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diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index e8e721c..ea31390 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -109,7 +109,7 @@ While you really can use this stuff to write fast code,
All these primitive data types and operations are exported by the
library GHC.Prim, for which there is
-detailed online documentation.
+detailed online documentation.
(This documentation is generated from the file compiler/prelude/primops.txt.pp.)
@@ -840,6 +840,19 @@ y) will not be coalesced.
+
+
+
+n+k patterns
+
+
+
+n+k pattern support is enabled by default. To disable
+it, you can use the flag.
+
+
+
+
@@ -874,7 +887,7 @@ As you can guess justOnes will evaluate to Just [1,1
-The Control.Monad.Fix library introduces the MonadFix class. It's definition is:
+The Control.Monad.Fix library introduces the MonadFix class. Its definition is:
class Monad m => MonadFix m where
@@ -1001,7 +1014,7 @@ This name is not supported by GHC.
Generalised list comprehensions are a further enhancement to the
- list comprehension syntatic sugar to allow operations such as sorting
+ list comprehension syntactic sugar to allow operations such as sorting
and grouping which are familiar from SQL. They are fully described in the
paper
Comprehensive comprehensions: comprehensions with "order by" and "group by",
@@ -1042,7 +1055,7 @@ then f
This statement requires that f have the type
- forall a. [a] -> [a]. You can see an example of it's use in the
+ forall a. [a] -> [a]. You can see an example of its use in the
motivating example, as this form is used to apply take 5.
@@ -1269,6 +1282,44 @@ definitions; you must define such a function in prefix form.
+
+Tuple sections
+
+
+ The flag enables Python-style partially applied
+ tuple constructors. For example, the following program
+
+ (, True)
+
+ is considered to be an alternative notation for the more unwieldy alternative
+
+ \x -> (x, True)
+
+You can omit any combination of arguments to the tuple, as in the following
+
+ (, "I", , , "Love", , 1337)
+
+which translates to
+
+ \a b c d -> (a, "I", b, c, "Love", d, 1337)
+
+
+
+
+ If you have unboxed tuples enabled, tuple sections
+ will also be available for them, like so
+
+ (# , True #)
+
+Because there is no unboxed unit tuple, the following expression
+
+ (# #)
+
+continues to stand for the unboxed singleton tuple data constructor.
+
+
+
+
Record field disambiguation
@@ -2364,14 +2415,34 @@ In this example we give a single signature for T1 and
The type signature of
each constructor is independent, and is implicitly universally quantified as usual.
-Different constructors may have different universally-quantified type variables
-and different type-class constraints.
-For example, this is fine:
+In particular, the type variable(s) in the "data T a where" header
+have no scope, and different constructors may have different universally-quantified type variables:
+
+ data T a where -- The 'a' has no scope
+ T1,T2 :: b -> T b -- Means forall b. b -> T b
+ T3 :: T a -- Means forall a. T a
+
+
+
+
+A constructor signature may mention type class constraints, which can differ for
+different constructors. For example, this is fine:
data T a where
- T1 :: Eq b => b -> T b
+ T1 :: Eq b => b -> b -> T b
T2 :: (Show c, Ix c) => c -> [c] -> T c
+When patten matching, these constraints are made available to discharge constraints
+in the body of the match. For example:
+
+ f :: T a -> String
+ f (T1 x y) | x==y = "yes"
+ | otherwise = "no"
+ f (T2 a b) = show a
+
+Note that f is not overloaded; the Eq constraint arising
+from the use of == is discharged by the pattern match on T1
+and similarly the Show constraint arising from the use of show.
@@ -2383,12 +2454,12 @@ have no scope. Indeed, one can write a kind signature instead:
or even a mixture of the two:
- data Foo a :: (* -> *) -> * where ...
+ data Bar a :: (* -> *) -> * where ...
The type variables (if given) may be explicitly kinded, so we could also write the header for Foo
like this:
- data Foo a (b :: * -> *) where ...
+ data Bar a (b :: * -> *) where ...
@@ -2419,27 +2490,48 @@ declaration. For example, these two declarations are equivalent
+The type signature may have quantified type variables that do not appear
+in the result type:
+
+ data Foo where
+ MkFoo :: a -> (a->Bool) -> Foo
+ Nil :: Foo
+
+Here the type variable a does not appear in the result type
+of either constructor.
