1 <?xml version="1.0" encoding="iso-8859-1"?>
6 <indexterm><primary>packages</primary></indexterm>
8 <para>A package is a library of Haskell modules known to the
9 compiler. GHC comes with several packages: see the accompanying
10 <ulink url="../libraries/index.html">library
11 documentation</ulink>. More packages to install can be obtained
13 url="http://hackage.haskell.org/packages/hackage.html">HackageDB</ulink>.</para>
15 <para>Using a package couldn't be simpler: if you're using
16 <option>––make</option> or GHCi, then most of the installed packages will be
17 automatically available to your program without any further options. The
18 exceptions to this rule are covered below in <xref
19 linkend="using-packages" />.</para>
21 <para>Building your own packages is also quite straightforward: we provide
22 the <ulink url="http://www.haskell.org/cabal/">Cabal</ulink> infrastructure which
23 automates the process of configuring, building, installing and distributing
24 a package. All you need to do is write a simple configuration file, put a
25 few files in the right places, and you have a package. See the
26 <ulink url="../Cabal/index.html">Cabal documentation</ulink>
27 for details, and also the Cabal libraries (<ulink url="&libraryCabalLocation;/Distribution-Simple.html">Distribution.Simple</ulink>,
30 <sect2 id="using-packages">
33 <indexterm><primary>packages</primary>
34 <secondary>using</secondary></indexterm>
36 <para>GHC only knows about packages that are
37 <emphasis>installed</emphasis>. To see which packages are installed, use
38 the <literal>ghc-pkg list</literal> command:</para>
42 /usr/lib/ghc-6.12.1/package.conf.d:
47 bin-package-db-0.0.0.0
54 (dph-prim-interface-0.4.0)
58 extensible-exceptions-0.1.1.0
75 template-haskell-2.4.0.0
82 <para>An installed package is either <emphasis>exposed</emphasis>
83 or <emphasis>hidden</emphasis> by default. Packages hidden by
84 default are listed in parentheses
85 (eg. <literal>(lang-1.0)</literal>), or possibly in blue if your
86 terminal supports colour, in the output of <literal>ghc-pkg
87 list</literal>. Command-line flags, described below, allow you
88 to expose a hidden package or hide an exposed one. Only modules
89 from exposed packages may be imported by your Haskell code; if
90 you try to import a module from a hidden package, GHC will emit
95 Note: if you're using Cabal, then the exposed or hidden status
96 of a package is irrelevant: the available packages are instead
97 determined by the dependencies listed in
98 your <literal>.cabal</literal> specification. The
99 exposed/hidden status of packages is only relevant when
100 using <literal>ghc</literal> or <literal>ghci</literal>
104 <para>To see which modules are provided by a package use the
105 <literal>ghc-pkg</literal> command (see <xref linkend="package-management"/>):</para>
108 $ ghc-pkg field network exposed-modules
109 exposed-modules: Network.BSD,
116 <para>The GHC command line options that control packages are:</para>
121 <option>-package <replaceable>P</replaceable></option>
122 <indexterm><primary><option>-package</option></primary></indexterm>
125 <para>This option causes the installed
126 package <replaceable>P</replaceable> to be exposed. The
127 package <replaceable>P</replaceable> can be specified in
128 full with its version number
129 (e.g. <literal>network-1.0</literal>) or the version
130 number can be omitted if there is only one version of the
131 package installed. If there are multiple versions
132 of <replaceable>P</replaceable> installed, then all other
133 versions will become hidden.</para>
135 <para>The <option>-package <replaceable>P</replaceable></option>
136 option also causes package <replaceable>P</replaceable> to
137 be linked into the resulting executable or shared
138 object. Whether a packages' library is linked statically
139 or dynamically is controlled by the flag
140 pair <option>-static</option>/<option>-dynamic</option>.</para>
142 <para>In <option>––make</option> mode
143 and <option>––interactive</option> mode (see
144 <xref linkend="modes" />), the compiler normally
145 determines which packages are required by the current
146 Haskell modules, and links only those. In batch mode
147 however, the dependency information isn't available, and
149 <option>-package</option> options must be given when linking. The one other time you might need to use
150 <option>-package</option> to force linking a package is
151 when the package does not contain any Haskell modules (it
152 might contain a C library only, for example). In that
153 case, GHC will never discover a dependency on it, so it
154 has to be mentioned explicitly.</para>
156 <para>For example, to link a program consisting of objects
157 <filename>Foo.o</filename> and <filename>Main.o</filename>, where
158 we made use of the <literal>network</literal> package, we need to
159 give GHC the <literal>-package</literal> flag thus:
161 <screen>$ ghc -o myprog Foo.o Main.o -package network</screen>
163 The same flag is necessary even if we compiled the modules from
164 source, because GHC still reckons it's in batch mode:
166 <screen>$ ghc -o myprog Foo.hs Main.hs -package network</screen></para>
172 <option>-package-id <replaceable>P</replaceable></option>
173 <indexterm><primary><option>-package-id</option></primary></indexterm>
177 Exposes a package like <option>-package</option>, but the
178 package is named by its ID rather than by name. This is a
179 more robust way to name packages, and can be used to
180 select packages that would otherwise be shadowed. Cabal
181 passes <option>-package-id</option> flags to GHC.
187 <term><option>-hide-all-packages</option>
188 <indexterm><primary><option>-hide-package</option></primary>
191 <para>Ignore the exposed flag on installed packages, and hide them
192 all by default. If you use
193 this flag, then any packages you require (including
194 <literal>base</literal>) need to be explicitly exposed using
195 <option>-package</option> options.</para>
197 <para>This is a good way to insulate your program from
198 differences in the globally exposed packages, and being
199 explicit about package dependencies is a Good Thing.
