ghc/docs/users_guide/packages.sgml

   1   <sect1 id="packages">
   2     <title>Packages</title>
   3     <indexterm><primary>packages</primary></indexterm>
   4
   5     <para>Packages are collections of libraries, conveniently grouped
   6     together as a single entity.  The package system is flexible: a
   7     package may consist of Haskell code, foreign language code (eg. C
   8     libraries), or a mixture of the two.  A package is a good way to
   9     group together related Haskell modules, and is essential if you
  10     intend to make the modules into a Windows DLL (see below).</para>
  11
  12     <para>Because packages can contain both Haskell and C libraries, they
  13     are also a good way to provide convenient access to a Haskell
  14     layer over a C library.</para>
  15
  16     <para>GHC comes with several packages (see <xref
  17     linkend="book-hslibs">), and packages can be added to or removed
  18     from an existing GHC installation, using the supplied
  19     <literal>ghc-pkg</literal><indexterm><primary><literal>ghc-pkg</literal></primary>
  20     </indexterm> tool, described in <xref
  21     linkend="package-management">.</para>
  22
  23     <sect2 id="using-packages">
  24       <title>Using a package</title>
  25       <indexterm><primary>packages</primary>
  26         <secondary>using</secondary></indexterm>
  27
  28       <para>To use a package, add the <literal>-package</literal> flag
  29       to the GHC command line:</para>
  30
  31       <variablelist>
  32         <varlistentry>
  33           <term><option>-package <replaceable>lib</replaceable></option></term>
  34           <indexterm><primary>-package <replaceable>lib</replaceable> option</primary></indexterm>
  35           <listitem>
  36             <para>This option brings into scope all the modules from
  37             package <literal><replaceable>lib</replaceable></literal> (they still have to
  38             be imported in your Haskell source, however).  It also
  39             causes the relevant libraries to be linked when linking is
  40             being done.</para>
  41           </listitem>
  42         </varlistentry>
  43       </variablelist>
  44
  45       <para>Some packages depend on other packages, for example the
  46       <literal>text</literal> package makes use of some of the modules
  47       in the <literal>lang</literal> package.  The package system
  48       takes care of all these dependencies, so that when you say
  49       <literal>-package text</literal> on the command line, you
  50       automatically get <literal>-package lang</literal> too.</para>
  51     </sect2>
  52
  53     <sect2 id="using-local-packages">
  54       <title>Maintaining a local set of packages</title>
  55
  56       <para>When GHC starts up, it automatically reads the default set
  57       of packages from a configuration file, normally named
  58       <filename>package.conf</filename> in your GHC installation
  59       directory.</para>
  60
  61       <para>You can load in additional package configuration files
  62       using the <option>-package-conf</option> option:</para>
  63
  64       <variablelist>
  65         <varlistentry>
  66           <term><option>-package-conf <replaceable>file</replaceable></option></term>
  67           <indexterm><primary><option>-package-conf <replaceable>file</replaceable></option></primary>
  68           </indexterm>
  69           <listitem>
  70             <para>Read in the package configuration file
  71             <replaceable>file</replaceable> in addition to the system
  72             default file.  This allows the user to have a local set of
  73             packages in addition to the system-wide ones.</para>
  74           </listitem>
  75         </varlistentry>
  76       </variablelist>
  77
  78       <para>To create your own package configuration file, just create
  79       a new file and put the string
  80       <quote><literal>[]</literal></quote> in it.  Packages can be
  81       added to the new configuration file using the
  82       <literal>ghc-pkg</literal> tool, described in <xref
  83       linkend="package-management">.</para>
  84     </sect2>
  85
  86     <sect2 id="building-packages">
  87       <title>Building a package from Haskell source</title>
  88       <indexterm><primary>packages</primary>
  89         <secondary>building</secondary></indexterm>
  90
  91       <para>It takes some special considerations to build a new
  92       package:</para>
  93
  94       <itemizedlist>
  95         <listitem>
  96           <para>A package may contain several Haskell modules. A
  97           package may span many directories, or many packages may
  98           exist in a single directory. Packages may not be mutually
  99           recursive.</para>
 100         </listitem>
 101
 102         <listitem>
 103           <para>A package has a name
 104           (e.g. <filename>std</filename>)</para>
