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://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 CVS repository.  There are
 127           several other similar lists for other parts of the CVS
 128           repository (eg. <literal>cvs-hslibs</literal>,
 129           <literal>cvs-happy</literal>, <literal>cvs-hdirect</literal>
 130           etc.)</para>
 131
 132           <variablelist>
 133             <varlistentry>
 134               <term>list email address:</term>
 135               <listitem>
 136                 <para><email>cvs-ghc@haskell.org</email></para>
 137               </listitem>
 138             </varlistentry>
 139
 140             <varlistentry>
 141               <term>subscribe at:</term>
 142               <listitem>
 143                 <para><ulink
 144               url="http://www.haskell.org/mailman/listinfo/cvs-ghc"><literal>http://www.haskell.org/mailman/listinfo/cvs-ghc</literal></ulink>.</para>
 145               </listitem>
 146             </varlistentry>
 147
 148             <varlistentry>
 149               <term>admin email address:</term>
 150               <listitem>
 151                 <para><email>cvs-ghc-admin@haskell.org</email></para>
 152               </listitem>
 153             </varlistentry>
 154
 155             <varlistentry>
 156               <term>list archives:</term>
 157               <listitem>
 158                 <para><ulink
 159           url="http://www.haskell.org/pipermail/cvs-ghc/"><literal>http://www.haskell.org/pipermail/cvs-ghc/</literal></ulink></para>
 160               </listitem>
 161             </varlistentry>
 162           </variablelist>
 163         </listitem>
 164       </varlistentry>
 165     </variablelist>
 166
 167     <para>There are several other haskell and GHC-related mailing
 168     lists served by <literal>www.haskell.org</literal>.  Go to <ulink
 169     url="http://www.haskell.org/mailman/listinfo/"><literal>http://www.haskell.org/mailman/listinfo/</literal></ulink>
 170     for the full list.</para>
 171
 172     <para>Some Haskell-related discussion also takes place in the
 173     Usenet newsgroup <literal>comp.lang.functional</literal>.</para>
 174
 175   </sect1>
 176
 177   <sect1 id="bug-reporting">
 178     <title>Reporting bugs in GHC</title>
 179     <indexterm><primary>bugs</primary><secondary>reporting</secondary>
 180     </indexterm>
 181     <indexterm><primary>reporting bugs</primary>
 182     </indexterm>
 183
 184     <para>
 185         Glasgow Haskell is a changing system so there are sure to be
 186         bugs in it. If you find one, please see
 187         <ulink url="http://hackage.haskell.org/trac/ghc/wiki/ReportABug">this wiki page</ulink>
 188         for information on how to report it.
 189     </para>
 190
 191   </sect1>
 192
 193   <sect1 id="version-numbering">
 194     <title>GHC version numbering policy</title>
 195     <indexterm><primary>version, of ghc</primary></indexterm>
 196
 197     <para>As of GHC version 6.8, we have adopted the following policy
 198     for numbering GHC versions:</para>
 199
 200     <variablelist>
 201       <varlistentry>
 202         <term>Stable Releases</term>
 203         <listitem>
 204           <para>Stable branches are numbered <literal><replaceable>x</replaceable>.<replaceable>y</replaceable></literal>, where
 205           <replaceable>y</replaceable> is <emphasis>even</emphasis>.
 206           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
 207           <replaceable>z</replaceable> (>= 1) is the patchlevel number.
 208           Patchlevels are bug-fix releases only, and never
 209           change the programmer interface to any system-supplied code.
 210           However, if you install a new patchlevel over an old one you
 211           will need to recompile any code that was compiled against the
 212           old libraries.</para>
 213
 214           <para>The value of <literal>__GLASGOW_HASKELL__</literal>
 215           (see <xref linkend="c-pre-processor"/>) for a major release
 216           <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>z</replaceable></literal>
 217           is the integer <replaceable>xyy</replaceable> (if
 218           <replaceable>y</replaceable> is a single digit, then a leading zero
 219           is added, so for example in version 6.8.2 of GHC we would have
 220           <literal>__GLASGOW_HASKELL__==608</literal>).</para>
 221           <indexterm>
 222             <primary><literal>__GLASGOW_HASKELL__</literal></primary>
 223           </indexterm>
 224         </listitem>
 225       </varlistentry>
 226
 227       <varlistentry>
 228         <term>Stable snapshots</term>
 229         <listitem>
 230           <para>
 231       We may make snapshot releases of the current
 232       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>.
 233           </para>
 234
 235           <para>Stable snapshot releases are named
 236           <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>z</replaceable>.<replaceable>YYYYMMDD</replaceable></literal>.
 237           where <literal><replaceable>YYYYMMDD</replaceable></literal> is the date of the sources
 238           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.
 239           For example, <literal>6.8.1.20040225</literal> would be a
 240           snapshot of the <literal>6.8</literal> branch during the development
 241       of <literal>6.8.2</literal>.</para>
 242
 243           <para>The value of <literal>__GLASGOW_HASKELL__</literal>
 244           for a snapshot release is the integer
 245           <replaceable>xyy</replaceable>.  You should never write any
 246           conditional code which tests for this value, however: since
 247           interfaces change on a day-to-day basis, and we don't have
 248           finer granularity in the values of
 249           <literal>__GLASGOW_HASKELL__</literal>, you should only
 250           conditionally compile using predicates which test whether
 251           <literal>__GLASGOW_HASKELL__</literal> is equal to, later
 252           than, or earlier than a given major release.</para>
 253           <indexterm>
 254             <primary><literal>__GLASGOW_HASKELL__</literal></primary>
 255           </indexterm>
 256         </listitem>
 257       </varlistentry>
 258
 259       <varlistentry>
 260         <term>Unstable snapshots</term>
 261         <listitem>
 262           <para>
 263       We may make snapshot releases of the
 264       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>.
 265           </para>
 266
 267           <para>Unstable snapshot releases are named
 268           <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>YYYYMMDD</replaceable></literal>.
 269           where <literal><replaceable>YYYYMMDD</replaceable></literal> is the date of the sources
 270           from which the snapshot was built.
 271           For example, <literal>6.7.20040225</literal> would be a
 272           snapshot of the HEAD before the creation of the
 273       <literal>6.8</literal> branch.</para>
 274
 275           <para>The value of <literal>__GLASGOW_HASKELL__</literal>
 276           for a snapshot release is the integer
 277           <replaceable>xyy</replaceable>.  You should never write any
 278           conditional code which tests for this value, however: since
 279           interfaces change on a day-to-day basis, and we don't have
 280           finer granularity in the values of
 281           <literal>__GLASGOW_HASKELL__</literal>, you should only
 282           conditionally compile using predicates which test whether
 283           <literal>__GLASGOW_HASKELL__</literal> is equal to, later
 284           than, or earlier than a given major release.</para>
 285           <indexterm>
 286             <primary><literal>__GLASGOW_HASKELL__</literal></primary>
 287           </indexterm>
 288         </listitem>
 289       </varlistentry>
 290     </variablelist>
 291
 292     <para>The version number of your copy of GHC can be found by
 293     invoking <literal>ghc</literal> with the
 294     <literal>&ndash;&ndash;version</literal> flag (see <xref
 295     linkend="options-help"/>).</para>
 296   </sect1>
 297
 298
 299 &relnotes;
 300
 301 </chapter>
 302
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