Document the fact that impredicative polymorphism is deprecated

Merge to 6.12

diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 0988279..6910a59 100644 (file)
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -5684,6 +5684,9 @@ for rank-2 types.
 <sect2 id="impredicative-polymorphism">
 <title>Impredicative polymorphism
 </title>
+<para><emphasis>NOTE: the impredicative-polymorphism feature is deprecated in GHC 6.12, and
+will be removed or replaced in GHC 6.14.</emphasis></para>
+
 <para>GHC supports <emphasis>impredicative polymorphism</emphasis>, 
 enabled with <option>-XImpredicativeTypes</option>.  
 This means