ghc/docs/users_guide/phases.sgml

   1   <sect1 id="options-phases">
   2     <title>Options related to a particular phase</title>
   3
   4     <sect2 id="replacing-phases">
   5       <title>Replacing the program for one or more phases</title>
   6       <indexterm><primary>phases, changing</primary></indexterm>
   7
   8       <para>You may specify that a different program be used for one
   9       of the phases of the compilation system, in place of whatever
  10       the <Command>ghc</Command> has wired into it.  For example, you
  11       might want to try a different assembler.  The following options
  12       allow you to change the external program used for a given
  13       compilation phase:</para>
  14
  15       <variablelist>
  16         <varlistentry>
  17           <term><option>-pgmL</option> <replaceable>cmd</replaceable></term>
  18           <indexterm><primary><option>-pgmL</option></primary>
  19           </indexterm>
  20           <listitem>
  21             <para>Use <replaceable>cmd</replaceable> as the literate
  22             pre-processor.</para>
  23           </listitem>
  24         </varlistentry>
  25
  26         <varlistentry>
  27           <term><option>-pgmP</option> <replaceable>cmd</replaceable></term>
  28           <indexterm><primary><option>-pgmP</option></primary>
  29           </indexterm>
  30           <listitem>
  31             <para>Use <replaceable>cmd</replaceable> as the C
  32             pre-processor (with <option>-cpp</option> only).</para>
  33           </listitem>
  34         </varlistentry>
  35
  36         <varlistentry>
  37           <term><option>-pgmc</option> <replaceable>cmd</replaceable></term>
  38           <indexterm><primary><option>-pgmc</option></primary>
  39           </indexterm>
  40           <listitem>
  41             <para>Use <replaceable>cmd</replaceable> as the C
  42             compiler.</para>
  43           </listitem>
  44         </varlistentry>
  45
  46         <varlistentry>
  47           <term><option>-pgma</option> <replaceable>cmd</replaceable></term>
  48           <indexterm><primary><option>-pgma</option></primary>
  49           </indexterm>
  50           <listitem>
  51             <para>Use <replaceable>cmd</replaceable> as the
  52             assembler.</para>
  53           </listitem>
  54         </varlistentry>
  55
  56         <varlistentry>
  57           <term><option>-pgml</option> <replaceable>cmd</replaceable></term>
  58           <indexterm><primary><option>-pgml</option></primary>
  59           </indexterm>
  60           <listitem>
  61             <para>Use <replaceable>cmd</replaceable> as the
  62             linker.</para>
  63           </listitem>
  64         </varlistentry>
  65
  66         <varlistentry>
  67           <term><option>-pgmdll</option> <replaceable>cmd</replaceable></term>
  68           <indexterm><primary><option>-pgmdll</option></primary>
  69           </indexterm>
  70           <listitem>
  71             <para>Use <replaceable>cmd</replaceable> as the DLL
  72             generator.</para>
  73           </listitem>
  74         </varlistentry>
  75
  76         <varlistentry>
  77           <term><option>-pgmdep</option> <replaceable>cmd</replaceable></term>
  78           <indexterm><primary><option>-pgmdep</option></primary>
  79           </indexterm>
  80           <listitem>
  81             <para>Use <replaceable>cmd</replaceable> as the dependency
  82             generator.</para>
  83           </listitem>
  84         </varlistentry>
  85
  86         <varlistentry>
  87           <term><option>-pgmF</option> <replaceable>cmd</replaceable></term>
  88           <indexterm><primary><option>-pgmF</option></primary>
  89           </indexterm>
  90           <listitem>
  91             <para>Use <replaceable>cmd</replaceable> as the
  92             pre-processor (with <option>-F</option> only).</para>
  93           </listitem>
  94         </varlistentry>
  95       </variablelist>
  96
  97     </sect2>
  98
  99     <sect2 id="forcing-options-through">
