f209d57b5af0a8ab718e6448931d1c448e79a95d
[ghc.git] / docs / users_guide / packages.xml
1 <?xml version="1.0" encoding="iso-8859-1"?>
2 <sect1 id="packages">
3 <title>
4 Packages
5 </title>
6 <indexterm><primary>packages</primary></indexterm>
7
8 <para>A package is a library of Haskell modules known to the compiler. GHC
9 comes with several packages: see the accompanying
10 <ulink url="../libraries/index.html">library documentation</ulink>.</para>
11
12 <para>Using a package couldn't be simpler: if you're using
13 <option>--make</option> or GHCi, then most of the installed packages will be
14 automatically available to your program without any further options. The
15 exceptions to this rule are covered below in <xref
16 linkend="using-packages" />.</para>
17
18 <para>Building your own packages is also quite straightforward: we provide
19 the <ulink url="http://www.haskell.org/cabal/">Cabal</ulink> infrastructure which
20 automates the process of configuring, building, installing and distributing
21 a package. All you need to do is write a simple configuration file, put a
22 few files in the right places, and you have a package. See the
23 <ulink url="../Cabal/index.html">Cabal documentation</ulink>
24 for details, and also the Cabal libraries (<ulink url="../libraries/Cabal/Distribution-Simple.html">Distribution.Simple</ulink>,
25 for example).</para>
26
27 <sect2 id="using-packages">
28 <title>Using Packages
29 </title>
30 <indexterm><primary>packages</primary>
31 <secondary>using</secondary></indexterm>
32
33 <para>To see which packages are installed, use the
34 <literal>ghc-pkg</literal> command:</para>
35
36 <screen>
37 $ ghc-pkg list
38 /usr/lib/ghc-6.4/package.conf:
39 base-1.0, haskell98-1.0, template-haskell-1.0, mtl-1.0, unix-1.0,
40 Cabal-1.0, haskell-src-1.0, parsec-1.0, network-1.0,
41 QuickCheck-1.0, HUnit-1.1, fgl-1.0, X11-1.1, HGL-3.1, OpenGL-2.0,
42 GLUT-2.0, stm-1.0, readline-1.0, (lang-1.0), (concurrent-1.0),
43 (posix-1.0), (util-1.0), (data-1.0), (text-1.0), (net-1.0),
44 (hssource-1.0), rts-1.0
45 </screen>
46
47 <para>Packages are either exposed or hidden. Only
48 modules from exposed packages may be imported by your Haskell code; if
49 you try to import a module from a hidden package, GHC will emit an error
50 message.</para>
51
52 <para>Each package has an exposed flag, which says whether it is exposed by
53 default or not. Packages hidden by default are listed in
54 parentheses (eg. <literal>(lang-1.0)</literal>) in the output from
55 <literal>ghc-pkg list</literal>. To expose a package which is hidden by
56 default, use the <option>-package</option>
57 flag (see below).</para>
58
59 <para>To see which modules are exposed by a package:</para>
60
61 <screen>
62 $ ghc-pkg field network exposed-modules
63 exposed-modules: Network.BSD,
64 Network.CGI,
65 Network.Socket,
66 Network.URI,
67 Network
68 </screen>
69
70 <para>In general, packages containing hierarchical modules are usually
71 exposed by default. However, it is possible for two packages to contain
72 the same module: in this case, only one of the packages should be
73 exposed. It is an error to import a module that belongs to more than one
74 exposed package.</para>
75
76 <para>The GHC command line options that control packages are:</para>
77
78 <variablelist>
79 <varlistentry>
80 <term>
81 <option>-package <replaceable>P</replaceable></option>
82 <indexterm><primary><option>-package</option></primary></indexterm>
83 </term>
84 <listitem>
85 <para>This option causes package <replaceable>P</replaceable> to be
86 exposed. The package <replaceable>P</replaceable> can be specified
87 in full with its version number
88 (e.g. <literal>network-1.0</literal>) or the version number can be
89 omitted if there is only one version of the package
90 installed.</para>
91
92 <para>If there are multiple versions of <replaceable>P</replaceable>
93 installed, then all other versions will become hidden.</para>
94
95 <para>The <option>-package <replaceable>P</replaceable></option>
96 option also causes package <replaceable>P</replaceable> to be
97 linked into the resulting executable. In
98 <option>&ndash;&ndash;make</option> mode and GHCi, the compiler
99 normally determines which packages are required by the current
100 Haskell modules, and links only those. In batch mode however, the
101 dependency information isn't available, and explicit
102 <option>-package</option> options must be given when linking.</para>
103
104 <para>For example, to link a program consisting of objects
105 <filename>Foo.o</filename> and <filename>Main.o</filename>, where
106 we made use of the <literal>network</literal> package, we need to
107 give GHC the <literal>-package</literal> flag thus:
108
109 <screen>$ ghc -o myprog Foo.o Main.o -package network</screen>
110
111 The same flag is necessary even if we compiled the modules from
112 source, because GHC still reckons it's in batch mode:
113
114 <screen>$ ghc -o myprog Foo.hs Main.hs -package network</screen>
115
116 In <literal>--make</literal> and <literal>--interactive</literal>
117 modes (<xref linkend="modes" />), however, GHC figures out the
118 packages required for linking without further assistance.</para>
119
120 <para>The one other time you might need to use
121 <option>-package</option> to force linking a package is when the
122 package does not contain any Haskell modules (it might contain a C
123 library only, for example). In that case, GHC
124 will never discover a dependency on it, so it has to be mentioned
125 explicitly.</para>
126 </listitem>
127 </varlistentry>
128
129 <varlistentry>
130 <term><option>-hide-all-packages</option>
131 <indexterm><primary><option>-hide-package</option></primary>
132 </indexterm></term>
133 <listitem>
134 <para>Ignore the exposed flag on installed packages, and hide them
135 all by default. If you use
136 this flag, then any packages you require (including
137 <literal>base</literal>) need to be explicitly exposed using
138 <option>-package</option> options.</para>
139
140 <para>This is a good way to insulate your program from
141 differences in the globally exposed packages, and being
142 explicit about package dependencies is a Good Thing.