+Although it is universally quantified in the type of the constructor, such
+a type variable is often called "existential".
+Indeed, the above declaration declares precisely the same type as
+the data Foo in .
+
+The type may contain a class context too, of course:
+
+ data Showable where
+ MkShowable :: Show a => a -> Showable
+
+
+
+
You can use record syntax on a GADT-style data type declaration:
data Person where
- Adult { name :: String, children :: [Person] } :: Person
- Child { name :: String } :: Person
+ Adult :: { name :: String, children :: [Person] } -> Person
+ Child :: Show a => { name :: !String, funny :: a } -> Person
As usual, for every constructor that has a field f, the type of
field f must be the same (modulo alpha conversion).
-
-
-At the moment, record updates are not yet possible with GADT-style declarations,
-so support is limited to record construction, selection and pattern matching.
-For example
-
- aPerson = Adult { name = "Fred", children = [] }
+The Child constructor above shows that the signature
+may have a context, existentially-quantified variables, and strictness annotations,
+just as in the non-record case. (NB: the "type" that follows the double-colon
+is not really a type, because of the record syntax and strictness annotations.
+A "type" of this form can appear only in a constructor signature.)
+
- shortName :: Person -> Bool
- hasChildren (Adult { children = kids }) = not (null kids)
- hasChildren (Child {}) = False
-
+
+Record updates are allowed with GADT-style declarations,
+only fields that have the following property: the type of the field
+mentions no existential type variables.
@@ -2538,7 +2630,7 @@ constructor).
-It's is permitted to declare an ordinary algebraic data type using GADT-style syntax.
+It is permitted to declare an ordinary algebraic data type using GADT-style syntax.
What makes a GADT into a GADT is not the syntax, but rather the presence of data constructors
whose result type is not just T a b.
@@ -2650,16 +2742,22 @@ GHC now allows stand-alone deriving declarations, enabled by
The syntax is identical to that of an ordinary instance declaration apart from (a) the keyword
deriving, and (b) the absence of the where part.
-You must supply a context (in the example the context is (Eq a)),
+Note the following points:
+
+
+You must supply an explicit context (in the example the context is (Eq a)),
exactly as you would in an ordinary instance declaration.
-(In contrast the context is inferred in a deriving clause
-attached to a data type declaration.)
+(In contrast, in a deriving clause
+attached to a data type declaration, the context is inferred.)
+
+
A deriving instance declaration
must obey the same rules concerning form and termination as ordinary instance declarations,
controlled by the same flags; see .
-
-
+
+
+
Unlike a deriving
declaration attached to a data declaration, the instance can be more specific
than the data type (assuming you also use
@@ -2673,8 +2771,31 @@ for example
This will generate a derived instance for (Foo [a]) and (Foo (Maybe a)),
but other types such as (Foo (Int,Bool)) will not be an instance of Eq.
+
+
+
+Unlike a deriving
+declaration attached to a data declaration,
+GHC does not restrict the form of the data type. Instead, GHC simply generates the appropriate
+boilerplate code for the specified class, and typechecks it. If there is a type error, it is
+your problem. (GHC will show you the offending code if it has a type error.)
+The merit of this is that you can derive instances for GADTs and other exotic
+data types, providing only that the boilerplate code does indeed typecheck. For example:
+
+ data T a where
+ T1 :: T Int
+ T2 :: T Bool
+
+ deriving instance Show (T a)
+
+In this example, you cannot say ... deriving( Show ) on the
+data type declaration for T,
+because T is a GADT, but you can generate
+the instance declaration using stand-alone deriving.
+
+The stand-alone syntax is generalised for newtypes in exactly the same
way that ordinary deriving clauses are generalised ().
For example:
@@ -2685,7 +2806,8 @@ For example:
GHC always treats the last parameter of the instance
(Foo in this example) as the type whose instance is being derived.
-
+
+
@@ -4257,7 +4379,7 @@ type family Elem c
example, consider the following declaration:
type family F a b :: * -> * -- F's arity is 2,
- -- although it's overall kind is * -> * -> * -> *
+ -- although its overall kind is * -> * -> * -> *
Given this declaration the following are examples of well-formed and
malformed types: