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Import Upstream version 20180207
[hcoop/debian/mlton.git] / doc / guide / localhost / CallingFromSMLToC
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22<a href="./Home">MLton 20180207</a>\r
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25<div id="header">\r
26<h1>CallingFromSMLToC</h1>\r
27</div>\r
28<div id="content">\r
29<div id="preamble">\r
30<div class="sectionbody">\r
31<div class="paragraph"><p>MLton&#8217;s <a href="ForeignFunctionInterface">ForeignFunctionInterface</a> allows an SML program to <em>import</em>\r
32C functions. Suppose you would like to import from C a function with\r
33the following prototype:</p></div>\r
34<div class="listingblock">\r
35<div class="content"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">foo</span> <span class="p">(</span><span class="kt">double</span> <span class="n">d</span><span class="p">,</span> <span class="kt">char</span> <span class="n">c</span><span class="p">);</span>\r
36</pre></div></div></div>\r
37<div class="paragraph"><p>MLton extends the syntax of SML to allow expressions like the following:</p></div>\r
38<div class="listingblock">\r
39<div class="content monospaced">\r
40<pre>_import "foo": real * char -&gt; int;</pre>\r
41</div></div>\r
42<div class="paragraph"><p>This expression denotes a function of type <span class="monospaced">real * char -&gt; int</span> whose\r
43behavior is implemented by calling the C function whose name is <span class="monospaced">foo</span>.\r
44Thinking in terms of C, imagine that there are C variables <span class="monospaced">d</span> of type\r
45<span class="monospaced">double</span>, <span class="monospaced">c</span> of type <span class="monospaced">unsigned char</span>, and <span class="monospaced">i</span> of type <span class="monospaced">int</span>. Then,\r
46the C statement <span class="monospaced">i = foo (d, c)</span> is executed and <span class="monospaced">i</span> is returned.</p></div>\r
47<div class="paragraph"><p>The general form of an <span class="monospaced">_import</span> expression is:</p></div>\r
48<div class="listingblock">\r
49<div class="content monospaced">\r
50<pre>_import "C function name" attr... : cFuncTy;</pre>\r
51</div></div>\r
52<div class="paragraph"><p>The type and the semicolon are not optional.</p></div>\r
53<div class="paragraph"><p>The function name is followed by a (possibly empty) sequence of\r
54attributes, analogous to C <span class="monospaced">__attribute__</span> specifiers.</p></div>\r
55</div>\r
56</div>\r
57<div class="sect1">\r
58<h2 id="_example">Example</h2>\r
59<div class="sectionbody">\r
60<div class="paragraph"><p><span class="monospaced">import.sml</span> imports the C function <span class="monospaced">ffi</span> and the C variable <span class="monospaced">FFI_INT</span>\r
61as follows.</p></div>\r
62<div class="listingblock">\r
63<div class="content"><div class="highlight"><pre><span class="cm">(* main.sml *)</span><span class="w"></span>\r
64\r
65<span class="cm">(* Declare ffi to be implemented by calling the C function ffi. *)</span><span class="w"></span>\r
66<span class="k">val</span><span class="w"> </span><span class="n">ffi</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">_</span><span class="n">import</span><span class="w"> </span><span class="s">&quot;ffi&quot;</span><span class="w"> </span><span class="n">public</span><span class="p">:</span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="n">array</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">char</span><span class="w"> </span><span class="n">ref</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">char</span><span class="p">;</span><span class="w"></span>\r
67<span class="k">open</span><span class="w"> </span><span class="n">Array</span><span class="w"></span>\r
68\r
69<span class="k">val</span><span class="w"> </span><span class="n">size</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">10</span><span class="w"></span>\r
70<span class="k">val</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">tabulate</span><span class="w"> </span><span class="p">(</span><span class="n">size</span><span class="p">,</span><span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="n">i</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">i</span><span class="p">)</span><span class="w"></span>\r
71<span class="k">val</span><span class="w"> </span><span class="n">ri</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="mi">0</span><span class="w"></span>\r
72<span class="k">val</span><span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="p">#</span><span class="s">&quot;0&quot;</span><span class="w"></span>\r
73<span class="k">val</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">17</span><span class="w"></span>\r
74\r
75<span class="cm">(* Call the C function *)</span><span class="w"></span>\r
76<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">ffi</span><span class="w"> </span><span class="p">(</span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">Array</span><span class="p">.</span><span class="n">length</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">ri</span><span class="p">,</span><span class="w"> </span><span class="n">rc</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"></span>\r
77\r
78<span class="cm">(* FFI_INT is declared as public in ffi-import.c *)</span><span class="w"></span>\r
79<span class="k">val</span><span class="w"> </span><span class="p">(</span><span class="n">nGet</span><span class="p">,</span><span class="w"> </span><span class="n">nSet</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">_</span><span class="n">symbol</span><span class="w"> </span><span class="s">&quot;FFI_INT&quot;</span><span class="w"> </span><span class="n">public</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">int</span><span class="p">)</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="p">(</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="p">);</span><span class="w"></span>\r
