doc/guide/localhost/ShowBasis

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  22 <a href="./Home">MLton 20180207</a>
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  26 <h1>ShowBasis</h1>
  27 </div>
  28 <div id="content">
  29 <div id="preamble">
  30 <div class="sectionbody">
  31 <div class="paragraph"><p>MLton has a flag, <span class="monospaced">-show-basis &lt;file&gt;</span>, that causes MLton to pretty
  32 print to <em>file</em> the basis defined by the input program.  For example,
  33 if <span class="monospaced">foo.sml</span> contains</p></div>
  34 <div class="listingblock">
  35 <div class="content"><div class="highlight"><pre><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="mi">1</span><span class="w"></span>
  36 </pre></div></div></div>
  37 <div class="paragraph"><p>then <span class="monospaced">mlton -show-basis foo.basis foo.sml</span> will create <span class="monospaced">foo.basis</span>
  38 with the following contents.</p></div>
  39 <div class="listingblock">
  40 <div class="content monospaced">
  41 <pre>val f: int -&gt; int</pre>
  42 </div></div>
  43 <div class="paragraph"><p>If you only want to see the basis and do not wish to compile the
  44 program, you can call MLton with <span class="monospaced">-stop tc</span>.</p></div>
  45 </div>
  46 </div>
  47 <div class="sect1">
  48 <h2 id="_displaying_signatures">Displaying signatures</h2>
  49 <div class="sectionbody">
  50 <div class="paragraph"><p>When displaying signatures, MLton prefixes types defined in the
  51 signature them with <span class="monospaced">_sig.</span> to distinguish them from types defined in the
  52 environment.  For example,</p></div>
  53 <div class="listingblock">
  54 <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  55 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
  56 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  57 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
  58 <span class="w">   </span><span class="k">end</span><span class="w"></span>
  59 </pre></div></div></div>
  60 <div class="paragraph"><p>is displayed as</p></div>
  61 <div class="listingblock">
  62 <div class="content monospaced">
  63 <pre>signature SIG =
  64    sig
  65       type t
  66       val x: _sig.t * int -&gt; unit
  67    end</pre>
  68 </div></div>
  69 <div class="paragraph"><p>Notice that <span class="monospaced">int</span> occurs without the <span class="monospaced">_sig.</span> prefix.</p></div>
  70 <div class="paragraph"><p>MLton also uses a canonical name for each type in the signature, and
  71 that name is used everywhere for that type, no matter what the input
  72 signature looked like.  For example:</p></div>
  73 <div class="listingblock">
  74 <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  75 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
  76 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  77 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  78 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  79 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">y</span><span class="p">:</span><span class="w"> </span><span class="n">u</span><span class="w"></span>
  80 <span class="w">   </span><span class="k">end</span><span class="w"></span>
  81 </pre></div></div></div>
  82 <div class="paragraph"><p>is displayed as</p></div>
  83 <div class="listingblock">
  84 <div class="content monospaced">
  85 <pre>signature SIG =
  86    sig
  87       type t
  88       type u = _sig.t
  89       val x: _sig.t
  90       val y: _sig.t
  91    end</pre>
  92 </div></div>
  93 <div class="paragraph"><p>Canonical names are always relative to the "top" of the signature,
  94 even when used in nested substructures.  For example:</p></div>
  95 <div class="listingblock">
  96 <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  97 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
  98 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  99 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">w</span><span class="p">:</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 100 <span class="w">      </span><span class="k">structure</span><span class="w"> </span><span class="n">U</span><span class="p">:</span><span class="w"></span>
 101 <span class="w">         </span><span class="k">sig</span><span class="w"></span>
 102 <span class="w">            </span><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"></span>
 103 <span class="w">            </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 104 <span class="w">            </span><span class="k">val</span><span class="w"> </span><span class="n">y</span><span class="p">:</span><span class="w"> </span><span class="n">u</span><span class="w"></span>
 105 <span class="w">         </span><span class="k">end</span><span class="w"></span>
 106 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">z</span><span class="p">:</span><span class="w"> </span><span class="n">U</span><span class="p">.</span><span class="n">u</span><span class="w"></span>
 107 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 108 </pre></div></div></div>
 109 <div class="paragraph"><p>is displayed as</p></div>
 110 <div class="listingblock">
 111 <div class="content monospaced">
 112 <pre>signature S =
 113    sig
 114       type t
 115       val w: _sig.t
 116       val z: _sig.U.u
 117       structure U:
 118          sig
 119             type u
 120             val x: _sig.t
 121             val y: _sig.U.u
 122          end
 123    end</pre>
 124 </div></div>
 125 </div>
 126 </div>
 127 <div class="sect1">
 128 <h2 id="_displaying_structures">Displaying structures</h2>
 129 <div class="sectionbody">
 130 <div class="paragraph"><p>When displaying structures, MLton uses signature constraints wherever
 131 possible, combined with <span class="monospaced">where type</span> clauses to specify the meanings
 132 of the types defined within the signature.  For example:</p></div>
 133 <div class="listingblock">
 134 <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 135 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
 136 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 137 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 138 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 139 <span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="p">:</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 140 <span class="w">   </span><span class="k">struct</span><span class="w"></span>
 141 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"></span>
 142 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">13</span><span class="w"></span>
 143 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 144 <span class="k">structure</span><span class="w"> </span><span class="n">S2</span><span class="p">:&gt;</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">S</span><span class="w"></span>
 145 </pre></div></div></div>
 146 <div class="paragraph"><p>is displayed as</p></div>
 147 <div class="listingblock">
 148 <div class="content monospaced">
 149 <pre>signature SIG =
 150    sig
 151       type t
 152       val x: _sig.t
 153    end
 154 structure S: SIG
 155              where type t = int
 156 structure S2: SIG
 157               where type t = S2.t</pre>
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