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diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 2c3bea0..a431dd6 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -1232,7 +1232,7 @@ it is not clear which of the two types is intended.
Haskell 98 regards all four as ambiguous, but with the
- flag, GHC will accept
+ flag, GHC will accept
the former two. The rules are precisely the same as those for instance
declarations in Haskell 98, where the method names on the left-hand side
of the method bindings in an instance declaration refer unambiguously
@@ -2002,10 +2002,10 @@ of the data constructor. For GADTs, the field may mention only types
that appear as a simple type-variable argument in the constructor's result
type. For example:
-data T a where { T1 { f1::a, f2::(a,b) } :: T a } -- b is existential
-upd1 t x = t { f1=x } -- OK: upd1 :: T a -> b -> T b
-upd2 t x = t { f2=x } -- BAD (f2's type mentions b, which is
- existentially quantified)
+data T a b where { T1 { f1::a, f2::b, f3::(b,c) } :: T a b } -- c is existential
+upd1 t x = t { f1=x } -- OK: upd1 :: T a b -> a' -> T a' b
+upd2 t x = t { f3=x } -- BAD (f3's type mentions c, which is
+ -- existentially quantified)
data G a b where { G1 { g1::a, g2::c } :: G a [c] }
upd3 g x = g { g1=x } -- OK: upd3 :: G a b -> c -> G c b
@@ -3860,37 +3860,71 @@ data instance GMap (Either a b) v = GMapEither (GMap a v) (GMap b v)
can be any number.
- Data and newtype instance declarations are only legit when an
- appropriate family declaration is in scope - just like class instances
- require the class declaration to be visible. Moreover, each instance
+ Data and newtype instance declarations are only permitted when an
+ appropriate family declaration is in scope - just as a class instance declaratoin
+ requires the class declaration to be visible. Moreover, each instance
declaration has to conform to the kind determined by its family
declaration. This implies that the number of parameters of an instance
declaration matches the arity determined by the kind of the family.
- Although, all data families are declared with
- the data keyword, instances can be
- either data or newtypes, or a mix
- of both.
+ A data family instance declaration can use the full exprssiveness of
+ ordinary data or newtype declarations:
+
+ Although, a data family is introduced with
+ the keyword "data", a data family instance can
+ use either data or newtype. For example:
+
+data family T a
+data instance T Int = T1 Int | T2 Bool
+newtype instance T Char = TC Bool
+
+
+ A data instance can use GADT syntax for the data constructors,
+ and indeed can define a GADT. For example:
+
+data family G a b
+data instance G [a] b where
+ G1 :: c -> G [Int] b
+ G2 :: G [a] Bool
+
+
+ You can use a deriving clause on a
+ data instance or newtype instance
+ declaration.
+
+
+
+
+
Even if type families are defined as toplevel declarations, functions
- that perform different computations for different family instances still
+ that perform different computations for different family instances may still
need to be defined as methods of type classes. In particular, the
following is not possible:
data family T a
data instance T Int = A
data instance T Char = B
-nonsence :: T a -> Int
-nonsence A = 1 -- WRONG: These two equations together...
-nonsence B = 2 -- ...will produce a type error.
+foo :: T a -> Int
+foo A = 1 -- WRONG: These two equations together...
+foo B = 2 -- ...will produce a type error.
+
+Instead, you would have to write foo as a class operation, thus:
+
+class C a where
+ foo :: T a -> Int
+instance Foo Int where
+ foo A = 1
+instance Foo Char where
+ foo B = 2
- Given the functionality provided by GADTs (Generalised Algebraic Data
+ (Given the functionality provided by GADTs (Generalised Algebraic Data
Types), it might seem as if a definition, such as the above, should be
feasible. However, type families are - in contrast to GADTs - are
open; i.e., new instances can always be added,
possibly in other
modules. Supporting pattern matching across different data instances
- would require a form of extensible case construct.
+ would require a form of extensible case construct.)
@@ -5322,9 +5356,13 @@ f xs = ys ++ ys
ys :: [a]
ys = reverse xs
-The type signature for f brings the type variable a into scope; it scopes over
-the entire definition of f.
-In particular, it is in scope at the type signature for ys.
+The type signature for f brings the type variable a into scope,
+because of the explicit forall ().
+The type variables bound by a forall scope over
+the entire definition of the accompanying value declaration.
+In this example, the type variable a scopes over the whole
+definition of f, including over
+the type signature for ys.
In Haskell 98 it is not possible to declare
a type for ys; a major benefit of scoped type variables is that
it becomes possible to do so.
@@ -5990,7 +6028,7 @@ main = do { print $ eval [$expr|1 + 2|]
module Expr where
import qualified Language.Haskell.TH as TH
-import Language.Haskell.TH.Quasi
+import Language.Haskell.TH.Quote
data Expr = IntExpr Integer
| AntiIntExpr String
@@ -7135,6 +7173,83 @@ happen.
+
+ ANN pragmas
+
+ GHC offers the ability to annotate various code constructs with additional
+ data by using three pragmas. This data can then be inspected at a later date by
+ using GHC-as-a-library.
+
+
+ Annotating values
+
+ ANN
+
+ Any expression that has both Typeable and Data instances may be attached to a top-level value
+ binding using an ANN pragma. In particular, this means you can use ANN
+ to annotate data constructors (e.g. Just) as well as normal values (e.g. take).
+ By way of example, to annotate the function foo with the annotation Just "Hello"
+ you would do this:
+
+
+{-# ANN foo (Just "Hello") #-}
+foo = ...
+
+
+
+ A number of restrictions apply to use of annotations:
+
+ The binder being annotated must be at the top level (i.e. no nested binders)
+ The binder being annotated must be declared in the current module
+ The expression you are annotating with must have a type with Typeable and Data instances
+ The Template Haskell staging restrictions apply to the
+ expression being annotated with, so for example you cannot run a function from the module being compiled.
+
+ To be precise, the annotation {-# ANN x e #-} is well staged if and only if $(e) would be
+ (disregarding the usual type restrictions of the splice syntax, and the usual restriction on splicing inside a splice - $([|1|]) is fine as an annotation, albeit redundant).
+
+
+ If you feel strongly that any of these restrictions are too onerous,
+ please give the GHC team a shout.
+
+
+ However, apart from these restrictions, many things are allowed, including expressions which not fully evaluated!
+ Annotation expressions will be evaluated by the compiler just like Template Haskell splices are. So, this annotation is fine:
+
+
+{-# ANN f SillyAnnotation { foo = (id 10) + $([| 20 |]), bar = 'f } #-}
+f = ...
+
+
+
+
+ Annotating types
+
+ ANN type
+ ANN
+
+ You can annotate types with the ANN pragma by using the type keyword. For example:
+
+
+{-# ANN type Foo (Just "A `Maybe String' annotation") #-}
+data Foo = ...
+
+
+
+
+ Annotating modules
+
+ ANN module
+ ANN
+
+ You can annotate modules with the ANN pragma by using the module keyword. For example:
+
+
+{-# ANN module (Just "A `Maybe String' annotation") #-}
+
+
+
+
LINE pragma