X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fglasgow_exts.xml;h=09fd3f509fd4efbab42e79ee8ffaa3e7e508f797;hb=bebf54b1fefef0c337955ec1e653b44f4ec63d10;hp=0ca2a5370abc302826e2843531e1eb3ffccf92b3;hpb=d8cd50453c7f78ceb9d975183031bcf6ebe4b7bd;p=ghc-hetmet.git
diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 0ca2a53..09fd3f5 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -3360,7 +3360,7 @@ signature.
For example:
-- 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)
@@ -3640,16 +3640,19 @@ declaration (after expansion of any type synonyms)
where
- The type t is an arbitrary type
+ The ci are partial applications of
+ classes of the form C t1'...tj', where the arity of C
+ is exactly j+1. That is, C lacks exactly one type argument.
- The vk+1...vn are type variables which do not occur in
- t, and
+ The k is chosen so that ci (T v1...vk) is well-kinded.
- The ci are partial applications of
- classes of the form C t1'...tj', where the arity of C
- is exactly j+1. That is, C lacks exactly one type argument.
+ The type t is an arbitrary type.
+
+
+ The type variables vk+1...vn do not occur in t,
+ nor in the ci, and
None of the ci is Read, Show,
@@ -3662,13 +3665,8 @@ where
Then, for each ci, the derived instance
declaration is:
- instance ci (t vk+1...v) => ci (T v1...vp)
+ instance ci t => ci (T v1...vk)
-where p is chosen so that T v1...vp is of the
-right kind for the last parameter of class Ci.
-
-
-
As an example which does not work, consider
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
+Generalised Algebraic Data Types (GADTs)
-Generalised Algebraic Data Types (GADTs) generalise ordinary algebraic data types by allowing you
+Generalised Algebraic Data Types generalise ordinary algebraic data types by allowing you
to give the type signatures of constructors explicitly. For example:
data Term a where
@@ -3803,7 +3801,12 @@ for these Terms:
eval (If b e1 e2) = if eval b then eval e1 else eval e2
eval (Pair e1 e2) = (eval e1, eval e2)
-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
+on the wiki,
+and Ralf Hinze's
+Fun with phantom types also has a number of examples. Note that papers
+may use different notation to that implemented in GHC.
The rest of this section outlines the extensions to GHC that support GADTs.