- <sect1 id="sec-ffi">
- <title>The foreign interface</title>
-
- <para>The foreign interface consists of the following components:</para>
-
- <itemizedlist>
- <listitem>
- <para>The Foreign Function Interface language specification
- (included in this manual, in <xref linkend="ffi">).
- You must use the <option>-fglasgow-exts</option> command-line option
- to make GHC understand the <literal>foreign</literal> declarations
- defined by the FFI.</para>
- </listitem>
-
- <listitem>
- <para>The <literal>Foreign</literal> module (see <xref
- linkend="sec-Foreign">) collects together several interfaces
- which are useful in specifying foreign language
- interfaces, including the following:</para>
-
- <itemizedlist>
- <listitem>
- <para>The <literal>ForeignObj</literal> module (see <xref
- linkend="sec-ForeignObj">), for managing pointers from
- Haskell into the outside world.</para>
- </listitem>
-
- <listitem>
- <para>The <literal>StablePtr</literal> module (see <xref
- linkend="sec-stable-pointers">), for managing pointers
- into Haskell from the outside world.</para>
- </listitem>
-
- <listitem>
- <para>The <literal>CTypes</literal> module (see <xref
- linkend="sec-CTypes">) gives Haskell equivalents for the
- standard C datatypes, for use in making Haskell bindings
- to existing C libraries.</para>
- </listitem>
-
- <listitem>
- <para>The <literal>CTypesISO</literal> module (see <xref
- linkend="sec-CTypesISO">) gives Haskell equivalents for C
- types defined by the ISO C standard.</para>
- </listitem>
-
- <listitem>
- <para>The <literal>Storable</literal> library, for
- primitive marshalling of data types between Haskell and
- the foreign language.</para>
- </listitem>
- </itemizedlist>
-
- </listitem>
- </itemizedlist>
-
-<para>The following sections also give some hints and tips on the use
-of the foreign function interface in GHC.</para>
-
-<sect2 id="glasgow-foreign-headers">
-<title>Using function headers
-</title>
-
-<para>
-<indexterm><primary>C calls, function headers</primary></indexterm>
-</para>
-
-<para>
-When generating C (using the <option>-fvia-C</option> directive), one can assist the
-C compiler in detecting type errors by using the <option>-#include</option> directive
-(<xref linkend="options-C-compiler">) to provide <filename>.h</filename> files containing function headers.
-</para>
-
-<para>
-For example,
-</para>
-
-<para>
-
-<programlisting>
-#include "HsFFI.h"
-
-void initialiseEFS (HsInt size);
-HsInt terminateEFS (void);
-HsForeignObj emptyEFS(void);
-HsForeignObj updateEFS (HsForeignObj a, HsInt i, HsInt x);
-HsInt lookupEFS (HsForeignObj a, HsInt i);
-</programlisting>
-</para>
-
- <para>The types <literal>HsInt</literal>,
- <literal>HsForeignObj</literal> etc. are described in <xref
- linkend="sec-mapping-table">.</para>
-
- <para>Note that this approach is only
- <emphasis>essential</emphasis> for returning
- <literal>float</literal>s (or if <literal>sizeof(int) !=
- sizeof(int *)</literal> on your architecture) but is a Good
- Thing for anyone who cares about writing solid code. You're
- crazy not to do it.</para>
-
-</sect2>
-
-</sect1>
-