doc/guide/localhost/CallingFromSMLToCFunctionPointer

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  22 <a href="./Home">MLton 20180207</a>
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  26 <h1>CallingFromSMLToCFunctionPointer</h1>
  27 </div>
  28 <div id="content">
  29 <div id="preamble">
  30 <div class="sectionbody">
  31 <div class="paragraph"><p>Just as MLton can <a href="CallingFromSMLToC">directly call C functions</a>, it
  32 is possible to make indirect function calls; that is, function calls
  33 through a function pointer.  MLton extends the syntax of SML to allow
  34 expressions like the following:</p></div>
  35 <div class="listingblock">
  36 <div class="content monospaced">
  37 <pre>_import * : MLton.Pointer.t -&gt; real * char -&gt; int;</pre>
  38 </div></div>
  39 <div class="paragraph"><p>This expression denotes a function of type</p></div>
  40 <div class="listingblock">
  41 <div class="content"><div class="highlight"><pre><span class="n">MLton</span><span class="p">.</span><span class="n">Pointer</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">char</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">int</span><span class="w"></span>
  42 </pre></div></div></div>
  43 <div class="paragraph"><p>whose behavior is implemented by calling the C function at the address
  44 denoted by the <span class="monospaced">MLton.Pointer.t</span> argument, and supplying the C
  45 function two arguments, a <span class="monospaced">double</span> and an <span class="monospaced">int</span>.  The C function
  46 pointer may be obtained, for example, by the dynamic linking loader
  47 (<span class="monospaced">dlopen</span>, <span class="monospaced">dlsym</span>, &#8230;).</p></div>
  48 <div class="paragraph"><p>The general form of an indirect <span class="monospaced">_import</span> expression is:</p></div>
  49 <div class="listingblock">
  50 <div class="content monospaced">
  51 <pre>_import * attr... : cPtrTy -&gt; cFuncTy;</pre>
  52 </div></div>
  53 <div class="paragraph"><p>The type and the semicolon are not optional.</p></div>
  54 </div>
  55 </div>
  56 <div class="sect1">
  57 <h2 id="_example">Example</h2>
  58 <div class="sectionbody">
  59 <div class="paragraph"><p>This example uses <span class="monospaced">dlopen</span> and friends (imported using normal
  60 <span class="monospaced">_import</span>) to dynamically load the math library (<span class="monospaced">libm</span>) and call the
  61 <span class="monospaced">cos</span> function. Suppose <span class="monospaced">iimport.sml</span> contains the following.</p></div>
  62 <div class="listingblock">
  63 <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">DYN_LINK</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  64 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
  65 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">hndl</span><span class="w"></span>
  66 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">mode</span><span class="w"></span>
  67 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">fptr</span><span class="w"></span>
  68
  69 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlopen</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">string</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">mode</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">hndl</span><span class="w"></span>
  70 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlsym</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">hndl</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">string</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">fptr</span><span class="w"></span>
  71 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlclose</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">hndl</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
  72
  73 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">RTLD_LAZY</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">mode</span><span class="w"></span>
  74 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">RTLD_NOW</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">mode</span><span class="w"></span>
  75 <span class="w">   </span><span class="k">end</span><span class="w"></span>
  76
  77 <span class="k">structure</span><span class="w"> </span><span class="n">DynLink</span><span class="w"> </span><span class="p">:&gt;</span><span class="w"> </span><span class="n">DYN_LINK</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  78 <span class="w">   </span><span class="k">struct</span><span class="w"></span>
  79 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">hndl</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">MLton</span><span class="p">.</span><span class="n">Pointer</span><span class="p">.</span><span class="n">t</span><span class="w"></span>
  80 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">mode</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Word32</span><span class="p">.</span><span class="n">word</span><span class="w"></span>
  81 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">fptr</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">MLton</span><span class="p">.</span><span class="n">Pointer</span><span class="p">.</span><span class="n">t</span><span class="w"></span>
  82
  83 <span class="w">      </span><span class="cm">(* These symbols come from a system libray, so the default import scope</span>
  84 <span class="cm">       * of external is correct.</span>
  85 <span class="cm">       *)</span><span class="w"></span>
  86 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlopen</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  87 <span class="w">         </span><span class="p">_</span><span class="n">import</span><span class="w"> </span><span class="s">&quot;dlopen&quot;</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">string</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">mode</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">hndl</span><span class="p">;</span><span class="w"></span>
