[[project @ 2005-03-09 17:47:09 by simonpj]
simonpj**20050309174709
 Document infix type operators
] {
hunk ./ghc/docs/users_guide/glasgow_exts.xml 928
-<title>Infix type constructors and classes</title>
+<title>Infix type constructors, classes, and type variables</title>
hunk ./ghc/docs/users_guide/glasgow_exts.xml 931
-GHC allows type constructors and classes to be operators, and to be written infix, very much 
-like expressions.  More specifically:
+GHC allows type constructors, classes, and type variables to be operators, and
+to be written infix, very much like expressions.  More specifically:
hunk ./ghc/docs/users_guide/glasgow_exts.xml 958
+  A type variable can be an (unqualified) operator e.g. <literal>+</literal>.
+  The lexical syntax is the same as that for variable operators, excluding "(.)",
+  "(!)", and "(*)".  In a binding position, the operator must be
+  parenthesised.  For example:
+<programlisting>
+   type T (+) = Int + Int
+   f :: T Either
+   f = Left 3
+ 
+   liftA2 :: Arrow (~>)
+	  => (a -> b -> c) -> (e ~> a) -> (e ~> b) -> (e ~> c)
+   liftA2 = ...
+</programlisting>
+  </para></listitem>
+<listitem><para>
hunk ./ghc/docs/users_guide/glasgow_exts.xml 991
-<listitem><para>
-  The only thing that differs between operators in types and operators in expressions is that
-  ordinary non-constructor operators, such as <literal>+</literal> and <literal>*</literal>
-  are not allowed in types. Reason: the uniform thing to do would be to make them type
-  variables, but that's not very useful.  A less uniform but more useful thing would be to
-  allow them to be type <emphasis>constructors</emphasis>.  But that gives trouble in export
-  lists.  So for now we just exclude them.
-  </para></listitem>
}