X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fglasgow_exts.xml;h=b46bf30fc21e1ba7200b8eaf7e3ebdee1bc2bcfe;hb=843a94574e7f25fc6156dd3786a9bd961c3f861d;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..b46bf30 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)
@@ -3640,16 +3658,19 @@ 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 +3683,8 @@ 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
@@ -3711,6 +3727,33 @@ the standard method is used or the one described here.)
+
+Stand-alone deriving declarations
+
+
+GHC now allows stand-alone deriving declarations:
+
+
+
+ data Foo = Bar Int | Baz String
+
+ deriving Eq for Foo
+
+
+Deriving instances of multi-parameter type classes for newtypes is
+also allowed:
+
+
+ newtype Foo a = MkFoo (State Int a)
+
+ deriving (MonadState Int) for Foo
+
+
+
+
+
+
+
Generalised typing of mutually recursive bindings
@@ -3780,9 +3823,9 @@ 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 +3846,12 @@ 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.