80\r
81<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="n">Int</span><span class="p">.</span><span class="n">toString</span><span class="w"> </span><span class="p">(</span><span class="n">nGet</span><span class="w"> </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>\r
82\r
83<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>\r
84<span class="w"> </span><span class="n">print</span><span class="w"> </span><span class="p">(</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;c&quot;</span><span class="w"> </span><span class="k">andalso</span><span class="w"> </span><span class="n">!ri</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">45</span><span class="w"> </span><span class="k">andalso</span><span class="w"> </span><span class="n">!rc</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">c</span><span class="w"></span>\r
85<span class="w"> </span><span class="k">then</span><span class="w"> </span><span class="s">&quot;success</span><span class="se">\n</span><span class="s">&quot;</span><span class="w"></span>\r
86<span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="s">&quot;fail</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">)</span><span class="w"></span>\r
87</pre></div></div></div>\r
88<div class="paragraph"><p><span class="monospaced">ffi-import.c</span> is</p></div>\r
89<div class="listingblock">\r
90<div class="content"><div class="highlight"><pre><span class="cp">#include</span> <span class="cpf">&quot;export.h&quot;</span><span class="cp"></span>\r
91\r
92<span class="n">Int32</span> <span class="n">FFI_INT</span> <span class="o">=</span> <span class="mi">13</span><span class="p">;</span>\r
93<span class="n">Word32</span> <span class="n">FFI_WORD</span> <span class="o">=</span> <span class="mh">0xFF</span><span class="p">;</span>\r
94<span class="n">Bool</span> <span class="n">FFI_BOOL</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>\r
95<span class="n">Real64</span> <span class="n">FFI_REAL</span> <span class="o">=</span> <span class="mf">3.14159</span><span class="p">;</span>\r
96\r
97<span class="n">Char8</span> <span class="nf">ffi</span> <span class="p">(</span><span class="n">Pointer</span> <span class="n">a1</span><span class="p">,</span> <span class="n">Int32</span> <span class="n">a1len</span><span class="p">,</span> <span class="n">Pointer</span> <span class="n">a2</span><span class="p">,</span> <span class="n">Pointer</span> <span class="n">a3</span><span class="p">,</span> <span class="n">Int32</span> <span class="n">n</span><span class="p">)</span> <span class="p">{</span>\r
98 <span class="kt">double</span> <span class="o">*</span><span class="n">ds</span> <span class="o">=</span> <span class="p">(</span><span class="kt">double</span><span class="o">*</span><span class="p">)</span><span class="n">a1</span><span class="p">;</span>\r
99 <span class="kt">int</span> <span class="o">*</span><span class="n">pi</span> <span class="o">=</span> <span class="p">(</span><span class="kt">int</span><span class="o">*</span><span class="p">)</span><span class="n">a2</span><span class="p">;</span>\r
100 <span class="kt">char</span> <span class="o">*</span><span class="n">pc</span> <span class="o">=</span> <span class="p">(</span><span class="kt">char</span><span class="o">*</span><span class="p">)</span><span class="n">a3</span><span class="p">;</span>\r
101 <span class="kt">int</span> <span class="n">i</span><span class="p">;</span>\r
102 <span class="kt">double</span> <span class="n">sum</span><span class="p">;</span>\r
103\r
104 <span class="n">sum</span> <span class="o">=</span> <span class="mf">0.0</span><span class="p">;</span>\r
105 <span class="k">for</span> <span class="p">(</span><span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o">&lt;</span> <span class="n">a1len</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>\r
106 <span class="n">sum</span> <span class="o">+=</span> <span class="n">ds</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>\r
107 <span class="n">ds</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">+=</span> <span class="n">n</span><span class="p">;</span>\r
108 <span class="p">}</span>\r
109 <span class="o">*</span><span class="n">pi</span> <span class="o">=</span> <span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="n">sum</span><span class="p">;</span>\r
110 <span class="o">*</span><span class="n">pc</span> <span class="o">=</span> <span class="sc">&#39;c&#39;</span><span class="p">;</span>\r
111 <span class="k">return</span> <span class="sc">&#39;c&#39;</span><span class="p">;</span>\r
112<span class="p">}</span>\r
113</pre></div></div></div>\r
114<div class="paragraph"><p>Compile and run the program.</p></div>\r
115<div class="listingblock">\r
116<div class="content monospaced">\r
117<pre>% mlton -default-ann 'allowFFI true' -export-header export.h import.sml ffi-import.c\r
118% ./import\r
11913\r
120success</pre>\r
121</div></div>\r
122</div>\r
123</div>\r
124<div class="sect1">\r
125<h2 id="_download">Download</h2>\r
126<div class="sectionbody">\r
127<div class="ulist"><ul>\r
128<li>\r
129<p>\r
130<a href="https://raw.github.com/MLton/mlton/master/doc/examples/ffi/import.sml"><span class="monospaced">import.sml</span></a>\r
131</p>\r
132</li>\r
133<li>\r
134<p>\r
135<a href="https://raw.github.com/MLton/mlton/master/doc/examples/ffi/ffi-import.c"><span class="monospaced">ffi-import.c</span></a>\r
136</p>\r
137</li>\r
138</ul></div>\r
139</div>\r
140</div>\r
141<div class="sect1">\r
142<h2 id="_next_steps">Next Steps</h2>\r
143<div class="sectionbody">\r
144<div class="ulist"><ul>\r
145<li>\r
146<p>\r
147<a href="CallingFromSMLToCFunctionPointer">CallingFromSMLToCFunctionPointer</a>\r
148</p>\r
149</li>\r
150</ul></div>\r
151</div>\r
152</div>\r
153</div>\r
154<div id="footnotes"><hr></div>\r
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