143 Cabal always passes the
144 <option>-hide-all-packages</option> flag to GHC, for
145 exactly this reason.</para>
146 </listitem>
147 </varlistentry>
148
149 <varlistentry>
150 <term><option>-hide-package</option> <replaceable>P</replaceable>
151 <indexterm><primary><option>-hide-package</option></primary>
152 </indexterm></term>
153 <listitem>
154 <para>This option does the opposite of <option>-package</option>: it
155 causes the specified package to be <firstterm>hidden</firstterm>,
156 which means that none of its modules will be available for import
157 by Haskell <literal>import</literal> directives.</para>
158
159 <para>Note that the package might still end up being linked into the
160 final program, if it is a dependency (direct or indirect) of
161 another exposed package.</para>
162 </listitem>
163 </varlistentry>
164
165 <varlistentry>
166 <term><option>-ignore-package</option> <replaceable>P</replaceable>
167 <indexterm><primary><option>-ignore-package</option></primary>
168 </indexterm></term>
169 <listitem>
170 <para>Causes the compiler to behave as if package
171 <replaceable>P</replaceable>, and any packages that depend on
172 <literal>P</literal>, are not installed at all.</para>
173
174 <para>Saying <literal>-ignore-package P</literal> is the same as
175 giving <literal>-hide-package</literal> flags for
176 <literal>P</literal> and all the packages that depend on
177 <literal>P</literal>. Sometimes we don't know ahead of time which
178 packages will be installed that depend on <literal>P</literal>,
179 which is when the <literal>-ignore-package</literal> flag can be
180 useful.</para>
181 </listitem>
182 </varlistentry>
183 </variablelist>
184 </sect2>
185
186 <sect2 id="package-overlaps">
187 <title>Consequences of packages</title>
188
189 <para>It is possible that by using packages you might end up with
190 a program that contains two modules with the same name: perhaps
191 you used a package P that has a <emphasis>hidden</emphasis> module
192 M, and there is also a module M in your program. Or perhaps the
193 dependencies of packages that you used contain some overlapping
194 modules. Perhaps the program even contains multiple versions of a
195 certain package, due to dependencies from other packages.</para>
196
197 <para>None of these scenarios gives rise to an error on its
198 own<footnote><para>it used to in GHC 6.4, but not since
199 6.6</para></footnote>, but they may have some interesting
200 consequences. For instance, if you have a type
201 <literal>M.T</literal> from version 1 of package
202 <literal>P</literal>, then this is <emphasis>not</emphasis> the
203 same as the type <literal>M.T</literal> from version 2 of package
204 <literal>P</literal>, and GHC will report an error if you try to
205 use one where the other is expected.</para>
206
207 <para>Formally speaking, in Haskell 98, an entity (function, type
208 or class) in a program is uniquely identified by the pair of the
209 module name in which it is defined and its name. In GHC, an
210 entity is uniquely defined by a triple: package, module, and
211 name.</para>
212 </sect2>
213
214 <sect2 id="package-databases">
215 <title>Package Databases</title>
216
217 <para>A package database is a file, normally called
218 <literal>package.conf</literal> which contains descriptions of installed
219 packages. GHC usually knows about two package databases:</para>
220
221 <itemizedlist>
222 <listitem>
223 <para>The global package database, which comes with your GHC
224 installation.</para>
225 </listitem>
226 <listitem>
227 <para>A package database private to each user. On Unix
228 systems this will be
229 <filename>$HOME/.ghc/<replaceable>arch</replaceable>-<replaceable>os</replaceable>-<replaceable>version</replaceable>/package.conf</filename>, and on
230 Windows it will be something like
231 <filename>C:\Documents&nbsp;And&nbsp;Settings\<replaceable>user</replaceable>\ghc</filename>.
232 The <literal>ghc-pkg</literal> tool knows where this file should be
233 located, and will create it if it doesn't exist (see <xref linkend="package-management" />).</para>
234 </listitem>
235 </itemizedlist>
236
237 <para>When GHC starts up, it reads the contents of these two package
238 databases, and builds up a list of the packages it knows about. You can
239 see GHC's package table by running GHC with the <option>-v</option>
240 flag.</para>
241
242 <para>Package databases may overlap: for example, packages in the user
243 database will override those of the same name in the global
244 database.</para>
245
246 <para>You can control the loading of package databses using the following
247 GHC options:</para>
248
249 <variablelist>
250 <varlistentry>
251 <term>
252 <option>-package-conf <replaceable>file</replaceable></option>
253 <indexterm><primary><option>-package-conf</option></primary></indexterm>
254 </term>
255 <listitem>
256 <para>Read in the package configuration file
257 <replaceable>file</replaceable> in addition to the system
258 default file and the user's local file. Packages in additional
259 files read this way will override those in the global and user
260 databases.</para>
261 </listitem>
262 </varlistentry>
263
264 <varlistentry>
265 <term><option>-no-user-package-conf</option>
266 <indexterm><primary><option>-no-user-package-conf</option></primary>
267 </indexterm>
268 </term>
269 <listitem>
270 <para>Prevent loading of the user's local package database.</para>
271 </listitem>
272 </varlistentry>
273 </variablelist>
274
275 <para>To create a new package database, just create
276 a new file and put the string
277 <quote><literal>[]</literal></quote> in it. Packages can be
278 added to the file using the
279 <literal>ghc-pkg</literal> tool, described in <xref
280 linkend="package-management"/>.</para>
281
282 <sect3 id="ghc-package-path">
283 <title>The <literal>GHC_PACKAGE_PATH</literal> environment variable</title>
284 <indexterm><primary>Environment variable</primary><secondary><literal>GHC_PACKAGE_PATH</literal></secondary>
285 </indexterm>
286 <indexterm><primary><literal>GHC_PACKAGE_PATH</literal></primary></indexterm>
287 <para>The <literal>GHC_PACKAGE_PATH</literal> environment variable may be
288 set to a <literal>:</literal>-separated (<literal>;</literal>-separated
289 on Windows) list of files containing package databases. This list of
290 package databases is used by GHC and ghc-pkg, with earlier databases in
291 the list overriding later ones. This order was chosen to match the
292 behaviour of the <literal>PATH</literal> environment variable; think of
293 it as a list of package databases that are searched left-to-right for
294 packages.</para>
295
296 <para>If <literal>GHC_PACKAGE_PATH</literal> ends in a separator, then
297 the default user and system package databases are appended, in that
298 order. e.g. to augment the usual set of packages with a database of
299 your own, you could say (on Unix):
300 <screen>
301 $ export GHC_PACKAGE_PATH=$HOME/.my-ghc-packages.conf:</screen>
302 (use <literal>;</literal> instead of <literal>:</literal> on
303 Windows).</para>
