
<pre>datatype 'b t = T of 'a * 'b
fun 'a f (x: 'a) =
   let 
      val y: int t = T (x, 1)
   in 
      13
   end
</pre>In order to safely move <tt>datatype</tt>s, this pass must close them, as well as add any free type variables as extra arguments to the type constructor.  For example, the above program would be translated to the following. 
<pre>datatype ('a, 'b) t = T of 'a * 'b
fun 'a f (x: 'a) = 
   let 
      val y: ('a, int) t = T (x, 1)
   in 
      13
   end
</pre>
</p>
<h2 id="head-53d5b31ac8da1ff19a82453fd040f529e241f6cd">Historical Notes</h2>
<p>
The Defunctorize pass originally eliminated  <a href="StandardML">Standard ML</a> functors by duplicating their body at each application.  These duties have been adopted by the <a href="Elaborate">Elaborate</a> pass. 
</p>
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Last edited on 2007-07-08 22:40:00 by <span title="c-71-57-91-146.hsd1.il.comcast.net"><a href="MatthewFluet">MatthewFluet</a></span>.
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