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<?xml version="1.0" encoding="iso-8859-1"?>
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<indexterm><primary>packages</primary></indexterm>
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<para>A package is a library of Haskell modules known to the
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compiler. GHC comes with several packages: see the accompanying
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<ulink url="../libraries/index.html">library
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documentation</ulink>. More packages to install can be obtained
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url="http://hackage.haskell.org/packages/hackage.html">HackageDB</ulink>.</para>
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<para>Using a package couldn't be simpler: if you're using
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<option>––make</option> or GHCi, then most of the installed packages will be
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automatically available to your program without any further options. The
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exceptions to this rule are covered below in <xref
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linkend="using-packages" />.</para>
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<para>Building your own packages is also quite straightforward: we provide
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the <ulink url="http://www.haskell.org/cabal/">Cabal</ulink> infrastructure which
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automates the process of configuring, building, installing and distributing
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a package. All you need to do is write a simple configuration file, put a
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few files in the right places, and you have a package. See the
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<ulink url="../Cabal/index.html">Cabal documentation</ulink>
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for details, and also the Cabal libraries (<ulink url="&libraryCabalLocation;/Distribution-Simple.html">Distribution.Simple</ulink>,
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<sect2 id="using-packages">
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<indexterm><primary>packages</primary>
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<secondary>using</secondary></indexterm>
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<para>GHC only knows about packages that are
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<emphasis>installed</emphasis>. To see which packages are installed, use
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the <literal>ghc-pkg list</literal> command:</para>
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/usr/lib/ghc-6.12.1/package.conf.d:
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bin-package-db-0.0.0.0
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(dph-prim-interface-0.4.0)
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extensible-exceptions-0.1.1.0
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template-haskell-2.4.0.0
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<para>An installed package is either <emphasis>exposed</emphasis>
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or <emphasis>hidden</emphasis> by default. Packages hidden by
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default are listed in parentheses
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(eg. <literal>(lang-1.0)</literal>), or possibly in blue if your
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terminal supports colour, in the output of <literal>ghc-pkg
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list</literal>. Command-line flags, described below, allow you
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to expose a hidden package or hide an exposed one. Only modules
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from exposed packages may be imported by your Haskell code; if
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you try to import a module from a hidden package, GHC will emit
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Note: if you're using Cabal, then the exposed or hidden status
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of a package is irrelevant: the available packages are instead
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determined by the dependencies listed in
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your <literal>.cabal</literal> specification. The
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exposed/hidden status of packages is only relevant when
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using <literal>ghc</literal> or <literal>ghci</literal>
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<para>To see which modules are provided by a package use the
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<literal>ghc-pkg</literal> command (see <xref linkend="package-management"/>):</para>
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$ ghc-pkg field network exposed-modules
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exposed-modules: Network.BSD,
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<para>The GHC command line options that control packages are:</para>
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<option>-package <replaceable>P</replaceable></option>
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<indexterm><primary><option>-package</option></primary></indexterm>
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<para>This option causes the installed
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package <replaceable>P</replaceable> to be exposed. The
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package <replaceable>P</replaceable> can be specified in
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full with its version number
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(e.g. <literal>network-1.0</literal>) or the version
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number can be omitted if there is only one version of the
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package installed. If there are multiple versions
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of <replaceable>P</replaceable> installed, then all other
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versions will become hidden.</para>
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<para>The <option>-package <replaceable>P</replaceable></option>
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option also causes package <replaceable>P</replaceable> to
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be linked into the resulting executable or shared
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object. Whether a packages' library is linked statically
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or dynamically is controlled by the flag
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pair <option>-static</option>/<option>-dynamic</option>.</para>
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<para>In <option>––make</option> mode
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and <option>––interactive</option> mode (see
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<xref linkend="modes" />), the compiler normally
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determines which packages are required by the current
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Haskell modules, and links only those. In batch mode
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however, the dependency information isn't available, and
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<option>-package</option> options must be given when linking. The one other time you might need to use
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<option>-package</option> to force linking a package is
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when the package does not contain any Haskell modules (it
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might contain a C library only, for example). In that
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case, GHC will never discover a dependency on it, so it
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has to be mentioned explicitly.</para>
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<para>For example, to link a program consisting of objects
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<filename>Foo.o</filename> and <filename>Main.o</filename>, where
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we made use of the <literal>network</literal> package, we need to
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give GHC the <literal>-package</literal> flag thus:
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<screen>$ ghc -o myprog Foo.o Main.o -package network</screen>
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The same flag is necessary even if we compiled the modules from
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source, because GHC still reckons it's in batch mode:
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<screen>$ ghc -o myprog Foo.hs Main.hs -package network</screen></para>
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<option>-package-id <replaceable>P</replaceable></option>
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<indexterm><primary><option>-package-id</option></primary></indexterm>
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Exposes a package like <option>-package</option>, but the
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package is named by its ID rather than by name. This is a
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more robust way to name packages, and can be used to
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select packages that would otherwise be shadowed. Cabal
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passes <option>-package-id</option> flags to GHC.