  88 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlerror</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  89 <span class="w">         </span><span class="p">_</span><span class="n">import</span><span class="w"> </span><span class="s">&quot;dlerror&quot;</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">MLton</span><span class="p">.</span><span class="n">Pointer</span><span class="p">.</span><span class="n">t</span><span class="p">;</span><span class="w"></span>
  90 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlsym</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  91 <span class="w">         </span><span class="p">_</span><span class="n">import</span><span class="w"> </span><span class="s">&quot;dlsym&quot;</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">hndl</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">string</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">fptr</span><span class="p">;</span><span class="w"></span>
  92 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlclose</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  93 <span class="w">         </span><span class="p">_</span><span class="n">import</span><span class="w"> </span><span class="s">&quot;dlclose&quot;</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">hndl</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int32</span><span class="p">.</span><span class="n">int</span><span class="p">;</span><span class="w"></span>
  94
  95 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">RTLD_LAZY</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mh">0wx00001</span><span class="w"> </span><span class="cm">(* Lazy function call binding.  *)</span><span class="w"></span>
  96 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">RTLD_NOW</span><span class="w">  </span><span class="p">=</span><span class="w"> </span><span class="mh">0wx00002</span><span class="w"> </span><span class="cm">(* Immediate function call binding.  *)</span><span class="w"></span>
  97
  98 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlerror</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"></span>
  99 <span class="w">         </span><span class="k">let</span><span class="w"></span>
 100 <span class="w">            </span><span class="k">val</span><span class="w"> </span><span class="n">addr</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">dlerror</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 101 <span class="w">         </span><span class="k">in</span><span class="w"></span>
 102 <span class="w">            </span><span class="k">if</span><span class="w"> </span><span class="n">addr</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">MLton</span><span class="p">.</span><span class="n">Pointer</span><span class="p">.</span><span class="n">null</span><span class="w"></span>
 103 <span class="w">               </span><span class="k">then</span><span class="w"> </span><span class="n">NONE</span><span class="w"></span>
 104 <span class="w">               </span><span class="k">else</span><span class="w"> </span><span class="k">let</span><span class="w"></span>
 105 <span class="w">                       </span><span class="k">fun</span><span class="w"> </span><span class="n">loop</span><span class="w"> </span><span class="p">(</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="n">cs</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 106 <span class="w">                          </span><span class="k">let</span><span class="w"></span>
 107 <span class="w">                             </span><span class="k">val</span><span class="w"> </span><span class="n">w</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">MLton</span><span class="p">.</span><span class="n">Pointer</span><span class="p">.</span><span class="n">getWord8</span><span class="w"> </span><span class="p">(</span><span class="n">addr</span><span class="p">,</span><span class="w"> </span><span class="n">index</span><span class="p">)</span><span class="w"></span>
 108 <span class="w">                             </span><span class="k">val</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Byte</span><span class="p">.</span><span class="n">byteToChar</span><span class="w"> </span><span class="n">w</span><span class="w"></span>
 109 <span class="w">                          </span><span class="k">in</span><span class="w"></span>
 110 <span class="w">                             </span><span class="k">if</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">#</span><span class="s">&quot;</span><span class="se">\000</span><span class="s">&quot;</span><span class="w"></span>
 111 <span class="w">                                </span><span class="k">then</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="p">(</span><span class="n">implode</span><span class="w"> </span><span class="p">(</span><span class="n">rev</span><span class="w"> </span><span class="n">cs</span><span class="p">))</span><span class="w"></span>
 112 <span class="w">                                </span><span class="k">else</span><span class="w"> </span><span class="n">loop</span><span class="w"> </span><span class="p">(</span><span class="n">index</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">c::cs</span><span class="p">)</span><span class="w"></span>
 113 <span class="w">                          </span><span class="k">end</span><span class="w"></span>
 114 <span class="w">                    </span><span class="k">in</span><span class="w"></span>
 115 <span class="w">                       </span><span class="n">loop</span><span class="w"> </span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">[])</span><span class="w"></span>
 116 <span class="w">                    </span><span class="k">end</span><span class="w"></span>
 117 <span class="w">         </span><span class="k">end</span><span class="w"></span>
 118
 119 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlopen</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="p">(</span><span class="n">filename</span><span class="p">,</span><span class="w"> </span><span class="n">mode</span><span class="p">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"></span>
 120 <span class="w">         </span><span class="k">let</span><span class="w"></span>
