ghc/docs/users_guide/using.sgml

   1 <chapter id="using-ghc">
   2   <title>Using GHC</title>
   3
   4   <indexterm><primary>GHC, using</primary></indexterm>
   5   <indexterm><primary>using GHC</primary></indexterm>
   6
   7     <para>GHC can work in one of three &ldquo;modes&rdquo;:</para>
   8
   9     <variablelist>
  10       <varlistentry>
  11         <term><cmdsynopsis><command>ghc</command>
  12             <arg choice=plain>--interactive</arg>
  13           </cmdsynopsis></term>
  14         <indexterm><primary>interactive mode</primary>
  15         </indexterm>
  16         <indexterm><primary>ghci</primary>
  17         </indexterm>
  18         <listitem>
  19           <para>Interactive mode, which is also available as
  20           <command>ghci</command>.  Interactive mode is described in
  21           more detail in <xref linkend="ghci">.</para>
  22         </listitem>
  23       </varlistentry>
  24
  25       <varlistentry>
  26         <term><cmdsynopsis><command>ghc</command>
  27             <arg choice=plain>--make</arg>
  28           </cmdsynopsis></term>
  29         <indexterm><primary>make mode</primary>
  30         </indexterm>
  31         <indexterm><primary><option>--make</option></primary>
  32         </indexterm>
  33         <listitem>
  34           <para>In this mode, GHC will build a multi-module Haskell
  35           program automatically, figuring out dependencies for itself.
  36           If you have a straightforward Haskell program, this is
  37           likely to be much easier, and faster, than using
  38           <command>make</command>.</para>
  39         </listitem>
  40       </varlistentry>
  41
  42       <varlistentry>
  43         <term><cmdsynopsis>
  44             <command>ghc</command>
  45             <group>
  46               <arg>-E</arg>
  47               <arg>-C</arg>
  48               <arg>-S</arg>
  49               <arg>-c</arg>
  50             </group>
  51           </cmdsynopsis></term>
  52         <indexterm><primary><option>--make</option></primary>
  53         </indexterm>
  54         <listitem>
  55           <para>This is the traditional batch-compiler mode, in which
  56           GHC can compile source files one at a time, or link objects
  57           together into an executable.</para>
  58         </listitem>
  59       </varlistentry>
  60     </variablelist>
  61
  62   <sect1>
  63     <title>Options overview</title>
  64
  65     <para>GHC's behaviour is controlled by
  66     <firstterm>options</firstterm>, which for historical reasons are
  67     also sometimes referred to as command-line flags or arguments.
  68     Options can be specified in three ways:</para>
  69
  70     <sect2>
  71       <title>Command-line arguments</title>
  72
  73       <indexterm><primary>structure, command-line</primary></indexterm>
  74       <indexterm><primary>command-line</primary><secondary>arguments</secondary></indexterm>
  75       <indexterm><primary>arguments</primary><secondary>command-line</secondary></indexterm>
  76
  77       <para>An invocation of GHC takes the following form:</para>
  78
  79 <Screen>
  80 ghc [argument...]
  81 </Screen>
  82
  83       <para>Command-line arguments are either options or file names.</para>
  84
  85       <para>Command-line options begin with <literal>-</literal>.
  86       They may <emphasis>not</emphasis> be grouped:
  87       <option>-vO</option> is different from <option>-v -O</option>.
  88       Options need not precede filenames: e.g., <literal>ghc *.o -o
  89       foo</literal>.  All options are processed and then applied to
  90       all files; you cannot, for example, invoke <literal>ghc -c -O1
  91       Foo.hs -O2 Bar.hs</literal> to apply different optimisation
  92       levels to the files <filename>Foo.hs</filename> and
  93       <filename>Bar.hs</filename>.</para>
  94     </sect2>
  95
  96     <Sect2 id="source-file-options">
  97       <title>Command line options in source files</title>
  98
  99       <indexterm><primary>source-file options</primary></indexterm>
 100
 101       <para>Sometimes it is useful to make the connection between a
 102       source file and the command-line options it requires quite
 103       tight. For instance, if a Haskell source file uses GHC
 104       extensions, it will always need to be compiled with the
 105       <option>-fglasgow-exts</option> option.  Rather than maintaining
 106       the list of per-file options in a <filename>Makefile</filename>,
 107       it is possible to do this directly in the source file using the
 108       <literal>OPTIONS</literal> pragma <indexterm><primary>OPTIONS
 109       pragma</primary></indexterm>:</para>
 110
 111 <ProgramListing>
 112 {-# OPTIONS -fglasgow-exts #-}
 113 module X where
 114 ...
 115 </ProgramListing>
 116
 117       <para><literal>OPTIONS</literal> pragmas are only looked for at
 118       the top of your source files, upto the first
 119       (non-literate,non-empty) line not containing
 120       <literal>OPTIONS</literal>. Multiple <literal>OPTIONS</literal>
 121       pragmas are recognised. Note that your command shell does not
 122       get to the source file options, they are just included literally
 123       in the array of command-line arguments the compiler driver
 124       maintains internally, so you'll be desperately disappointed if
 125       you try to glob etc. inside <literal>OPTIONS</literal>.</para>
 126
 127       <para>NOTE: the contents of OPTIONS are prepended to the
 128       command-line options, so you <emphasis>do</emphasis> have the
 129       ability to override OPTIONS settings via the command
 130       line.</para>
 131
 132       <para>It is not recommended to move all the contents of your
 133       Makefiles into your source files, but in some circumstances, the
 134       <literal>OPTIONS</literal> pragma is the Right Thing. (If you
 135       use <option>-keep-hc-file-too</option> and have OPTION flags in
 136       your module, the OPTIONS will get put into the generated .hc
 137       file).</para>
 138     </sect2>
 139
 140     <sect2>
 141       <title>Setting options in GHCi</title>
 142
 143       <para>Options may also be modified from within GHCi, using the
 144       <literal>:set</literal> command.  See <xref linkend="ghci-set">
 145       for more details.</para>
 146     </sect2>
 147   </sect1>
 148
 149   <sect1 id="static-dynamic-flags">
 150     <title>Static vs. Dynamic options</title>
 151     <indexterm><primary>static</primary><secondary>options</secondary>
 152     </indexterm>
 153     <indexterm><primary>dynamic</primary><secondary>options</secondary>
 154     </indexterm>
 155
 156     <para>Each of GHC's command line options is classified as either
 157     <firstterm>static</firstterm> or <firstterm>dynamic</firstterm>.
 158     A static flag may only be specified on the command line, whereas a
 159     dynamic flag may also be given in an <literal>OPTIONS</literal>
 160     pragma in a source file or set from the GHCi command-line with
 161     <literal>:set</literal>.</para>
 162
 163     <para>As a rule of thumb, all the language options are dynamic, as
 164     are the warning options and the debugging options.  The rest are
 165     static, with the notable exceptions of <option>-v</option>,
 166     <option>-cpp</option>, <option>-fasm</option>,
 167     <option>-fvia-C</option>, and <option>-#include</option>.