304
305 <para>To check whether your <literal>GHC_PACKAGE_PATH</literal> setting
306 is doing the right thing, <literal>ghc-pkg list</literal> will list all
307 the databases in use, in the reverse order they are searched.</para>
308
309 </sect3>
310 </sect2>
311
312 <sect2 id="building-packages">
313 <title>Building a package from Haskell source</title>
314 <indexterm><primary>packages</primary>
315 <secondary>building</secondary></indexterm>
316
317 <para>We don't recommend building packages the hard way. Instead, use the
318 <ulink url="../Cabal/index.html">Cabal</ulink> infrastructure
319 if possible. If your package is particularly complicated or requires a
320 lot of configuration, then you might have to fall back to the low-level
321 mechanisms, so a few hints for those brave souls follow.</para>
322
323 <itemizedlist>
324 <listitem>
325 <para>You need to build an "installed package info" file for
326 passing to <literal>ghc-pkg</literal> when installing your
327 package. The contents of this file are described in <xref
328 linkend="installed-pkg-info" />.</para>
329 </listitem>
330
331 <listitem>
332 <para>The Haskell code in a package may be built into one or
333 more archive libraries
334 (e.g. <filename>libHSfoo.a</filename>), or a single DLL on
335 Windows (e.g. <filename>HSfoo.dll</filename>). The
336 restriction to a single DLL on Windows is because the
337 package system is used to tell the compiler when it should
338 make an inter-DLL call rather than an intra-DLL call
339 (inter-DLL calls require an extra
340 indirection). <emphasis>Building packages as DLLs doesn't
341 work at the moment; see <xref linkend="win32-dlls-create"/>
342 for the gory details.</emphasis>
343 </para>
344
345 <para>Building a static library is done by using the
346 <literal>ar</literal> tool, like so:</para>
347
348 <screen>ar cqs libHSfoo.a A.o B.o C.o ...</screen>
349
350 <para>where <filename>A.o</filename>,
351 <filename>B.o</filename> and so on are the compiled Haskell
352 modules, and <filename>libHSfoo.a</filename> is the library
353 you wish to create. The syntax may differ slightly on your
354 system, so check the documentation if you run into
355 difficulties.</para>
356
357 <para>Versions of the Haskell libraries for use with GHCi
358 may also be included: GHCi cannot load <literal>.a</literal>
359 files directly, instead it will look for an object file
360 called <filename>HSfoo.o</filename> and load that. On some
361 systems, the <literal>ghc-pkg</literal> tool can
362 automatically build the GHCi version of each library, see
363 <xref linkend="package-management"/>. To build these
364 libraries by hand from the <literal>.a</literal> archive, it
365 is possible to use GNU <command>ld</command> as
366 follows:</para>
367
368 <screen>ld -r &ndash;&ndash;whole-archive -o HSfoo.o libHSfoo.a</screen>
369
370 <para>(replace
371 <literal>&ndash;&ndash;--whole-archive</literal> with
372 <literal>&ndash;all_load</literal> on MacOS X)</para>
373
374 <para>GHC does not maintain detailed cross-package
375 dependency information. It does remember which modules in
376 other packages the current module depends on, but not which
377 things within those imported things.</para>
378 </listitem>
379 </itemizedlist>
380
381 <para>To compile a module which is to be part of a new package,
382 use the <literal>-package-name</literal> option:</para>
383
384 <variablelist>
385 <varlistentry>
386 <term><option>-package-name <replaceable>foo</replaceable></option>
387 <indexterm><primary><literal>-package-name</literal></primary>
388 <secondary>option</secondary></indexterm></term>
389 <listitem>
390 <para>This option is added to the command line when
391 compiling a module that is destined to be part of package
392 <literal>foo</literal>. If this flag is omitted then the
393 default package <literal>main</literal> is assumed.</para>
394
395 <para>Note: the argument to <option>-package-name</option>
396 should be the full package identifier for the package,
397 that is it should include the version number. For example:
398 <literal>-package mypkg-1.2</literal>.</para>
399 </listitem>
400 </varlistentry>
401 </variablelist>
402
403 <para>Failure to use the <literal>-package-name</literal> option
404 when compiling a package will probably result in disaster, but
405 you will only discover later when you attempt to import modules
406 from the package. At this point GHC will complain that the
407 package name it was expecting the module to come from is not the
408 same as the package name stored in the <literal>.hi</literal>
409 file.</para>
410
411 <para>It is worth noting that on Windows, when each package
412 is built as a DLL, since a reference to a DLL costs an extra
413 indirection, intra-package references are cheaper than
414 inter-package references. Of course, this applies to the
415 <filename>main</filename> package as well.</para>
416 </sect2>
417
418 <sect2 id="package-management">
419 <title>Package management (the <literal>ghc-pkg</literal> command)</title>
420 <indexterm><primary>packages</primary>
421 <secondary>management</secondary></indexterm>
422
423 <para>The <literal>ghc-pkg</literal> tool allows packages to be
424 added or removed from a package database. By default,
425 the system-wide package database is modified, but alternatively
426 the user's local package database or another specified
427 file can be used.</para>
428
429 <para>To see what package databases are in use, say
430 <literal>ghc-pkg&nbsp;list</literal>. The stack of databases that
431 <literal>ghc-pkg</literal> knows about can be modified using the
432 <literal>GHC_PACKAGE_PATH</literal> environment variable (see <xref
433 linkend="ghc-package-path" />, and using
434 <literal>--package-conf</literal> options on the
435 <literal>ghc-pkg</literal> command line.</para>
436
437 <para>When asked to modify a database, <literal>ghc-pkg</literal> modifies
438 the global database by default. Specifying <option>--user</option>
439 causes it to act on the user database, or <option>--package-conf</option>
440 can be used to act on another database entirely. When multiple of these
441 options are given, the rightmost one is used as the database to act
442 upon.</para>
443
444 <para>If the environment variable <literal>GHC_PACKAGE_PATH</literal> is
445 set, and its value does not end in a separator (<literal>:</literal> on
446 Unix, <literal>;</literal> on Windows), then the last database is
447 considered to be the global database, and will be modified by default by
448 <literal>ghc-pkg</literal>. The intention here is that
449 <literal>GHC_PACKAGE_PATH</literal> can be used to create a virtual
450 package environment into which Cabal packages can be installed without
451 setting anything other than <literal>GHC_PACKAGE_PATH</literal>.</para>
452
453 <para>The <literal>ghc-pkg</literal> program may be run in the ways listed
454 below. Where a package name is required, the package can be named in
455 full including the version number
456 (e.g. <literal>network-1.0</literal>), or without the version number.