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<term><option>-hide-all-packages</option>
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<indexterm><primary><option>-hide-package</option></primary>
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<para>Ignore the exposed flag on installed packages, and hide them
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all by default. If you use
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this flag, then any packages you require (including
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<literal>base</literal>) need to be explicitly exposed using
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<option>-package</option> options.</para>
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<para>This is a good way to insulate your program from
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differences in the globally exposed packages, and being
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explicit about package dependencies is a Good Thing.
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Cabal always passes the
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<option>-hide-all-packages</option> flag to GHC, for
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exactly this reason.</para>
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<term><option>-hide-package</option> <replaceable>P</replaceable>
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<indexterm><primary><option>-hide-package</option></primary>
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<para>This option does the opposite of <option>-package</option>: it
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causes the specified package to be <firstterm>hidden</firstterm>,
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which means that none of its modules will be available for import
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by Haskell <literal>import</literal> directives.</para>
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<para>Note that the package might still end up being linked into the
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final program, if it is a dependency (direct or indirect) of
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another exposed package.</para>
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<term><option>-ignore-package</option> <replaceable>P</replaceable>
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<indexterm><primary><option>-ignore-package</option></primary>
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<para>Causes the compiler to behave as if package
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<replaceable>P</replaceable>, and any packages that depend on
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<literal>P</literal>, are not installed at all.</para>
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<para>Saying <literal>-ignore-package P</literal> is the same as
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giving <literal>-hide-package</literal> flags for
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<literal>P</literal> and all the packages that depend on
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<literal>P</literal>. Sometimes we don't know ahead of time which
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packages will be installed that depend on <literal>P</literal>,
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which is when the <literal>-ignore-package</literal> flag can be
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<term><option>-no-auto-link-packages</option>
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<indexterm><primary><option>-no-auto-link-packages</option></primary>
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<para>By default, GHC will automatically link in the
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<literal>haskell98</literal> package. This flag disables that
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<term><option>-package-name</option> <replaceable>foo</replaceable>
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<indexterm><primary><option>-package-name</option></primary>
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<para>Tells GHC the the module being compiled forms part of
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package <replaceable>foo</replaceable>.
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If this flag is omitted (a very common case) then the
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default package <literal>main</literal> is assumed.</para>
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<para>Note: the argument to <option>-package-name</option>
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package <literal>name-version</literal> for the package.
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<literal>-package mypkg-1.2</literal>.</para>
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<sect2 id="package-main">
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<title>The main package</title>
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<para>Every complete Haskell program must define <literal>main</literal> in
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module <literal>Main</literal>
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in package <literal>main</literal>. (Omitting the <option>-package-name</option> flag compiles
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code for package <literal>main</literal>.) Failure to do so leads to a somewhat obscure
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link-time error of the form:
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/usr/bin/ld: Undefined symbols:
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<sect2 id="package-overlaps">
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<title>Consequences of packages for the Haskell language</title>
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<para>It is possible that by using packages you might end up with
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a program that contains two modules with the same name: perhaps
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you used a package P that has a <emphasis>hidden</emphasis> module
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M, and there is also a module M in your program. Or perhaps the
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dependencies of packages that you used contain some overlapping
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modules. Perhaps the program even contains multiple versions of a
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certain package, due to dependencies from other packages.</para>
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<para>None of these scenarios gives rise to an error on its
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own<footnote><para>it used to in GHC 6.4, but not since
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6.6</para></footnote>, but they may have some interesting
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consequences. For instance, if you have a type
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<literal>M.T</literal> from version 1 of package
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<literal>P</literal>, then this is <emphasis>not</emphasis> the
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same as the type <literal>M.T</literal> from version 2 of package
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<literal>P</literal>, and GHC will report an error if you try to
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use one where the other is expected.</para>
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<para>Formally speaking, in Haskell 98, an entity (function, type
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or class) in a program is uniquely identified by the pair of the
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module name in which it is defined and its name. In GHC, an
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entity is uniquely defined by a triple: package, module, and
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<sect2 id="package-databases">
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<title>Package Databases</title>
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A package database is where the details about installed packages
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are stored. It is a directory, usually
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called <literal>package.conf.d</literal>, that contains a file
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for each package, together with a binary cache of the package
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data in the file <literal>package.cache</literal>. Normally
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you won't need to look at or modify the contents of a package
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database directly; all management of package databases can be
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done through the <literal>ghc-pkg</literal> tool (see
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<xref linkend="package-management" />).