 168
 169     The flag reference tables (<xref linkend="flag-reference">) lists
 170     the status of each flag.</para>
 171   </sect1>
 172
 173   <sect1 id="file-suffixes">
 174     <title>Meaningful file suffixes</title>
 175
 176     <indexterm><primary>suffixes, file</primary></indexterm>
 177     <indexterm><primary>file suffixes for GHC</primary></indexterm>
 178
 179     <para>File names with &ldquo;meaningful&rdquo; suffixes (e.g.,
 180     <filename>.lhs</filename> or <filename>.o</filename>) cause the
 181     &ldquo;right thing&rdquo; to happen to those files.</para>
 182
 183     <variablelist>
 184
 185       <varlistentry>
 186         <term><filename>.lhs</filename></term>
 187         <indexterm><primary><literal>lhs</literal> suffix</primary></indexterm>
 188         <listitem>
 189           <para>A &ldquo;literate Haskell&rdquo; module.</para>
 190         </listitem>
 191       </varlistentry>
 192
 193       <varlistentry>
 194         <term><filename>.hs</filename></term>
 195         <listitem>
 196           <para>A not-so-literate Haskell module.</para>
 197         </listitem>
 198       </varlistentry>
 199
 200       <varlistentry>
 201         <term><filename>.hi</filename></term>
 202         <listitem>
 203           <para>A Haskell interface file, probably
 204           compiler-generated.</para>
 205         </listitem>
 206       </varlistentry>
 207
 208       <varlistentry>
 209         <term><filename>.hc</filename></term>
 210         <listitem>
 211           <para>Intermediate C file produced by the Haskell
 212           compiler.</para>
 213         </listitem>
 214       </varlistentry>
 215
 216       <varlistentry>
 217         <term><filename>.c</filename></term>
 218         <listitem>
 219           <para>A C&nbsp;file not produced by the Haskell
 220           compiler.</para>
 221         </listitem>
 222       </varlistentry>
 223
 224       <varlistentry>
 225         <term><filename>.s</filename></term>
 226         <listitem>
 227           <para>An assembly-language source file, usually produced by
 228           the compiler.</para>
 229         </listitem>
 230       </varlistentry>
 231
 232       <varlistentry>
 233         <term><filename>.o</filename></term>
 234         <listitem>
 235           <para>An object file, produced by an assembler.</para>
 236         </listitem>
 237       </varlistentry>
 238     </variablelist>
 239
 240     <para>Files with other suffixes (or without suffixes) are passed
 241     straight to the linker.</para>
 242
 243   </sect1>
 244
 245   <sect1 id="options-help">
 246     <title>Help and verbosity options</title>
 247
 248     <IndexTerm><Primary>help options</Primary></IndexTerm>
 249     <IndexTerm><Primary>verbosity options</Primary></IndexTerm>
 250
 251     <variablelist>
 252       <varlistentry>
 253         <term><literal>-help</literal></term>
 254         <term><literal>-?</literal></term>
 255         <indexterm><primary><literal>-?</literal></primary></indexterm>
 256         <indexterm><primary><literal>-help</literal></primary></indexterm>
 257         <listitem>
 258           <para>Cause GHC to spew a long usage message to standard
 259           output and then exit.</para>
 260         </listitem>
 261       </varlistentry>
 262
 263       <varlistentry>
 264         <term><literal>-v</literal></term>
 265         <indexterm><primary><literal>-v</literal></primary></indexterm>
 266         <listitem>
 267           <para>The <option>-v</option> option makes GHC
 268           <emphasis>verbose</emphasis>: it reports its version number
 269           and shows (on stderr) exactly how it invokes each phase of
 270           the compilation system.  Moreover, it passes the
 271           <option>-v</option> flag to most phases; each reports its
 272           version number (and possibly some other information).</para>
 273
 274           <para>Please, oh please, use the <option>-v</option> option
 275           when reporting bugs!  Knowing that you ran the right bits in
 276           the right order is always the first thing we want to
 277           verify.</para>
 278         </listitem>
 279       </varlistentry>
 280
 281       <varlistentry>
 282         <term><literal>-v</literal><replaceable>n</replaceable></term>
 283         <indexterm><primary><option>-v</option></primary></indexterm>
 284         <listitem>
 285           <para>To provide more control over the compiler's verbosity,
 286           the <option>-v</option> flag takes an optional numeric
 287           argument.  Specifying <option>-v</option> on its own is
 288           equivalent to <option>-v3</option>, and the other levels
 289           have the following meanings:</para>
 290
 291           <variablelist>
 292             <varlistentry>
 293               <term><literal>-v0</literal></term>
 294               <listitem>
 295                 <para>Disable all non-essential messages (this is the
 296                 default).</para>
 297               </listitem>
 298             </varlistentry>
 299
 300             <varlistentry>
 301               <term><literal>-v1</literal></term>
 302               <listitem>
 303                 <para>Minimal verbosity: print one line per
 304                 compilation (this is the default when
 305                 <option>--make</option> or
 306                 <option>--interactive</option> is on).</para>
 307               </listitem>
 308             </varlistentry>
 309
 310             <varlistentry>
 311               <term><literal>-v2</literal></term>
 312               <listitem>
 313                 <para>Print the name of each compilation phase as it
 314                 is executed. (equivalent to
 315                 <option>-dshow-passes</option>).</para>
 316               </listitem>
 317             </varlistentry>
 318
 319             <varlistentry>
 320               <term><literal>-v3</literal></term>
 321               <listitem>
 322                 <para>The same as <option>-v2</option>, except that in
 323                 addition the full command line (if appropriate) for
 324                 each compilation phase is also printed.</para>
 325               </listitem>
 326             </varlistentry>
 327
 328             <varlistentry>
 329               <term><literal>-v4</literal></term>
 330               <listitem>
 331                 <para>The same as <option>-v3</option> except that the
 332                 intermediate program representation after each
 333                 compilation phase is also printed (excluding
 334                 preprocessed and C/assembly files).</para>
 335               </listitem>
 336             </varlistentry>
 337           </variablelist>
 338         </listitem>
 339       </varlistentry>
 340
 341       <varlistentry>
 342         <term><literal>--version</literal></term>
 343         <indexterm><primary><literal>--version</literal></primary></indexterm>
 344         <listitem>
 345           <para>Print a one-line string including GHC's version number.</para>
 346         </listitem>
 347       </varlistentry>
 348
 349       <varlistentry>
 350         <term><literal>--numeric-version</literal></term>
 351         <indexterm><primary><literal>--numeric-version</literal></primary></indexterm>
 352         <listitem>
 353           <para>Print GHC's numeric version number only.</para>
 354         </listitem>
 355       </varlistentry>
 356     </variablelist>
 357   </sect1>
 358
 359   <sect1 id="make-mode">
 360     <title>Using <command>ghc</command> <option>--make</option></title>
 361
 362     <indexterm><primary><option>--make</option></primary>
 363     </indexterm>
 364     <indexterm><primary>separate compilation</primary>
 365     </indexterm>
 366
 367     <para>When given the <option>--make</option> option, GHC will
 368     build a multi-module Haskell program by following dependencies
 369     from a single root module (usually <literal>Main</literal>).  For
 370     example, if your <literal>Main</literal> module is in a file
 371     called <filename>Main.hs</filename>, you could compile and link
 372     the program like this:</para>
 373
 374 <screen>
 375 ghc --make Main.hs
 376 </screen>
 377
 378     <para>The command line must contain one source file or module
 379     name; GHC will figure out all the modules in the program by
 380     following the imports from this initial module.  It will then
 381     attempt to compile each module which is out of date, and finally
 382     if the top module is <literal>Main</literal>, the program
 383     will also be linked into an executable.</para>
 384
 385     <para>The main advantages to using <literal>ghc --make</literal>
 386     over traditional <literal>Makefile</literal>s are:</para>
 387
 388     <itemizedlist>
 389       <listitem>
 390         <para>GHC doesn't have to be restarted for each compilation,
 391         which means it can cache information between compilations.
 392         Compiling a muli-module program with <literal>ghc
 393         --make</literal> can be up to twice as fast as running
 394         <literal>ghc</literal> individually on each source
 395         file.</para>
 396       </listitem>
 397       <listitem>
 398         <para>You don't have to write a
 399         <literal>Makefile</literal>.</para>
 400       </listitem>
 401       <indexterm><primary><literal>Makefile</literal>s</primary><secondary>avoiding</secondary>
 402       </indexterm>
 403       <listitem>
 404         <para>GHC re-calculates the dependencies each time it is
 405         invoked, so the dependencies never get out of sync with the
 406         source.</para>
 407       </listitem>
 408     </itemizedlist>
 409
 410     <para>Any of the command-line options described in the rest of
 411     this chapter can be used with <option>--make</option>, but note
 412     that any options you give on the command line will apply to all
 413     the source files compiled, so if you want any options to apply to
 414     a single source file only, you'll need to use an
 415     <literal>OPTIONS</literal> pragma (see <xref
 416     linkend="source-file-options">).</para>
 417
 418     <para>If the program needs to be linked with additional objects
 419     (say, some auxilliary C code), these can be specified on the
 420     command line as usual.</para>
 421   </sect1>
 422
 423   <Sect1 id="options-order">
 424     <title>GHC without <option>--make</option></title>
 425
 426     <para>Without <option>--make</option>, GHC will compile one or
 427     more source files given on the command line.</para>
 428
 429     <para>The first phase to run is determined by each input-file
 430     suffix, and the last phase is determined by a flag.  If no
 431     relevant flag is present, then go all the way through linking.
 432     This table summarises:</para>
 433
 434     <informaltable>
 435       <tgroup cols="4">
 436         <colspec align="left">
 437         <colspec align="left">
 438         <colspec align="left">
 439         <colspec align="left">
 440
 441         <thead>
 442           <row>
 443             <entry>Phase of the compilation system</entry>
 444             <entry>Suffix saying &ldquo;start here&rdquo;</entry>
 445             <entry>Flag saying &ldquo;stop after&rdquo;</entry>
 446             <entry>(suffix of) output file</entry>
 447           </row>
 448         </thead>
 449         <tbody>
 450           <row>
 451             <entry>literate pre-processor</entry>
 452             <entry><literal>.lhs</literal></entry>
 453             <entry>-</entry>
 454             <entry><literal>.hs</literal></entry>
 455           </row>
 456
 457           <row>
 458             <entry>C pre-processor (opt.)
