X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=docs%2Fusers_guide%2Fglasgow_exts.xml;h=f8ad5c1b0ac8a79f9ee96c6a4227e6abafcaa6e7;hp=09fd3f509fd4efbab42e79ee8ffaa3e7e508f797;hb=9da4639011348fb6c318e3cba4b08622f811d9c4;hpb=bebf54b1fefef0c337955ec1e653b44f4ec63d10

diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 09fd3f5..f8ad5c1 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -3301,6 +3301,7 @@ changing the program.</para></listitem>
 A <emphasis>lexically scoped type variable</emphasis> can be bound by:
 <itemizedlist>
 <listitem><para>A declaration type signature (<xref linkend="decl-type-sigs"/>)</para></listitem>
+<listitem><para>An expression type signature (<xref linkend="exp-type-sigs"/>)</para></listitem>
 <listitem><para>A pattern type signature (<xref linkend="pattern-type-sigs"/>)</para></listitem>
 <listitem><para>Class and instance declarations (<xref linkend="cls-inst-scoped-tyvars"/>)</para></listitem>
 </itemizedlist>
@@ -3352,6 +3353,23 @@ quantification rules.
 </para>
 </sect3>
 
+<sect3 id="exp-type-sigs">
+<title>Expression type signatures</title>
+
+<para>An expression type signature that has <emphasis>explicit</emphasis>
+quantification (using <literal>forall</literal>) brings into scope the
+explicitly-quantified
+type variables, in the annotated expression.  For example:
+<programlisting>
+  f = runST ( (op >>= \(x :: STRef s Int) -> g x) :: forall s. ST s Bool )
+</programlisting>
+Here, the type signature <literal>forall a. ST s Bool</literal> brings the 
+type variable <literal>s</literal> into scope, in the annotated expression 
+<literal>(op >>= \(x :: STRef s Int) -> g x)</literal>.
+</para>
+
+</sect3>
+
 <sect3 id="pattern-type-sigs">
 <title>Pattern type signatures</title>
 <para>