docs/users_guide/intro.xml

   1 <?xml version="1.0" encoding="iso-8859-1"?>
   2 <chapter id="introduction-GHC">
   3   <title>Introduction to GHC</title>
   4
   5   <para>This is a guide to using the Glasgow Haskell Compiler (GHC):
   6   an interactive and batch compilation system for the <ulink
   7   url="http://www.haskell.org/">Haskell&nbsp;98</ulink>
   8   language.</para>
   9
  10   <para>GHC has two main components: an interactive Haskell
  11   interpreter (also known as GHCi), described in <xref
  12   linkend="ghci"/>, and a batch compiler, described throughout <xref
  13   linkend="using-ghc"/>.  In fact, GHC consists of a single program
  14   which is just run with different options to provide either the
  15   interactive or the batch system.</para>
  16
  17   <para>The batch compiler can be used alongside GHCi: compiled
  18   modules can be loaded into an interactive session and used in the
  19   same way as interpreted code, and in fact when using GHCi most of
  20   the library code will be pre-compiled.  This means you get the best
  21   of both worlds: fast pre-compiled library code, and fast compile
  22   turnaround for the parts of your program being actively
  23   developed.</para>
  24
  25   <para>GHC supports numerous language extensions, including
  26   concurrency, a foreign function interface, exceptions, type system
  27   extensions such as multi-parameter type classes, local universal and
  28   existential quantification, functional dependencies, scoped type
  29   variables and explicit unboxed types.  These are all described in
  30   <xref linkend="ghc-language-features"/>.</para>
  31
  32   <para>GHC has a comprehensive optimiser, so when you want to Really
  33   Go For It (and you've got time to spare) GHC can produce pretty fast
  34   code.  Alternatively, the default option is to compile as fast as
  35   possible while not making too much effort to optimise the generated
  36   code (although GHC probably isn't what you'd describe as a fast
  37   compiler :-).</para>
  38
  39   <para>GHC's profiling system supports &ldquo;cost centre
  40   stacks&rdquo;: a way of seeing the profile of a Haskell program in a
  41   call-graph like structure.  See <xref linkend="profiling"/> for more
  42   details.</para>
  43
  44   <para>GHC comes with a number of libraries. These are
  45   described in separate documentation.</para>
  46
  47   <sect1 id="mailing-lists-GHC">
  48     <title>Meta-information: Web sites, mailing lists, etc.</title>
  49
  50     <indexterm><primary>mailing lists, Glasgow Haskell</primary></indexterm>
  51     <indexterm><primary>Glasgow Haskell mailing lists</primary></indexterm>
  52
  53     <para>On the World-Wide Web, there are several URLs of likely
  54     interest:</para>
  55
  56     <itemizedlist>
  57       <listitem>
  58         <para><ulink url="http://www.haskell.org/" >Haskell home
  59         page</ulink></para>
  60       </listitem>
  61
  62       <listitem>
  63         <para><ulink url="http://www.haskell.org/ghc/">GHC home
  64         page</ulink></para>
  65       </listitem>
  66
  67       <listitem>
  68         <para><ulink
  69         url="http://www.cs.nott.ac.uk/~gmh/faq.html">comp.lang.functional
  70         FAQ</ulink></para>
  71       </listitem>
  72
  73     </itemizedlist>
  74
  75     <para>We run the following mailing lists about Glasgow Haskell.
  76     We encourage you to join, as you feel is appropriate.</para>
  77
  78     <variablelist>
  79       <varlistentry>
  80         <term>glasgow-haskell-users:</term>
  81         <listitem>
  82           <para>This list is for GHC users to chat among themselves.