 459            </entry>
 460             <entry><literal>.hs</literal> (with
 461             <option>-cpp</option>)</entry>
 462             <entry><option>-E</option></entry>
 463             <entry><literal>.hspp</literal></entry>
 464           </row>
 465
 466           <row>
 467             <entry>Haskell compiler</entry>
 468             <entry><literal>.hs</literal></entry>
 469             <entry><option>-C</option>, <option>-S</option></entry>
 470             <entry><literal>.hc</literal>, <literal>.s</literal></entry>
 471           </row>
 472
 473           <row>
 474             <entry>C compiler (opt.)</entry>
 475             <entry><literal>.hc</literal> or <literal>.c</literal></entry>
 476             <entry><option>-S</option></entry>
 477             <entry><literal>.s</literal></entry>
 478           </row>
 479
 480           <row>
 481             <entry>assembler</entry>
 482             <entry><literal>.s</literal></entry>
 483             <entry><option>-c</option></entry>
 484             <entry><literal>.o</literal></entry>
 485           </row>
 486
 487           <row>
 488             <entry>linker</entry>
 489             <entry><replaceable>other</replaceable></entry>
 490             <entry>-</entry>
 491             <entry><filename>a.out</filename></entry>
 492           </row>
 493         </tbody>
 494       </tgroup>
 495     </informaltable>
 496
 497     <indexterm><primary><option>-C</option></primary></indexterm>
 498     <indexterm><primary><option>-E</option></primary></indexterm>
 499     <indexterm><primary><option>-S</option></primary></indexterm>
 500     <indexterm><primary><option>-c</option></primary></indexterm>
 501
 502     <para>Thus, a common invocation would be: <literal>ghc -c
 503     Foo.hs</literal></para>
 504
 505     <para>Note: What the Haskell compiler proper produces depends on
 506     whether a native-code generator<indexterm><primary>native-code
 507     generator</primary></indexterm> is used (producing assembly
 508     language) or not (producing C).  See <xref
 509     linkend="options-codegen"> for more details.</para>
 510
 511     <para>Note: C pre-processing is optional, the
 512     <option>-ccp</option><indexterm><primary><option>-cpp</option></primary>
 513       </indexterm>flag turns it on.  See <xref
 514     linkend="c-pre-processor"> for more details.</para>
 515
 516     <para>Note: The option <option>-E</option><IndexTerm><Primary>-E
 517     option</Primary></IndexTerm> runs just the pre-processing passes
 518     of the compiler, dumping the result in a file.  Note that this
 519     differs from the previous behaviour of dumping the file to
 520     standard output.</para>
 521   </sect1>
 522
 523   <sect1 id="options-output">
 524     <title>Re-directing the compilation output(s)</title>
 525
 526     <indexterm><primary>output-directing options</primary></indexterm>
 527     <indexterm><primary>redirecting compilation output</primary></indexterm>
 528
 529
 530     <variablelist>
 531       <varlistentry>
 532         <term><literal>-o</literal></term>
 533         <indexterm><primary><literal>-o</literal></primary></indexterm>
 534         <listitem>
 535           <para>GHC's compiled output normally goes into a
 536           <filename>.hc</filename>, <filename>.o</filename>, etc.,
 537           file, depending on the last-run compilation phase.  The
 538           option <option>-o foo</option><IndexTerm><Primary>-o
 539           option</Primary></IndexTerm> re-directs the output of that
 540           last-run phase to file <filename>foo</filename>.</para>
 541
 542           <para>Note: this &ldquo;feature&rdquo; can be
 543           counterintuitive: <command>ghc -C -o foo.o foo.hs</command>
 544           will put the intermediate C code in the file
 545           <filename>foo.o</filename>, name notwithstanding!</para>
 546         </listitem>
 547       </varlistentry>
 548
 549       <varlistentry>
 550         <term><literal>-odir</literal></term>
 551         <indexterm><primary><literal>-odir</literal></primary></indexterm>
 552         <listitem>
 553           <para>The <option>-o</option> option isn't of much use if
 554           you have <emphasis>several</emphasis> input files&hellip;
 555           Non-interface output files are normally put in the same
 556           directory as their corresponding input file came from.  You
 557           may specify that they be put in another directory using the
 558           <option>-odir &lt;dir&gt;</option><IndexTerm><Primary>-odir
 559           &lt;dir&gt; option</Primary></IndexTerm> (the &ldquo;Oh,
 560           dear&rdquo; option).  For example:</para>
 561
 562 <Screen>
 563 % ghc -c parse/Foo.hs parse/Bar.hs gurgle/Bumble.hs -odir `arch`
 564 </Screen>
 565
 566           <para>The output files, <filename>Foo.o</filename>,
 567           <filename>Bar.o</filename>, and
 568           <filename>Bumble.o</filename> would be put into a
 569           subdirectory named after the architecture of the executing
 570           machine (<filename>sun4</filename>,
 571           <filename>mips</filename>, etc).  The directory must already
 572           exist; it won't be created.</para>
 573
 574           <para>Note that the <option>-odir</option> option does
 575           <emphasis>not</emphasis> affect where the interface files
 576           are put.  In the above example, they would still be put in
 577           <filename>parse/Foo.hi</filename>,
 578           <filename>parse/Bar.hi</filename>, and
 579           <filename>gurgle/Bumble.hi</filename>.</para>
 580         </listitem>
 581       </varlistentry>
 582
 583       <varlistentry>
 584         <term><option>-ohi</option>  <replaceable>file</replaceable></term>
 585         <indexterm><primary><option>-ohi</option></primary>
 586         </indexterm>
 587         <listitem>
 588           <para>The interface output may be directed to another file
 589           <filename>bar2/Wurble.iface</filename> with the option
 590           <option>-ohi bar2/Wurble.iface</option> (not
 591           recommended).</para>
 592
 593           <para>WARNING: if you redirect the interface file somewhere
 594           that GHC can't find it, then the recompilation checker may
 595           get confused (at the least, you won't get any recompilation
 596           avoidance).  We recommend using a combination of
 597           <option>-hidir</option> and <option>-hisuf</option> options
 598           instead, if possible.</para>
 599
 600           <para>To avoid generating an interface at all, you could use
 601           this option to redirect the interface into the bit bucket:
 602           <literal>-ohi /dev/null</literal>, for example.</para>
 603         </listitem>
 604       </varlistentry>
 605
 606       <varlistentry>
 607         <term><option>-hidir</option>  <replaceable>directory</replaceable></term>
 608         <indexterm><primary><option>-hidir</option></primary>
 609         </indexterm>
 610         <listitem>
 611           <para>Redirects all generated interface files into
 612           <replaceable>directory</replaceable>, instead of the default
 613           which is to place the interface file in the same directory
 614           as the source file.</para>
 615         </listitem>
 616       </varlistentry>
 617
 618       <varlistentry>
 619         <term><option>-osuf</option> <replaceable>suffix</replaceable></term>
 620         <term><option>-hisuf</option> <replaceable>suffix</replaceable></term>
 621         <term><option>-hcsuf</option> <replaceable>suffix</replaceable></term>
 622         <indexterm><primary><option>-osuf</option></primary></indexterm>
 623         <indexterm><primary><option>-hisuf</option></primary></indexterm>
 624         <indexterm><primary><option>-hcsuf</option></primary></indexterm>
 625         <listitem>
 626           <para>EXOTICA: The <option>-osuf</option>
 627           <replaceable>suffix</replaceable> will change the
 628           <literal>.o</literal> file suffix for object files to
 629           whatever you specify.  We use this when compiling libraries,
 630           so that objects for the profiling versions of the libraries
 631           don't clobber the normal ones.</para>
 632
 633           <para>Similarly, the <option>-hisuf</option>
 634           <replaceable>suffix</replaceable> will change the
 635           <literal>.hi</literal> file suffix for non-system interface
 636           files (see <XRef LinkEnd="hi-options">).</para>
 637
 638           <para>Finally, the option <option>-hcsuf</option>
 639           <replaceable>suffix</replaceable> will change the
 640           <literal>.hc</literal> file suffix for compiler-generated
 641           intermediate C files.</para>
 642
 643           <para>The <option>-hisuf</option>/<option>-osuf</option>
 644           game is useful if you want to compile a program with both
 645           GHC and HBC (say) in the same directory.  Let HBC use the
 646           standard <filename>.hi</filename>/<filename>.o</filename>
 647           suffixes; add <option>-hisuf g&lowbar;hi -osuf
 648           g&lowbar;o</option> to your <command>make</command> rule for
 649           GHC compiling&hellip;</para>
 650         </listitem>
 651       </varlistentry>
 652     </variablelist>
 653
 654     <sect2 id="keeping-intermediates">
 655       <title>Keeping Intermediate Files</title>
 656       <indexterm><primary>intermediate files, saving</primary>
 657       </indexterm>
 658       <indexterm><primary><literal>.hc</literal> files, saving</primary>
 659       </indexterm>
 660       <indexterm><primary><literal>.s</literal> files, saving</primary>
 661       </indexterm>
 662
 663
 664       <para>The following options are useful for keeping certain
 665       intermediate files around, when normally GHC would throw these
 666       away after compilation:</para>
 667
 668       <variablelist>
 669         <varlistentry>
 670           <term><literal>-keep-hc-files</literal></term>
 671           <indexterm>
 672             <primary><literal>-keep-hc-files</literal></primary>
 673           </indexterm>
 674           <listitem>
 675             <para>Keep intermediate <literal>.hc</literal> files when
 676             doing <literal>.hs</literal>-to-<literal>.o</literal>
 677             compilations via C (NOTE: <literal>.hc</literal> files
 678             aren't generated when using the native code generator, you
 679             may need to use <literal>-fvia-C</literal> to force them
 680             to be produced).</para>
 681           </listitem>
 682         </varlistentry>
 683
 684         <varlistentry>
 685           <term><literal>-keep-s-files</literal></term>
 686           <indexterm>
 687             <primary><literal>-keep-s-files</literal></primary>
 688           </indexterm>
 689           <listitem>
 690             <para>Keep intermediate <literal>.s</literal> files.</para>
 691           </listitem>
 692         </varlistentry>
 693
 694         <varlistentry>
 695           <term><literal>-keep-raw-s-files</literal></term>
 696           <indexterm>
 697             <primary><literal>-keep-raw-s-files</literal></primary>
 698           </indexterm>
 699           <listitem>
 700             <para>Keep intermediate <literal>.raw-s</literal> files.