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GHC knows about two package databases in particular:
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<para>The global package database, which comes with your GHC
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e.g. <filename>/usr/lib/ghc-6.12.1/package.conf.d</filename>.</para>
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<para>A package database private to each user. On Unix
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<filename>$HOME/.ghc/<replaceable>arch</replaceable>-<replaceable>os</replaceable>-<replaceable>version</replaceable>/package.conf.d</filename>, and on
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Windows it will be something like
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<filename>C:\Documents And Settings\<replaceable>user</replaceable>\ghc\package.conf.d</filename>.
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The <literal>ghc-pkg</literal> tool knows where this file should be
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located, and will create it if it doesn't exist (see <xref linkend="package-management" />).</para>
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<para>When GHC starts up, it reads the contents of these two package
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databases, and builds up a list of the packages it knows about. You can
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see GHC's package table by running GHC with the <option>-v</option>
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<para>Package databases may overlap: for example, packages in the
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user database will override (<emphasis>shadow</emphasis>) those
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of the same name and version in the global database.</para>
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<para>You can control the loading of package databases using the following
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<option>-package-conf <replaceable>file</replaceable></option>
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<indexterm><primary><option>-package-conf</option></primary></indexterm>
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<para>Read in the package configuration file
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<replaceable>file</replaceable> in addition to the system
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default file and the user's local file. Packages in additional
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files read this way will override those in the global and user
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<term><option>-no-user-package-conf</option>
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<indexterm><primary><option>-no-user-package-conf</option></primary>
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<para>Prevent loading of the user's local package database.</para>
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<sect3 id="ghc-package-path">
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<title>The <literal>GHC_PACKAGE_PATH</literal> environment variable</title>
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<indexterm><primary>Environment variable</primary><secondary><literal>GHC_PACKAGE_PATH</literal></secondary>
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<indexterm><primary><literal>GHC_PACKAGE_PATH</literal></primary></indexterm>
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<para>The <literal>GHC_PACKAGE_PATH</literal> environment variable may be
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set to a <literal>:</literal>-separated (<literal>;</literal>-separated
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on Windows) list of files containing package databases. This list of
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package databases is used by GHC and ghc-pkg, with earlier databases in
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the list overriding later ones. This order was chosen to match the
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behaviour of the <literal>PATH</literal> environment variable; think of
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it as a list of package databases that are searched left-to-right for
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<para>If <literal>GHC_PACKAGE_PATH</literal> ends in a separator, then
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the default user and system package databases are appended, in that
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order. e.g. to augment the usual set of packages with a database of
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your own, you could say (on Unix):
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$ export GHC_PACKAGE_PATH=$HOME/.my-ghc-packages.conf:</screen>
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(use <literal>;</literal> instead of <literal>:</literal> on
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<para>To check whether your <literal>GHC_PACKAGE_PATH</literal> setting
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is doing the right thing, <literal>ghc-pkg list</literal> will list all
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the databases in use, in the reverse order they are searched.</para>
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<sect2 id="package-ids">
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<title>Package IDs, dependencies, and broken packages</title>
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<para>Each installed package has a unique identifier (the
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“installed package ID”, or just “package
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ID” for short) , which distinguishes it from all other
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installed packages on the system. To see the package IDs
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associated with each installed package, use <literal>ghc-pkg
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list -v</literal>:</para>
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using cache: /usr/lib/ghc-6.12.1/package.conf.d/package.cache
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/usr/lib/ghc-6.12.1/package.conf.d
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Cabal-1.7.4 (Cabal-1.7.4-48f5247e06853af93593883240e11238)
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array-0.2.0.1 (array-0.2.0.1-9cbf76a576b6ee9c1f880cf171a0928d)
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base-3.0.3.0 (base-3.0.3.0-6cbb157b9ae852096266e113b8fac4a2)
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base-4.2.0.0 (base-4.2.0.0-247bb20cde37c3ef4093ee124e04bc1c)
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The string in parentheses after the package name is the package
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ID: it normally begins with the package name and version, and
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ends in a hash string derived from the compiled package.
