ghc/docs/users_guide/intro.sgml

   1 <chapter id="introduction-GHC">
   2   <title>Introduction to GHC</title>
   3
   4   <para>This is a guide to using the Glasgow Haskell Compiler (GHC):
   5   an interactive and batch compilation system for the <ulink
   6   url="http://www.haskell.org/">Haskell&nbsp;98</ulink>
   7   language.</para>
   8
   9   <para>GHC has two main components: an interactive Haskell
  10   interpreter (also known as GHCi), described in <xref
  11   linkend="ghci">, and a batch compiler, described throughout <xref
  12   linkend="using-ghc">.  In fact, GHC consists of a single program
  13   which is just run with different options to provide either the
  14   interactive or the batch system.</para>
  15
  16   <para>The batch compiler can be used alongside GHCi: compiled
  17   modules can be loaded into an interactive session and used in the
  18   same way as interpreted code, and in fact when using GHCi most of
  19   the library code will be pre-compiled.  This means you get the best
  20   of both worlds: fast pre-compiled library code, and fast compile
  21   turnaround for the parts of your program being actively
  22   developed.</para>
  23
  24   <para>GHC supports numerous language extensions, including
  25   concurrency, a foreign function interface, exceptions, type system
  26   extensions such as multi-parameter type classes, local universal and
  27   existential quantification, functional dependencies, scoped type
  28   variables and explicit unboxed types.  These are all described in
  29   <xref linkend="ghc-language-features">.</para>
  30
  31   <para>GHC has a comprehensive optimiser, so when you want to Really
  32   Go For It (and you've got time to spare) GHC can produce pretty fast
  33   code.  Alternatively, the default option is to compile as fast as
  34   possible while not making too much effort to optimise the generated
  35   code (although GHC probably isn't what you'd describe as a fast
  36   compiler :-).</para>
  37
  38   <para>GHC's profiling system supports &ldquo;cost centre
  39   stacks&rdquo;: a way of seeing the profile of a Haskell program in a
  40   call-graph like structure.  See <xref linkend="profiling"> for more
  41   details.</para>
  42
  43   <para>GHC comes with a large collection of libraries, with
  44   everything from parser combinators to networking.  These are all
  45   described in <xref linkend="book-hslibs">.</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/Department/Staff/mpj/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
  83           themselves.</para>
  84
  85           <variablelist>
  86             <varlistentry>
  87               <term>list email address:</term>
  88               <listitem>
  89                 <para><email>glasgow-haskell-users@haskell.org</email></para>
  90               </listitem>
  91             </varlistentry>
  92
  93             <varlistentry>
  94               <term>subscribe at:</term>
  95               <listitem>
  96                 <para><ulink
  97               url="http://www.haskell.org/mailman/listinfo/glasgow-haskell-users"><literal>http://www.haskell.org/mailman/listinfo/glasgow-haskell-users</literal></ulink>.</para>
  98               </listitem>
  99             </varlistentry>
 100
 101             <varlistentry>
 102               <term>admin email address:</term>
 103               <listitem>
 104                 <para><email>glasgow-haskell-users-admin@haskell.org</email></para>
 105               </listitem>
 106             </varlistentry>
 107
 108             <varlistentry>
 109               <term>list archives:</term>
 110               <listitem>
 111                 <para><ulink
 112           url="http://www.haskell.org/pipermail/glasgow-haskell-users/"><literal>http://www.haskell.org/pipermail/glasgow-haskell-users/</literal></ulink></para>
 113               </listitem>
 114             </varlistentry>
 115           </variablelist>
 116         </listitem>
 117       </varlistentry>
 118
 119       <varlistentry>
 120         <term>glasgow-haskell-bugs:</term>
 121         <listitem>
 122           <para>Send bug reports for GHC to this address!  The sad and
 123           lonely people who subscribe to this list will muse upon
 124           what's wrong and what you might do about it.</para>
 125
 126           <variablelist>
 127             <varlistentry>
 128               <term>list email address:</term>
 129               <listitem>
 130                 <para><email>glasgow-haskell-bugs@haskell.org</email></para>
 131               </listitem>
 132             </varlistentry>
 133
 134             <varlistentry>
 135               <term>subscribe at:</term>
 136               <listitem>
 137                 <para><ulink
 138               url="http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs"><literal>http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs</literal></ulink>.</para>
 139               </listitem>
 140             </varlistentry>
 141
 142             <varlistentry>
 143               <term>admin email address:</term>
 144               <listitem>
 145                 <para><email>glasgow-haskell-bugs-admin@haskell.org</email></para>
 146               </listitem>
 147             </varlistentry>
 148
 149             <varlistentry>
 150               <term>list archives:</term>
 151               <listitem>
 152                 <para><ulink
 153           url="http://www.haskell.org/pipermail/glasgow-haskell-bugs/"><literal>http://www.haskell.org/pipermail/glasgow-haskell-bugs/</literal></ulink></para>
 154               </listitem>
 155             </varlistentry>
 156           </variablelist>
 157         </listitem>
 158       </varlistentry>
 159
 160       <varlistentry>