 701             These are the direct output from the C compiler, before
 702             GHC does &ldquo;assembly mangling&rdquo; to produce the
 703             <literal>.s</literal> file.  Again, these are not produced
 704             when using the native code generator.</para>
 705           </listitem>
 706         </varlistentry>
 707
 708         <varlistentry>
 709           <term><literal>-keep-tmp-files</literal></term>
 710           <indexterm>
 711             <primary><literal>-keep-tmp-files</literal></primary>
 712           </indexterm>
 713           <indexterm>
 714             <primary>temporary files</primary>
 715             <secondary>keeping</secondary>
 716           </indexterm>
 717           <listitem>
 718             <para>Instructs the GHC driver not to delete any of its
 719             temporary files, which it normally keeps in
 720             <literal>/tmp</literal> (or possibly elsewhere; see <xref
 721             linkend="temp-files">).  Running GHC with
 722             <literal>-v</literal> will show you what temporary files
 723             were generated along the way.</para>
 724           </listitem>
 725         </varlistentry>
 726       </variablelist>
 727     </sect2>
 728
 729     <sect2 id="temp-files">
 730       <title>Redirecting temporary files</title>
 731
 732       <indexterm>
 733         <primary>temporary files</primary>
 734         <secondary>redirecting</secondary>
 735       </indexterm>
 736
 737       <variablelist>
 738         <varlistentry>
 739           <term><literal>-tmpdir</literal></term>
 740           <indexterm><primary><literal>-tmpdir</literal></primary></indexterm>
 741           <listitem>
 742             <para>If you have trouble because of running out of space
 743             in <filename>/tmp</filename> (or wherever your
 744             installation thinks temporary files should go), you may
 745             use the <option>-tmpdir
 746             &lt;dir&gt;</option><IndexTerm><Primary>-tmpdir
 747             &lt;dir&gt; option</Primary></IndexTerm> option to specify
 748             an alternate directory.  For example, <option>-tmpdir
 749             .</option> says to put temporary files in the current
 750             working directory.</para>
 751
 752             <para>Alternatively, use your <Constant>TMPDIR</Constant>
 753             environment variable.<IndexTerm><Primary>TMPDIR
 754             environment variable</Primary></IndexTerm> Set it to the
 755             name of the directory where temporary files should be put.
 756             GCC and other programs will honour the
 757             <Constant>TMPDIR</Constant> variable as well.</para>
 758
 759             <para>Even better idea: Set the
 760             <Constant>DEFAULT_TMPDIR</Constant> make variable when
 761             building GHC, and never worry about
 762             <Constant>TMPDIR</Constant> again. (see the build
 763             documentation).</para>
 764           </listitem>
 765         </varlistentry>
 766       </variablelist>
 767     </sect2>
 768
 769   </sect1>
 770
 771   <sect1 id="options-sanity">
 772     <title>Warnings and sanity-checking</title>
 773
 774     <indexterm><primary>sanity-checking options</primary></indexterm>
 775     <indexterm><primary>warnings</primary></indexterm>
 776
 777
 778     <para>GHC has a number of options that select which types of
 779     non-fatal error messages, otherwise known as warnings, can be
 780     generated during compilation.  By default, you get a standard set
 781     of warnings which are generally likely to indicate bugs in your
 782     program.  These are:
 783     <option>-fwarn-overlpapping-patterns</option>,
 784     <option>-fwarn-deprecations</option>,
 785     <option>-fwarn-duplicate-exports</option>,
 786     <option>-fwarn-missing-fields</option>, and
 787     <option>-fwarn-missing-methods</option>.  The following flags are
 788     simple ways to select standard &ldquo;packages&rdquo; of warnings:
 789     </para>
 790
 791     <VariableList>
 792
 793       <varlistentry>
 794         <term><option>-W</option>:</term>
 795         <listitem>
 796           <IndexTerm><Primary>-W option</Primary></IndexTerm>
 797           <para>Provides the standard warnings plus
 798           <option>-fwarn-incomplete-patterns</option>,
 799           <option>-fwarn-unused-matches</option>,
 800           <option>-fwarn-unused-imports</option>,
 801           <option>-fwarn-misc</option>, and
 802           <option>-fwarn-unused-binds</option>.</para>
 803         </listitem>
 804       </varlistentry>
 805
 806       <varlistentry>
 807         <term><option>-w</option>:</term>
 808         <listitem>
 809           <IndexTerm><Primary><option>-w</option></Primary></IndexTerm>
 810           <para>Turns off all warnings, including the standard ones.</para>
 811         </listitem>
 812       </varlistentry>
 813
 814       <varlistentry>
 815         <term><option>-Wall</option>:</term>
 816         <listitem>
 817           <indexterm><primary><option>-Wall</option></primary></indexterm>
 818           <para>Turns on all warning options.</para>
 819         </listitem>
 820       </varlistentry>
 821
 822     </variablelist>
 823
 824     <para>The full set of warning options is described below.  To turn
 825     off any warning, simply give the corresponding
 826     <option>-fno-warn-...</option> option on the command line.</para>
 827
 828     <variablelist>
 829
 830       <varlistentry>
 831         <term><option>-fwarn-deprecations</option>:</term>
 832         <listitem>
 833           <indexterm><primary><option>-fwarn-deprecations</option></primary>
 834           </indexterm>
 835           <indexterm><primary>deprecations</primary></indexterm>
 836           <para>Causes a warning to be emitted when a deprecated
 837           function or type is used.  Entities can be marked as
 838           deprecated using a pragma, see <xref
 839           linkend="deprecated-pragma">.</para>
 840         </listitem>
 841       </varlistentry>
 842
 843       <varlistentry>
 844         <term><option>-fwarn-duplicate-exports</option>:</term>
 845         <listitem>
 846           <indexterm><primary><option>-fwarn-duplicate-exports</option></primary></indexterm>
 847           <indexterm><primary>duplicate exports, warning</primary></indexterm>
 848           <indexterm><primary>export lists, duplicates</primary></indexterm>
 849
 850           <para>Have the compiler warn about duplicate entries in
 851           export lists. This is useful information if you maintain
 852           large export lists, and want to avoid the continued export
 853           of a definition after you've deleted (one) mention of it in
 854           the export list.</para>
 855
 856           <para>This option is on by default.</para>
 857         </listitem>
 858       </varlistentry>
 859
 860       <varlistentry>
 861         <term><option>-fwarn-hi-shadowing</option>:</term>
 862         <listitem>
 863           <indexterm><primary><option>-fwarn-hi-shadowing</option></primary></indexterm>
 864           <indexterm><primary>shadowing</primary>
 865             <secondary>interface files</secondary></indexterm>
 866
 867           <para>Causes the compiler to emit a warning when a module or
 868           interface file in the current directory is shadowing one
 869           with the same module name in a library or other
 870           directory.</para>
 871         </listitem>
 872       </varlistentry>
 873
 874       <varlistentry>
 875         <term><option>-fwarn-incomplete-patterns</option>:</term>
 876         <listitem>
 877           <indexterm><primary><option>-fwarn-incomplete-patterns</option></primary></indexterm>
 878           <indexterm><primary>incomplete patterns, warning</primary></indexterm>
 879           <indexterm><primary>patterns, incomplete</primary></indexterm>
 880
 881           <para>Similarly for incomplete patterns, the function
 882           <function>g</function> below will fail when applied to
 883           non-empty lists, so the compiler will emit a warning about
 884           this when <option>-fwarn-incomplete-patterns</option> is
 885           enabled.</para>
 886
 887 <programlisting>
 888 g [] = 2
 889 </programlisting>
 890
 891           <para>This option isn't enabled be default because it can be
 892           a bit noisy, and it doesn't always indicate a bug in the
 893           program.  However, it's generally considered good practice
 894           to cover all the cases in your functions.</para>
 895         </listitem>
 896       </varlistentry>
 897
 898       <varlistentry>
 899         <term><option>-fwarn-misc</option>:</term>
 900         <indexterm><primary><option>-fwarn-misc</option></primary></indexterm>
 901         <listitem>
 902           <para>Turns on warnings for various harmless but untidy
 903           things.  This currently includes: importing a type with
 904           <literal>(..)</literal> when the export is abstract, and
 905           listing duplicate class assertions in a qualified type.</para>
 906         </listitem>
 907       </varlistentry>
 908
 909       <varlistentry>
 910         <term><option>-fwarn-missing-fields</option>:</term>
 911         <listitem>
 912           <indexterm><primary><option>-fwarn-missing-fields</option></primary></indexterm>
 913           <indexterm><primary>missing fields, warning</primary></indexterm>
 914           <indexterm><primary>fields, missing</primary></indexterm>
 915
 916           <para>This option is on by default, and warns you whenever
 917           the construction of a labelled field constructor isn't
 918           complete, missing initializers for one or more fields. While
 919           not an error (the missing fields are initialised with
 920           bottoms), it is often an indication of a programmer error.</para>
 921         </listitem>
 922       </varlistentry>
 923
 924       <varlistentry>
 925         <term><option>-fwarn-missing-methods</option>:</term>
 926         <listitem>
 927           <indexterm><primary><option>-fwarn-missing-methods</option></primary></indexterm>
 928           <indexterm><primary>missing methods, warning</primary></indexterm>
 929           <indexterm><primary>methods, missing</primary></indexterm>
 930
 931           <para>This option is on by default, and warns you whenever
 932           an instance declaration is missing one or more methods, and
 933           the corresponding class declaration has no default
 934           declaration for them.</para>
 935         </listitem>
 936       </varlistentry>
 937
 938       <varlistentry>
 939         <term><option>-fwarn-missing-signatures</option>:</term>
 940         <listitem>
 941           <indexterm><primary><option>-fwarn-missing-signatures</option></primary></indexterm>
 942           <indexterm><primary>type signatures, missing</primary></indexterm>
 943
 944           <para>If you would like GHC to check that every top-level
 945           function/value has a type signature, use the
 946           <option>-fwarn-missing-signatures</option> option.  This
 947           option is off by default.</para>
 948         </listitem>
 949       </varlistentry>
 950
 951       <varlistentry>
 952         <term><option>-fwarn-name-shadowing</option>:</term>
 953         <listitem>
 954           <indexterm><primary><option>-fwarn-name-shadowing</option></primary></indexterm>
 955           <indexterm><primary>shadowing, warning</primary></indexterm>
 956
 957           <para>This option causes a warning to be emitted whenever an
 958           inner-scope value has the same name as an outer-scope value,
 959           i.e. the inner value shadows the outer one.  This can catch
 960           typographical errors that turn into hard-to-find bugs, e.g.,
 961           in the inadvertent cyclic definition <literal>let x = ... x
 962           ... in</literal>.</para>
 963
 964           <para>Consequently, this option does
 965           <emphasis>will</emphasis> complain about cyclic recursive
 966           definitions.</para>
 967         </listitem>
 968       </varlistentry>
 969
 970       <varlistentry>
 971         <term><option>-fwarn-overlapping-patterns</option>:</term>
 972         <indexterm><primary><option>-fwarn-overlapping-patterns</option></primary></indexterm>
 973         <indexterm><primary>overlapping patterns, warning</primary></indexterm>
 974         <indexterm><primary>patterns, overlapping</primary></indexterm>
 975         <listitem>
 976           <para>By default, the compiler will warn you if a set of
 977           patterns are overlapping, i.e.,</para>
 978
 979 <programlisting>
 980 f :: String -&#62; Int
 981 f []     = 0
 982 f (_:xs) = 1
 983 f "2"    = 2
 984 </programlisting>
 985
 986           <para>where the last pattern match in <Function>f</Function>
 987           won't ever be reached, as the second pattern overlaps
 988           it. More often than not, redundant patterns is a programmer
 989           mistake/error, so this option is enabled by default.</para>
 990         </listitem>
 991       </varlistentry>
 992
 993       <varlistentry>
 994         <term><option>-fwarn-simple-patterns</option>:</term>
 995         <listitem>
 996           <indexterm><primary><option>-fwarn-simple-patterns</option></primary>
 997           </indexterm>
 998           <para>Causes the compiler to warn about lambda-bound
 999           patterns that can fail, eg. <literal>\(x:xs)->...</literal>.