457 Naming a package without the version number matches all versions of the
458 package; the specified action will be applied to all the matching
459 packages. A package specifier that matches all version of the package
460 can also be written <replaceable>pkg</replaceable><literal>-*</literal>,
461 to make it clearer that multiple packages are being matched.</para>
462
463 <variablelist>
464 <varlistentry>
465 <term><literal>ghc-pkg register <replaceable>file</replaceable></literal></term>
466 <listitem>
467 <para>Reads a package specification from
468 <replaceable>file</replaceable> (which may be &ldquo;<literal>-</literal>&rdquo;
469 to indicate standard input),
470 and adds it to the database of installed packages. The syntax of
471 <replaceable>file</replaceable> is given in <xref
472 linkend="installed-pkg-info" />.</para>
473
474 <para>The package specification must be a package that isn't already
475 installed.</para>
476 </listitem>
477 </varlistentry>
478
479 <varlistentry>
480 <term><literal>ghc-pkg update <replaceable>file</replaceable></literal></term>
481 <listitem>
482 <para>The same as <literal>register</literal>, except that if a
483 package of the same name is already installed, it is
484 replaced by the new one.</para>
485 </listitem>
486 </varlistentry>
487
488 <varlistentry>
489 <term><literal>ghc-pkg unregister <replaceable>P</replaceable></literal></term>
490 <listitem>
491 <para>Remove the specified package from the database.</para>
492 </listitem>
493 </varlistentry>
494
495 <varlistentry>
496 <term><literal>ghc-pkg expose <replaceable>P</replaceable></literal></term>
497 <listitem>
498 <para>Sets the <literal>exposed</literal> flag for package
499 <replaceable>P</replaceable> to <literal>True</literal>.</para>
500 </listitem>
501 </varlistentry>
502
503 <varlistentry>
504 <term><literal>ghc-pkg hide <replaceable>P</replaceable></literal></term>
505 <listitem>
506 <para>Sets the <literal>exposed</literal> flag for package
507 <replaceable>P</replaceable> to <literal>False</literal>.</para>
508 </listitem>
509 </varlistentry>
510
511 <varlistentry>
512 <term><literal>ghc-pkg list [<replaceable>P</replaceable>] [<option>--simple-output</option>]</literal></term>
513 <listitem>
514 <para>This option displays the currently installed
515 packages, for each of the databases known to
516 <literal>ghc-pkg</literal>. That includes the global database, the
517 user's local database, and any further files specified using the
518 <option>-f</option> option on the command line.</para>
519
520 <para>Hidden packages (those for which the <literal>exposed</literal>
521 flag is <literal>False</literal>) are shown in parentheses in the
522 list of packages.</para>
523
524 <para>If an optional package identifier <replaceable>P</replaceable>
525 is given, then only packages matching that identifier are
526 shown.</para>
527
528 <para>If the option <option>--simple-output</option> is given, then
529 the packages are listed on a single line separated by spaces, and
530 the database names are not included. This is intended to make it
531 easier to parse the output of <literal>ghc-pkg list</literal> using
532 a script.</para>
533 </listitem>
534 </varlistentry>
535
536 <varlistentry>
537 <term><literal>ghc-pkg latest <replaceable>P</replaceable></literal></term>
538 <listitem>
539 <para>Prints the latest available version of package
540 <replaceable>P</replaceable>.</para>
541 </listitem>
542 </varlistentry>
543
544 <varlistentry>
545 <term><literal>ghc-pkg describe <replaceable>P</replaceable></literal></term>
546 <listitem>
547 <para>Emit the full description of the specified package. The
548 description is in the form of an
549 <literal>InstalledPackageInfo</literal>, the same as the input file
550 format for <literal>ghc-pkg register</literal>. See <xref
551 linkend="installed-pkg-info" /> for details.</para>
552 </listitem>
553 </varlistentry>
554
555 <varlistentry>
556 <term><literal>ghc-pkg field <replaceable>P</replaceable> <replaceable>field</replaceable></literal></term>
557 <listitem>
558 <para>Show just a single field of the installed package description
559 for <literal>P</literal>.</para>
560 </listitem>
561 </varlistentry>
562 </variablelist>
563
564 <para>Additionally, the following flags are accepted by
565 <literal>ghc-pkg</literal>:</para>
566
567 <variablelist>
568 <varlistentry>
569 <term>
570 <option>&ndash;&ndash;auto-ghci-libs</option><indexterm><primary><option>&ndash;&ndash;auto-ghci-libs</option></primary>
571 </indexterm>
572 </term>
573 <listitem>
574 <para>Automatically generate the GHCi
575 <filename>.o</filename> version of each
576 <filename>.a</filename> Haskell library, using GNU ld (if
577 that is available). Without this option,
578 <literal>ghc-pkg</literal> will warn if GHCi versions of
579 any Haskell libraries in the package don't exist.</para>
580
581 <para>GHCi <literal>.o</literal> libraries don't
582 necessarily have to live in the same directory as the
583 corresponding <literal>.a</literal> library. However,
584 this option will cause the GHCi library to be created in
585 the same directory as the <literal>.a</literal>
586 library.</para>
587 </listitem>
588 </varlistentry>
589
590 <varlistentry>
591 <term>
592 <option>-f</option> <replaceable>file</replaceable>
593 <indexterm><primary><option>-f</option></primary>
594 </indexterm>
595 </term>
596 <term>
597 <option>-package-conf</option> <replaceable>file</replaceable>