 161         <term>cvs-ghc:</term>
 162         <listitem>
 163           <para>The hardcore GHC developers hang out here.  This list
 164           also gets commit message from the CVS repository.  There are
 165           several other similar lists for other parts of the CVS
 166           repository (eg. <literal>cvs-hslibs</literal>,
 167           <literal>cvs-happy</literal>, <literal>cvs-hdirect</literal>
 168           etc.)</para>
 169
 170           <variablelist>
 171             <varlistentry>
 172               <term>list email address:</term>
 173               <listitem>
 174                 <para><email>cvs-ghc@haskell.org</email></para>
 175               </listitem>
 176             </varlistentry>
 177
 178             <varlistentry>
 179               <term>subscribe at:</term>
 180               <listitem>
 181                 <para><ulink
 182               url="http://www.haskell.org/mailman/listinfo/cvs-ghc"><literal>http://www.haskell.org/mailman/listinfo/cvs-ghc</literal></ulink>.</para>
 183               </listitem>
 184             </varlistentry>
 185
 186             <varlistentry>
 187               <term>admin email address:</term>
 188               <listitem>
 189                 <para><email>cvs-ghc-admin@haskell.org</email></para>
 190               </listitem>
 191             </varlistentry>
 192
 193             <varlistentry>
 194               <term>list archives:</term>
 195               <listitem>
 196                 <para><ulink
 197           url="http://www.haskell.org/pipermail/cvs-ghc/"><literal>http://www.haskell.org/pipermail/cvs-ghc/</literal></ulink></para>
 198               </listitem>
 199             </varlistentry>
 200           </variablelist>
 201         </listitem>
 202       </varlistentry>
 203     </variablelist>
 204
 205     <para>There are several other haskell and GHC-related mailing
 206     lists served by <literal>www.haskell.org</literal>.  Go to <ulink
 207     url="http://www.haskell.org/mailman/listinfo/"><literal>http://www.haskell.org/mailman/listinfo/</literal></ulink>
 208     for the full list.</para>
 209
 210     <para>Some Haskell-related discussion also takes place in the
 211     Usenet newsgroup <literal>comp.lang.functional</literal>.</para>
 212
 213   </sect1>
 214
 215   <sect1 id="version-numbering">
 216     <title>GHC version numbering policy</title>
 217     <indexterm><primary>version, of ghc</primary></indexterm>
 218
 219     <para>As of GHC version 4.08, we have adopted the following
 220     policy for numbering GHC versions:</para>
 221
 222     <variablelist>
 223       <varlistentry>
 224         <term>Stable Releases</term>
 225         <listitem>
 226           <para>These are numbered <literal>x.yy.z</literal>, where
 227           <literal>yy</literal> is <emphasis>even</emphasis>, and
 228           <literal>z</literal> is the patchlevel number (the trailing
 229           <literal>.z</literal> can be omitted if <literal>z</literal>
 230           is zero).  Patchlevels are bug-fix releases only, and never
 231           change the programmer interface to any system-supplied code.
 232           However, if you install a new patchlevel over an old one you
 233           will need to recompile any code that was compiled against the
 234           old libraries.</para>
 235
 236           <para>The value of <literal>__GLASGOW_HASKELL__</literal>
 237           (see <xref linkend="c-pre-processor">) for a major release
 238           <literal>x.yy.z</literal> is the integer
 239           <literal>xyy</literal>.</para>
 240           <indexterm>
 241             <primary><literal>__GLASGOW_HASKELL__</literal></primary>
 242           </indexterm>
 243         </listitem>
 244       </varlistentry>
 245
 246       <varlistentry>
 247         <term>Snapshots/unstable releases</term>
 248         <listitem>
 249           <para>We may make snapshot releases of the current
 250           development sources from time to time, and the current
 251           sources are always available via the CVS repository (see the
 252           GHC web site for details).</para>
 253
 254           <para>Snapshot releases are named
 255           <literal>x.yy.YYYYMMDD</literal> where <literal>yy</literal>
 256           is <emphasis>odd</emphasis>, and <literal>YYYYMMDD</literal>
 257           is the date of the sources from which the snapshot was
 258           built.  In theory, you can check out the exact same sources
 259           from the CVS repository using this date.</para>
 260
 261           <para>The value of <literal>__GLASGOW_HASKELL__</literal>
 262           for a snapshot release is the integer
 263           <literal>xyy</literal>.  You should never write any
 264           conditional code which tests for this value, however: since
 265           interfaces change on a day-to-day basis, and we don't have
 266           finer granularity in the values of
 267           <literal>__GLASGOW_HASKELL__</literal>, you should only
 268           conditionally compile using predicates which test whether
 269           <literal>__GLASGOW_HASKELL__</literal> is equal to, later
 270           than, or earlier than a given major release.</para>
 271           <indexterm>
 272             <primary><literal>__GLASGOW_HASKELL__</literal></primary>
 273           </indexterm>
 274         </listitem>
 275       </varlistentry>
 276     </variablelist>
 277
 278     <para>The version number of your copy of GHC can be found by
 279     invoking <literal>ghc</literal> with the
 280     <literal>--version</literal> flag (see <xref
 281     linkend="options-help">).</para>
 282   </sect1>
 283
 284
 285 &relnotes
 286
 287 </Chapter>
 288
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