1000           Normally, these aren't treated as incomplete patterns by
1001           <option>-fwarn-incomplete-patterns</option>.</para>
1002         </listitem>
1003       </varlistentry>
1004
1005       <varlistentry>
1006         <term><option>-fwarn-type-defaults</option>:</term>
1007         <listitem>
1008           <indexterm><primary><option>-fwarn-type-defaults</option></primary></indexterm>
1009           <indexterm><primary>defaulting mechanism, warning</primary></indexterm>
1010           <para>Have the compiler warn/inform you where in your source
1011           the Haskell defaulting mechanism for numeric types kicks
1012           in. This is useful information when converting code from a
1013           context that assumed one default into one with another,
1014           e.g., the `default default' for Haskell 1.4 caused the
1015           otherwise unconstrained value <Constant>1</Constant> to be
1016           given the type <literal>Int</literal>, whereas Haskell 98
1017           defaults it to <literal>Integer</literal>.  This may lead to
1018           differences in performance and behaviour, hence the
1019           usefulness of being non-silent about this.</para>
1020
1021           <para>This warning is off by default.</para>
1022         </listitem>
1023       </varlistentry>
1024
1025       <varlistentry>
1026         <term><option>-fwarn-unused-binds</option>:</term>
1027         <listitem>
1028           <indexterm><primary><option>-fwarn-unused-binds</option></primary></indexterm>
1029           <indexterm><primary>unused binds, warning</primary></indexterm>
1030           <indexterm><primary>binds, unused</primary></indexterm>
1031           <para>Report any function definitions (and local bindings)
1032           which are unused.  For top-level functions, the warning is
1033           only given if the binding is not exported.</para>
1034         </listitem>
1035       </varlistentry>
1036
1037       <varlistentry>
1038         <term><option>-fwarn-unused-imports</option>:</term>
1039         <listitem>
1040           <indexterm><primary><option>-fwarn-unused-imports</option></primary></indexterm>
1041           <indexterm><primary>unused imports, warning</primary></indexterm>
1042           <indexterm><primary>imports, unused</primary></indexterm>
1043
1044           <para>Report any objects that are explicitly imported but
1045           never used.</para>
1046         </listitem>
1047       </varlistentry>
1048
1049       <varlistentry>
1050         <term><option>-fwarn-unused-matches</option>:</term>
1051         <listitem>
1052           <indexterm><primary><option>-fwarn-unused-matches</option></primary></indexterm>
1053           <indexterm><primary>unused matches, warning</primary></indexterm>
1054           <indexterm><primary>matches, unused</primary></indexterm>
1055
1056           <para>Report all unused variables which arise from pattern
1057           matches, including patterns consisting of a single variable.
1058           For instance <literal>f x y = []</literal> would report
1059           <VarName>x</VarName> and <VarName>y</VarName> as unused.  To
1060           eliminate the warning, all unused variables can be replaced
1061           with wildcards.</para>
1062         </listitem>
1063       </varlistentry>
1064
1065     </VariableList>
1066
1067     <para>If you're feeling really paranoid, the
1068     <option>-dcore-lint</option>
1069     option<indexterm><primary><option>-dcore-lint</option></primary></indexterm>
1070     is a good choice.  It turns on heavyweight intra-pass
1071     sanity-checking within GHC.  (It checks GHC's sanity, not
1072     yours.)</para>
1073
1074   </sect1>
1075
1076   &separate;
1077   &packages;
1078
1079   <sect1 id="options-optimise">
1080     <title>Optimisation (code improvement)</title>
1081
1082     <indexterm><primary>optimisation</primary></indexterm>
1083     <indexterm><primary>improvement, code</primary></indexterm>
1084
1085     <para>The <option>-O*</option> options specify convenient
1086     &ldquo;packages&rdquo; of optimisation flags; the
1087     <option>-f*</option> options described later on specify
1088     <emphasis>individual</emphasis> optimisations to be turned on/off;
1089     the <option>-m*</option> options specify
1090     <emphasis>machine-specific</emphasis> optimisations to be turned
1091     on/off.</para>
1092
1093     <sect2 id="optimise-pkgs">
1094       <title><option>-O*</option>: convenient &ldquo;packages&rdquo; of optimisation flags.</title>
1095
1096       <para>There are <emphasis>many</emphasis> options that affect
1097       the quality of code produced by GHC.  Most people only have a
1098       general goal, something like &ldquo;Compile quickly&rdquo; or
1099       &ldquo;Make my program run like greased lightning.&rdquo; The
1100       following &ldquo;packages&rdquo; of optimisations (or lack
1101       thereof) should suffice.</para>
1102
1103       <para>Once you choose a <option>-O*</option>
1104       &ldquo;package,&rdquo; stick with it&mdash;don't chop and
1105       change.  Modules' interfaces <emphasis>will</emphasis> change
1106       with a shift to a new <option>-O*</option> option, and you may
1107       have to recompile a large chunk of all importing modules before
1108       your program can again be run safely (see <XRef
1109       LinkEnd="recomp">).</para>
1110
1111       <variablelist>
1112
1113         <varlistentry>
1114           <term>No <option>-O*</option>-type option specified:</term>
1115           <indexterm><primary>-O* not specified</primary></indexterm>
1116           <listitem>
1117             <para>This is taken to mean: &ldquo;Please compile
1118             quickly; I'm not over-bothered about compiled-code
1119             quality.&rdquo; So, for example: <command>ghc -c
1120             Foo.hs</command></para>
1121           </listitem>
1122         </varlistentry>
1123
1124         <varlistentry>
1125           <term><option>-O0</option>:</term>
1126           <indexterm><primary><option>-O0</option></primary></indexterm>
1127           <listitem>
1128             <para>Means &ldquo;turn off all optimisation&rdquo;,
1129             reverting to the same settings as if no
1130             <option>-O</option> options had been specified.  Saying
1131             <option>-O0</option> can be useful if
1132             eg. <command>make</command> has inserted a
1133             <option>-O</option> on the command line already.</para>
1134           </listitem>
1135         </varlistentry>
1136
1137         <varlistentry>
1138           <term><option>-O</option> or <option>-O1</option>:</term>
1139           <indexterm><primary>-O option</primary></indexterm>
1140           <indexterm><primary>-O1 option</primary></indexterm>
1141           <indexterm><primary>optimise</primary><secondary>normally</secondary></indexterm>
1142           <listitem>
1143             <para>Means: &ldquo;Generate good-quality code without
1144             taking too long about it.&rdquo; Thus, for example:
1145             <command>ghc -c -O Main.lhs</command></para>
1146           </listitem>
1147         </varlistentry>
1148
1149         <varlistentry>
1150           <term><option>-O2</option>:</term>
1151           <indexterm><primary>-O2 option</primary></indexterm>
1152           <indexterm><primary>optimise</primary><secondary>aggressively</secondary></indexterm>
1153           <listitem>
1154             <para>Means: &ldquo;Apply every non-dangerous
1155             optimisation, even if it means significantly longer
1156             compile times.&rdquo;</para>
1157
1158             <para>The avoided &ldquo;dangerous&rdquo; optimisations
1159             are those that can make runtime or space
1160             <emphasis>worse</emphasis> if you're unlucky.  They are
1161             normally turned on or off individually.</para>
1162
1163             <para>At the moment, <option>-O2</option> is
1164             <emphasis>unlikely</emphasis> to produce better code than
1165             <option>-O</option>.</para>
1166           </listitem>
1167         </varlistentry>
1168
1169         <varlistentry>
1170           <term><option>-O2-for-C</option>:</term>
1171           <indexterm><primary>-O2-for-C option</primary></indexterm>
1172           <indexterm><primary>gcc, invoking with -O2</primary></indexterm>
1173           <listitem>
1174             <para>Says to run GCC with <option>-O2</option>, which may
1175             be worth a few percent in execution speed.  Don't forget
1176             <option>-fvia-C</option>, lest you use the native-code
1177             generator and bypass GCC altogether!</para>
1178           </listitem>
1179         </varlistentry>
1180
1181         <varlistentry>
1182           <term><option>-Ofile &lt;file&gt;</option>:</term>
1183           <indexterm><primary>-Ofile &lt;file&gt; option</primary></indexterm>
1184           <indexterm><primary>optimising, customised</primary></indexterm>
1185           <listitem>
1186             <para>(NOTE: not supported yet in GHC 5.x.  Please ask if
1187             you're interested in this.)</para>
1188
1189             <para>For those who need <emphasis>absolute</emphasis>
1190             control over <emphasis>exactly</emphasis> what options are
1191             used (e.g., compiler writers, sometimes :-), a list of
1192             options can be put in a file and then slurped in with
1193             <option>-Ofile</option>.</para>
1194
1195             <para>In that file, comments are of the
1196             <literal>&num;</literal>-to-end-of-line variety; blank
1197             lines and most whitespace is ignored.</para>
1198
1199             <para>Please ask if you are baffled and would like an
1200             example of <option>-Ofile</option>!</para>
1201           </listitem>
1202         </varlistentry>
1203       </variablelist>
1204
1205       <para>We don't use a <option>-O*</option> flag for day-to-day
1206       work.  We use <option>-O</option> to get respectable speed;
1207       e.g., when we want to measure something.  When we want to go for
1208       broke, we tend to use <option>-O -fvia-C -O2-for-C</option> (and
1209       we go for lots of coffee breaks).</para>
1210
1211       <para>The easiest way to see what <option>-O</option> (etc.)