598 <indexterm><primary><option>-package-conf</option></primary>
599 </indexterm>
600 </term>
601 <listitem>
602 <para>Adds <replaceable>file</replaceable> to the stack of package
603 databases. Additionally, <replaceable>file</replaceable> will
604 also be the database modified by a <literal>register</literal>,
605 <literal>unregister</literal>, <literal>expose</literal> or
606 <literal>hide</literal> command, unless it is overriden by a later
607 <option>--package-conf</option>, <option>--user</option> or
608 <option>--global</option> option.</para>
609 </listitem>
610 </varlistentry>
611
612 <varlistentry>
613 <term>
614 <option>&ndash;&ndash;force</option>
615 <indexterm><primary>
616 <option>&ndash;&ndash;force</option>
617 </primary></indexterm>
618 </term>
619 <listitem>
620 <para>Causes <literal>ghc-pkg</literal> to ignore missing
621 dependencies, directories and libraries when registering a package,
622 and just go ahead and add it anyway. This might be useful if your
623 package installation system needs to add the package to
624 GHC before building and installing the files.</para>
625 </listitem>
626 </varlistentry>
627
628 <varlistentry>
629 <term>
630 <option>&ndash;&ndash;global</option><indexterm><primary><option>&ndash;&ndash;global</option></primary>
631 </indexterm>
632 </term>
633 <listitem>
634 <para>Operate on the global package database (this is the default).
635 This flag affects the <literal>register</literal>,
636 <literal>update</literal>, <literal>unregister</literal>,
637 <literal>expose</literal>, and <literal>hide</literal>
638 commands.</para>
639 </listitem>
640 </varlistentry>
641
642 <varlistentry>
643 <term>
644 <option>&ndash;&ndash;help</option><indexterm><primary><option>&ndash;&ndash;help</option></primary>
645 </indexterm>
646 </term>
647 <term>
648 <option>-?</option><indexterm><primary><option>-?</option></primary>
649 </indexterm>
650 </term>
651 <listitem>
652 <para>Outputs the command-line syntax.</para>
653 </listitem>
654 </varlistentry>
655
656 <varlistentry>
657 <term>
658 <option>&ndash;&ndash;user</option><indexterm><primary><option>&ndash;&ndash;user</option></primary>
659 </indexterm>
660 </term>
661 <listitem>
662 <para>Operate on the current user's local package database.
663 This flag affects the <literal>register</literal>,
664 <literal>update</literal>, <literal>unregister</literal>,
665 <literal>expose</literal>, and <literal>hide</literal>
666 commands.</para>
667 </listitem>
668 </varlistentry>
669
670 <varlistentry>
671 <term>
672 <option>-V</option><indexterm><primary><option>-V</option></primary>
673 </indexterm>
674 </term>
675 <term>
676 <option>&ndash;&ndash;version</option><indexterm><primary><option>&ndash;&ndash;version</option></primary>
677 </indexterm>
678 </term>
679 <listitem>
680 <para>Output the <literal>ghc-pkg</literal> version number.</para>
681 </listitem>
682 </varlistentry>
683 </variablelist>
684
685 <para>When modifying the package database
686 <replaceable>file</replaceable>, a copy of the original file is
687 saved in <replaceable>file</replaceable><literal>.old</literal>,
688 so in an emergency you can always restore the old settings by
689 copying the old file back again.</para>
690
691 </sect2>
692
693 <sect2 id="installed-pkg-info">
694 <title>
695 <literal>InstalledPackageInfo</literal>: a package specification
696 </title>
697
698 <para>A package specification is a Haskell record; in particular, it is the
699 record <ulink
700 url="../libraries/Cabal/Distribution-InstalledPackageInfo.html#%tInstalledPackageInfo">InstalledPackageInfo</ulink> in the module Distribution.InstalledPackageInfo, which is part of the Cabal package distributed with GHC.</para>
701
702 <para>An <literal>InstalledPackageInfo</literal> has a human
703 readable/writable syntax. The functions
704 <literal>parseInstalledPackageInfo</literal> and
705 <literal>showInstalledPackageInfo</literal> read and write this syntax
706 respectively. Here's an example of the
707 <literal>InstalledPackageInfo</literal> for the <literal>unix</literal> package:</para>
708
709 <screen>
710 $ ghc-pkg describe unix
711 name: unix
712 version: 1.0
713 license: BSD3
714 copyright:
715 maintainer: libraries@haskell.org
716 stability:
717 homepage:
718 package-url:
719 description:
720 category:
721 author:
722 exposed: True
723 exposed-modules: System.Posix,
724 System.Posix.DynamicLinker.Module,
725 System.Posix.DynamicLinker.Prim,
726 System.Posix.Directory,
727 System.Posix.DynamicLinker,
728 System.Posix.Env,
729 System.Posix.Error,
730 System.Posix.Files,
731 System.Posix.IO,
732 System.Posix.Process,
733 System.Posix.Resource,
734 System.Posix.Temp,
735 System.Posix.Terminal,
736 System.Posix.Time,
737 System.Posix.Unistd,
738 System.Posix.User,
739 System.Posix.Signals.Exts
740 import-dirs: /usr/lib/ghc-6.4/libraries/unix
741 library-dirs: /usr/lib/ghc-6.4/libraries/unix
742 hs-libraries: HSunix
743 extra-libraries: HSunix_cbits, dl
744 include-dirs: /usr/lib/ghc-6.4/libraries/unix/include
745 includes: HsUnix.h
746 depends: base-1.0
747 </screen>
748
749 <para>The full <ulink url="../Cabal/index.html">Cabal documentation</ulink>
750 is still in preparation (at time of writing), so in the meantime
751 here is a brief description of the syntax of this file:</para>
752
753 <para>A package description consists of a number of field/value pairs. A
754 field starts with the field name in the left-hand column followed by a
