X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=docs%2Fusers_guide%2Fglasgow_exts.xml;h=f8ad5c1b0ac8a79f9ee96c6a4227e6abafcaa6e7;hp=afb4447e245d5c4d9f917b555e2dc708ace72bab;hb=9da4639011348fb6c318e3cba4b08622f811d9c4;hpb=f078c03636b809f4a8bc1caa1deecd58ff5491fe
diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index afb4447..f8ad5c1 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -3301,6 +3301,7 @@ changing the program.
A lexically scoped type variable can be bound by:
A declaration type signature ()
+An expression type signature ()
A pattern type signature ()
Class and instance declarations ()
@@ -3352,6 +3353,23 @@ quantification rules.
+
+Expression type signatures
+
+An expression type signature that has explicit
+quantification (using forall) brings into scope the
+explicitly-quantified
+type variables, in the annotated expression. For example:
+
+ f = runST ( (op >>= \(x :: STRef s Int) -> g x) :: forall s. ST s Bool )
+
+Here, the type signature forall a. ST s Bool brings the
+type variable s into scope, in the annotated expression
+(op >>= \(x :: STRef s Int) -> g x).
+
+
+
+
Pattern type signatures
@@ -3360,7 +3378,7 @@ 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)
@@ -3778,9 +3796,9 @@ 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
@@ -3801,7 +3819,12 @@ 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.