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Dependencies between packages are expressed in terms of package
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IDs, rather than just packages and versions. For example, take
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a look at the dependencies of the <literal>haskell98</literal>
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$ ghc-pkg field haskell98 depends
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depends: array-0.2.0.1-9cbf76a576b6ee9c1f880cf171a0928d
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base-4.2.0.0-247bb20cde37c3ef4093ee124e04bc1c
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directory-1.0.0.2-f51711bc872c35ce4a453aa19c799008
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old-locale-1.0.0.1-d17c9777c8ee53a0d459734e27f2b8e9
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old-time-1.0.0.1-1c0d8ea38056e5087ef1e75cb0d139d1
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process-1.0.1.1-d8fc6d3baf44678a29b9d59ca0ad5780
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random-1.0.0.1-423d08c90f004795fd10e60384ce6561
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The purpose of the package ID is to detect problems caused by
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re-installing a package without also recompiling the packages
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that depend on it. Recompiling dependencies is necessary,
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because the newly compiled package may have a differnt ABI
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(Application Binary Interface) than the previous version, even
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if both packages were built from the same source code using the
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same compiler. With package IDs, a recompiled
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package will have a different package ID from the previous
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version, so packages that depended on the previous version are
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now orphaned - one of their dependencies is not satisfied.
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Packages that are broken in this way are shown in
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the <literal>ghc-pkg list</literal> output either in red (if
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possible) or otherwise surrounded by braces. In the following
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example, we have recompiled and reinstalled
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the <literal>filepath</literal> package, and this has caused
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various dependencies including <literal>Cabal</literal> to
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WARNING: there are broken packages. Run 'ghc-pkg check' for more details.
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/usr/lib/ghc-6.12.1/package.conf.d:
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Additionally, <literal>ghc-pkg list</literal> reminds you that
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there are broken packages and suggests <literal>ghc-pkg
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check</literal>, which displays more information about the
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nature of the failure:
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There are problems in package ghc-6.12.1:
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dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
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There are problems in package haskeline-0.6.2:
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dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
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There are problems in package Cabal-1.7.4:
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dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
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There are problems in package process-1.0.1.1:
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dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
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There are problems in package directory-1.0.0.2:
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dependency "filepath-1.1.0.1-87511764eb0af2bce4db05e702750e63" doesn't exist
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The following packages are broken, either because they have a problem
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listed above, or because they depend on a broken package.
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bin-package-db-0.0.0.0
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To fix the problem, you need to recompile the broken packages
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against the new dependencies. The easiest way to do this is to
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use <literal>cabal-install</literal>, or download the packages
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url="http://hackage.haskell.org/packages/hackage.html">HackageDB</ulink>
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and build and install them as normal.</para>
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<para>Be careful not to recompile any packages that GHC itself
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depends on, as this may render the <literal>ghc</literal>
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package itself broken, and <literal>ghc</literal> cannot be
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simply recompiled. The only way to recover from this would be
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to re-install GHC.</para>
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<sect2 id="package-management">
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<title>Package management (the <literal>ghc-pkg</literal> command)</title>
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<indexterm><primary>packages</primary>
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<secondary>management</secondary></indexterm>
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<para>The <literal>ghc-pkg</literal> tool is for querying and
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modifying package databases. To see what package databases are
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<literal>ghc-pkg list</literal>. The stack of databases that
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<literal>ghc-pkg</literal> knows about can be modified using the
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<literal>GHC_PACKAGE_PATH</literal> environment variable (see <xref
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linkend="ghc-package-path" />, and using
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<literal>--package-conf</literal> options on the
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<literal>ghc-pkg</literal> command line.</para>
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<para>When asked to modify a database, <literal>ghc-pkg</literal> modifies
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the global database by default. Specifying <option>--user</option>
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causes it to act on the user database, or <option>--package-conf</option>
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can be used to act on another database entirely. When multiple of these
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options are given, the rightmost one is used as the database to act
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<para>Commands that query the package database (list, latest,
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describe, field, dot) operate on the list of databases specified by
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the flags <option>--user</option>, <option>--global</option>, and
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<option>--package-conf</option>. If none of these flags are
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given, the default is <option>--global</option>
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<option>--user</option>.</para>
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<para>If the environment variable <literal>GHC_PACKAGE_PATH</literal> is
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set, and its value does not end in a separator (<literal>:</literal> on
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Unix, <literal>;</literal> on Windows), then the last database is
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considered to be the global database, and will be modified by default by
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<literal>ghc-pkg</literal>. The intention here is that
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<literal>GHC_PACKAGE_PATH</literal> can be used to create a virtual
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package environment into which Cabal packages can be installed without
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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
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below. Where a package name is required, the package can be named in
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full including the version number
579
(e.g. <literal>network-1.0</literal>), or without the version number.