200 Cabal always passes the
201 <option>-hide-all-packages</option> flag to GHC, for
202 exactly this reason.</para>
207 <term><option>-hide-package</option> <replaceable>P</replaceable>
208 <indexterm><primary><option>-hide-package</option></primary>
211 <para>This option does the opposite of <option>-package</option>: it
212 causes the specified package to be <firstterm>hidden</firstterm>,
213 which means that none of its modules will be available for import
214 by Haskell <literal>import</literal> directives.</para>
216 <para>Note that the package might still end up being linked into the
217 final program, if it is a dependency (direct or indirect) of
218 another exposed package.</para>
223 <term><option>-ignore-package</option> <replaceable>P</replaceable>
224 <indexterm><primary><option>-ignore-package</option></primary>
227 <para>Causes the compiler to behave as if package
228 <replaceable>P</replaceable>, and any packages that depend on
229 <literal>P</literal>, are not installed at all.</para>
231 <para>Saying <literal>-ignore-package P</literal> is the same as
232 giving <literal>-hide-package</literal> flags for
233 <literal>P</literal> and all the packages that depend on
234 <literal>P</literal>. Sometimes we don't know ahead of time which
235 packages will be installed that depend on <literal>P</literal>,
236 which is when the <literal>-ignore-package</literal> flag can be
242 <term><option>-no-auto-link-packages</option>
243 <indexterm><primary><option>-no-auto-link-packages</option></primary>
246 <para>By default, GHC will automatically link in the
247 <literal>haskell98</literal> package. This flag disables that
253 <term><option>-package-name</option> <replaceable>foo</replaceable>
254 <indexterm><primary><option>-package-name</option></primary>
257 <para>Tells GHC the the module being compiled forms part of
258 package <replaceable>foo</replaceable>.
259 If this flag is omitted (a very common case) then the
260 default package <literal>main</literal> is assumed.</para>
261 <para>Note: the argument to <option>-package-name</option>
263 package <literal>name-version</literal> for the package.
265 <literal>-package mypkg-1.2</literal>.</para>
271 <sect2 id="package-main">
272 <title>The main package</title>
274 <para>Every complete Haskell program must define <literal>main</literal> in
275 module <literal>Main</literal>
276 in package <literal>main</literal>. (Omitting the <option>-package-name</option> flag compiles
277 code for package <literal>main</literal>.) Failure to do so leads to a somewhat obscure
278 link-time error of the form:
280 /usr/bin/ld: Undefined symbols:
288 <sect2 id="package-overlaps">
289 <title>Consequences of packages for the Haskell language</title>
291 <para>It is possible that by using packages you might end up with
292 a program that contains two modules with the same name: perhaps
293 you used a package P that has a <emphasis>hidden</emphasis> module
294 M, and there is also a module M in your program. Or perhaps the
295 dependencies of packages that you used contain some overlapping
296 modules. Perhaps the program even contains multiple versions of a
297 certain package, due to dependencies from other packages.</para>
299 <para>None of these scenarios gives rise to an error on its
300 own<footnote><para>it used to in GHC 6.4, but not since
301 6.6</para></footnote>, but they may have some interesting
302 consequences. For instance, if you have a type
303 <literal>M.T</literal> from version 1 of package
304 <literal>P</literal>, then this is <emphasis>not</emphasis> the
305 same as the type <literal>M.T</literal> from version 2 of package
306 <literal>P</literal>, and GHC will report an error if you try to
307 use one where the other is expected.</para>
309 <para>Formally speaking, in Haskell 98, an entity (function, type
310 or class) in a program is uniquely identified by the pair of the
311 module name in which it is defined and its name. In GHC, an
312 entity is uniquely defined by a triple: package, module, and
316 <sect2 id="package-databases">
317 <title>Package Databases</title>
320 A package database is where the details about installed packages
321 are stored. It is a directory, usually
322 called <literal>package.conf.d</literal>, that contains a file
323 for each package, together with a binary cache of the package
324 data in the file <literal>package.cache</literal>. Normally
325 you won't need to look at or modify the contents of a package
326 database directly; all management of package databases can be
327 done through the <literal>ghc-pkg</literal> tool (see
328 <xref linkend="package-management" />).
332 GHC knows about two package databases in particular:
337 <para>The global package database, which comes with your GHC
339 e.g. <filename>/usr/lib/ghc-6.12.1/package.conf.d</filename>.</para>
342 <para>A package database private to each user. On Unix
344 <filename>$HOME/.ghc/<replaceable>arch</replaceable>-<replaceable>os</replaceable>-<replaceable>version</replaceable>/package.conf.d</filename>, and on
345 Windows it will be something like
346 <filename>C:\Documents And Settings\<replaceable>user</replaceable>\ghc\package.conf.d</filename>.