 105         </listitem>
 106
 107         <listitem>
 108           <para>The Haskell code in a package may be built into one or
 109           more archive libraries (e.g. <filename>libHSfoo.a</filename>),
 110           or a single DLL on Windows
 111           (e.g. <filename>HSfoo.dll</filename>).  The restriction to a
 112           single DLL on Windows is that the package system is used to
 113           tell the compiler when it should make an inter-DLL call
 114           rather than an intra-DLL call (inter-DLL calls require an
 115           extra indirection). <emphasis>Building packages as DLLs
 116           doesn't work at the moment; see <XRef
 117           LinkEnd="win32-dlls-create"> for the gory details.</emphasis>
 118           </para>
 119
 120           <para>Versions of the Haskell libraries for use with GHCi
 121           may also be included: GHCi cannot load <literal>.a</literal>
 122           files directly, instead it will look for an object file
 123           called <filename>HSfoo.o</filename> and load that.  The
 124           <literal>ghc-pkg</literal> tool can automatically build the
 125           GHCi version of each library, see <xref
 126           linkend="package-management">.  To build these libraries by
 127           hand from the <literal>.a</literal> archive, it is possible
 128           to use GNU <command>ld</command> as follows:</para>
 129
 130 <screen>ld -r --whole-archive -o HSfoo.o libHSfoo.a</screen>
 131         </listitem>
 132
 133         <listitem>
 134           <para>GHC does not maintain detailed cross-package
 135           dependency information.  It does remember which modules in
 136           other packages the current module depends on, but not which
 137           things within those imported things.</para>
 138         </listitem>
 139       </itemizedlist>
 140
 141       <para>To compile a module which is to be part of a new package,
 142       use the <literal>-package-name</literal> option:</para>
 143
 144       <variablelist>
 145         <varlistentry>
 146           <term><option>-package-name <replaceable>foo</replaceable></option></term>
 147           <indexterm><primary><literal>-package-name</literal></primary>
 148             <secondary>option</secondary></indexterm>
 149           <listitem>
 150             <para>This option is added to the command line when
 151             compiling a module that is destined to be part of package
 152             <literal>foo</literal>.  If this flag is omitted then the
 153             default package <literal>Main</literal> is assumed.</para>
 154           </listitem>
 155         </varlistentry>
 156       </variablelist>
 157
 158       <para>Failure to use the <literal>-package-name</literal> option
 159       when compiling a package will result in disaster on Windows, but
 160       is relatively harmless on Unix at the moment (it will just cause
 161       a few extra dependencies in some interface files).  However,
 162       bear in mind that we might add support for Unix shared libraries
 163       at some point in the future.</para>
 164
 165       <para>It is worth noting that on Windows, when each package
 166       is built as a DLL, since a reference to a DLL costs an extra
 167       indirection, intra-package references are cheaper than
 168       inter-package references. Of course, this applies to the
 169       <filename>Main</filename> package as well.</para>
 170     </sect2>
 171
 172     <sect2 id="package-management">
 173       <title>Package management</title>
 174       <indexterm><primary>packages</primary>
 175         <secondary>management</secondary></indexterm>
 176
 177       <para>The <literal>ghc-pkg</literal> tool allows packages to be
 178       added or removed from a package configuration file.  By default,
 179       the system-wide configuration file is used, but alternatively
 180       packages can be added or removed from a user-specified
 181       configuration file using the <option>--config-file</option>
 182       option.  An empty package configuration file consists of the
 183       string <quote><literal>[]</literal></quote>.</para>
 184
 185       <para>The <literal>ghc-pkg</literal> program accepts the
 186       following options:</para>
 187
 188       <variablelist>
 189         <varlistentry>
 190           <term><option>--add-package</option></term>
 191           <term><option>-a</option></term>
 192           <indexterm><primary><option>--add-package</option></primary>
 193               </indexterm>
 194           <listitem>
 195             <para>Reads a package specification (see below) on stdin,
 196             and adds it to the database of installed packages.  The
 197             package specification must be a package that isn't already
 198             installed.</para>
 199           </listitem>
 200         </varlistentry>
 201
 202         <varlistentry>
 203           <term><option>--auto-ghci-libs</option></term>
