[commit: ghc] master: Add notes about type-family overlap in GHCi (see Trac #7102) (232f1a2)
Simon Peyton Jones <[email protected]>
| Newsgroups | gmane.comp.lang.haskell.cvs.ghc |
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Repository : ssh://darcs.haskell.org//srv/darcs/ghc On branch : master http://hackage.haskell.org/trac/ghc/changeset/232f1a2702684fe7f82a084213714adfa6162392 >--------------------------------------------------------------- commit 232f1a2702684fe7f82a084213714adfa6162392 Author: Simon Peyton Jones <[email protected]> Date: Wed Oct 31 17:03:28 2012 +0000 Add notes about type-family overlap in GHCi (see Trac #7102) >--------------------------------------------------------------- docs/users_guide/ghci.xml | 6 +++++- docs/users_guide/glasgow_exts.xml | 1 + 2 files changed, 6 insertions(+), 1 deletions(-) diff --git a/docs/users_guide/ghci.xml b/docs/users_guide/ghci.xml index 94be422..3d1aecc 100644 --- a/docs/users_guide/ghci.xml +++ b/docs/users_guide/ghci.xml @@ -614,7 +614,7 @@ Prelude> <sect2 id="ghci-decls"> <title>Type, class and other declarations</title> - <para>[<emphasis role="bold">New in version 7.4.1</emphasis>] At the GHCi + <para>At the GHCi prompt you can also enter any top-level Haskell declaration, including <literal>data</literal>, <literal>type</literal>, <literal>newtype</literal>, <literal>class</literal>, <literal>instance</literal>, <literal>deriving</literal>, and <literal>foreign</literal> declarations. For @@ -662,6 +662,10 @@ Prelude> an attempt to distinguish it from the new <literal>T</literal>, which is displayed as simply <literal>T</literal>.</para> + <para>Class and type-family instance declarations are simply added to the list of available isntances, with one + exception. Since type-family instances are not permitted to overlap, but you might want to re-define one, + a type-family instance <emphasis>replaces</emphasis> any earlier type instance with an identical left hand side. + (See <xref linkend="type-families"/>.)</para> </sect2> <sect2 id="ghci-scope"> diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml index b036674..fa0f3aa 100644 --- a/docs/users_guide/glasgow_exts.xml +++ b/docs/users_guide/glasgow_exts.xml @@ -4891,6 +4891,7 @@ type instance G (a, Int) = [a] type instance G (Char, a) = [a] -- ILLEGAL overlap, as [Char] /= [Int] </programlisting> </para> + <para> However see <xref linkend="ghci-decls"/> for the overlap rules in GHCi.</para> </sect3> <sect3 id="type-family-decidability">