347 The <literal>ghc-pkg</literal> tool knows where this file should be
348 located, and will create it if it doesn't exist (see <xref linkend="package-management" />).</para>
352 <para>When GHC starts up, it reads the contents of these two package
353 databases, and builds up a list of the packages it knows about. You can
354 see GHC's package table by running GHC with the <option>-v</option>
357 <para>Package databases may overlap: for example, packages in the
358 user database will override (<emphasis>shadow</emphasis>) those
359 of the same name and version in the global database.</para>
361 <para>You can control the loading of package databases using the following
367 <option>-package-conf <replaceable>file</replaceable></option>
368 <indexterm><primary><option>-package-conf</option></primary></indexterm>
371 <para>Read in the package configuration file
372 <replaceable>file</replaceable> in addition to the system
373 default file and the user's local file. Packages in additional
374 files read this way will override those in the global and user
380 <term><option>-no-user-package-conf</option>
381 <indexterm><primary><option>-no-user-package-conf</option></primary>
385 <para>Prevent loading of the user's local package database.</para>
390 <sect3 id="ghc-package-path">
391 <title>The <literal>GHC_PACKAGE_PATH</literal> environment variable</title>
392 <indexterm><primary>Environment variable</primary><secondary><literal>GHC_PACKAGE_PATH</literal></secondary>
394 <indexterm><primary><literal>GHC_PACKAGE_PATH</literal></primary></indexterm>
395 <para>The <literal>GHC_PACKAGE_PATH</literal> environment variable may be
396 set to a <literal>:</literal>-separated (<literal>;</literal>-separated
397 on Windows) list of files containing package databases. This list of
398 package databases is used by GHC and ghc-pkg, with earlier databases in
399 the list overriding later ones. This order was chosen to match the
400 behaviour of the <literal>PATH</literal> environment variable; think of
401 it as a list of package databases that are searched left-to-right for
404 <para>If <literal>GHC_PACKAGE_PATH</literal> ends in a separator, then
405 the default user and system package databases are appended, in that
406 order. e.g. to augment the usual set of packages with a database of
407 your own, you could say (on Unix):
409 $ export GHC_PACKAGE_PATH=$HOME/.my-ghc-packages.conf:</screen>
410 (use <literal>;</literal> instead of <literal>:</literal> on
413 <para>To check whether your <literal>GHC_PACKAGE_PATH</literal> setting
414 is doing the right thing, <literal>ghc-pkg list</literal> will list all
415 the databases in use, in the reverse order they are searched.</para>
420 <sect2 id="package-ids">
421 <title>Package IDs, dependencies, and broken packages</title>
423 <para>Each installed package has a unique identifier (the
424 “installed package ID”, or just “package
425 ID” for short) , which distinguishes it from all other
426 installed packages on the system. To see the package IDs
427 associated with each installed package, use <literal>ghc-pkg
428 list -v</literal>:</para>
432 using cache: /usr/lib/ghc-6.12.1/package.conf.d/package.cache
433 /usr/lib/ghc-6.12.1/package.conf.d
434 Cabal-1.7.4 (Cabal-1.7.4-48f5247e06853af93593883240e11238)
435 array-0.2.0.1 (array-0.2.0.1-9cbf76a576b6ee9c1f880cf171a0928d)
436 base-3.0.3.0 (base-3.0.3.0-6cbb157b9ae852096266e113b8fac4a2)
437 base-4.2.0.0 (base-4.2.0.0-247bb20cde37c3ef4093ee124e04bc1c)
442 The string in parentheses after the package name is the package
443 ID: it normally begins with the package name and version, and
444 ends in a hash string derived from the compiled package.
445 Dependencies between packages are expressed in terms of package
446 IDs, rather than just packages and versions. For example, take
447 a look at the dependencies of the <literal>haskell98</literal>
452 $ ghc-pkg field haskell98 depends
453 depends: array-0.2.0.1-9cbf76a576b6ee9c1f880cf171a0928d
454 base-4.2.0.0-247bb20cde37c3ef4093ee124e04bc1c
455 directory-1.0.0.2-f51711bc872c35ce4a453aa19c799008
456 old-locale-1.0.0.1-d17c9777c8ee53a0d459734e27f2b8e9
457 old-time-1.0.0.1-1c0d8ea38056e5087ef1e75cb0d139d1
458 process-1.0.1.1-d8fc6d3baf44678a29b9d59ca0ad5780
459 random-1.0.0.1-423d08c90f004795fd10e60384ce6561
463 The purpose of the package ID is to detect problems caused by
464 re-installing a package without also recompiling the packages
465 that depend on it. Recompiling dependencies is necessary,
466 because the newly compiled package may have a differnt ABI
467 (Application Binary Interface) than the previous version, even
468 if both packages were built from the same source code using the
469 same compiler. With package IDs, a recompiled
470 package will have a different package ID from the previous
471 version, so packages that depended on the previous version are
472 now orphaned - one of their dependencies is not satisfied.
473 Packages that are broken in this way are shown in
474 the <literal>ghc-pkg list</literal> output either in red (if
475 possible) or otherwise surrounded by braces. In the following
476 example, we have recompiled and reinstalled
477 the <literal>filepath</literal> package, and this has caused
478 various dependencies including <literal>Cabal</literal> to
483 WARNING: there are broken packages. Run 'ghc-pkg check' for more details.
484 /usr/lib/ghc-6.12.1/package.conf.d:
492 Additionally, <literal>ghc-pkg list</literal> reminds you that
493 there are broken packages and suggests <literal>ghc-pkg
494 check</literal>, which displays more information about the
495 nature of the failure:
500 There are problems in package ghc-6.12.1:
501 dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
502 There are problems in package haskeline-0.6.2:
503 dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
504 There are problems in package Cabal-1.7.4:
505 dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
506 There are problems in package process-1.0.1.1:
507 dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
508 There are problems in package directory-1.0.0.2:
509 dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
511 The following packages are broken, either because they have a problem
512 listed above, or because they depend on a broken package.
518 bin-package-db-0.0.0.0
524 To fix the problem, you need to recompile the broken packages
525 against the new dependencies. The easiest way to do this is to
526 use <literal>cabal-install</literal>, or download the packages
528 url="http://hackage.haskell.org/packages/hackage.html">HackageDB</ulink>
529 and build and install them as normal.</para>
531 <para>Be careful not to recompile any packages that GHC itself
532 depends on, as this may render the <literal>ghc</literal>
533 package itself broken, and <literal>ghc</literal> cannot be
534 simply recompiled. The only way to recover from this would be
535 to re-install GHC.</para>
538 <sect2 id="package-management">
539 <title>Package management (the <literal>ghc-pkg</literal> command)</title>
540 <indexterm><primary>packages</primary>
541 <secondary>management</secondary></indexterm>
543 <para>The <literal>ghc-pkg</literal> tool is for querying and
544 modifying package databases. To see what package databases are
546 <literal>ghc-pkg list</literal>. The stack of databases that
547 <literal>ghc-pkg</literal> knows about can be modified using the
548 <literal>GHC_PACKAGE_PATH</literal> environment variable (see <xref
549 linkend="ghc-package-path" />, and using
550 <literal>--package-conf</literal> options on the
551 <literal>ghc-pkg</literal> command line.</para>
553 <para>When asked to modify a database, <literal>ghc-pkg</literal> modifies
554 the global database by default. Specifying <option>--user</option>
555 causes it to act on the user database, or <option>--package-conf</option>
556 can be used to act on another database entirely. When multiple of these
557 options are given, the rightmost one is used as the database to act
560 <para>Commands that query the package database (list, latest,
561 describe, field, dot) operate on the list of databases specified by
562 the flags <option>--user</option>, <option>--global</option>, and
563 <option>--package-conf</option>. If none of these flags are
564 given, the default is <option>--global</option>
565 <option>--user</option>.</para>
567 <para>If the environment variable <literal>GHC_PACKAGE_PATH</literal> is
568 set, and its value does not end in a separator (<literal>:</literal> on
569 Unix, <literal>;</literal> on Windows), then the last database is
570 considered to be the global database, and will be modified by default by
571 <literal>ghc-pkg</literal>. The intention here is that
572 <literal>GHC_PACKAGE_PATH</literal> can be used to create a virtual
573 package environment into which Cabal packages can be installed without
574 setting anything other than <literal>GHC_PACKAGE_PATH</literal>.</para>
576 <para>The <literal>ghc-pkg</literal> program may be run in the ways listed
577 below. Where a package name is required, the package can be named in
578 full including the version number
579 (e.g. <literal>network-1.0</literal>), or without the version number.