 100       <title>Forcing options to a particular phase</title>
 101       <indexterm><primary>forcing GHC-phase options</primary></indexterm>
 102
 103       <para>Options can be forced through to a particlar compilation
 104       phase, using the following flags:</para>
 105
 106       <variablelist>
 107         <varlistentry>
 108           <term><option>-optL</option> <replaceable>option</replaceable></term>
 109           <indexterm><primary><option>-optL</option></primary>
 110           </indexterm>
 111           <listitem>
 112             <para>Pass <replaceable>option</replaceable> to the
 113             literate pre-processor</para>
 114           </listitem>
 115         </varlistentry>
 116         <varlistentry>
 117           <term><option>-optP</option>  <replaceable>option</replaceable></term>
 118           <indexterm><primary><option>-optP</option></primary>
 119           </indexterm>
 120           <listitem>
 121             <para>Pass <replaceable>option</replaceable> to CPP (makes
 122             sense only if <option>-cpp</option> is also on).</para>
 123           </listitem>
 124         </varlistentry>
 125         <varlistentry>
 126           <term><option>-optF</option> <replaceable>option</replaceable></term>
 127           <indexterm><primary><option>-optF</option></primary>
 128           </indexterm>
 129           <listitem>
 130             <para>Pass <replaceable>option</replaceable> to the
 131             custom pre-processor (see <xref linkend="pre-processor">).</para>
 132           </listitem>
 133         </varlistentry>
 134         <varlistentry>
 135           <term><option>-optc</option>  <replaceable>option</replaceable></term>
 136           <indexterm><primary><option>-optc</option></primary>
 137           </indexterm>
 138           <listitem>
 139             <para>Pass <replaceable>option</replaceable> to the C compiler.</para>
 140           </listitem>
 141         </varlistentry>
 142         <varlistentry>
 143           <term><option>-opta</option>  <replaceable>option</replaceable></term>
 144           <indexterm><primary><option>-opta</option></primary>
 145           </indexterm>
 146           <listitem>
 147             <para>Pass <replaceable>option</replaceable> to the assembler.</para>
 148           </listitem>
 149         </varlistentry>
 150         <varlistentry>
 151           <term><option>-optl</option>  <replaceable>option</replaceable></term>
 152           <indexterm><primary><option>-optl</option></primary>
 153           </indexterm>
 154           <listitem>
 155             <para>Pass <replaceable>option</replaceable> to the linker.</para>
 156           </listitem>
 157         </varlistentry>
 158         <varlistentry>
 159           <term><option>-optdll</option>  <replaceable>option</replaceable></term>
 160           <indexterm><primary><option>-optdll</option></primary>
 161           </indexterm>
 162           <listitem>
 163             <para>Pass <replaceable>option</replaceable> to the DLL generator.</para>
 164           </listitem>
 165         </varlistentry>
 166         <varlistentry>
 167           <term><option>-optdep</option>  <replaceable>option</replaceable></term>
 168           <indexterm><primary><option>-optdep</option></primary>
 169           </indexterm>
 170           <listitem>
 171             <para>Pass <replaceable>option</replaceable> to the
 172             dependency generator.</para>
 173           </listitem>
 174         </varlistentry>
 175       </variablelist>
 176
 177       <para>So, for example, to force an <option>-Ewurble</option>
 178       option to the assembler, you would tell the driver
 179       <option>-opta-Ewurble</option> (the dash before the E is
 180       required).</para>
 181
 182       <para>GHC is itself a Haskell program, so if you need to pass
 183       options directly to GHC's runtime system you can enclose them in
 184       <literal>+RTS ... -RTS</literal> (see <xref
 185       linkend="runtime-control">).</para>
 186
 187     </sect2>
