Repository : ssh://g...@git.haskell.org/ghc
On branch : master
Link :
http://ghc.haskell.org/trac/ghc/changeset/c4ffdbad3d40887b9b1e8287c90966649ea8571f/ghc
>---------------------------------------------------------------
commit c4ffdbad3d40887b9b1e8287c90966649ea8571f
Author: Krzysztof Gogolewski <krz.gogolew...@gmail.com>
Date: Fri Sep 27 08:55:44 2013 +0200
Fix manual regarding current state of implicit quantification
See also #4426
>---------------------------------------------------------------
c4ffdbad3d40887b9b1e8287c90966649ea8571f
docs/users_guide/glasgow_exts.xml | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/docs/users_guide/glasgow_exts.xml
b/docs/users_guide/glasgow_exts.xml
index 43fa155..d818904 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -6941,7 +6941,11 @@ explicit context. For example in the first argument of
the
constructor <function>MkSwizzle</function>, an implicit "<literal>forall
a.</literal>" is
prefixed to the argument type. The implicit <literal>forall</literal>
quantifies all type variables that are not already in scope, and are
-mentioned in the type quantified over.
+mentioned in the type quantified over. (Arguably, it would be better
+to <emphasis>require</emphasis> explicit quantification on constructor
arguments
+where that is what is wanted.
+See <ulink url="http://ghc.haskell.org/trac/ghc/ticket/4426";>Trac
#4426</ulink>.)
+
</para>
<para>
@@ -6949,19 +6953,17 @@ As for type signatures, implicit quantification happens
for non-overloaded
types too. So if you write this:
<programlisting>
- data T a = MkT (Either a b) (b -> b)
+ f :: (a -> a) -> a
</programlisting>
it's just as if you had written this:
<programlisting>
- data T a = MkT (forall b. Either a b) (forall b. b -> b)
+ f :: forall a. (a -> a) -> a
</programlisting>
-That is, since the type variable <literal>b</literal> isn't in scope, it's
-implicitly universally quantified. (Arguably, it would be better
-to <emphasis>require</emphasis> explicit quantification on constructor
arguments
-where that is what is wanted. Feedback welcomed.)
+That is, since the type variable <literal>a</literal> isn't in scope, it's
+implicitly universally quantified.
</para>
<para>
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