 121 <span class="w">            </span><span class="k">val</span><span class="w"> </span><span class="n">filename</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">filename</span><span class="w"> </span><span class="n">^</span><span class="w"> </span><span class="s">&quot;</span><span class="se">\000</span><span class="s">&quot;</span><span class="w"></span>
 122 <span class="w">            </span><span class="k">val</span><span class="w"> </span><span class="n">hndl</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">dlopen</span><span class="w"> </span><span class="p">(</span><span class="n">filename</span><span class="p">,</span><span class="w"> </span><span class="n">mode</span><span class="p">)</span><span class="w"></span>
 123 <span class="w">         </span><span class="k">in</span><span class="w"></span>
 124 <span class="w">            </span><span class="k">if</span><span class="w"> </span><span class="n">hndl</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">MLton</span><span class="p">.</span><span class="n">Pointer</span><span class="p">.</span><span class="n">null</span><span class="w"></span>
 125 <span class="w">               </span><span class="k">then</span><span class="w"> </span><span class="k">raise</span><span class="w"> </span><span class="n">Fail</span><span class="w"> </span><span class="p">(</span><span class="k">case</span><span class="w"> </span><span class="n">dlerror</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 126 <span class="w">                                   </span><span class="n">NONE</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;???&quot;</span><span class="w"></span>
 127 <span class="w">                                 </span><span class="p">|</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"></span>
 128 <span class="w">               </span><span class="k">else</span><span class="w"> </span><span class="n">hndl</span><span class="w"></span>
 129 <span class="w">         </span><span class="k">end</span><span class="w"></span>
 130
 131 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlsym</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="p">(</span><span class="n">hndl</span><span class="p">,</span><span class="w"> </span><span class="n">symbol</span><span class="p">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"></span>
 132 <span class="w">         </span><span class="k">let</span><span class="w"></span>
 133 <span class="w">            </span><span class="k">val</span><span class="w"> </span><span class="n">symbol</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">symbol</span><span class="w"> </span><span class="n">^</span><span class="w"> </span><span class="s">&quot;</span><span class="se">\000</span><span class="s">&quot;</span><span class="w"></span>
 134 <span class="w">            </span><span class="k">val</span><span class="w"> </span><span class="n">fptr</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">dlsym</span><span class="w"> </span><span class="p">(</span><span class="n">hndl</span><span class="p">,</span><span class="w"> </span><span class="n">symbol</span><span class="p">)</span><span class="w"></span>
 135 <span class="w">         </span><span class="k">in</span><span class="w"></span>
 136 <span class="w">            </span><span class="k">case</span><span class="w"> </span><span class="n">dlerror</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 137 <span class="w">               </span><span class="n">NONE</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">fptr</span><span class="w"></span>
 138 <span class="w">             </span><span class="p">|</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="k">raise</span><span class="w"> </span><span class="n">Fail</span><span class="w"> </span><span class="n">s</span><span class="w"></span>
 139 <span class="w">         </span><span class="k">end</span><span class="w"></span>
 140
 141 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">dlclose</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="n">hndl</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"></span>
 142 <span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="n">MLton</span><span class="p">.</span><span class="n">Platform</span><span class="p">.</span><span class="n">OS</span><span class="p">.</span><span class="n">host</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">MLton</span><span class="p">.</span><span class="n">Platform</span><span class="p">.</span><span class="n">OS</span><span class="p">.</span><span class="n">Darwin</span><span class="w"></span>
 143 <span class="w">            </span><span class="k">then</span><span class="w"> </span><span class="p">()</span><span class="w">  </span><span class="cm">(* Darwin reports the following error message if you</span>
 144 <span class="cm">                      * try to close a dynamic library.</span>
 145 <span class="cm">                      *   &quot;dynamic libraries cannot be closed&quot;</span>
 146 <span class="cm">                      * So, we disable dlclose on Darwin.</span>
 147 <span class="cm">                      *)</span><span class="w"></span>
 148 <span class="w">         </span><span class="k">else</span><span class="w"></span>
 149 <span class="w">            </span><span class="k">let</span><span class="w"></span>
 150 <span class="w">               </span><span class="k">val</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">dlclose</span><span class="w"> </span><span class="n">hndl</span><span class="w"></span>
 151 <span class="w">            </span><span class="k">in</span><span class="w"></span>
 152 <span class="w">               </span><span class="k">if</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">0</span><span class="w"></span>
 153 <span class="w">                  </span><span class="k">then</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 154 <span class="w">               </span><span class="k">else</span><span class="w"> </span><span class="k">raise</span><span class="w"> </span><span class="n">Fail</span><span class="w"> </span><span class="p">(</span><span class="k">case</span><span class="w"> </span><span class="n">dlerror</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 155 <span class="w">                                   </span><span class="n">NONE</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;???&quot;</span><span class="w"></span>