1212       &ldquo;really mean&rdquo; is to run with <option>-v</option>,
1213       then stand back in amazement.</para>
1214     </sect2>
1215
1216     <sect2 id="options-f">
1217       <title><option>-f*</option>: platform-independent flags</title>
1218
1219       <indexterm><primary>-f* options (GHC)</primary></indexterm>
1220       <indexterm><primary>-fno-* options (GHC)</primary></indexterm>
1221
1222       <para>These flags turn on and off individual optimisations.
1223       They are normally set via the <option>-O</option> options
1224       described above, and as such, you shouldn't need to set any of
1225       them explicitly (indeed, doing so could lead to unexpected
1226       results).  However, there are one or two that may be of
1227       interest:</para>
1228
1229       <variablelist>
1230         <varlistentry>
1231           <term><option>-fexcess-precision</option>:</term>
1232           <listitem>
1233             <indexterm><primary><option>-fexcess-precision</option></primary></indexterm>
1234             <para>When this option is given, intermediate floating
1235             point values can have a <emphasis>greater</emphasis>
1236             precision/range than the final type.  Generally this is a
1237             good thing, but some programs may rely on the exact
1238             precision/range of
1239             <literal>Float</literal>/<literal>Double</literal> values
1240             and should not use this option for their compilation.</para>
1241           </listitem>
1242         </varlistentry>
1243
1244         <varlistentry>
1245           <term><option>-fignore-asserts</option>:</term>
1246           <listitem>
1247             <indexterm><primary><option>-fignore-asserts</option></primary></indexterm>
1248             <para>Causes GHC to ignore uses of the function
1249             <literal>Exception.assert</literal> in source code (in
1250             other words, rewriting <literal>Exception.assert p
1251             e</literal> to <literal>e</literal> (see <xref
1252             linkend="sec-assertions">).  This flag is turned on by
1253             <option>-O</option>.
1254             </para>
1255           </listitem>
1256         </varlistentry>
1257
1258         <varlistentry>
1259           <term><option>-fno-strictness</option></term>
1260           <indexterm><primary><option>-fno-strictness</option></primary>
1261           </indexterm>
1262           <listitem>
1263             <para>Turns off the strictness analyser; sometimes it eats
1264             too many cycles.</para>
1265           </listitem>
1266         </varlistentry>
1267
1268         <varlistentry>
1269           <term><option>-fno-cpr-analyse</option></term>
1270           <indexterm><primary><option>-fno-cpr-analyse</option></primary>
1271           </indexterm>
1272           <listitem>
1273             <para>Turns off the CPR (constructed product result)
1274             analysis; it is somewhat experimental.</para>
1275           </listitem>
1276         </varlistentry>
1277
1278         <varlistentry>
1279           <term><option>-funbox-strict-fields</option>:</term>
1280           <listitem>
1281             <indexterm><primary><option>-funbox-strict-fields</option></primary></indexterm>
1282             <indexterm><primary>strict constructor fields</primary></indexterm>
1283             <indexterm><primary>constructor fields, strict</primary></indexterm>
1284
1285             <para>This option causes all constructor fields which are
1286             marked strict (i.e. &ldquo;!&rdquo;) to be unboxed or
1287             unpacked if possible.  For example:</para>
1288
1289 <ProgramListing>
1290 data T = T !Float !Float
1291 </ProgramListing>
1292
1293             <para>will create a constructor <literal>T</literal>
1294             containing two unboxed floats if the
1295             <option>-funbox-strict-fields</option> flag is given.
1296             This may not always be an optimisation: if the
1297             <Function>T</Function> constructor is scrutinised and the
1298             floats passed to a non-strict function for example, they
1299             will have to be reboxed (this is done automatically by the
1300             compiler).</para>
1301
1302             <para>This option should only be used in conjunction with
1303             <option>-O</option>, in order to expose unfoldings to the
1304             compiler so the reboxing can be removed as often as
1305             possible.  For example:</para>
1306
1307 <ProgramListing>
1308 f :: T -&#62; Float
1309 f (T f1 f2) = f1 + f2
1310 </ProgramListing>
1311
1312             <para>The compiler will avoid reboxing
1313             <Function>f1</Function> and <Function>f2</Function> by
1314             inlining <Function>+</Function> on floats, but only when
1315             <option>-O</option> is on.</para>
1316
1317             <para>Any single-constructor data is eligible for
1318             unpacking; for example</para>
1319
1320 <ProgramListing>
1321 data T = T !(Int,Int)
1322 </ProgramListing>
1323
1324             <para>will store the two <literal>Int</literal>s directly
1325             in the <Function>T</Function> constructor, by flattening
1326             the pair.  Multi-level unpacking is also supported:</para>
1327
1328 <ProgramListing>
1329 data T = T !S
1330 data S = S !Int !Int
1331 </ProgramListing>
1332
1333             <para>will store two unboxed <literal>Int&num;</literal>s
1334             directly in the <Function>T</Function> constructor.</para>
1335           </listitem>
1336         </varlistentry>
1337
1338         <varlistentry>
1339           <term><option>-funfolding-update-in-place&lt;n&gt;</option></term>
1340           <indexterm><primary><option>-funfolding-update-in-place</option></primary></indexterm>
1341           <listitem>
1342             <para>Switches on an experimental "optimisation".
1343             Switching it on makes the compiler a little keener to
1344             inline a function that returns a constructor, if the
1345             context is that of a thunk.
1346 <ProgramListing>
1347    x = plusInt a b
1348 </ProgramListing>
1349             If we inlined plusInt we might get an opportunity to use
1350             update-in-place for the thunk 'x'.</para>
1351           </listitem>
1352         </varlistentry>
1353
1354         <varlistentry>
1355           <term><option>-funfolding-creation-threshold&lt;n&gt;</option>:</term>
1356           <listitem>
1357             <indexterm><primary><option>-funfolding-creation-threshold</option></primary></indexterm>
1358             <indexterm><primary>inlining, controlling</primary></indexterm>
1359             <indexterm><primary>unfolding, controlling</primary></indexterm>
1360
1361             <para>(Default: 45) Governs the maximum size that GHC will
1362             allow a function unfolding to be.   (An unfolding has a
1363             &ldquo;size&rdquo; that reflects the cost in terms of
1364             &ldquo;code bloat&rdquo; of expanding that unfolding at
1365             at a call site. A bigger function would be assigned a
1366             bigger cost.) </para>
1367
1368             <para> Consequences: (a) nothing larger than this will be
1369             inlined (unless it has an INLINE pragma); (b) nothing
1370             larger than this will be spewed into an interface
1371             file. </para>
1372
1373
1374             <para> Increasing this figure is more likely to result in longer
1375             compile times than faster code.  The next option is more
1376             useful:</para>
1377           </listitem>
1378         </varlistentry>
1379
1380         <varlistentry>
1381           <term><option>-funfolding-use-threshold&lt;n&gt;</option>:</term>
1382           <listitem>
1383             <indexterm><primary><option>-funfolding-use-threshold</option></primary></indexterm>
1384             <indexterm><primary>inlining, controlling</primary></indexterm>
1385             <indexterm><primary>unfolding, controlling</primary></indexterm>
1386
1387             <para>(Default: 8) This is the magic cut-off figure for
1388             unfolding: below this size, a function definition will be
1389             unfolded at the call-site, any bigger and it won't.  The
1390             size computed for a function depends on two things: the
1391             actual size of the expression minus any discounts that
1392             apply (see <option>-funfolding-con-discount</option>).</para>
1393           </listitem>
1394         </varlistentry>
1395       </variablelist>
1396
1397     </sect2>
1398
1399   </sect1>
1400
1401 &phases;
1402
1403 <Sect1 id="sec-using-concurrent">
1404 <title>Using Concurrent Haskell</title>
1405
1406 <para>
1407 <indexterm><primary>Concurrent Haskell&mdash;use</primary></indexterm>
1408 </para>
1409
1410 <para>
1411 GHC (as of version 4.00) supports Concurrent Haskell by default,
1412 without requiring a special option or libraries compiled in a certain
1413 way.  To get access to the support libraries for Concurrent Haskell
1414 (i.e. <literal>Concurrent</literal> and friends), use the
1415 <option>-package concurrent</option> option.