580 Naming a package without the version number matches all versions of the
581 package; the specified action will be applied to all the matching
582 packages. A package specifier that matches all version of the package
583 can also be written <replaceable>pkg</replaceable><literal>-*</literal>,
584 to make it clearer that multiple packages are being matched.</para>
588 <term><literal>ghc-pkg init <replaceable>path</replaceable></literal></term>
590 <para>Creates a new, empty, package database
591 at <replaceable>path</replaceable>, which must not already
597 <term><literal>ghc-pkg register <replaceable>file</replaceable></literal></term>
599 <para>Reads a package specification from
600 <replaceable>file</replaceable> (which may be “<literal>-</literal>”
601 to indicate standard input),
602 and adds it to the database of installed packages. The syntax of
603 <replaceable>file</replaceable> is given in <xref
604 linkend="installed-pkg-info" />.</para>
606 <para>The package specification must be a package that isn't already
612 <term><literal>ghc-pkg update <replaceable>file</replaceable></literal></term>
614 <para>The same as <literal>register</literal>, except that if a
615 package of the same name is already installed, it is
616 replaced by the new one.</para>
621 <term><literal>ghc-pkg unregister <replaceable>P</replaceable></literal></term>
623 <para>Remove the specified package from the database.</para>
628 <term><literal>ghc-pkg expose <replaceable>P</replaceable></literal></term>
630 <para>Sets the <literal>exposed</literal> flag for package
631 <replaceable>P</replaceable> to <literal>True</literal>.</para>
636 <term><literal>ghc-pkg check</literal></term>
638 <para>Check consistency of dependencies in the package
639 database, and report packages that have missing
645 <term><literal>ghc-pkg hide <replaceable>P</replaceable></literal></term>
647 <para>Sets the <literal>exposed</literal> flag for package
648 <replaceable>P</replaceable> to <literal>False</literal>.</para>
653 <term><literal>ghc-pkg list [<replaceable>P</replaceable>] [<option>--simple-output</option>]</literal></term>
655 <para>This option displays the currently installed
656 packages, for each of the databases known to
657 <literal>ghc-pkg</literal>. That includes the global database, the
658 user's local database, and any further files specified using the
659 <option>-f</option> option on the command line.</para>
661 <para>Hidden packages (those for which the <literal>exposed</literal>
662 flag is <literal>False</literal>) are shown in parentheses in the
663 list of packages.</para>
665 <para>If an optional package identifier <replaceable>P</replaceable>
666 is given, then only packages matching that identifier are
669 <para>If the option <option>--simple-output</option> is given, then
670 the packages are listed on a single line separated by spaces, and
671 the database names are not included. This is intended to make it
672 easier to parse the output of <literal>ghc-pkg list</literal> using
678 <term><literal>ghc-pkg find-module <replaceable>M</replaceable> [<option>--simple-output</option>]</literal></term>
680 <para>This option lists registered packages exposing module
681 <replaceable>M</replaceable>. Examples:</para>
683 $ ghc-pkg find-module Var
684 c:/fptools/validate/ghc/driver/package.conf.inplace:
687 $ ghc-pkg find-module Data.Sequence
688 c:/fptools/validate/ghc/driver/package.conf.inplace:
691 <para>Otherwise, it behaves like <literal>ghc-pkg list</literal>,
692 including options.</para>
698 <term><literal>ghc-pkg latest <replaceable>P</replaceable></literal></term>
700 <para>Prints the latest available version of package
701 <replaceable>P</replaceable>.</para>
706 <term><literal>ghc-pkg describe <replaceable>P</replaceable></literal></term>
708 <para>Emit the full description of the specified package. The
709 description is in the form of an
710 <literal>InstalledPackageInfo</literal>, the same as the input file
711 format for <literal>ghc-pkg register</literal>. See <xref
712 linkend="installed-pkg-info" /> for details.</para>
714 <para>If the pattern matches multiple packages, the
715 description for each package is emitted, separated by the
716 string <literal>---</literal> on a line by itself.</para>
721 <term><literal>ghc-pkg field <replaceable>P</replaceable> <replaceable>field</replaceable>[,<replaceable>field</replaceable>]*</literal></term>
723 <para>Show just a single field of the installed package description
724 for <literal>P</literal>. Multiple fields can be selected by separating
725 them with commas</para>
730 <term><literal>ghc-pkg dot</literal></term>
733 Generate a graph of the package dependencies in a form
734 suitable for input for the <ulink url="http://www.graphviz.org/">graphviz</ulink> tools. For example,
735 to generate a PDF of the dependency graph:</para>
737 ghc-pkg dot | tred | dot -Tpdf >pkgs.pdf
743 <term><literal>ghc-pkg dump</literal></term>
745 <para>Emit the full description of every package, in the
746 form of an <literal>InstalledPackageInfo</literal>.