  83           If you have a specific question about GHC, please check the
  84           <ulink
  85           url="http://www.haskell.org/haskellwiki/GHC/FAQ">FAQ</ulink>
  86           first.</para>
  87
  88           <variablelist>
  89             <varlistentry>
  90               <term>list email address:</term>
  91               <listitem>
  92                 <para><email>glasgow-haskell-users@haskell.org</email></para>
  93               </listitem>
  94             </varlistentry>
  95
  96             <varlistentry>
  97               <term>subscribe at:</term>
  98               <listitem>
  99                 <para><ulink
 100               url="http://www.haskell.org/mailman/listinfo/glasgow-haskell-users"><literal>http://www.haskell.org/mailman/listinfo/glasgow-haskell-users</literal></ulink>.</para>
 101               </listitem>
 102             </varlistentry>
 103
 104             <varlistentry>
 105               <term>admin email address:</term>
 106               <listitem>
 107                 <para><email>glasgow-haskell-users-admin@haskell.org</email></para>
 108               </listitem>
 109             </varlistentry>
 110
 111             <varlistentry>
 112               <term>list archives:</term>
 113               <listitem>
 114                 <para><ulink
 115           url="http://www.haskell.org/pipermail/glasgow-haskell-users/"><literal>http://www.haskell.org/pipermail/glasgow-haskell-users/</literal></ulink></para>
 116               </listitem>
 117             </varlistentry>
 118           </variablelist>
 119         </listitem>
 120       </varlistentry>
 121
 122       <varlistentry>
 123         <term>cvs-ghc:</term>
 124         <listitem>
 125           <para>The hardcore GHC developers hang out here.  This list
 126           also gets commit message from the GHC darcs repository.  There are
 127           other lists for other darcs
 128           repositories (most notably <literal>cvs-libraries</literal>).
 129           </para>
 130
 131           <variablelist>
 132             <varlistentry>
 133               <term>list email address:</term>
 134               <listitem>
 135                 <para><email>cvs-ghc@haskell.org</email></para>
 136               </listitem>
 137             </varlistentry>
 138
 139             <varlistentry>
 140               <term>subscribe at:</term>
 141               <listitem>
 142                 <para><ulink
 143               url="http://www.haskell.org/mailman/listinfo/cvs-ghc"><literal>http://www.haskell.org/mailman/listinfo/cvs-ghc</literal></ulink>.</para>
 144               </listitem>
 145             </varlistentry>
 146
 147             <varlistentry>
 148               <term>admin email address:</term>
 149               <listitem>
 150                 <para><email>cvs-ghc-admin@haskell.org</email></para>
 151               </listitem>
 152             </varlistentry>
 153
 154             <varlistentry>
 155               <term>list archives:</term>
 156               <listitem>
 157                 <para><ulink
 158           url="http://www.haskell.org/pipermail/cvs-ghc/"><literal>http://www.haskell.org/pipermail/cvs-ghc/</literal></ulink></para>
 159               </listitem>
 160             </varlistentry>
 161           </variablelist>
 162         </listitem>
 163       </varlistentry>
 164     </variablelist>
 165
 166     <para>There are several other haskell and GHC-related mailing
 167     lists served by <literal>www.haskell.org</literal>.  Go to <ulink
 168     url="http://www.haskell.org/mailman/listinfo/"><literal>http://www.haskell.org/mailman/listinfo/</literal></ulink>
 169     for the full list.</para>
 170
 171     <para>Some Haskell-related discussion also takes place in the
 172     Usenet newsgroup <literal>comp.lang.functional</literal>.</para>
 173
 174   </sect1>
 175
 176   <sect1 id="bug-reporting">
 177     <title>Reporting bugs in GHC</title>
 178     <indexterm><primary>bugs</primary><secondary>reporting</secondary>
 179     </indexterm>
 180     <indexterm><primary>reporting bugs</primary>
 181     </indexterm>
 182
 183     <para>
 184         Glasgow Haskell is a changing system so there are sure to be
 185         bugs in it. If you find one, please see
 186         <ulink url="http://hackage.haskell.org/trac/ghc/wiki/ReportABug">this wiki page</ulink>
 187         for information on how to report it.
 188     </para>
 189
 190   </sect1>
 191
 192   <sect1 id="version-numbering">
 193     <title>GHC version numbering policy</title>
 194     <indexterm><primary>version, of ghc</primary></indexterm>
 195
 196     <para>As of GHC version 6.8, we have adopted the following policy
 197     for numbering GHC versions:</para>
 198
 199     <variablelist>
 200       <varlistentry>
 201         <term>Stable Releases</term>
 202         <listitem>
 203           <para>Stable branches are numbered <literal><replaceable>x</replaceable>.<replaceable>y</replaceable></literal>, where
 204           <replaceable>y</replaceable> is <emphasis>even</emphasis>.
 205           Releases on the stable branch <literal><replaceable>x</replaceable>.<replaceable>y</replaceable></literal> are numbered <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>z</replaceable></literal>, where
 206           <replaceable>z</replaceable> (>= 1) is the patchlevel number.
 207           Patchlevels are bug-fix releases only, and never
 208           change the programmer interface to any system-supplied code.
 209           However, if you install a new patchlevel over an old one you
 210           will need to recompile any code that was compiled against the
 211           old libraries.</para>
 212
 213           <para>The value of <literal>__GLASGOW_HASKELL__</literal>
 214           (see <xref linkend="c-pre-processor"/>) for a major release
 215           <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>z</replaceable></literal>
 216           is the integer <replaceable>xyy</replaceable> (if
 217           <replaceable>y</replaceable> is a single digit, then a leading zero
 218           is added, so for example in version 6.8.2 of GHC we would have
 219           <literal>__GLASGOW_HASKELL__==608</literal>).</para>
 220           <indexterm>
 221             <primary><literal>__GLASGOW_HASKELL__</literal></primary>
 222           </indexterm>
 223         </listitem>
 224       </varlistentry>
 225
 226       <varlistentry>
 227         <term>Stable snapshots</term>
 228         <listitem>
 229           <para>
 230       We may make snapshot releases of the current
 231       stable branch <ulink url="http://www.haskell.org/ghc/dist/stable/dist/">available for download</ulink>, and the latest sources are available from <ulink url="http://hackage.haskell.org/trac/ghc/wiki/DarcsRepositories">the darcs repositories</ulink>.
 232           </para>
 233
 234           <para>Stable snapshot releases are named
 235           <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>z</replaceable>.<replaceable>YYYYMMDD</replaceable></literal>.
 236           where <literal><replaceable>YYYYMMDD</replaceable></literal> is the date of the sources
 237           from which the snapshot was built, and <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>z+1</replaceable></literal> is the next release to be made on that branch.
 238           For example, <literal>6.8.1.20040225</literal> would be a
 239           snapshot of the <literal>6.8</literal> branch during the development
 240       of <literal>6.8.2</literal>.</para>
 241
 242           <para>The value of <literal>__GLASGOW_HASKELL__</literal>
 243           for a snapshot release is the integer
 244           <replaceable>xyy</replaceable>.  You should never write any
 245           conditional code which tests for this value, however: since
 246           interfaces change on a day-to-day basis, and we don't have
 247           finer granularity in the values of
 248           <literal>__GLASGOW_HASKELL__</literal>, you should only
 249           conditionally compile using predicates which test whether
 250           <literal>__GLASGOW_HASKELL__</literal> is equal to, later
 251           than, or earlier than a given major release.</para>
 252           <indexterm>
 253             <primary><literal>__GLASGOW_HASKELL__</literal></primary>
 254           </indexterm>
 255         </listitem>
 256       </varlistentry>
 257
 258       <varlistentry>
 259         <term>Unstable snapshots</term>
 260         <listitem>
 261           <para>
 262       We may make snapshot releases of the
 263       HEAD <ulink url="http://www.haskell.org/ghc/dist/current/dist/">available for download</ulink>, and the latest sources are available from <ulink url="http://hackage.haskell.org/trac/ghc/wiki/DarcsRepositories">the darcs repositories</ulink>.
 264           </para>
 265
 266           <para>Unstable snapshot releases are named
 267           <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>YYYYMMDD</replaceable></literal>.
 268           where <literal><replaceable>YYYYMMDD</replaceable></literal> is the date of the sources
 269           from which the snapshot was built.
 270           For example, <literal>6.7.20040225</literal> would be a
 271           snapshot of the HEAD before the creation of the
 272       <literal>6.8</literal> branch.</para>
 273
 274           <para>The value of <literal>__GLASGOW_HASKELL__</literal>
 275           for a snapshot release is the integer
 276           <replaceable>xyy</replaceable>.  You should never write any
 277           conditional code which tests for this value, however: since
 278           interfaces change on a day-to-day basis, and we don't have
 279           finer granularity in the values of
 280           <literal>__GLASGOW_HASKELL__</literal>, you should only
 281           conditionally compile using predicates which test whether
 282           <literal>__GLASGOW_HASKELL__</literal> is equal to, later
 283           than, or earlier than a given major release.</para>
 284           <indexterm>
 285             <primary><literal>__GLASGOW_HASKELL__</literal></primary>
 286           </indexterm>
 287         </listitem>
 288       </varlistentry>
 289     </variablelist>
 290
 291     <para>The version number of your copy of GHC can be found by
 292     invoking <literal>ghc</literal> with the
 293     <literal>&ndash;&ndash;version</literal> flag (see <xref
 294     linkend="options-help"/>).</para>
 295   </sect1>
 296
 297
 298 &relnotes;
 299
 300 </chapter>
 301
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