1416 </para>
1417
1418 <para>
1419 Three RTS options are provided for modifying the behaviour of the
1420 threaded runtime system.  See the descriptions of
1421 <option>-C[&lt;us&gt;]</option>, <option>-q</option>, and
1422 <option>-t&lt;num&gt;</option> in <XRef LinkEnd="parallel-rts-opts">.
1423 </para>
1424
1425 <para>
1426 Concurrent Haskell is described in more detail in <XRef
1427 LinkEnd="sec-Concurrent">.
1428 </para>
1429
1430 </Sect1>
1431
1432 <Sect1 id="sec-using-parallel">
1433 <title>Using Parallel Haskell</title>
1434
1435 <para>
1436 <indexterm><primary>Parallel Haskell&mdash;use</primary></indexterm>
1437 </para>
1438
1439 <para>
1440 &lsqb;You won't be able to execute parallel Haskell programs unless PVM3
1441 (Parallel Virtual Machine, version 3) is installed at your site.&rsqb;
1442 </Para>
1443
1444 <para>
1445 To compile a Haskell program for parallel execution under PVM, use the
1446 <Option>-parallel</Option> option,<IndexTerm><Primary>-parallel
1447 option</Primary></IndexTerm> both when compiling <Emphasis>and
1448 linking</Emphasis>.  You will probably want to <Literal>import
1449 Parallel</Literal> into your Haskell modules.
1450 </Para>
1451
1452 <para>
1453 To run your parallel program, once PVM is going, just invoke it
1454 &ldquo;as normal&rdquo;.  The main extra RTS option is
1455 <Option>-qp&lt;n&gt;</Option>, to say how many PVM
1456 &ldquo;processors&rdquo; your program to run on.  (For more details of
1457 all relevant RTS options, please see <XRef
1458 LinkEnd="parallel-rts-opts">.)
1459 </para>
1460
1461 <para>
1462 In truth, running Parallel Haskell programs and getting information
1463 out of them (e.g., parallelism profiles) is a battle with the vagaries of
1464 PVM, detailed in the following sections.
1465 </para>
1466
1467 <Sect2 id="pvm-dummies">
1468 <Title>Dummy's guide to using PVM</Title>
1469
1470 <para>
1471 <indexterm><primary>PVM, how to use</primary></indexterm>
1472 <indexterm><primary>Parallel Haskell&mdash;PVM use</primary></indexterm>
1473 Before you can run a parallel program under PVM, you must set the
1474 required environment variables (PVM's idea, not ours); something like,
1475 probably in your <filename>.cshrc</filename> or equivalent:
1476
1477 <ProgramListing>
1478 setenv PVM_ROOT /wherever/you/put/it
1479 setenv PVM_ARCH `$PVM_ROOT/lib/pvmgetarch`
1480 setenv PVM_DPATH $PVM_ROOT/lib/pvmd
1481 </ProgramListing>
1482
1483 </para>
1484
1485 <para>
1486 Creating and/or controlling your &ldquo;parallel machine&rdquo; is a purely-PVM
1487 business; nothing specific to Parallel Haskell. The following paragraphs
1488 describe how to configure your parallel machine interactively.
1489 </Para>
1490
1491 <Para>
1492 If you use parallel Haskell regularly on the same machine configuration it
1493 is a good idea to maintain a file with all machine names and to make the
1494 environment variable PVM_HOST_FILE point to this file. Then you can avoid
1495 the interactive operations described below by just saying
1496 </Para>
1497
1498 <ProgramListing>
1499 pvm $PVM_HOST_FILE
1500 </ProgramListing>
1501
1502 <Para>
1503 You use the <Command>pvm</Command><IndexTerm><Primary>pvm command</Primary></IndexTerm> command to start PVM on your
1504 machine.  You can then do various things to control/monitor your
1505 &ldquo;parallel machine;&rdquo; the most useful being:
1506 </para>
1507
1508 <para>
1509 <InformalTable>
1510 <TGroup Cols=2>
1511 <ColSpec Align="Left">
1512 <TBody>
1513
1514 <row>
1515 <entry><KeyCombo><KeyCap>Control</KeyCap><KeyCap>D</KeyCap></KeyCombo></entry>
1516 <entry>exit <command>pvm</command>, leaving it running</entry>
1517 </row>
1518
1519 <row>
1520 <entry><command>halt</command></entry>
1521 <entry>kill off this &ldquo;parallel machine&rdquo; &amp; exit</entry>
1522 </row>
1523
1524 <row>
1525 <entry><command>add &lt;host&gt;</command></entry>
1526 <entry>add <command>&lt;host&gt;</command> as a processor</entry>
1527 </row>
1528
1529 <row>
1530 <entry><command>delete &lt;host&gt;</command></entry>
1531 <entry>delete <command>&lt;host&gt;</command></entry>
1532 </row>
1533
1534 <row>
1535 <entry><command>reset</command></entry>
1536 <entry>kill what's going, but leave PVM up</entry>
1537 </row>
1538
1539 <row>
1540 <entry><command>conf</command></entry>
1541 <entry>list the current configuration</entry>
1542 </row>
1543
1544 <row>
1545 <entry><command>ps</command></entry>
1546 <entry>report processes' status</entry>
1547 </row>
1548
1549 <row>
1550 <entry><command>pstat &lt;pid&gt;</command></entry>
1551 <entry>status of a particular process</entry>
1552 </row>
1553
1554 </TBody>
1555 </TGroup>
1556 </InformalTable>
1557 </para>
1558
1559 <para>
1560 The PVM documentation can tell you much, much more about <command>pvm</command>!
1561 </para>
1562
1563 </sect2>
1564
1565 <Sect2 id="par-profiles">
1566 <Title>Parallelism profiles</Title>
1567
1568 <para>
1569 <indexterm><primary>parallelism profiles</primary></indexterm>
1570 <indexterm><primary>profiles, parallelism</primary></indexterm>
1571 <indexterm><primary>visualisation tools</primary></indexterm>
1572 </para>
1573
1574 <para>
1575 With Parallel Haskell programs, we usually don't care about the
1576 results&mdash;only with &ldquo;how parallel&rdquo; it was!  We want pretty pictures.
1577 </para>
1578
1579 <Para>
1580 Parallelism profiles (&agrave; la <Command>hbcpp</Command>) can be generated with the
1581 <Option>-qP</Option><IndexTerm><Primary>-qP RTS option (concurrent, parallel)</Primary></IndexTerm> RTS option.  The
1582 per-processor profiling info is dumped into files named
1583 <Filename>&lt;full-path&gt;&lt;program&gt;.gr</Filename>.  These are then munged into a PostScript picture,
1584 which you can then display.  For example, to run your program
1585 <Filename>a.out</Filename> on 8 processors, then view the parallelism profile, do:
1586 </Para>
1587
1588 <Para>
1589
1590 <Screen>
1591 <prompt>&dollar;</prompt> ./a.out +RTS -qP -qp8
1592 <prompt>&dollar;</prompt> grs2gr *.???.gr &#62; temp.gr # combine the 8 .gr files into one
1593 <prompt>&dollar;</prompt> gr2ps -O temp.gr              # cvt to .ps; output in temp.ps
1594 <prompt>&dollar;</prompt> ghostview -seascape temp.ps   # look at it!
1595 </Screen>
1596
1597 </Para>
1598
1599 <para>
1600 The scripts for processing the parallelism profiles are distributed
1601 in <filename>ghc/utils/parallel/</filename>.
1602 </para>
1603
1604 </sect2>
1605
1606 <Sect2>
1607 <Title>Other useful info about running parallel programs</Title>
1608
1609 <Para>
1610 The &ldquo;garbage-collection statistics&rdquo; RTS options can be useful for
1611 seeing what parallel programs are doing.  If you do either
1612 <Option>+RTS -Sstderr</Option><IndexTerm><Primary>-Sstderr RTS option</Primary></IndexTerm> or <Option>+RTS -sstderr</Option>, then
1613 you'll get mutator, garbage-collection, etc., times on standard
1614 error. The standard error of all PE's other than the `main thread'
1615 appears in <filename>/tmp/pvml.nnn</filename>, courtesy of PVM.
1616 </para>
1617
1618 <para>
1619 Whether doing <option>+RTS -Sstderr</option> or not, a handy way to watch
1620 what's happening overall is: <command>tail -f /tmp/pvml.nnn</command>.
1621 </para>
1622
1623 </sect2>
1624
1625 <Sect2 id="parallel-rts-opts">
1626 <title>RTS options for Concurrent/Parallel Haskell
1627 </title>
1628
1629 <para>
1630 <indexterm><primary>RTS options, concurrent</primary></indexterm>
1631 <indexterm><primary>RTS options, parallel</primary></indexterm>
1632 <indexterm><primary>Concurrent Haskell&mdash;RTS options</primary></indexterm>
1633 <indexterm><primary>Parallel Haskell&mdash;RTS options</primary></indexterm>
1634 </para>
1635
1636 <para>
1637 Besides the usual runtime system (RTS) options
1638 (<XRef LinkEnd="runtime-control">), there are a few options particularly
1639 for concurrent/parallel execution.