747 Multiple package descriptions are separated by the
748 string <literal>---</literal> on a line by itself.</para>
750 <para>This is almost the same as <literal>ghc-pkg describe '*'</literal>, except that <literal>ghc-pkg dump</literal>
751 is intended for use by tools that parse the results, so
752 for example where <literal>ghc-pkg describe '*'</literal>
753 will emit an error if it can't find any packages that
754 match the pattern, <literal>ghc-pkg dump</literal> will
755 simply emit nothing.</para>
760 <term><literal>ghc-pkg recache</literal></term>
763 Re-creates the binary cache
764 file <filename>package.cache</filename> for the selected
765 database. This may be necessary if the cache has somehow
766 become out-of-sync with the contents of the database
767 (<literal>ghc-pkg</literal> will warn you if this might be
771 The other time when <literal>ghc-pkg recache</literal> is
772 useful is for registering packages manually: it is
773 possible to register a package by simply putting the
774 appropriate file in the package database directory and
775 invoking <literal>ghc-pkg recache</literal> to update the
776 cache. This method of registering packages may be more
777 convenient for automated packaging systems.
784 Substring matching is supported for <replaceable>M</replaceable> in
785 <literal>find-module</literal> and for <replaceable>P</replaceable> in
786 <literal>list</literal>, <literal>describe</literal>, and
787 <literal>field</literal>, where a <literal>'*'</literal> indicates open
788 substring ends (<literal>prefix*</literal>, <literal>*suffix</literal>,
789 <literal>*infix*</literal>). Examples (output omitted):
792 -- list all regex-related packages
793 ghc-pkg list '*regex*' --ignore-case
794 -- list all string-related packages
795 ghc-pkg list '*string*' --ignore-case
796 -- list OpenGL-related packages
797 ghc-pkg list '*gl*' --ignore-case
798 -- list packages exporting modules in the Data hierarchy
799 ghc-pkg find-module 'Data.*'
800 -- list packages exporting Monad modules
801 ghc-pkg find-module '*Monad*'
802 -- list names and maintainers for all packages
803 ghc-pkg field '*' name,maintainer
804 -- list location of haddock htmls for all packages
805 ghc-pkg field '*' haddock-html
806 -- dump the whole database
810 <para>Additionally, the following flags are accepted by
811 <literal>ghc-pkg</literal>:</para>
816 <option>––auto-ghci-libs</option><indexterm><primary><option>––auto-ghci-libs</option></primary>
820 <para>Automatically generate the GHCi
821 <filename>.o</filename> version of each
822 <filename>.a</filename> Haskell library, using GNU ld (if
823 that is available). Without this option,
824 <literal>ghc-pkg</literal> will warn if GHCi versions of
825 any Haskell libraries in the package don't exist.</para>
827 <para>GHCi <literal>.o</literal> libraries don't
828 necessarily have to live in the same directory as the
829 corresponding <literal>.a</literal> library. However,
830 this option will cause the GHCi library to be created in
831 the same directory as the <literal>.a</literal>
838 <option>-f</option> <replaceable>file</replaceable>
839 <indexterm><primary><option>-f</option></primary>
843 <option>-package-conf</option> <replaceable>file</replaceable>
844 <indexterm><primary><option>-package-conf</option></primary>
848 <para>Adds <replaceable>file</replaceable> to the stack of package
849 databases. Additionally, <replaceable>file</replaceable> will
850 also be the database modified by a <literal>register</literal>,
851 <literal>unregister</literal>, <literal>expose</literal> or
852 <literal>hide</literal> command, unless it is overridden by a later
853 <option>--package-conf</option>, <option>--user</option> or
854 <option>--global</option> option.</para>
860 <option>––force</option>
862 <option>––force</option>
863 </primary></indexterm>
866 <para>Causes <literal>ghc-pkg</literal> to ignore missing
867 dependencies, directories and libraries when registering a package,
868 and just go ahead and add it anyway. This might be useful if your
869 package installation system needs to add the package to
870 GHC before building and installing the files.</para>
876 <option>––global</option><indexterm><primary><option>––global</option></primary>
880 <para>Operate on the global package database (this is the default).
881 This flag affects the <literal>register</literal>,
882 <literal>update</literal>, <literal>unregister</literal>,
883 <literal>expose</literal>, and <literal>hide</literal>
890 <option>––help</option><indexterm><primary><option>––help</option></primary>
894 <option>-?</option><indexterm><primary><option>-?</option></primary>
898 <para>Outputs the command-line syntax.</para>
904 <option>––user</option><indexterm><primary><option>––user</option></primary>
908 <para>Operate on the current user's local package database.