 188
 189     <sect2 id="c-pre-processor">
 190       <title>Options affecting the C pre-processor</title>
 191
 192       <indexterm><primary>pre-processing: cpp</primary></indexterm>
 193       <indexterm><primary>C pre-processor options</primary></indexterm>
 194       <indexterm><primary>cpp, pre-processing with</primary></indexterm>
 195
 196       <variablelist>
 197
 198         <varlistentry>
 199           <term><option>-cpp</option></term>
 200           <indexterm><primary><option>-cpp</option></primary></indexterm>
 201           <listitem>
 202             <para>The C pre-processor <command>cpp</command> is run
 203             over your Haskell code only if the <option>-cpp</option>
 204             option <indexterm><primary>-cpp
 205             option</primary></indexterm> is given.  Unless you are
 206             building a large system with significant doses of
 207             conditional compilation, you really shouldn't need
 208             it.</para>
 209           </listitem>
 210         </varlistentry>
 211
 212         <varlistentry>
 213           <term><option>-D</option><replaceable>symbol</replaceable><optional>=<replaceable>value</replaceable></optional></term>
 214           <indexterm><primary><option>-D</option></primary></indexterm>
 215           <listitem>
 216             <para>Define macro <replaceable>symbol</replaceable> in the
 217             usual way.  NB: does <emphasis>not</emphasis> affect
 218             <option>-D</option> macros passed to the C&nbsp;compiler
 219             when compiling via C!  For those, use the
 220             <option>-optc-Dfoo</option> hack&hellip; (see <xref
 221             linkend="forcing-options-through">).</para>
 222           </listitem>
 223         </varlistentry>
 224
 225         <varlistentry>
 226           <term><option>-U</option><replaceable>symbol</replaceable></term>
 227           <indexterm><primary><option>-U</option></primary></indexterm>
 228           <listitem>
 229             <para> Undefine macro <replaceable>symbol</replaceable> in the
 230             usual way.</para>
 231           </listitem>
 232         </varlistentry>
 233
 234         <varlistentry>
 235           <term><option>-I</option><replaceable>dir</replaceable></term>
 236           <indexterm><primary><option>-I</option></primary></indexterm>
 237           <listitem>
 238             <para> Specify a directory in which to look for
 239             <literal>&num;include</literal> files, in the usual C
 240             way.</para>
 241           </listitem>
 242         </varlistentry>
 243       </variablelist>
 244
 245       <para>The GHC driver pre-defines several macros when processing
 246       Haskell source code (<filename>.hs</filename> or
 247       <filename>.lhs</filename> files):</para>
 248
 249       <variablelist>
 250
 251         <varlistentry>
 252           <term><constant>&lowbar;&lowbar;HASKELL98&lowbar;&lowbar;</constant></term>
 253           <indexterm><primary><literal>&lowbar;&lowbar;HASKELL98&lowbar;&lowbar;</literal></primary></indexterm>
 254           <listitem>
 255             <para>If defined, this means that GHC supports the
 256             language defined by the Haskell 98 report.</para>
 257           </listitem>
 258         </varlistentry>
 259
 260         <varlistentry>
 261           <term><constant>&lowbar;&lowbar;HASKELL&lowbar;&lowbar;=98</constant></term>
 262           <indexterm><primary><constant>&lowbar;&lowbar;HASKELL&lowbar;&lowbar;=98</constant></primary></indexterm>
 263           <listitem>
 264             <para>In GHC 4.04 and later, the
 265             <constant>&lowbar;&lowbar;HASKELL&lowbar;&lowbar;</constant>
 266             macro is defined as having the value
 267             <constant>98</constant>.</para>
 268           </listitem>
 269         </varlistentry>
 270
 271         <varlistentry>
 272           <term><constant>&lowbar;&lowbar;HASKELL1&lowbar;&lowbar;</constant></term>
 273           <indexterm><primary><constant>&lowbar;&lowbar;HASKELL1&lowbar;&lowbar;
