1 <?xml version="1.0" encoding="iso-8859-1"?>
2 <chapter id="introduction-GHC">
3 <title>Introduction to GHC</title>
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 98</ulink>
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>
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
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>
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
39 <para>GHC's profiling system supports “cost centre
40 stacks”: a way of seeing the profile of a Haskell program in a
41 call-graph like structure. See <xref linkend="profiling"/> for more
44 <para>GHC comes with a large collection of libraries, with
45 everything from parser combinators to networking. The libraries are
46 described in separate documentation.</para>
48 <sect1 id="mailing-lists-GHC">
49 <title>Meta-information: Web sites, mailing lists, etc.</title>
51 <indexterm><primary>mailing lists, Glasgow Haskell</primary></indexterm>
52 <indexterm><primary>Glasgow Haskell mailing lists</primary></indexterm>
54 <para>On the World-Wide Web, there are several URLs of likely
59 <para><ulink url="http://www.haskell.org/" >Haskell home
64 <para><ulink url="http://www.haskell.org/ghc/">GHC home
70 url="http://www.cs.nott.ac.uk/~gmh/faq.html">comp.lang.functional
76 <para>We run the following mailing lists about Glasgow Haskell.
77 We encourage you to join, as you feel is appropriate.</para>
81 <term>glasgow-haskell-users:</term>
83 <para>This list is for GHC users to chat among themselves.
84 If you have a specific question about GHC, please check the
86 url="http://hackage.haskell.org/trac/ghc/wiki/FAQ">FAQ</ulink>
91 <term>list email address:</term>
93 <para><email>glasgow-haskell-users@haskell.org</email></para>
98 <term>subscribe at:</term>
101 url="http://www.haskell.org/mailman/listinfo/glasgow-haskell-users"><literal>http://www.haskell.org/mailman/listinfo/glasgow-haskell-users</literal></ulink>.</para>
106 <term>admin email address:</term>
108 <para><email>glasgow-haskell-users-admin@haskell.org</email></para>
113 <term>list archives:</term>
116 url="http://www.haskell.org/pipermail/glasgow-haskell-users/"><literal>http://www.haskell.org/pipermail/glasgow-haskell-users/</literal></ulink></para>
124 <term>glasgow-haskell-bugs:</term>
126 <para>Send bug reports for GHC to this address! The sad and
127 lonely people who subscribe to this list will muse upon
128 what's wrong and what you might do about it.</para>
132 <term>list email address:</term>
134 <para><email>glasgow-haskell-bugs@haskell.org</email></para>
139 <term>subscribe at:</term>
142 url="http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs"><literal>http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs</literal></ulink>.</para>
147 <term>admin email address:</term>
149 <para><email>glasgow-haskell-bugs-admin@haskell.org</email></para>
154 <term>list archives:</term>
157 url="http://www.haskell.org/pipermail/glasgow-haskell-bugs/"><literal>http://www.haskell.org/pipermail/glasgow-haskell-bugs/</literal></ulink></para>
165 <term>cvs-ghc:</term>
167 <para>The hardcore GHC developers hang out here. This list
168 also gets commit message from the CVS repository. There are
169 several other similar lists for other parts of the CVS
170 repository (eg. <literal>cvs-hslibs</literal>,
171 <literal>cvs-happy</literal>, <literal>cvs-hdirect</literal>
176 <term>list email address:</term>
178 <para><email>cvs-ghc@haskell.org</email></para>
183 <term>subscribe at:</term>
186 url="http://www.haskell.org/mailman/listinfo/cvs-ghc"><literal>http://www.haskell.org/mailman/listinfo/cvs-ghc</literal></ulink>.</para>
191 <term>admin email address:</term>
193 <para><email>cvs-ghc-admin@haskell.org</email></para>
198 <term>list archives:</term>
201 url="http://www.haskell.org/pipermail/cvs-ghc/"><literal>http://www.haskell.org/pipermail/cvs-ghc/</literal></ulink></para>
209 <para>There are several other haskell and GHC-related mailing
210 lists served by <literal>www.haskell.org</literal>. Go to <ulink
211 url="http://www.haskell.org/mailman/listinfo/"><literal>http://www.haskell.org/mailman/listinfo/</literal></ulink>
212 for the full list.</para>
214 <para>Some Haskell-related discussion also takes place in the
215 Usenet newsgroup <literal>comp.lang.functional</literal>.</para>
219 <sect1 id="bug-reporting">
220 <title>Reporting bugs in GHC</title>
221 <indexterm><primary>bugs</primary><secondary>reporting</secondary>
223 <indexterm><primary>reporting bugs</primary>
227 Glasgow Haskell is a changing system so there are sure to be
228 bugs in it. If you find one, please see
229 <ulink url="http://hackage.haskell.org/trac/ghc/wiki/ReportABug">this wiki page</ulink>
230 for information on how to report it.