909 This flag affects the <literal>register</literal>,
910 <literal>update</literal>, <literal>unregister</literal>,
911 <literal>expose</literal>, and <literal>hide</literal>
918 <option>-v</option><optional><replaceable>n</replaceable></optional><indexterm><primary><option>-v</option></primary><secondary>ghc-pkg
919 option</secondary></indexterm>
922 <option>--verbose</option><optional>=<replaceable>n</replaceable></optional><indexterm><primary><option>--verbose</option></primary><secondary>ghc-pkg option</secondary></indexterm>
926 Control verbosity. Verbosity levels range from 0-2, where
927 the default is 1, and <option>-v</option> alone selects
935 <option>-V</option><indexterm><primary><option>-V</option></primary>
939 <option>––version</option><indexterm><primary><option>––version</option></primary>
943 <para>Output the <literal>ghc-pkg</literal> version number.</para>
950 <sect2 id="building-packages">
951 <title>Building a package from Haskell source</title>
952 <indexterm><primary>packages</primary>
953 <secondary>building</secondary></indexterm>
955 <para>We don't recommend building packages the hard way. Instead, use the
956 <ulink url="../Cabal/index.html">Cabal</ulink> infrastructure
957 if possible. If your package is particularly complicated or requires a
958 lot of configuration, then you might have to fall back to the low-level
959 mechanisms, so a few hints for those brave souls follow.</para>
961 <para>You need to build an "installed package info" file for
962 passing to <literal>ghc-pkg</literal> when installing your
963 package. The contents of this file are described in
964 <xref linkend="installed-pkg-info" />.</para>
966 <para>The Haskell code in a package may be built into one or more
967 archive libraries (e.g. <filename>libHSfoo.a</filename>), or a
969 (e.g. <filename>libHSfoo.dll/.so/.dylib</filename>). The
970 restriction to a single shared object is because the package
971 system is used to tell the compiler when it should make an
972 inter-shared-object call rather than an intra-shared-object-call
973 call (inter-shared-object calls require an extra
976 <listitem><para>Building a static library is done by using the
977 <literal>ar</literal> tool, like so:</para>
979 <screen>ar cqs libHSfoo-1.0.a A.o B.o C.o ...</screen>
981 <para>where <filename>A.o</filename>,
982 <filename>B.o</filename> and so on are the compiled Haskell
983 modules, and <filename>libHSfoo.a</filename> is the library you
984 wish to create. The syntax may differ slightly on your system,
985 so check the documentation if you run into difficulties.</para>
988 <para>Versions of the Haskell libraries for use with GHCi may also
989 abe included: GHCi cannot load <literal>.a</literal> files
990 directly, instead it will look for an object file
991 called <filename>HSfoo.o</filename> and load that. On some
992 systems, the <literal>ghc-pkg</literal> tool can automatically
993 build the GHCi version of each library, see
994 <xref linkend="package-management"/>. To build these libraries
995 by hand from the <literal>.a</literal> archive, it is possible
996 to use GNU <command>ld</command> as follows:</para>
998 <screen>ld -r ––whole-archive -o HSfoo.o libHSfoo.a</screen>
1001 <literal>––whole-archive</literal> with
1002 <literal>–all_load</literal> on MacOS X)</para>
1005 <para>When building the package as shared library, GHC can be used to
1006 perform the link step. This hides some of the details
1007 out the underlying linker and provides a common
1008 interface to all shared object variants that are supported
1009 by GHC (DLLs, ELF DSOs, and Mac OS dylibs). The shared
1010 object must be named in specific way for two reasons: (1)
1011 the name must contain the GHC compiler version, so that two
1012 library variants don't collide that are compiled by
1013 different versions of GHC and that therefore are most likely
1014 incompatible with respect to calling conventions, (2) it
1015 must be different from the static name otherwise we would
1016 not be able to control the linker as precisely as necessary
1018 the <option>-static</option>/<option>-dynamic</option> flags
1019 work, see <xref linkend="options-linker" />.</para>
1021 <screen>ghc -shared libHSfoo-1.0-ghc<replaceable>GHCVersion</replaceable>.so A.o B.o C.o</screen>
1022 <para>Using GHC's version number in the shared object name
1023 allows different library versions compiled by different GHC
1024 versions to be installed in standard system locations,
1025 e.g. under *nix /usr/lib. To obtain the version number of
1026 GHC invoke <literal>ghc --numeric-version</literal> and use
1028 of <replaceable>GHCVersion</replaceable>. See also
1029 <xref linkend="options-codegen" /> on how object files must
1030 be prepared for shared object linking.</para>
1034 <para>To compile a module which is to be part of a new package,
1035 use the <literal>-package-name</literal> option (<xref linkend="using-packages"/>).
1036 Failure to use the <literal>-package-name</literal> option
1037 when compiling a package will probably result in disaster, but
1038 you will only discover later when you attempt to import modules
1039 from the package. At this point GHC will complain that the
1040 package name it was expecting the module to come from is not the
1041 same as the package name stored in the <literal>.hi</literal>
1044 <para>It is worth noting with shared objects, when each package
1045 is built as a single shared object file, since a reference to a shared object costs an extra
1046 indirection, intra-package references are cheaper than
1047 inter-package references. Of course, this applies to the
1048 <filename>main</filename> package as well.</para>
1051 <sect2 id="installed-pkg-info">
1053 <literal>InstalledPackageInfo</literal>: a package specification
1056 <para>A package specification is a Haskell record; in particular, it is the
1058 url="&libraryCabalLocation;/Distribution-InstalledPackageInfo.html#%tInstalledPackageInfo">InstalledPackageInfo</ulink> in the module Distribution.InstalledPackageInfo, which is part of the Cabal package distributed with GHC.</para>
1060 <para>An <literal>InstalledPackageInfo</literal> has a human
1061 readable/writable syntax. The functions
1062 <literal>parseInstalledPackageInfo</literal> and
1063 <literal>showInstalledPackageInfo</literal> read and write this syntax
1064 respectively. Here's an example of the
1065 <literal>InstalledPackageInfo</literal> for the <literal>unix</literal> package:</para>