 274           </constant></primary></indexterm>
 275           <listitem>
 276             <para>If defined to <replaceable>n</replaceable>, that
 277             means GHC supports the Haskell language defined in the
 278             Haskell report version <emphasis>1.n</emphasis>.
 279             Currently 5.  This macro is deprecated, and will probably
 280             disappear in future versions.</para>
 281           </listitem>
 282         </varlistentry>
 283
 284         <varlistentry>
 285           <term><constant>&lowbar;&lowbar;GLASGOW&lowbar;HASKELL&lowbar;&lowbar;</constant></term>
 286           <indexterm><primary><constant>&lowbar;&lowbar;GLASGOW&lowbar;HASKELL&lowbar;&lowbar;</constant></primary></indexterm>
 287           <listitem>
 288             <para>For version <replaceable>n</replaceable> of the GHC
 289             system, this will be <literal>&num;define</literal>d to
 290             <replaceable>100n</replaceable>.  For example, for version
 291             5.00, it is 500.</para>
 292
 293             <para>With any luck,
 294             <constant>&lowbar;&lowbar;GLASGOW&lowbar;HASKELL&lowbar;&lowbar;</constant>
 295             will be undefined in all other implementations that
 296             support C-style pre-processing.</para>
 297
 298             <para>(For reference: the comparable symbols for other
 299             systems are:
 300             <constant>&lowbar;&lowbar;HUGS&lowbar;&lowbar;</constant>
 301             for Hugs,
 302             <constant>&lowbar;&lowbar;NHC&lowbar;&lowbar;</constant>
 303             for nhc98, and
 304             <constant>&lowbar;&lowbar;HBC&lowbar;&lowbar;</constant>
 305             for Chalmers.)</para>
 306
 307             <para>NB. This macro is set when pre-processing both
 308             Haskell source and C source, including the C source
 309             generated from a Haskell module
 310             (i.e. <filename>.hs</filename>, <filename>.lhs</filename>,
 311             <filename>.c</filename> and <filename>.hc</filename>
 312             files).</para>
 313           </listitem>
 314         </varlistentry>
 315
 316         <varlistentry>
 317           <term><constant>&lowbar;&lowbar;CONCURRENT&lowbar;HASKELL&lowbar;&lowbar;</constant></term>
 318           <indexterm><primary><constant>&lowbar;&lowbar;CONCURRENT&lowbar;HASKELL&lowbar;&lowbar;</constant></primary></indexterm>
 319           <listitem>
 320             <para>This symbol is defined when pre-processing Haskell
 321             (input) and pre-processing C (GHC output).  Since GHC from
 322             verion 4.00 now supports concurrent haskell by default,
 323             this symbol is always defined.</para>
 324           </listitem>
 325         </varlistentry>
 326
 327         <varlistentry>
 328           <term><constant>&lowbar;&lowbar;PARALLEL&lowbar;HASKELL&lowbar;&lowbar;</constant></term>
 329           <indexterm><primary><constant>&lowbar;&lowbar;PARALLEL&lowbar;HASKELL&lowbar;&lowbar;</constant></primary></indexterm>
 330           <listitem>
 331             <para>Only defined when <option>-parallel</option> is in
 332             use!  This symbol is defined when pre-processing Haskell
 333             (input) and pre-processing C (GHC output).</para>
 334           </listitem>
 335         </varlistentry>
 336       </variablelist>
 337
 338       <sect3 id="cpp-string-gaps">
 339         <title>CPP and string gaps</title>
 340
 341         <para>A small word of warning: <option>-cpp</option> is not
 342         friendly to &ldquo;string gaps&rdquo;.<indexterm><primary>-cpp
 343         vs string gaps</primary></indexterm><indexterm><primary>string
 344         gaps vs -cpp</primary></indexterm>.  In other words, strings
 345         such as the following:</para>
 346
 347 <ProgramListing>
 348 strmod = "\
 349 \ p \
 350 \ "
 351 </ProgramListing>
 352
 353         <para>don't work with <option>-cpp</option>;
 354         <filename>/usr/bin/cpp</filename> elides the backslash-newline
 355         pairs.</para>
 356
 357         <para>However, it appears that if you add a space at the end
 358         of the line, then <command>cpp</command> (at least GNU
 359         <command>cpp</command> and possibly other
 360         <command>cpp</command>s) leaves the backslash-space pairs
 361         alone and the string gap works as expected.</para>
 362       </sect3>
 363     </sect2>
 364
 365     <sect2 id="pre-processor">
 366       <title>Options affecting a Haskell pre-processor</title>
 367
 368       <indexterm><primary>pre-processing: custom</primary></indexterm>
 369       <indexterm><primary>Pre-processor options</primary></indexterm>
 370
 371       <variablelist>
 372         <varlistentry>
 373           <term><option>-F</option></term>
 374           <indexterm><primary><option>-F</option></primary></indexterm>
 375           <listitem>
 376             <para>A custom pre-processor is run over your Haskell
 377             source file only if the <option>-F</option> option
 378             <indexterm><primary>-F</primary></indexterm> is given.
 379             </para>
 380             <para>
 381             Running a custom pre-processor at compile-time is in some
 382             settings appropriate and useful. The <option>-F</option>
 383             option lets you run a pre-processor as part of the overall
 384             GHC compilation pipeline, which has the advantage over
 385             running a Haskell pre-processor separately in that it
 386             works in interpreted mode and you can continue to take
 387             reap the benefits of GHC's recompilation checker.
 388             </para>
 389             <para>
 390             The pre-processor is run just before the Haskell
 391             compiler proper processes the Haskell input, but after
 392             the literate markup has been stripped away and (possibly)
 393             the C pre-processor has washed the Haskell input.
