From: simonpj <unknown>
Date: Fri, 11 Oct 2002 08:04:29 +0000 (+0000)
Subject: [project @ 2002-10-11 08:04:29 by simonpj]
X-Git-Tag: Approx_11550_changesets_converted~1571
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=a8cf15f207bb5b3d7173cf8e2f9314ad9a80d40b;p=ghc-hetmet.git

[project @ 2002-10-11 08:04:29 by simonpj]
Add a note about existential data constructors
---

diff --git a/ghc/docs/users_guide/glasgow_exts.sgml b/ghc/docs/users_guide/glasgow_exts.sgml
index ef2028c..a3ff83c 100644
--- a/ghc/docs/users_guide/glasgow_exts.sgml
+++ b/ghc/docs/users_guide/glasgow_exts.sgml
@@ -1898,8 +1898,13 @@ bindings. So this is illegal:
   f3 x = a==b where { Baz1 a b = x }
 </programlisting>
 
+Instead, use a <literal>case</literal> expression:
 
-You can only pattern-match
+<programlisting>
+  f3 x = case x of Baz1 a b -> a==b
+</programlisting>
+
+In general, you can only pattern-match
 on an existentially-quantified constructor in a <literal>case</literal> expression or
 in the patterns of a function definition.