1068 $ ghc-pkg describe unix
1071 id: unix-2.3.1.0-de7803f1a8cd88d2161b29b083c94240
1074 maintainer: libraries@haskell.org
1078 description: This package gives you access to the set of operating system
1079 services standardised by POSIX 1003.1b (or the IEEE Portable
1080 Operating System Interface for Computing Environments -
1083 The package is not supported under Windows (except under Cygwin).
1087 exposed-modules: System.Posix System.Posix.DynamicLinker.Module
1088 System.Posix.DynamicLinker.Prim System.Posix.Directory
1089 System.Posix.DynamicLinker System.Posix.Env System.Posix.Error
1090 System.Posix.Files System.Posix.IO System.Posix.Process
1091 System.Posix.Process.Internals System.Posix.Resource
1092 System.Posix.Temp System.Posix.Terminal System.Posix.Time
1093 System.Posix.Unistd System.Posix.User System.Posix.Signals
1094 System.Posix.Signals.Exts System.Posix.Semaphore
1095 System.Posix.SharedMem
1097 import-dirs: /usr/lib/ghc-6.12.1/unix-2.3.1.0
1098 library-dirs: /usr/lib/ghc-6.12.1/unix-2.3.1.0
1099 hs-libraries: HSunix-2.3.1.0
1100 extra-libraries: rt util dl
1101 extra-ghci-libraries:
1102 include-dirs: /usr/lib/ghc-6.12.1/unix-2.3.1.0/include
1103 includes: HsUnix.h execvpe.h
1104 depends: base-4.2.0.0-247bb20cde37c3ef4093ee124e04bc1c
1110 haddock-interfaces: /usr/share/doc/ghc/html/libraries/unix/unix.haddock
1111 haddock-html: /usr/share/doc/ghc/html/libraries/unix
1114 <para>Here is a brief description of the syntax of this file:</para>
1116 <para>A package description consists of a number of field/value pairs. A
1117 field starts with the field name in the left-hand column followed by a
1118 “<literal>:</literal>”, and the value continues until the next line that begins in the
1119 left-hand column, or the end of file.</para>
1121 <para>The syntax of the value depends on the field. The various field
1126 <term>freeform</term>
1128 <para>Any arbitrary string, no interpretation or parsing is
1135 <para>A sequence of non-space characters, or a sequence of arbitrary
1136 characters surrounded by quotes <literal>"...."</literal>.</para>
1140 <term>string list</term>
1142 <para>A sequence of strings, separated by commas. The sequence may
1148 <para>In addition, there are some fields with special syntax (e.g. package
1149 names, version, dependencies).</para>
1151 <para>The allowed fields, with their types, are:</para>
1156 <literal>name</literal>
1157 <indexterm><primary><literal>name</literal></primary><secondary>package specification</secondary></indexterm>
1160 <para>The package's name (without the version).</para>
1166 <literal>id</literal>
1167 <indexterm><primary><literal>id</literal></primary><secondary>package specification</secondary></indexterm>
1170 <para>The package ID. It is up to you to choose a suitable
1177 <literal>version</literal>
1178 <indexterm><primary><literal>version</literal></primary><secondary>package specification</secondary></indexterm>
1181 <para>The package's version, usually in the form
1182 <literal>A.B</literal> (any number of components are allowed).</para>
1188 <literal>license</literal>
1189 <indexterm><primary><literal>auto</literal></primary><secondary>package specification</secondary></indexterm>
1192 <para>(string) The type of license under which this package is distributed.
1193 This field is a value of the <ulink
1194 url="&libraryCabalLocation;/Distribution-License.html#t:License"><literal>License</literal></ulink> type.</para>
1200 <literal>license-file</literal>
1201 <indexterm><primary><literal>license-file</literal></primary><secondary>package specification</secondary></indexterm>
1204 <para>(optional string) The name of a file giving detailed license
1205 information for this package.</para>
1211 <literal>copyright</literal>
1212 <indexterm><primary><literal>copyright</literal></primary><secondary>package specification</secondary></indexterm>
1215 <para>(optional freeform) The copyright string.</para>
1221 <literal>maintainer</literal>
1222 <indexterm><primary><literal>maintainer</literal></primary><secondary>package specification</secondary></indexterm>
1225 <para>(optinoal freeform) The email address of the package's maintainer.</para>
1231 <literal>stability</literal>
1232 <indexterm><primary><literal>stability</literal></primary><secondary>package specification</secondary></indexterm>
1235 <para>(optional freeform) A string describing the stability of the package
1236 (eg. stable, provisional or experimental).</para>
1242 <literal>homepage</literal>
1243 <indexterm><primary><literal>homepage</literal></primary><secondary>package specification</secondary></indexterm>
1246 <para>(optional freeform) URL of the package's home page.</para>
1252 <literal>package-url</literal>
1253 <indexterm><primary><literal>package-url</literal></primary><secondary>package specification</secondary></indexterm>
1256 <para>(optional freeform) URL of a downloadable distribution for this
1257 package. The distribution should be a Cabal package.</para>
1263 <literal>description</literal>
1264 <indexterm><primary><literal>description</literal></primary><secondary>package specification</secondary></indexterm>
1267 <para>(optional freeform) Description of the package.</para>
1273 <literal>category</literal>
1274 <indexterm><primary><literal>category</literal></primary><secondary>package specification</secondary></indexterm>
1277 <para>(optinoal freeform) Which category the package belongs to. This field
1278 is for use in conjunction with a future centralised package
1279 distribution framework, tentatively titled Hackage.</para>
1285 <literal>author</literal>
1286 <indexterm><primary><literal>author</literal></primary><secondary>package specification</secondary></indexterm>
1289 <para>(optional freeform) Author of the package.</para>
1295 <literal>exposed</literal>
1296 <indexterm><primary><literal>exposed</literal></primary><secondary>package specification</secondary></indexterm>
1299 <para>(bool) Whether the package is exposed or not.</para>
1305 <literal>exposed-modules</literal>
1306 <indexterm><primary><literal>exposed-modules</literal></primary><secondary>package specification</secondary></indexterm>
1309 <para>(string list) modules exposed by this package.</para>
1315 <literal>hidden-modules</literal>
1316 <indexterm><primary><literal>hidden-modules</literal></primary><secondary>package specification</secondary></indexterm>
1319 <para>(string list) modules provided by this package,
1320 but not exposed to the programmer. These modules cannot be
1321 imported, but they are still subject to the overlapping constraint:
1322 no other package in the same program may provide a module of the
1329 <literal>import-dirs</literal>
1330 <indexterm><primary><literal>import-dirs</literal></primary><secondary>package specification</secondary></indexterm>
1333 <para>(string list) A list of directories containing interface files
1334 (<literal>.hi</literal> files) for this package.</para>
1336 <para>If the package contains profiling libraries, then
1337 the interface files for those library modules should have
1338 the suffix <literal>.p_hi</literal>. So the package can
1339 contain both normal and profiling versions of the same
1340 library without conflict (see also
1341 <literal>library_dirs</literal> below).</para>