 394             </para>
 395           </listitem>
 396         </varlistentry>
 397         <varlistentry>
 398           <term><option>-pgmF</option> <replaceable>cmd</replaceable></term>
 399           <indexterm><primary><option>-pgmF</option> <replaceable>cmd</replaceable></primary></indexterm>
 400           <listitem>
 401             <para>Use <replaceable>cmd</replaceable> as the Haskell
 402           pre-processor. When invoked, the
 403           <replaceable>cmd</replaceable> pre-processor is given at
 404           least three arguments on its command-line: the first
 405           argument is the name of the original source file, the second
 406           is the name of the file holding the input, and the third is
 407           the name of the file where
 408           <replaceable>cmd</replaceable> should write its output to.
 409           </para>
 410           <para>Additional arguments to the
 411           <replaceable>cmd</replaceable> pre-processor can be passed
 412           in using the <option>-optF</option> option. These are fed to
 413           <replaceable>cmd</replaceable> on the command line after the
 414           three standard input and output arguments.
 415         </para>
 416           </listitem>
 417         </varlistentry>
 418       </variablelist>
 419     </sect2>
 420
 421     <sect2 id="options-C-compiler">
 422       <title>Options affecting the C compiler (if applicable)</title>
 423
 424       <indexterm><primary>include-file options</primary></indexterm>
 425       <indexterm><primary>C compiler options</primary></indexterm>
 426       <indexterm><primary>GCC options</primary></indexterm>
 427
 428       <para>If you are compiling with lots of foreign calls, you may
 429       need to tell the C&nbsp;compiler about some
 430       <literal>&num;include</literal> files.  There is no real pretty
 431       way to do this, but you can use this hack from the
 432       command-line:</para>
 433
 434 <Screen>
 435 % ghc -c '-#include &lt;X/Xlib.h&gt;' Xstuff.lhs
 436 </Screen>
 437
 438     </sect2>
 439
 440     <sect2 id="options-codegen">
 441       <title>Options affecting code generation</title>
 442
 443       <variablelist>
 444         <varlistentry>
 445           <term><option>-fasm</option></term>
 446           <indexterm><primary><option>-fasm</option></primary></indexterm>
 447           <listitem>
 448             <para>Use GHC's native code generator rather than
 449             compiling via C.  This will compile faster (up to twice as
 450             fast), but may produce code that is slightly slower than
 451             compiling via C.  <option>-fasm</option> is the default
 452             when optimisation is off (see <xref
 453             linkend="options-optimise">).</para>
 454           </listitem>
 455         </varlistentry>
 456
 457         <varlistentry>
 458           <term><option>-fvia-C</option></term>
 459           <indexterm><primary><option>-fvia-C</option></primary>
 460           </indexterm>
 461           <listitem>
 462             <para>Compile via C instead of using the native code
 463             generator.  This is default for optimised compilations,
 464             and on architectures for which GHC doesn't have a native
 465             code generator.</para>
 466           </listitem>
 467         </varlistentry>
 468
 469         <varlistentry>
 470           <term><option>-fno-code</option></term>
 471           <indexterm><primary><option>-fno-code</option></primary>
 472           </indexterm>
 473           <listitem>
 474             <para>Omit code generation (and all later phases)
 475             altogether.  Might be of some use if you just want to see
 476             dumps of the intermediate compilation phases.</para>
 477           </listitem>
 478         </varlistentry>
 479       </variablelist>
 480     </sect2>
 481
 482     <sect2 id="options-linker">
 483       <title>Options affecting linking</title>
 484
 485       <indexterm><primary>linker options</primary></indexterm>
 486       <indexterm><primary>ld options</primary></indexterm>
 487
 488
 489       <para>GHC has to link your code with various libraries, possibly
 490       including: user-supplied, GHC-supplied, and system-supplied
 491       (<option>-lm</option> math library, for example).</para>
 492
 493       <variablelist>
 494
 495         <varlistentry>
 496           <term><option>-l</option><replaceable>lib</replaceable></term>
 497           <indexterm><primary><option>-l</option></primary></indexterm>
 498           <listitem>
 499             <para>Link in the <replaceable>lib</replaceable> library.