235 <sect1 id="version-numbering">
236 <title>GHC version numbering policy</title>
237 <indexterm><primary>version, of ghc</primary></indexterm>
239 <para>As of GHC version 6.8, we have adopted the following policy
240 for numbering GHC versions:</para>
244 <term>Stable Releases</term>
246 <para>Stable branches are numbered <literal><replaceable>x</replaceable>.<replaceable>y</replaceable></literal>, where
247 <replaceable>y</replaceable> is <emphasis>even</emphasis>.
248 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
249 <replaceable>z</replaceable> (>= 1) is the patchlevel number.
250 Patchlevels are bug-fix releases only, and never
251 change the programmer interface to any system-supplied code.
252 However, if you install a new patchlevel over an old one you
253 will need to recompile any code that was compiled against the
254 old libraries.</para>
256 <para>The value of <literal>__GLASGOW_HASKELL__</literal>
257 (see <xref linkend="c-pre-processor"/>) for a major release
258 <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>z</replaceable></literal>
259 is the integer <replaceable>xyy</replaceable> (if
260 <replaceable>y</replaceable> is a single digit, then a leading zero
261 is added, so for example in version 6.8.2 of GHC we would have
262 <literal>__GLASGOW_HASKELL__==608</literal>).</para>
264 <primary><literal>__GLASGOW_HASKELL__</literal></primary>
270 <term>Stable snapshots</term>
273 We may make snapshot releases of the current
274 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>.
277 <para>Stable snapshot releases are named
278 <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>z</replaceable>.<replaceable>YYYYMMDD</replaceable></literal>.
279 where <literal><replaceable>YYYYMMDD</replaceable></literal> is the date of the sources
280 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.
281 For example, <literal>6.8.1.20040225</literal> would be a
282 snapshot of the <literal>6.8</literal> branch during the development
283 of <literal>6.8.2</literal>.</para>
285 <para>The value of <literal>__GLASGOW_HASKELL__</literal>
286 for a snapshot release is the integer
287 <replaceable>xyy</replaceable>. You should never write any
288 conditional code which tests for this value, however: since
289 interfaces change on a day-to-day basis, and we don't have
290 finer granularity in the values of
291 <literal>__GLASGOW_HASKELL__</literal>, you should only
292 conditionally compile using predicates which test whether
293 <literal>__GLASGOW_HASKELL__</literal> is equal to, later
294 than, or earlier than a given major release.</para>
296 <primary><literal>__GLASGOW_HASKELL__</literal></primary>
302 <term>Unstable snapshots</term>
305 We may make snapshot releases of the
306 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>.
309 <para>Unstable snapshot releases are named
310 <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>YYYYMMDD</replaceable></literal>.
311 where <literal><replaceable>YYYYMMDD</replaceable></literal> is the date of the sources
312 from which the snapshot was built.
313 For example, <literal>6.7.20040225</literal> would be a
314 snapshot of the HEAD before the creation of the
315 <literal>6.8</literal> branch.</para>
317 <para>The value of <literal>__GLASGOW_HASKELL__</literal>
318 for a snapshot release is the integer
319 <replaceable>xyy</replaceable>. You should never write any
320 conditional code which tests for this value, however: since
321 interfaces change on a day-to-day basis, and we don't have
322 finer granularity in the values of
323 <literal>__GLASGOW_HASKELL__</literal>, you should only
324 conditionally compile using predicates which test whether
325 <literal>__GLASGOW_HASKELL__</literal> is equal to, later
326 than, or earlier than a given major release.</para>
328 <primary><literal>__GLASGOW_HASKELL__</literal></primary>
334 <para>The version number of your copy of GHC can be found by
335 invoking <literal>ghc</literal> with the
336 <literal>––version</literal> flag (see <xref
337 linkend="options-help"/>).</para>
346 ;;; Local Variables: ***
348 ;;; sgml-parent-document: ("users_guide.xml" "book" "chapter") ***