 156 <span class="w">                                 </span><span class="p">|</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"></span>
 157 <span class="w">            </span><span class="k">end</span><span class="w"></span>
 158 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 159
 160 <span class="k">val</span><span class="w"> </span><span class="n">dll</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 161 <span class="w">   </span><span class="k">let</span><span class="w"></span>
 162 <span class="w">      </span><span class="k">open</span><span class="w"> </span><span class="n">MLton</span><span class="p">.</span><span class="n">Platform</span><span class="p">.</span><span class="n">OS</span><span class="w"></span>
 163 <span class="w">   </span><span class="k">in</span><span class="w"></span>
 164 <span class="w">      </span><span class="k">case</span><span class="w"> </span><span class="n">host</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 165 <span class="w">         </span><span class="n">Cygwin</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;cygwin1.dll&quot;</span><span class="w"></span>
 166 <span class="w">       </span><span class="p">|</span><span class="w"> </span><span class="n">Darwin</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;libm.dylib&quot;</span><span class="w"></span>
 167 <span class="w">       </span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;libm.so&quot;</span><span class="w"></span>
 168 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 169
 170 <span class="k">val</span><span class="w"> </span><span class="n">hndl</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">DynLink</span><span class="p">.</span><span class="n">dlopen</span><span class="w"> </span><span class="p">(</span><span class="n">dll</span><span class="p">,</span><span class="w"> </span><span class="n">DynLink</span><span class="p">.</span><span class="n">RTLD_LAZY</span><span class="p">)</span><span class="w"></span>
 171
 172 <span class="k">local</span><span class="w"></span>
 173 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">double_to_double</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 174 <span class="w">      </span><span class="p">_</span><span class="n">import</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">DynLink</span><span class="p">.</span><span class="n">fptr</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">real</span><span class="p">;</span><span class="w"></span>
 175 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">cos_fptr</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">DynLink</span><span class="p">.</span><span class="n">dlsym</span><span class="w"> </span><span class="p">(</span><span class="n">hndl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;cos&quot;</span><span class="p">)</span><span class="w"></span>
 176 <span class="k">in</span><span class="w"></span>
 177 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">cos</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">double_to_double</span><span class="w"> </span><span class="n">cos_fptr</span><span class="w"></span>
 178 <span class="k">end</span><span class="w"></span>
 179
 180 <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">print</span><span class="w"> </span><span class="p">(</span><span class="n">concat</span><span class="w"> </span><span class="p">[</span><span class="s">&quot;    Math.cos(2.0) = &quot;</span><span class="p">,</span><span class="w"> </span><span class="n">Real</span><span class="p">.</span><span class="n">toString</span><span class="w"> </span><span class="p">(</span><span class="n">Math</span><span class="p">.</span><span class="n">cos</span><span class="w"> </span><span class="mf">2.0</span><span class="p">),</span><span class="w"> </span><span class="s">&quot;</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"></span>
 181 <span class="w">                       </span><span class="s">&quot;libm.so::cos(2.0) = &quot;</span><span class="p">,</span><span class="w"> </span><span class="n">Real</span><span class="p">.</span><span class="n">toString</span><span class="w"> </span><span class="p">(</span><span class="n">cos</span><span class="w"> </span><span class="mf">2.0</span><span class="p">),</span><span class="w"> </span><span class="s">&quot;</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">])</span><span class="w"></span>
 182
 183 <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">DynLink</span><span class="p">.</span><span class="n">dlclose</span><span class="w"> </span><span class="n">hndl</span><span class="w"></span>
 184 </pre></div></div></div>
 185 <div class="paragraph"><p>Compile and run <span class="monospaced">iimport.sml</span>.</p></div>
 186 <div class="listingblock">
 187 <div class="content monospaced">
 188 <pre>% mlton -default-ann 'allowFFI true'    \
 189         -target-link-opt linux -ldl     \
 190         -target-link-opt solaris -ldl   \
 191          iimport.sml
 192 % iimport
 193     Math.cos(2.0) = ~0.416146836547
 194 libm.so::cos(2.0) = ~0.416146836547</pre>
 195 </div></div>
 196 <div class="paragraph"><p>This example also shows the <span class="monospaced">-target-link-opt</span> option, which uses the
 197 switch when linking only when on the specified platform.  Compile with
 198 <span class="monospaced">-verbose 1</span> to see in more detail what&#8217;s being passed to <span class="monospaced">gcc</span>.</p></div>
 199 </div>
 200 </div>
 201 <div class="sect1">
 202 <h2 id="_download">Download</h2>
 203 <div class="sectionbody">
 204 <div class="ulist"><ul>
 205 <li>
 206 <p>
 207 <a href="https://raw.github.com/MLton/mlton/master/doc/examples/ffi/iimport.sml"><span class="monospaced">iimport.sml</span></a>
 208 </p>
 209 </li>
 210 </ul></div>
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