 204           <term><option>-g</option></term>
 205           <indexterm><primary><option>--auto-ghci-libs</option></primary>
 206               </indexterm>
 207           <listitem>
 208             <para>Automatically generate the GHCi
 209             <filename>.o</filename> version of each
 210             <filename>.a</filename> Haskell library, using GNU ld (if
 211             that is available).  Without this option,
 212             <literal>ghc-pkg</literal> will warn if GHCi versions of
 213             any Haskell libraries in the package don't exist.</para>
 214
 215             <para>GHCi <literal>.o</literal> libraries don't
 216             necessarily have to live in the same directory as the
 217             corresponding <literal>.a</literal> library.  However,
 218             this option will cause the GHCi library to be created in
 219             the same directory as the <literal>.a</literal>
 220             library.</para>
 221           </listitem>
 222         </varlistentry>
 223
 224         <varlistentry>
 225           <term><option>--config-file <replaceable>file</replaceable></option></term>
 226           <term><option>-f <replaceable>file</replaceable></option></term>
 227           <indexterm><primary><option>--config-file</option></primary>
 228               </indexterm>
 229           <listitem>
 230             <para>Use <replaceable>file</replaceable> instead of the
 231             default package configuration file.  This, in conjunction
 232             with GHC's <option>-package-conf</option> option, allows
 233             a user to have a local set of packages in addition to the
 234             system-wide installed set.</para>
 235           </listitem>
 236         </varlistentry>
 237
 238         <varlistentry>
 239           <term><option>--list-packages</option></term>
 240           <term><option>-l</option></term>
 241           <indexterm><primary><option>--list-packages</option></primary></indexterm>
 242           <listitem>
 243             <para>This option displays the list of currently installed
 244             packages.</para>
 245
 246 <screen>
 247   $ ghc-pkg --list-packages
 248   gmp, rts, std, lang, concurrent, data, net, posix, text, util
 249 </screen>
 250
 251             <para>Note that your GHC installation might have a
 252             slightly different set of packages installed.</para>
 253
 254             <para>The <literal>gmp</literal> and
 255             <literal>rts</literal> packages are always present, and
 256             represent the multi-precision integer and runtime system
 257             libraries respectively.  The <literal>std</literal>
 258             package contains the Haskell prelude and standard
 259             libraries.  The rest of the packages are optional
 260             libraries.</para>
 261           </listitem>
 262         </varlistentry>
 263
 264         <varlistentry>
 265           <term><option>--remove-package <replaceable>foo</replaceable></option></term>
 266           <term><option>-r <replaceable>foo</replaceable></option></term>
 267           <indexterm><primary><option>--delete-package</option></primary>
 268               </indexterm>
 269           <listitem>
 270             <para>Removes the specified package from the installed
 271             configuration.</para>
 272           </listitem>
 273         </varlistentry>
 274       </variablelist>
 275
 276       <para>When modifying the configuration file
 277       <replaceable>file</replaceable>, a copy of the original file is
 278       saved in <replaceable>file</replaceable><literal>.old</literal>,
 279       so in an emergency you can always restore the old settings by
 280       copying the old file back again.</para>
 281
 282       <para>A package specification looks like this:</para>
 283
 284 <screen>
 285   Package {
 286      name            = "mypkg",
 287      import_dirs     = ["/usr/local/lib/imports/mypkg"],
 288      source_dirs     = [],
 289      library_dirs    = ["/usr/local/lib"],
 290      hs_libraries    = ["HSmypkg" ],
 291      extra_libraries = ["HSmypkg_cbits"],
 292      include_dirs    = [],
 293      c_includes      = ["HsMyPkg.h"],
 294      package_deps    = ["text", "data"],
 295      extra_ghc_opts  = [],
 296      extra_cc_opts   = [],
 297      extra_ld_opts   = ["-lmy_clib"]
 298   }
 299 </screen>
 300
 301       <para>Components of a package specification may be specified in
 302       any order, and are:</para>
 303
 304       <variablelist>
 305         <varlistentry>
 306           <term><literal>name</literal></term>
 307           <indexterm><primary><literal>name</literal></primary>
 308             <secondary>package specification</secondary></indexterm>
 309           <listitem>
 310             <para>The package's name, for use with
 311             the <literal>-package</literal> flag and as listed in the
 312             <literal>--list-packages</literal> list.