1640 </para>
1641
1642 <para>
1643 <VariableList>
1644
1645 <VarListEntry>
1646 <Term><Option>-qp&lt;N&gt;</Option>:</Term>
1647 <ListItem>
1648 <Para>
1649 <IndexTerm><Primary>-qp&lt;N&gt; RTS option</Primary></IndexTerm>
1650 (PARALLEL ONLY) Use <Literal>&lt;N&gt;</Literal> PVM processors to run this program;
1651 the default is 2.
1652 </para>
1653 </listitem>
1654 </varlistentry>
1655 <varlistentry>
1656 <term><option>-C[&lt;us&gt;]</option>:</term>
1657 <listitem>
1658 <para>
1659 <indexterm><primary>-C&lt;us&gt; RTS option</primary></indexterm> Sets
1660 the context switch interval to <literal>&lt;s&gt;</literal> seconds.
1661 A context switch will occur at the next heap block allocation after
1662 the timer expires (a heap block allocation occurs every 4k of
1663 allocation).  With <option>-C0</option> or <option>-C</option>,
1664 context switches will occur as often as possible (at every heap block
1665 allocation).  By default, context switches occur every 20ms
1666 milliseconds.  Note that GHC's internal timer ticks every 20ms, and
1667 the context switch timer is always a multiple of this timer, so 20ms
1668 is the maximum granularity available for timed context switches.
1669 </para>
1670 </listitem>
1671 </varlistentry>
1672 <varlistentry>
1673 <term><option>-q[v]</option>:</term>
1674 <listitem>
1675 <para>
1676 <indexterm><primary>-q RTS option</primary></indexterm>
1677 (PARALLEL ONLY) Produce a quasi-parallel profile of thread activity,
1678 in the file <FIlename>&lt;program&gt;.qp</FIlename>.  In the style of <command>hbcpp</command>, this profile
1679 records the movement of threads between the green (runnable) and red
1680 (blocked) queues.  If you specify the verbose suboption (<option>-qv</option>), the
1681 green queue is split into green (for the currently running thread
1682 only) and amber (for other runnable threads).  We do not recommend
1683 that you use the verbose suboption if you are planning to use the
1684 <Command>hbcpp</Command> profiling tools or if you are context switching at every heap
1685 check (with <Option>-C</Option>).
1686 -->
1687 </Para>
1688 </ListItem>
1689 </VarListEntry>
1690 <VarListEntry>
1691 <Term><Option>-qt&lt;num&gt;</Option>:</Term>
1692 <ListItem>
1693 <Para>
1694 <IndexTerm><Primary>-qt&lt;num&gt; RTS option</Primary></IndexTerm>
1695 (PARALLEL ONLY) Limit the thread pool size, i.e. the number of concurrent
1696 threads per processor to <Literal>&lt;num&gt;</Literal>.  The default is
1697 32.  Each thread requires slightly over 1K <Emphasis>words</Emphasis> in
1698 the heap for thread state and stack objects.  (For 32-bit machines, this
1699 translates to 4K bytes, and for 64-bit machines, 8K bytes.)
1700 </Para>
1701 </ListItem>
1702 </VarListEntry>
1703 <!-- no more -HWL
1704 <VarListEntry>
1705 <Term><Option>-d</Option>:</Term>
1706 <ListItem>
1707 <Para>
1708 <IndexTerm><Primary>-d RTS option (parallel)</Primary></IndexTerm>
1709 (PARALLEL ONLY) Turn on debugging.  It pops up one xterm (or GDB, or
1710 something&hellip;) per PVM processor.  We use the standard <Command>debugger</Command>
1711 script that comes with PVM3, but we sometimes meddle with the
1712 <Command>debugger2</Command> script.  We include ours in the GHC distribution,
1713 in <Filename>ghc/utils/pvm/</Filename>.
1714 </Para>
1715 </ListItem>
1716 </VarListEntry>
1717 -->
1718 <VarListEntry>
1719 <Term><Option>-qe&lt;num&gt;</Option>:</Term>
1720 <ListItem>
1721 <Para>
1722 <IndexTerm><Primary>-qe&lt;num&gt; RTS option
1723 (parallel)</Primary></IndexTerm> (PARALLEL ONLY) Limit the spark pool size
1724 i.e. the number of pending sparks per processor to
1725 <Literal>&lt;num&gt;</Literal>. The default is 100. A larger number may be
1726 appropriate if your program generates large amounts of parallelism
1727 initially.
1728 </Para>
1729 </ListItem>
1730 </VarListEntry>
1731 <VarListEntry>
1732 <Term><Option>-qQ&lt;num&gt;</Option>:</Term>
1733 <ListItem>
1734 <Para>
1735 <IndexTerm><Primary>-qQ&lt;num&gt; RTS option (parallel)</Primary></IndexTerm>
1736 (PARALLEL ONLY) Set the size of packets transmitted between processors
1737 to <Literal>&lt;num&gt;</Literal>. The default is 1024 words. A larger number may be
1738 appropriate if your machine has a high communication cost relative to
1739 computation speed.
1740 </Para>
1741 </ListItem>
1742 </VarListEntry>
1743 <VarListEntry>
1744 <Term><Option>-qh&lt;num&gt;</Option>:</Term>
1745 <ListItem>
1746 <Para>
1747 <IndexTerm><Primary>-qh&lt;num&gt; RTS option (parallel)</Primary></IndexTerm>
1748 (PARALLEL ONLY) Select a packing scheme. Set the number of non-root thunks to pack in one packet to
1749 &lt;num&gt;-1 (0 means infinity). By default GUM uses full-subgraph
1750 packing, i.e. the entire subgraph with the requested closure as root is
1751 transmitted (provided it fits into one packet). Choosing a smaller value
1752 reduces the amount of pre-fetching of work done in GUM. This can be
1753 advantageous for improving data locality but it can also worsen the balance
1754 of the load in the system.
1755 </Para>
1756 </ListItem>
1757 </VarListEntry>
1758 <VarListEntry>
1759 <Term><Option>-qg&lt;num&gt;</Option>:</Term>
1760 <ListItem>
1761 <Para>
1762 <IndexTerm><Primary>-qg&lt;num&gt; RTS option
1763 (parallel)</Primary></IndexTerm> (PARALLEL ONLY) Select a globalisation
1764 scheme. This option affects the
1765 generation of global addresses when transferring data. Global addresses are
1766 globally unique identifiers required to maintain sharing in the distributed
1767 graph structure. Currently this is a binary option. With &lt;num&gt;=0 full globalisation is used
1768 (default). This means a global address is generated for every closure that
1769 is transmitted. With &lt;num&gt;=1 a thunk-only globalisation scheme is
1770 used, which generated global address only for thunks. The latter case may
1771 lose sharing of data but has a reduced overhead in packing graph structures
1772 and maintaining internal tables of global addresses.
1773 </Para>
1774 </ListItem>
1775 </VarListEntry>
1776 </VariableList>
1777 </para>
1778
1779 </sect2>
1780
1781 </Sect1>
1782
1783   <sect1 id="options-platform">
1784     <title>Platform-specific Flags</title>
1785
1786     <indexterm><primary>-m* options</primary></indexterm>
1787     <indexterm><primary>platform-specific options</primary></indexterm>
1788     <indexterm><primary>machine-specific options</primary></indexterm>
1789
1790     <para>Some flags only make sense for particular target
1791     platforms.</para>
1792
1793     <variablelist>
1794
1795       <varlistentry>
1796         <term><option>-mv8</option>:</term>
1797         <listitem>
1798           <para>(SPARC machines)<indexterm><primary>-mv8 option (SPARC
1799           only)</primary></indexterm> Means to pass the like-named
1800           option to GCC; it says to use the Version 8 SPARC
1801           instructions, notably integer multiply and divide.  The
1802           similiar <option>-m*</option> GCC options for SPARC also
1803           work, actually.</para>
1804         </listitem>
1805       </varlistentry>
1806
1807       <varlistentry>
1808         <term><option>-monly-[32]-regs</option>:</term>
1809         <listitem>
1810           <para>(iX86 machines)<indexterm><primary>-monly-N-regs
1811           option (iX86 only)</primary></indexterm> GHC tries to
1812           &ldquo;steal&rdquo; four registers from GCC, for performance
1813           reasons; it almost always works.  However, when GCC is
1814           compiling some modules with four stolen registers, it will
1815           crash, probably saying:
1816
1817 <Screen>
1818 Foo.hc:533: fixed or forbidden register was spilled.
1819 This may be due to a compiler bug or to impossible asm
1820 statements or clauses.
1821 </Screen>
1822
1823           Just give some registers back with
1824           <option>-monly-N-regs</option>.  Try `3' first, then `2'.
1825           If `2' doesn't work, please report the bug to us.</para>
1826         </listitem>
1827       </varlistentry>
1828     </variablelist>
1829
1830   </sect1>
1831
1832 &runtime;
1833 &debug;
1834 &flags;
1835
1836 </Chapter>
1837
1838 <!-- Emacs stuff:
1839      ;;; Local Variables: ***
1840      ;;; mode: sgml ***
1841      ;;; sgml-parent-document: ("users_guide.sgml" "book" "chapter") ***
1842      ;;; End: ***
1843  -->