1347 <literal>library-dirs</literal>
1348 <indexterm><primary><literal>library-dirs</literal></primary><secondary>package specification</secondary></indexterm>
1351 <para>(string list) A list of directories containing libraries for this
1358 <literal>hs-libraries</literal>
1359 <indexterm><primary><literal>hs-libraries</literal></primary><secondary>package specification</secondary></indexterm>
1362 <para>(string list) A list of libraries containing Haskell code for this
1363 package, with the <literal>.a</literal> or
1364 <literal>.dll</literal> suffix omitted. When packages are
1365 built as libraries, the
1366 <literal>lib</literal> prefix is also omitted.</para>
1368 <para>For use with GHCi, each library should have an
1369 object file too. The name of the object file does
1370 <emphasis>not</emphasis> have a <literal>lib</literal>
1371 prefix, and has the normal object suffix for your
1374 <para>For example, if we specify a Haskell library as
1375 <filename>HSfoo</filename> in the package spec, then the
1376 various flavours of library that GHC actually uses will be
1380 <term><filename>libHSfoo.a</filename></term>
1382 <para>The name of the library on Unix and Windows
1383 (mingw) systems. Note that we don't support
1384 building dynamic libraries of Haskell code on Unix
1389 <term><filename>HSfoo.dll</filename></term>
1391 <para>The name of the dynamic library on Windows
1392 systems (optional).</para>
1396 <term><filename>HSfoo.o</filename></term>
1397 <term><filename>HSfoo.obj</filename></term>
1399 <para>The object version of the library used by
1409 <literal>extra-libraries</literal>
1410 <indexterm><primary><literal>extra-libraries</literal></primary><secondary>package specification</secondary></indexterm>
1413 <para>(string list) A list of extra libraries for this package. The
1414 difference between <literal>hs-libraries</literal> and
1415 <literal>extra-libraries</literal> is that
1416 <literal>hs-libraries</literal> normally have several
1417 versions, to support profiling, parallel and other build
1418 options. The various versions are given different
1419 suffixes to distinguish them, for example the profiling
1420 version of the standard prelude library is named
1421 <filename>libHSbase_p.a</filename>, with the
1422 <literal>_p</literal> indicating that this is a profiling
1423 version. The suffix is added automatically by GHC for
1424 <literal>hs-libraries</literal> only, no suffix is added
1426 <literal>extra-libraries</literal>.</para>
1428 <para>The libraries listed in
1429 <literal>extra-libraries</literal> may be any libraries
1430 supported by your system's linker, including dynamic
1431 libraries (<literal>.so</literal> on Unix,
1432 <literal>.DLL</literal> on Windows).</para>
1434 <para>Also, <literal>extra-libraries</literal> are placed
1435 on the linker command line after the
1436 <literal>hs-libraries</literal> for the same package. If
1437 your package has dependencies in the other direction (i.e.
1438 <literal>extra-libraries</literal> depends on
1439 <literal>hs-libraries</literal>), and the libraries are
1440 static, you might need to make two separate
1447 <literal>include-dirs</literal>
1448 <indexterm><primary><literal>include-dirs</literal></primary><secondary>package specification</secondary></indexterm>
1451 <para>(string list) A list of directories containing C includes for this
1458 <literal>includes</literal>
1459 <indexterm><primary><literal>includes</literal></primary><secondary>package specification</secondary></indexterm>
1462 <para>(string list) A list of files to include for via-C compilations
1463 using this package. Typically the include file(s) will
1464 contain function prototypes for any C functions used in
1465 the package, in case they end up being called as a result
1466 of Haskell functions from the package being
1473 <literal>depends</literal>
1474 <indexterm><primary><literal>depends</literal></primary><secondary>package specification</secondary></indexterm>
1477 <para>(package id list) Packages on which this package
1484 <literal>hugs-options</literal>
1485 <indexterm><primary><literal>hugs-options</literal></primary><secondary>package specification</secondary></indexterm>
1488 <para>(string list) Options to pass to Hugs for this package.</para>
1494 <literal>cc-options</literal>
1495 <indexterm><primary><literal>cc-options</literal></primary><secondary>package specification</secondary></indexterm>
1498 <para>(string list) Extra arguments to be added to the gcc command line
1499 when this package is being used (only for via-C
1500 compilations).</para>
1506 <literal>ld-options</literal>
1507 <indexterm><primary><literal>ld-options</literal></primary><secondary>package specification</secondary></indexterm>
1510 <para>(string list) Extra arguments to be added to the
1511 <command>gcc</command> command line (for linking) when
1512 this package is being used.</para>
1518 <literal>framework-dirs</literal>
1519 <indexterm><primary><literal>framework-dirs</literal></primary><secondary>package specification</secondary></indexterm>
1522 <para>(string list) On Darwin/MacOS X, a list of directories containing
1523 frameworks for this package. This corresponds to the
1524 <option>-framework-path</option> option. It is ignored on all other
1531 <literal>frameworks</literal>
1532 <indexterm><primary><literal>frameworks</literal></primary><secondary>package specification</secondary></indexterm>
1535 <para>(string list) On Darwin/MacOS X, a list of frameworks to link to. This
1536 corresponds to the <option>-framework</option> option. Take a look
1537 at Apple's developer documentation to find out what frameworks
1538 actually are. This entry is ignored on all other platforms.</para>
1544 <literal>haddock-interfaces</literal>
1545 <indexterm><primary><literal>haddock-interfaces</literal></primary><secondary>package specification</secondary></indexterm>
1548 <para>(string list) A list of filenames containing <ulink
1549 url="http://www.haskell.org/haddock/">Haddock</ulink> interface
1550 files (<literal>.haddock</literal> files) for this package.</para>
1556 <literal>haddock-html</literal>
1557 <indexterm><primary><literal>haddock-html</literal></primary><secondary>package specification</secondary></indexterm>
1560 <para>(optional string) The directory containing the Haddock-generated HTML
1561 for this package.</para>
1566 <!-- This isn't true any more. I'm not sure if we still need it -SDM
1568 The <literal>ghc-pkg</literal> tool performs expansion of
1569 environment variables occurring in input package specifications.
1570 So, if the <literal>mypkg</literal> was added to the package
1571 database as follows:
1574 $ installdir=/usr/local/lib ghc-pkg -a < mypkg.pkg
1578 The occurrence of <literal>${installdir}</literal> is replaced
1579 with <literal>/usr/local/lib</literal> in the package data that
1580 is added for <literal>mypkg</literal>.
1584 This feature enables the distribution of package specification
1585 files that can be easily configured when installing.
1588 <para>For examples of more package specifications, take a look
1589 at the <literal>package.conf</literal> in your GHC
1590 installation.</para>
1598 ;;; Local Variables: ***
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