755 &ldquo;<literal>:</literal>&rdquo;, and the value continues until the next line that begins in the
756 left-hand column, or the end of file.</para>
757
758 <para>The syntax of the value depends on the field. The various field
759 types are:</para>
760
761 <variablelist>
762 <varlistentry>
763 <term>freeform</term>
764 <listitem>
765 <para>Any arbitrary string, no interpretation or parsing is
766 done.</para>
767 </listitem>
768 </varlistentry>
769 <varlistentry>
770 <term>string</term>
771 <listitem>
772 <para>A sequence of non-space characters, or a sequence of arbitrary
773 characters surrounded by quotes <literal>"...."</literal>.</para>
774 </listitem>
775 </varlistentry>
776 <varlistentry>
777 <term>string list</term>
778 <listitem>
779 <para>A sequence of strings, separated by commas. The sequence may
780 be empty.</para>
781 </listitem>
782 </varlistentry>
783 </variablelist>
784
785 <para>In addition, there are some fields with special syntax (e.g. package
786 names, version, dependencies).</para>
787
788 <para>The allowed fields, with their types, are:</para>
789
790 <variablelist>
791 <varlistentry>
792 <term>
793 <literal>name</literal>
794 <indexterm><primary><literal>name</literal></primary><secondary>package specification</secondary></indexterm>
795 </term>
796 <listitem>
797 <para>The package's name (without the version).</para>
798 </listitem>
799 </varlistentry>
800
801 <varlistentry>
802 <term>
803 <literal>version</literal>
804 <indexterm><primary><literal>version</literal></primary><secondary>package specification</secondary></indexterm>
805 </term>
806 <listitem>
807 <para>The package's version, usually in the form
808 <literal>A.B</literal> (any number of components are allowed).</para>
809 </listitem>
810 </varlistentry>
811
812 <varlistentry>
813 <term>
814 <literal>license</literal>
815 <indexterm><primary><literal>auto</literal></primary><secondary>package specification</secondary></indexterm>
816 </term>
817 <listitem>
818 <para>(string) The type of license under which this package is distributed.
819 This field is a value of the <ulink
820 url="../libraries/Cabal/Distribution-License.html#t:License"><literal>License</literal></ulink> type.</para>
821 </listitem>
822 </varlistentry>
823
824 <varlistentry>
825 <term>
826 <literal>license-file</literal>
827 <indexterm><primary><literal>license-file</literal></primary><secondary>package specification</secondary></indexterm>
828 </term>
829 <listitem>
830 <para>(optional string) The name of a file giving detailed license
831 information for this package.</para>
832 </listitem>
833 </varlistentry>
834
835 <varlistentry>
836 <term>
837 <literal>copyright</literal>
838 <indexterm><primary><literal>copyright</literal></primary><secondary>package specification</secondary></indexterm>
839 </term>
840 <listitem>
841 <para>(optional freeform) The copyright string.</para>
842 </listitem>
843 </varlistentry>
844
845 <varlistentry>
846 <term>
847 <literal>maintainer</literal>
848 <indexterm><primary><literal>maintainer</literal></primary><secondary>package specification</secondary></indexterm>
849 </term>
850 <listitem>
851 <para>(optinoal freeform) The email address of the package's maintainer.</para>
852 </listitem>
853 </varlistentry>
854
855 <varlistentry>
856 <term>
857 <literal>stability</literal>
858 <indexterm><primary><literal>stability</literal></primary><secondary>package specification</secondary></indexterm>
859 </term>
860 <listitem>
861 <para>(optional freeform) A string describing the stability of the package
862 (eg. stable, provisional or experimental).</para>
863 </listitem>
864 </varlistentry>
865
866 <varlistentry>
867 <term>
868 <literal>homepage</literal>
869 <indexterm><primary><literal>homepage</literal></primary><secondary>package specification</secondary></indexterm>
870 </term>
871 <listitem>
872 <para>(optional freeform) URL of the package's home page.</para>
873 </listitem>
874 </varlistentry>
875
876 <varlistentry>
877 <term>
878 <literal>package-url</literal>
879 <indexterm><primary><literal>package-url</literal></primary><secondary>package specification</secondary></indexterm>
880 </term>
881 <listitem>
882 <para>(optional freeform) URL of a downloadable distribution for this
883 package. The distribution should be a Cabal package.</para>
884 </listitem>
885 </varlistentry>
886
887 <varlistentry>
888 <term>
889 <literal>description</literal>
890 <indexterm><primary><literal>description</literal></primary><secondary>package specification</secondary></indexterm>
891 </term>
892 <listitem>
893 <para>(optional freeform) Description of the package.</para>
894 </listitem>
895 </varlistentry>
896
897 <varlistentry>
898 <term>
899 <literal>category</literal>
900 <indexterm><primary><literal>category</literal></primary><secondary>package specification</secondary></indexterm>
901 </term>
902 <listitem>
903 <para>(optinoal freeform) Which category the package belongs to. This field
904 is for use in conjunction with a future centralised package
905 distribution framework, tentatively titled Hackage.</para>
906 </listitem>
907 </varlistentry>
908
909 <varlistentry>
910 <term>
911 <literal>author</literal>
912 <indexterm><primary><literal>author</literal></primary><secondary>package specification</secondary></indexterm>
913 </term>
914 <listitem>
915 <para>(optional freeform) Author of the package.</para>
916 </listitem>
917 </varlistentry>
918
919 <varlistentry>
920 <term>
921 <literal>exposed</literal>
