[Documentation for impredicative polymorphism
simonpj@microsoft.com**20060907111540] {
hunk ./docs/users_guide/glasgow_exts.xml 3201
-
+<sect2 id="impredicative-polymorphism">
+<title>Impredicative polymorphism
+</title>
+<para>GHC supports <emphasis>impredicative polymorphism</emphasis>.  This means
+that you can call a polymorphic function at a polymorphic type, and
+parameterise data structures over polymorphic types.  For example:
+<programlisting>
+  f :: Maybe (forall a. [a] -> [a]) -> Maybe ([Int], [Char])
+  f (Just g) = Just (g [3], g "hello")
+  f Nothing  = Nothing
+</programlisting>
+Notice here that the <literal>Maybe</literal> type is parameterised by the
+<emphasis>polymorphic</emphasis> type <literal>(forall a. [a] ->
+[a])</literal>.
+</para>
+<para>The technical details of this extension are described in the paper
+<ulink url="http://research.microsoft.com/%7Esimonpj/papers/boxy">Boxy types:
+type inference for higher-rank types and impredicativity</ulink>,
+which appeared at ICFP 2006.  
+</para>
+</sect2>
hunk ./docs/users_guide/glasgow_exts.xml 3776
-<para> The extensions to GHC are these:
+<para>
+The rest of this section outlines the extensions to GHC that support GADTs. 
+It is far from comprehensive, but the design closely follows that described in
+the paper <ulink
+url="http://research.microsoft.com/%7Esimonpj/papers/gadt/index.htm">Simple
+unification-based type inference for GADTs</ulink>,
+which appeared in ICFP 2006.
hunk ./docs/users_guide/glasgow_exts.xml 3925
-<para>Template Haskell allows you to do compile-time meta-programming in Haskell.  There is a "home page" for
-Template Haskell at <ulink url="http://www.haskell.org/th/">
-http://www.haskell.org/th/</ulink>, while
-the background to
+<para>Template Haskell allows you to do compile-time meta-programming in
+Haskell.  
+The background to
hunk ./docs/users_guide/glasgow_exts.xml 3931
-The details of the Template Haskell design are still in flux.  Make sure you
-consult the <ulink url="http://www.haskell.org/ghc/docs/latest/html/libraries/index.html">online library reference material</ulink> 
+</para>
+<para>
+There is a Wiki page about
+Template Haskell at <ulink url="http://haskell.org/haskellwiki/Template_Haskell">
+http://www.haskell.org/th/</ulink>, and that is the best place to look for
+further details.
+You may also 
+consult the <ulink
+url="http://www.haskell.org/ghc/docs/latest/html/libraries/index.html">online
+Haskell library reference material</ulink> 
hunk ./docs/users_guide/glasgow_exts.xml 3944
-Not all of these changes are in GHC 6.2.]
+Not all of these changes are in GHC 6.6.]
}