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<title>Unicode - MLton Standard ML Compiler (SML Compiler)</title>
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      Unicode
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The current release of MLton does not support Unicode.  We are working on adding support. 
    <ul>

    <li>
<p>
 <tt>WideChar</tt> structure. 
</p>
</li>
    <li>
<p>
 UTF-8 encoded source files. 
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<p>
There is no real support for Unicode in the <a href="DefinitionOfStandardML">Definition</a>; there are only a few throw-away sentences along the lines of "ASCII must be a subset of the character set in programs". 
</p>
<p>
Neither is there real support for Unicode in the <a href="BasisLibrary">Basis Library</a>. The general consensus (which includes the opinions of the editors of the Basis Library) is that the <tt>WideChar</tt> structure is insufficient for the purposes of Unicode.  There is no <tt>LargeChar</tt> structure, which in itself is a deficiency, since a programmer can not program against the largest supported character size. 
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<p>
MLton has some preliminary support for 16 and 32 bit characters and strings.  It is even possible to include arbitrary Unicode characters in 32-bit strings using a <tt>\Uxxxxxxxx</tt> escape sequence.  (This longer escape sequence is a minor extension over the Definition which only allows <tt>\uxxxx</tt>.)  This is by no means completely satisfactory in terms of support for Unicode, but it is what is currently available. 
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<p>
There are periodic flurries of questions and discussion about Unicode in MLton/SML.  In December 2004, there was a discussion that led to some seemingly sound design decisions.  The discussion started at: 
</p>

            <ul>

   <a href="http://mlton.org/pipermail/mlton/2004-December/026396.html"><img src="moin-www.png" alt="[WWW]" height="11" width="11">http://mlton.org/pipermail/mlton/2004-December/026396.html</a> 
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<p>
There is a good summary of points at: 
</p>

            <ul>

   <a href="http://mlton.org/pipermail/mlton/2004-December/026440.html"><img src="moin-www.png" alt="[WWW]" height="11" width="11">http://mlton.org/pipermail/mlton/2004-December/026440.html</a> 
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<p>
In November 2005, there was a followup discussion and the beginning of some coding. 
</p>

        <ul>

  <a href="http://mlton.org/pipermail/mlton/2005-November/028300.html"><img src="moin-www.png" alt="[WWW]" height="11" width="11">http://mlton.org/pipermail/mlton/2005-November/028300.html</a> 
        </ul>


<p>
We are optimistic that support will appear in the next MLton release. 
</p>
<h2 id="head-a4bc8bf5caf54b18cea9f58e83dd4acb488deb17">Also see</h2>
<p>
The <a href="fxp">fxp</a> XML parser has some support for dealing with Unicode documents. 
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Last edited on 2007-08-15 22:07:35 by <span title="fenrir.uchicago.edu"><a href="MatthewFluet">MatthewFluet</a></span>.
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