922 <indexterm><primary><literal>exposed</literal></primary><secondary>package specification</secondary></indexterm>
923 </term>
924 <listitem>
925 <para>(bool) Whether the package is exposed or not.</para>
926 </listitem>
927 </varlistentry>
928
929 <varlistentry>
930 <term>
931 <literal>exposed-modules</literal>
932 <indexterm><primary><literal>exposed-modules</literal></primary><secondary>package specification</secondary></indexterm>
933 </term>
934 <listitem>
935 <para>(string list) modules exposed by this package.</para>
936 </listitem>
937 </varlistentry>
938
939 <varlistentry>
940 <term>
941 <literal>hidden-modules</literal>
942 <indexterm><primary><literal>hidden-modules</literal></primary><secondary>package specification</secondary></indexterm>
943 </term>
944 <listitem>
945 <para>(string list) modules provided by this package,
946 but not exposed to the programmer. These modules cannot be
947 imported, but they are still subject to the overlapping constraint:
948 no other package in the same program may provide a module of the
949 same name.</para>
950 </listitem>
951 </varlistentry>
952
953 <varlistentry>
954 <term>
955 <literal>import-dirs</literal>
956 <indexterm><primary><literal>import-dirs</literal></primary><secondary>package specification</secondary></indexterm>
957 </term>
958 <listitem>
959 <para>(string list) A list of directories containing interface files
960 (<literal>.hi</literal> files) for this package.</para>
961
962 <para>If the package contains profiling libraries, then
963 the interface files for those library modules should have
964 the suffix <literal>.p_hi</literal>. So the package can
965 contain both normal and profiling versions of the same
966 library without conflict (see also
967 <literal>library_dirs</literal> below).</para>
968 </listitem>
969 </varlistentry>
970
971 <varlistentry>
972 <term>
973 <literal>library-dirs</literal>
974 <indexterm><primary><literal>library-dirs</literal></primary><secondary>package specification</secondary></indexterm>
975 </term>
976 <listitem>
977 <para>(string list) A list of directories containing libraries for this
978 package.</para>
979 </listitem>
980 </varlistentry>
981
982 <varlistentry>
983 <term>
984 <literal>hs-libraries</literal>
985 <indexterm><primary><literal>hs-libraries</literal></primary><secondary>package specification</secondary></indexterm>
986 </term>
987 <listitem>
988 <para>(string list) A list of libraries containing Haskell code for this
989 package, with the <literal>.a</literal> or
990 <literal>.dll</literal> suffix omitted. When packages are
991 built as libraries, the
992 <literal>lib</literal> prefix is also omitted.</para>
993
994 <para>For use with GHCi, each library should have an
995 object file too. The name of the object file does
996 <emphasis>not</emphasis> have a <literal>lib</literal>
997 prefix, and has the normal object suffix for your
998 platform.</para>
999
1000 <para>For example, if we specify a Haskell library as
1001 <filename>HSfoo</filename> in the package spec, then the
1002 various flavours of library that GHC actually uses will be
1003 called:</para>
1004 <variablelist>
1005 <varlistentry>
1006 <term><filename>libHSfoo.a</filename></term>
1007 <listitem>
1008 <para>The name of the library on Unix and Windows
1009 (mingw) systems. Note that we don't support
1010 building dynamic libraries of Haskell code on Unix
1011 systems.</para>
1012 </listitem>
1013 </varlistentry>
1014 <varlistentry>
1015 <term><filename>HSfoo.dll</filename></term>
1016 <listitem>
1017 <para>The name of the dynamic library on Windows
1018 systems (optional).</para>
1019 </listitem>
1020 </varlistentry>
1021 <varlistentry>
1022 <term><filename>HSfoo.o</filename></term>
1023 <term><filename>HSfoo.obj</filename></term>
1024 <listitem>
1025 <para>The object version of the library used by
1026 GHCi.</para>
1027 </listitem>
1028 </varlistentry>
1029 </variablelist>
1030 </listitem>
1031 </varlistentry>
1032
1033 <varlistentry>
1034 <term>
1035 <literal>extra-libraries</literal>
1036 <indexterm><primary><literal>extra-libraries</literal></primary><secondary>package specification</secondary></indexterm>
1037 </term>
1038 <listitem>
1039 <para>(string list) A list of extra libraries for this package. The
1040 difference between <literal>hs-libraries</literal> and
1041 <literal>extra-libraries</literal> is that
1042 <literal>hs-libraries</literal> normally have several
1043 versions, to support profiling, parallel and other build
1044 options. The various versions are given different
1045 suffixes to distinguish them, for example the profiling
1046 version of the standard prelude library is named
1047 <filename>libHSbase_p.a</filename>, with the
1048 <literal>_p</literal> indicating that this is a profiling
1049 version. The suffix is added automatically by GHC for
1050 <literal>hs-libraries</literal> only, no suffix is added
1051 for libraries in
1052 <literal>extra-libraries</literal>.</para>
1053
1054 <para>The libraries listed in
1055 <literal>extra-libraries</literal> may be any libraries
1056 supported by your system's linker, including dynamic
1057 libraries (<literal>.so</literal> on Unix,
1058 <literal>.DLL</literal> on Windows).</para>
1059
1060 <para>Also, <literal>extra-libraries</literal> are placed
1061 on the linker command line after the
1062 <literal>hs-libraries</literal> for the same package. If
1063 your package has dependencies in the other direction (i.e.
