Various documentation improvements suggested by Bulat Ziganshin

[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 0ca2a53..09fd3f5 100644 (file)
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -3360,7 +3360,7 @@ signature</emphasis>.
 For example:
 <programlisting>
   -- f and g assume that 'a' is already in scope
-  f = \(x::Int, y) -> x
+  f = \(x::Int, y::a) -> x
   g (x::a) = x
   h ((x,y) :: (Int,Bool)) = (y,x)
 </programlisting>
@@ -3640,16 +3640,19 @@ declaration (after expansion of any type synonyms)
 where 
  <itemizedlist>
 <listitem><para>
-  The type <literal>t</literal> is an arbitrary type
+  The <literal>ci</literal> are partial applications of
+  classes of the form <literal>C t1'...tj'</literal>, where the arity of <literal>C</literal>
+  is exactly <literal>j+1</literal>.  That is, <literal>C</literal> lacks exactly one type argument.
 </para></listitem>
 <listitem><para>
-  The <literal>vk+1...vn</literal> are type variables which do not occur in 
-  <literal>t</literal>, and
+  The <literal>k</literal> is chosen so that <literal>ci (T v1...vk)</literal> is well-kinded.
 </para></listitem>
 <listitem><para>
-  The <literal>ci</literal> are partial applications of
-  classes of the form <literal>C t1'...tj'</literal>, where the arity of <literal>C</literal>
-  is exactly <literal>j+1</literal>.  That is, <literal>C</literal> lacks exactly one type argument.
+  The type <literal>t</literal> is an arbitrary type.
+</para></listitem>
+<listitem><para>
+  The type variables <literal>vk+1...vn</literal> do not occur in <literal>t</literal>, 
+  nor in the <literal>ci</literal>, and
 </para></listitem>
 <listitem><para>
   None of the <literal>ci</literal> is <literal>Read</literal>, <literal>Show</literal>, 
@@ -3662,13 +3665,8 @@ where
 Then, for each <literal>ci</literal>, the derived instance
 declaration is:
 <programlisting> 
-  instance ci (t vk+1...v) => ci (T v1...vp)
+  instance ci t => ci (T v1...vk)
 </programlisting>
-where <literal>p</literal> is chosen so that <literal>T v1...vp</literal> is of the 
-right <emphasis>kind</emphasis> for the last parameter of class <literal>Ci</literal>.
-</para>
-<para>
-
 As an example which does <emphasis>not</emphasis> work, consider 
 <programlisting> 
   newtype NonMonad m s = NonMonad (State s m s) deriving Monad 
@@ -3780,9 +3778,9 @@ pattern binding must have the same context.  For example, this is fine:
 <!-- ====================== Generalised algebraic data types =======================  -->
 
 <sect1 id="gadt">
-<title>Generalised Algebraic Data Types</title>
+<title>Generalised Algebraic Data Types (GADTs)</title>
 
-<para>Generalised Algebraic Data Types (GADTs) generalise ordinary algebraic data types by allowing you
+<para>Generalised Algebraic Data Types generalise ordinary algebraic data types by allowing you
 to give the type signatures of constructors explicitly.  For example:
 <programlisting>
   data Term a where
@@ -3803,7 +3801,12 @@ for these <literal>Terms</literal>:
   eval (If b e1 e2) = if eval b then eval e1 else eval e2
   eval (Pair e1 e2) = (eval e1, eval e2)
 </programlisting>
-These and many other examples are given in papers by Hongwei Xi, and Tim Sheard.
+These and many other examples are given in papers by Hongwei Xi, and
+Tim Sheard. There is a longer introduction
+<ulink url="http://haskell.org/haskellwiki/GADT">on the wiki</ulink>,
+and Ralf Hinze's
+<ulink url="http://www.informatik.uni-bonn.de/~ralf/publications/With.pdf">Fun with phantom types</ulink> also has a number of examples. Note that papers
+may use different notation to that implemented in GHC.
 </para>
 <para>
 The rest of this section outlines the extensions to GHC that support GADTs.