 500             On Unix systems, this will be in a file called
 501             <filename>lib<replaceable>lib</replaceable>.a</filename>
 502             or
 503             <filename>lib<replaceable>lib</replaceable>.so</filename>
 504             which resides somewhere on the library directories path.</para>
 505
 506             <para>Because of the sad state of most UNIX linkers, the
 507             order of such options does matter.  If library
 508             <replaceable>foo</replaceable> requires library
 509             <replaceable>bar</replaceable>, then in general
 510             <option>-l</option><replaceable>foo</replaceable> should
 511             come <emphasis>before</emphasis>
 512             <option>-l</option><replaceable>bar</replaceable> on the
 513             command line.</para>
 514
 515             <para>There's one other gotcha to bear in mind when using
 516             external libraries: if the library contains a
 517             <literal>main()</literal> function, then this will be
 518             linked in preference to GHC's own
 519             <literal>main()</literal> function
 520             (eg. <literal>libf2c</literal> and <literal>libl</literal>
 521             have their own <literal>main()</literal>s).  This is
 522             because GHC's <literal>main()</literal> comes from the
 523             <literal>HSrts</literal> library, which is normally
 524             included <emphasis>after</emphasis> all the other
 525             libraries on the linker's command line.  To force GHC's
 526             <literal>main()</literal> to be used in preference to any
 527             other <literal>main()</literal>s from external libraries,
 528             just add the option <option>-lHSrts</option> before any
 529             other libraries on the command line.</para>
 530           </listitem>
 531         </varlistentry>
 532
 533         <varlistentry>
 534           <term><option>-no-link</option></term>
 535           <indexterm>
 536             <primary><option>-no-link</option></primary>
 537           </indexterm>
 538           <listitem>
 539             <para>Omit the link step.  This flag can be useful if you
 540             want to avoid linking in <option>--make</option> mode,
 541             where linking is normally done automatically if the program
 542             contains a <literal>Main</literal> module.</para>
 543           </listitem>
 544         </varlistentry>
 545
 546         <varlistentry>
 547           <term><option>-package</option> <replaceable>name</replaceable></term>
 548           <indexterm><primary><option>-package</option></primary></indexterm>
 549           <listitem>
 550             <para>If you are using a Haskell &ldquo;package&rdquo;
 551             (see <xref linkend="packages">), don't forget to add the
 552             relevant <option>-package</option> option when linking the
 553             program too: it will cause the appropriate libraries to be
 554             linked in with the program.  Forgetting the
 555             <option>-package</option> option will likely result in
 556             several pages of link errors.</para>
 557           </listitem>
 558         </varlistentry>
 559
 560         <varlistentry>
 561           <term><option>-framework</option> <replaceable>name</replaceable></term>
 562           <indexterm><primary><option>-framework</option></primary></indexterm>
 563           <listitem>
 564             <para>On Darwin/MacOS X only, link in the framework <replaceable>name</replaceable>.
 565             This option corresponds to the <option>-framework</option> option for Apple's Linker.
 566             Please note that frameworks and packages are two different things - frameworks don't
 567             contain any haskell code. Rather, they are Apple's way of packaging shared libraries.
 568             To link to Apple's &ldquo;Carbon&rdquo; API, for example, you'd use
 569             <option>-framework Carbon</option>.
 570             </para>
 571           </listitem>
 572         </varlistentry>
 573
 574         <varlistentry>
 575           <term><option>-L</option><replaceable>dir</replaceable></term>
 576           <indexterm><primary><option>-L</option></primary></indexterm>
 577           <listitem>
 578             <para>Where to find user-supplied libraries&hellip;
 579             Prepend the directory <replaceable>dir</replaceable> to
 580             the library directories path.</para>
 581           </listitem>
 582         </varlistentry>
 583
 584         <varlistentry>
 585           <term><option>-framework-path</option><replaceable>dir</replaceable></term>
 586           <indexterm><primary><option>-framework-path</option></primary></indexterm>
 587           <listitem>
 588             <para>On Darwin/MacOS X only, prepend the directory <replaceable>dir</replaceable> to
 589             the framework directories path. This option corresponds to the <option>-F</option>
 590             option for Apple's Linker (<option>-F</option> already means something else for GHC).</para>
 591           </listitem>
 592         </varlistentry>
 593
 594         <varlistentry>
 595           <term><option>-split-objs</option></term>
 596           <indexterm><primary><option>-split-objs</option></primary></indexterm>
 597           <listitem>
 598             <para>Tell the linker to split the single object file that
 599             would normally be generated into multiple object files,
 600             one per top-level Haskell function or type in the module.