1064 <literal>extra-libraries</literal> depends on
1065 <literal>hs-libraries</literal>), and the libraries are
1066 static, you might need to make two separate
1067 packages.</para>
1068 </listitem>
1069 </varlistentry>
1070
1071 <varlistentry>
1072 <term>
1073 <literal>include-dirs</literal>
1074 <indexterm><primary><literal>include-dirs</literal></primary><secondary>package specification</secondary></indexterm>
1075 </term>
1076 <listitem>
1077 <para>(string list) A list of directories containing C includes for this
1078 package.</para>
1079 </listitem>
1080 </varlistentry>
1081
1082 <varlistentry>
1083 <term>
1084 <literal>includes</literal>
1085 <indexterm><primary><literal>includes</literal></primary><secondary>package specification</secondary></indexterm>
1086 </term>
1087 <listitem>
1088 <para>(string list) A list of files to include for via-C compilations
1089 using this package. Typically the include file(s) will
1090 contain function prototypes for any C functions used in
1091 the package, in case they end up being called as a result
1092 of Haskell functions from the package being
1093 inlined.</para>
1094 </listitem>
1095 </varlistentry>
1096
1097 <varlistentry>
1098 <term>
1099 <literal>depends</literal>
1100 <indexterm><primary><literal>depends</literal></primary><secondary>package specification</secondary></indexterm>
1101 </term>
1102 <listitem>
1103 <para>(package name list) Packages on which this package depends. This field contains
1104 packages with explicit versions are required, except that when
1105 submitting a package to <literal>ghc-pkg register</literal>, the
1106 versions will be filled in if they are unambiguous.</para>
1107 </listitem>
1108 </varlistentry>
1109
1110 <varlistentry>
1111 <term>
1112 <literal>hugs-options</literal>
1113 <indexterm><primary><literal>hugs-options</literal></primary><secondary>package specification</secondary></indexterm>
1114 </term>
1115 <listitem>
1116 <para>(string list) Options to pass to Hugs for this package.</para>
1117 </listitem>
1118 </varlistentry>
1119
1120 <varlistentry>
1121 <term>
1122 <literal>cc-options</literal>
1123 <indexterm><primary><literal>cc-options</literal></primary><secondary>package specification</secondary></indexterm>
1124 </term>
1125 <listitem>
1126 <para>(string list) Extra arguments to be added to the gcc command line
1127 when this package is being used (only for via-C
1128 compilations).</para>
1129 </listitem>
1130 </varlistentry>
1131
1132 <varlistentry>
1133 <term>
1134 <literal>ld-options</literal>
1135 <indexterm><primary><literal>ld-options</literal></primary><secondary>package specification</secondary></indexterm>
1136 </term>
1137 <listitem>
1138 <para>(string list) Extra arguments to be added to the
1139 <command>gcc</command> command line (for linking) when
1140 this package is being used.</para>
1141 </listitem>
1142 </varlistentry>
1143
1144 <varlistentry>
1145 <term>
1146 <literal>framework-dirs</literal>
1147 <indexterm><primary><literal>framework-dirs</literal></primary><secondary>package specification</secondary></indexterm>
1148 </term>
1149 <listitem>
1150 <para>(string list) On Darwin/MacOS X, a list of directories containing
1151 frameworks for this package. This corresponds to the
1152 <option>-framework-path</option> option. It is ignored on all other
1153 platforms.</para>
1154 </listitem>
1155 </varlistentry>
1156
1157 <varlistentry>
1158 <term>
1159 <literal>frameworks</literal>
1160 <indexterm><primary><literal>frameworks</literal></primary><secondary>package specification</secondary></indexterm>
1161 </term>
1162 <listitem>
1163 <para>(string list) On Darwin/MacOS X, a list of frameworks to link to. This
1164 corresponds to the <option>-framework</option> option. Take a look
1165 at Apple's developer documentation to find out what frameworks
1166 actually are. This entry is ignored on all other platforms.</para>
1167 </listitem>
1168 </varlistentry>
1169
1170 <varlistentry>
1171 <term>
1172 <literal>haddock-interfaces</literal>
1173 <indexterm><primary><literal>haddock-interfaces</literal></primary><secondary>package specification</secondary></indexterm>
1174 </term>
1175 <listitem>
1176 <para>(string list) A list of filenames containing <ulink
1177 url="http://www.haskell.org/haddock/">Haddock</ulink> interface
1178 files (<literal>.haddock</literal> files) for this package.</para>
1179 </listitem>
1180 </varlistentry>
1181
1182 <varlistentry>
1183 <term>
1184 <literal>haddock-html</literal>
1185 <indexterm><primary><literal>haddock-html</literal></primary><secondary>package specification</secondary></indexterm>
1186 </term>
1187 <listitem>
1188 <para>(optional string) The directory containing the Haddock-generated HTML
1189 for this package.</para>
1190 </listitem>
1191 </varlistentry>
1192 </variablelist>
1193
1194 <!-- This isn't true any more. I'm not sure if we still need it -SDM
1195 <para>
1196 The <literal>ghc-pkg</literal> tool performs expansion of
1197 environment variables occurring in input package specifications.
1198 So, if the <literal>mypkg</literal> was added to the package
1199 database as follows:
1200 </para>
1201 <screen>
1202 $ installdir=/usr/local/lib ghc-pkg -a &lt; mypkg.pkg
1203 </screen>
1204
1205 <para>
1206 The occurrence of <literal>${installdir}</literal> is replaced
1207 with <literal>/usr/local/lib</literal> in the package data that
1208 is added for <literal>mypkg</literal>.
1209 </para>
1210
1211 <para>
1212 This feature enables the distribution of package specification
1213 files that can be easily configured when installing.
1214 </para>
1215
1216 <para>For examples of more package specifications, take a look
1217 at the <literal>package.conf</literal> in your GHC
1218 installation.</para>
1219
1220 -->
1221
1222 </sect2>
1223 </sect1>
1224
1225 <!-- Emacs stuff:
1226 ;;; Local Variables: ***
1227 ;;; mode: xml ***
1228 ;;; sgml-parent-document: ("users_guide.xml" "book" "chapter" "sect1") ***
1229 ;;; End: ***
1230 -->