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MLton has a flag, <tt>-show-basis&nbsp;</tt> <em>file</em>, that causes MLton to pretty print to <em>file</em> the basis defined by the input program.  For example, if <tt>foo.sml</tt> contains 
<pre class=code>
<B><FONT COLOR="#A020F0">fun</FONT></B> f x = x + <B><FONT COLOR="#5F9EA0">1</FONT></B>
</PRE>
<p>
 then <tt>mlton&nbsp;-show-basis&nbsp;foo.basis&nbsp;foo.sml</tt> will create <tt>foo.basis</tt> with the following contents. 
<pre>val f: int -&gt; int
</pre>If you only want to see the basis and do not wish to compile the program, you can call MLton with <tt>-stop&nbsp;tc</tt>. 
</p>
<h2 id="head-f68fa1f6c99a6935aec560696799f2414d893d6f">Displaying signatures</h2>
<p>
When displaying signatures, MLton prefixes types defined in the signature them with <tt>?.</tt> to distinguish them from types defined in the environment.  For example,  
<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
   <B><FONT COLOR="#0000FF">sig</FONT></B>
      <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
      </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> x: t * int -&gt; unit
   <B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 is displayed as 
<pre>signature SIG = 
   sig
      type t = ?.t
      val x: (?.t * int) -&gt; unit
   end
</pre>Notice that <tt>int</tt> occurs without the <tt>?.</tt> prefix. 
</p>
<p>
MLton also uses a canonical name for each type in the signature, and that name is used everywhere for that type, no matter what the input signature looked like.  For example: 
<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
   <B><FONT COLOR="#0000FF">sig</FONT></B>
      <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
      </FONT></B><B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> t
      </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> x: t
      <B><FONT COLOR="#A020F0">val</FONT></B> y: u
   <B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 is displayed as 
<pre>signature SIG = 
   sig
      type t = ?.t
      type u = ?.t
      val x: ?.t
      val y: ?.t
   end
</pre>
</p>
<p>
Canonical names are always relative to the "top" of the signature, even when used in nested substructures.  For example: 
<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> S =
   <B><FONT COLOR="#0000FF">sig</FONT></B>
      <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
      </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> w: t
      <B><FONT COLOR="#0000FF">structure</FONT></B> U:
         <B><FONT COLOR="#0000FF">sig</FONT></B>
            <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u
            </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> x: t
            <B><FONT COLOR="#A020F0">val</FONT></B> y: u
         <B><FONT COLOR="#0000FF">end</FONT></B>
      <B><FONT COLOR="#A020F0">val</FONT></B> z: U.u
   <B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 is displayed as 
<pre>signature S = 
   sig
      type t = ?.t
      val w: ?.t
      val z: ?.U.u
      structure U:
         sig
            type u = ?.U.u
            val x: ?.t
            val y: ?.U.u
         end
   end
</pre>
</p>
<h2 id="head-c6c2aa845cc7b36e66f2c4aa799b976c96116919">Displaying structures</h2>
<p>
When displaying structures, MLton uses signature constraints wherever possible, combined with <tt>where&nbsp;type</tt> clauses to specify the meanings of the types defined within the signature. 
</p>

<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
   <B><FONT COLOR="#0000FF">sig</FONT></B>
      <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
      </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> x: t
   <B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">structure</FONT></B> S: SIG =
   <B><FONT COLOR="#0000FF">struct</FONT></B>
      <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> int
      </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> x = <B><FONT COLOR="#5F9EA0">13</FONT></B>
   <B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">structure</FONT></B> S2:&gt; SIG = S
</PRE>
<p>
 is displayed as 
<pre>structure S: SIG
             where type t = int
structure S2: SIG
              where type t = S2.t
signature SIG = 
   sig
      type t = ?.t
      val x: ?.t
   end
</pre>
</p>
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<p>
<hr>
Last edited on 2005-12-02 01:48:03 by <span title="ppp-71-139-183-221.dsl.snfc21.pacbell.net"><a href="StephenWeeks">StephenWeeks</a></span>.
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