 601             We use this feature for building GHC's libraries libraries
 602             (warning: don't use it unless you know what you're
 603             doing!).</para>
 604           </listitem>
 605         </varlistentry>
 606
 607         <varlistentry>
 608           <term><option>-static</option></term>
 609           <indexterm><primary><option>-static</option></primary></indexterm>
 610           <listitem>
 611             <para>Tell the linker to avoid shared Haskell libraries,
 612             if possible.  This is the default.</para>
 613           </listitem>
 614         </varlistentry>
 615
 616         <varlistentry>
 617           <term><option>-dynamic</option></term>
 618           <indexterm><primary><option>-dynamic</option></primary></indexterm>
 619           <listitem>
 620             <para>Tell the linker to use shared Haskell libraries, if
 621             available (this option is only supported on Windows at the
 622             moment, and also note that your distribution of GHC may
 623             not have been supplied with shared libraries).</para>
 624           </listitem>
 625         </varlistentry>
 626
 627         <varlistentry>
 628           <term><option>-main-is <replaceable>thing</replaceable></option></term>
 629           <indexterm><primary><option>-main-is</option></primary></indexterm>
 630           <indexterm><primary>specifying your own main function</primary></indexterm>
 631           <listitem>
 632             <para> The normal rule in Haskell is that your program must supply a <literal>main</literal>
 633               function in module <literal>Main</literal>.  When testing, it is often convenient
 634               to change which function is the "main" one, and the <option>-main-is</option> flag
 635               allows you to do so.  The  <replaceable>thing</replaceable> can be one of:
 636               <itemizedlist>
 637                 <listitem><para>A lower-case identifier <literal>foo</literal>.  GHC assumes that the main function is <literal>Main.foo</literal>.</para></listitem>
 638                 <listitem><para>An module name <literal>A</literal>.  GHC assumes that the main function is <literal>A.main</literal>.</para></listitem>
 639                 <listitem><para>An qualified name <literal>A.foo</literal>.  GHC assumes that the main function is <literal>A.foo</literal>.</para></listitem>
 640                 </itemizedlist>
 641               Strictly speaking, <option>-main-is</option> is not a link-phase flag at all; it has no effect on the link step.
 642               The flag must be specified when compiling the module containing the specified main function (e.g. module <literal>A</literal>
 643               in the latter two items above.  It has no effect for other modules (and hence can safely be given to <literal>ghc --make</literal>).
 644               </para>
 645           </listitem>
 646         </varlistentry>
 647
 648         <varlistentry>
 649           <term><option>-no-hs-main</option></term>
 650           <indexterm><primary><option>-no-hs-main</option></primary></indexterm>
 651           <indexterm><primary>linking Haskell libraries with foreign code</primary></indexterm>
 652           <listitem>
 653             <para>In the event you want to include ghc-compiled code
 654             as part of another (non-Haskell) program, the RTS will not
 655             be supplying its definition of <function>main()</function>
 656             at link-time, you will have to. To signal that to the
 657             compiler when linking, use
 658             <option>-no-hs-main</option>. See also <xref linkend="using-own-main">.</para>
 659
 660             <para>Notice that since the command-line passed to the
 661             linker is rather involved, you probably want to use
 662             <command>ghc</command> to do the final link of your
 663             `mixed-language' application. This is not a requirement
 664             though, just try linking once with <option>-v</option> on
 665             to see what options the driver passes through to the
 666             linker.</para>
 667
 668             <para>The <option>-no-hs-main</option> flag can also be
 669             used to persuade the compiler to do the link step in
 670             <option>--make</option> mode when there is no Haskell
 671             <literal>Main</literal> module present (normally the
 672             compiler will not attempt linking when there is no
 673             <literal>Main</literal>).</para>
 674           </listitem>
 675         </varlistentry>
 676       </variablelist>
 677     </sect2>
 678
 679   </sect1>
 680
 681 <!-- Emacs stuff:
 682      ;;; Local Variables: ***
 683      ;;; mode: sgml ***
 684      ;;; sgml-parent-document: ("users_guide.sgml" "book" "chapter") ***
 685      ;;; End: ***
 686  -->