remove 'mode: xml' emacs settings (#2208)

[ghc-hetmet.git] / docs / users_guide / glasgow_exts.xml

diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 4668bbb..9fea7a4 100644 (file)
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -400,14 +400,6 @@ Indeed, the bindings can even be recursive.
               <entry>LEFTWARDS ARROW</entry>
            </row>
           </tbody>
-         <tbody>
-           <row>
-             <entry>..</entry>
-             <entry>&hellip;</entry>
-             <entry>0x22EF</entry>
-             <entry>MIDLINE HORIZONTAL ELLIPSIS</entry>
-           </row>
-          </tbody>
 
          <tbody>
            <row>
@@ -826,10 +818,8 @@ let {(x -> y) = e1 ;
      (y -> x) = e2 } in x
 </programlisting>
 
-(We may lift this
-restriction in the future; the only cost is that type checking patterns
-would get a little more complicated.)  
-
+(For some amplification on this design choice see 
+<ulink url="http://hackage.haskell.org/trac/ghc/ticket/4061">Trac #4061</ulink>.)
 
 </para>
 </listitem>
@@ -911,7 +901,7 @@ it, you can use the <option>-XNoNPlusKPatterns</option> flag.
 
     <!-- ===================== Recursive do-notation ===================  -->
 
-<sect2 id="mdo-notation">
+<sect2 id="recursive-do-notation">
 <title>The recursive do-notation
 </title>
 
@@ -932,7 +922,7 @@ justOnes = do { rec { xs &lt;- Just (1:xs) }
 As you can guess <literal>justOnes</literal> will evaluate to <literal>Just [-1,-1,-1,...</literal>.
 </para>
 <para>
-The background and motivation for recusrive do-notation is described in
+The background and motivation for recursive do-notation is described in
 <ulink url="http://sites.google.com/site/leventerkok/">A recursive do for Haskell</ulink>,
 by Levent Erkok, John Launchbury,
 Haskell Workshop 2002, pages: 29-37. Pittsburgh, Pennsylvania. 
@@ -1047,7 +1037,7 @@ It supports rebindable syntax (see <xref linkend="rebindable-syntax"/>).
 </para>
 </sect3>
 
-<sect3> <title> Mdo-notation (deprecated) </title>
+<sect3 id="mdo-notation"> <title> Mdo-notation (deprecated) </title>
 
 <para> GHC used to support the flag <option>-XRecursiveDo</option>,
 which enabled the keyword <literal>mdo</literal>, precisely as described in
@@ -1697,7 +1687,7 @@ and the fixity declaration applies wherever the binding is in scope.
 For example, in a <literal>let</literal>, it applies in the right-hand
 sides of other <literal>let</literal>-bindings and the body of the
 <literal>let</literal>C. Or, in recursive <literal>do</literal>
-expressions (<xref linkend="mdo-notation"/>), the local fixity
+expressions (<xref linkend="recursive-do-notation"/>), the local fixity
 declarations of a <literal>let</literal> statement scope over other
 statements in the group, just as the bound name does.
 </para>
@@ -1904,6 +1894,26 @@ not <literal>*</literal> then an explicit kind annotation must be used
 Nevertheless, they can be useful when defining "phantom types".</para>
 </sect2>
 
+<sect2 id="datatype-contexts">
+<title>Data type contexts</title>
+
+<para>Haskell allows datatypes to be given contexts, e.g.</para>
+
+<programlisting>
+data Eq a => Set a = NilSet | ConsSet a (Set a)
+</programlisting>
+
+<para>give constructors with types:</para>
+
+<programlisting>
+NilSet :: Set a
+ConsSet :: Eq a => a -> Set a -> Set a
+</programlisting>
+
+<para>In GHC this feature is an extension called
+<literal>DatatypeContexts</literal>, and on by default.</para>
+</sect2>
+
 <sect2 id="infix-tycons">
 <title>Infix type constructors, classes, and type variables</title>
 
@@ -9087,7 +9097,6 @@ standard behaviour.
 
 <!-- Emacs stuff:
      ;;; Local Variables: ***
-     ;;; mode: xml ***
      ;;; sgml-parent-document: ("users_guide.xml" "book" "chapter" "sect1") ***
      ;;; ispell-local-dictionary: "british" ***
      ;;; End: ***