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Naming a package without the version number matches all versions of the
581
package; the specified action will be applied to all the matching
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packages. A package specifier that matches all version of the package
583
can also be written <replaceable>pkg</replaceable><literal>-*</literal>,
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to make it clearer that multiple packages are being matched.</para>
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<term><literal>ghc-pkg init <replaceable>path</replaceable></literal></term>
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<para>Creates a new, empty, package database
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at <replaceable>path</replaceable>, which must not already
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<term><literal>ghc-pkg register <replaceable>file</replaceable></literal></term>
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<para>Reads a package specification from
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<replaceable>file</replaceable> (which may be “<literal>-</literal>”
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to indicate standard input),
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and adds it to the database of installed packages. The syntax of
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<replaceable>file</replaceable> is given in <xref
604
linkend="installed-pkg-info" />.</para>
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<para>The package specification must be a package that isn't already
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<term><literal>ghc-pkg update <replaceable>file</replaceable></literal></term>
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<para>The same as <literal>register</literal>, except that if a
615
package of the same name is already installed, it is
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replaced by the new one.</para>
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<term><literal>ghc-pkg unregister <replaceable>P</replaceable></literal></term>
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<para>Remove the specified package from the database.</para>
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<term><literal>ghc-pkg expose <replaceable>P</replaceable></literal></term>
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<para>Sets the <literal>exposed</literal> flag for package
631
<replaceable>P</replaceable> to <literal>True</literal>.</para>
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<term><literal>ghc-pkg check</literal></term>
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<para>Check consistency of dependencies in the package
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database, and report packages that have missing
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<term><literal>ghc-pkg hide <replaceable>P</replaceable></literal></term>
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<para>Sets the <literal>exposed</literal> flag for package
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<replaceable>P</replaceable> to <literal>False</literal>.</para>
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<term><literal>ghc-pkg list [<replaceable>P</replaceable>] [<option>--simple-output</option>]</literal></term>
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<para>This option displays the currently installed
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packages, for each of the databases known to
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<literal>ghc-pkg</literal>. That includes the global database, the
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user's local database, and any further files specified using the
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<option>-f</option> option on the command line.</para>
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<para>Hidden packages (those for which the <literal>exposed</literal>
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flag is <literal>False</literal>) are shown in parentheses in the
663
list of packages.</para>
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<para>If an optional package identifier <replaceable>P</replaceable>
666
is given, then only packages matching that identifier are
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<para>If the option <option>--simple-output</option> is given, then
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the packages are listed on a single line separated by spaces, and
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the database names are not included. This is intended to make it
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easier to parse the output of <literal>ghc-pkg list</literal> using
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<term><literal>ghc-pkg find-module <replaceable>M</replaceable> [<option>--simple-output</option>]</literal></term>
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<para>This option lists registered packages exposing module
681
<replaceable>M</replaceable>. Examples:</para>
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$ ghc-pkg find-module Var
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c:/fptools/validate/ghc/driver/package.conf.inplace:
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$ ghc-pkg find-module Data.Sequence
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c:/fptools/validate/ghc/driver/package.conf.inplace:
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<para>Otherwise, it behaves like <literal>ghc-pkg list</literal>,
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including options.</para>
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<term><literal>ghc-pkg latest <replaceable>P</replaceable></literal></term>
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<para>Prints the latest available version of package
701
<replaceable>P</replaceable>.</para>
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<term><literal>ghc-pkg describe <replaceable>P</replaceable></literal></term>
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<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: ***
1599
;;; sgml-parent-document: ("users_guide.xml" "book" "chapter" "sect1") ***
added
removed
docs/users_guide/packages.xml