 313             </para>
 314           </listitem>
 315         </varlistentry>
 316
 317         <varlistentry>
 318           <term><literal>import_dirs</literal></term>
 319           <indexterm><primary><literal>import_dirs</literal></primary>
 320             <secondary>package specification</secondary></indexterm>
 321           <listitem>
 322             <para>A list of directories containing interface files
 323             (<literal>.hi</literal> files) for this package.</para>
 324           </listitem>
 325         </varlistentry>
 326
 327         <varlistentry>
 328           <term><literal>source_dirs</literal></term>
 329           <indexterm><primary><literal>source_dirs</literal></primary>
 330             <secondary>package specification</secondary></indexterm>
 331           <listitem>
 332             <para>A list of directories containing Haskell source
 333             files for this package.  This field isn't used by GHC, but
 334             could potentially be used by an all-interpreted system
 335             like Hugs.</para>
 336           </listitem>
 337         </varlistentry>
 338
 339         <varlistentry>
 340           <term><literal>library_dirs</literal></term>
 341           <indexterm><primary><literal>library_dirs</literal></primary>
 342             <secondary>package specification</secondary></indexterm>
 343           <listitem>
 344             <para>A list of directories containing libraries for this
 345             package.</para>
 346           </listitem>
 347         </varlistentry>
 348
 349         <varlistentry>
 350           <term><literal>hs_libraries</literal></term>
 351           <indexterm><primary><literal>hs_libraries</literal></primary>
 352             <secondary>package specification</secondary></indexterm>
 353           <listitem>
 354             <para>A list of libraries containing Haskell code for this
 355             package, with the <literal>.a</literal> or
 356             <literal>.dll</literal> suffix omitted.  When packages are
 357             built as libraries, the
 358             <literal>lib</literal> prefix is also omitted.</para>
 359
 360             <para>For use with GHCi, each library should have an
 361             object file too.  The name of the object file does
 362             <emphasis>not</emphasis> have a <literal>lib</literal>
 363             prefix, and has the normal object suffix for your
 364             platform.</para>
 365
 366             <para>For example, if we specify a Haskell library as
 367             <filename>HSfoo</filename> in the package spec, then the
 368             various flavours of library that GHC actually uses will be
 369             called:</para>
 370             <variablelist>
 371               <varlistentry>
 372                 <term><filename>libHSfoo.a</filename></term>
 373                 <listitem>
 374                   <para>The name of the library on Unix
 375                   systems.</para>
 376                 </listitem>
 377               </varlistentry>
 378               <varlistentry>
 379                 <term><filename>HSfoo.dll</filename></term>
 380                 <listitem>
 381                   <para>The name of the dynamic library on Windows
 382                   systems.</para>
 383                 </listitem>
 384               </varlistentry>
 385               <varlistentry>
 386                 <term><filename>HSfoo.o</filename></term>
 387                 <term><filename>HSfoo.obj</filename></term>
 388                 <listitem>
 389                   <para>The object version of the library used by
 390                   GHCi.</para>
 391                 </listitem>
 392               </varlistentry>
 393             </variablelist>
 394
 395           </listitem>
 396         </varlistentry>
 397
 398         <varlistentry>
 399           <term><literal>extra_libraries</literal></term>
 400           <indexterm><primary><literal>extra_libraries</literal></primary>
 401             <secondary>package specification</secondary></indexterm>
 402           <listitem>
 403             <para>A list of extra libraries for this package.  The
 404             difference between <literal>hs_libraries</literal> and
 405             <literal>extra_libraries</literal> is that
 406             <literal>hs_libraries</literal> normally have several
 407             versions, to support profiling, parallel and other build
 408             options.  The various versions are given different
 409             suffixes to distinguish them, for example the profiling
 410             version of the standard prelude library is named
 411             <filename>libHSstd_p.a</filename>, with the
 412             <literal>_p</literal> indicating that this is a profiling
 413             version.  The suffix is added automatically by GHC for
 414             <literal>hs_libraries</literal> only, no suffix is added
 415             for libraries in
 416             <literal>extra_libraries</literal>.</para>
 417
 418             <para>Also, <literal>extra_libraries</literal> are placed
 419             on the linker command line after the
 420             <literal>hs_libraries</literal> for the same package.  If
 421             your package has dependencies in the other direction (i.e.
 422             <literal>extra_libraries</literal> depends on
 423             <literal>hs_libraries</literal>), and the libraries are
 424             static, you might need to make two separate
 425             packages.</para>
 426           </listitem>
 427         </varlistentry>
 428
 429         <varlistentry>
 430           <term><literal>include_dirs</literal></term>
 431           <indexterm><primary><literal>include_dirs</literal></primary>
 432             <secondary>package specification</secondary></indexterm>
 433           <listitem>
 434             <para>A list of directories containing C includes for this
 435             package (maybe the empty list).</para>
 436           </listitem>
 437         </varlistentry>
 438
 439         <varlistentry>
 440           <term><literal>c_includes</literal></term>
 441           <indexterm><primary><literal>c_includes</literal></primary>
 442             <secondary>package specification</secondary></indexterm>
 443           <listitem>
 444             <para>A list of files to include for via-C compilations
 445             using this package.  Typically this include file will
 446             contain function prototypes for any C functions used in
 447             the package, in case they end up being called as a result
 448             of Haskell functions from the package being
 449             inlined.</para>
 450           </listitem>
 451         </varlistentry>
 452
 453         <varlistentry>
 454           <term><literal>package_deps</literal></term>
 455           <indexterm><primary><literal>package_deps</literal></primary>
 456             <secondary>package specification</secondary></indexterm>
 457           <listitem>
 458             <para>A list of packages which this package depends
 459             on.</para>
 460           </listitem>
 461         </varlistentry>
 462
 463         <varlistentry>
 464           <term><literal>extra_ghc_opts</literal></term>
 465           <indexterm><primary><literal>extra_ghc_opts</literal></primary>
 466             <secondary>package specification</secondary></indexterm>
 467           <listitem>
 468             <para>Extra arguments to be added to the GHC command line
 469             when this package is being used.</para>
 470           </listitem>
 471         </varlistentry>
 472
 473         <varlistentry>
 474           <term><literal>extra_cc_opts</literal></term>
 475           <indexterm><primary><literal>extra_cc_opts</literal></primary>
 476             <secondary>package specification</secondary></indexterm>
 477           <listitem>
 478             <para>Extra arguments to be added to the gcc command line
 479             when this package is being used (only for via-C
 480             compilations).</para>
 481           </listitem>
 482         </varlistentry>
 483
 484         <varlistentry>
 485           <term><literal>extra_ld_opts</literal></term>
 486           <indexterm><primary><literal>extra_ld_opts</literal></primary>
 487             <secondary>package specification</secondary></indexterm>
 488           <listitem>
 489             <para>Extra arguments to be added to the gcc command line
 490             (for linking) when this package is being used.</para>
 491           </listitem>
 492         </varlistentry>
 493       </variablelist>
 494
 495       <para>For examples of more package specifications, take a look
 496       at the <literal>package.conf</literal> in your GHC
 497       installation.</para>
 498     </sect2>
 499   </sect1>
 500
 501 <!-- Emacs stuff:
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