base-4.0.0.0: Basic librariesSource codeContentsIndex
GHC.Exts
Portabilitynon-portable (GHC Extensions)
Stabilityinternal
Maintainercvs-ghc@haskell.org
Contents
Representations of some basic types
The maximum tuple size
Primitive operations
Fusion
Overloaded string literals
Debugging
Ids with special behaviour
Transform comprehensions
Description
GHC Extensions: this is the Approved Way to get at GHC-specific extensions.
Synopsis
data Word = W# Word#
data Ptr a = Ptr Addr#
data FunPtr a = FunPtr Addr#
maxTupleSize :: Int
shiftL# :: Word# -> Int# -> Word#
shiftRL# :: Word# -> Int# -> Word#
iShiftL# :: Int# -> Int# -> Int#
iShiftRA# :: Int# -> Int# -> Int#
iShiftRL# :: Int# -> Int# -> Int#
build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
augment :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a] -> [a]
class IsString a where
fromString :: String -> a
breakpoint :: a -> a
breakpointCond :: Bool -> a -> a
lazy :: a -> a
inline :: a -> a
newtype Down a = Down a
groupWith :: Ord b => (a -> b) -> [a] -> [[a]]
sortWith :: Ord b => (a -> b) -> [a] -> [a]
the :: Eq a => [a] -> a
Representations of some basic types
data Word Source
A Word is an unsigned integral type, with the same size as Int.
Constructors
W# Word#
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data Ptr a Source

A value of type Ptr a represents a pointer to an object, or an array of objects, which may be marshalled to or from Haskell values of type a.

The type a will often be an instance of class Foreign.Storable.Storable which provides the marshalling operations. However this is not essential, and you can provide your own operations to access the pointer. For example you might write small foreign functions to get or set the fields of a C struct.

Constructors
Ptr Addr#
show/hide Instances
data FunPtr a Source

A value of type FunPtr a is a pointer to a function callable from foreign code. The type a will normally be a foreign type, a function type with zero or more arguments where

  • the argument types are marshallable foreign types, i.e. Char, Int, Prelude.Double, Prelude.Float, Bool, Data.Int.Int8, Data.Int.Int16, Data.Int.Int32, Data.Int.Int64, Data.Word.Word8, Data.Word.Word16, Data.Word.Word32, Data.Word.Word64, Ptr a, FunPtr a, Foreign.StablePtr.StablePtr a or a renaming of any of these using newtype.
  • the return type is either a marshallable foreign type or has the form Prelude.IO t where t is a marshallable foreign type or ().

A value of type FunPtr a may be a pointer to a foreign function, either returned by another foreign function or imported with a a static address import like 

 foreign import ccall "stdlib.h &free"
   p_free :: FunPtr (Ptr a -> IO ())

or a pointer to a Haskell function created using a wrapper stub declared to produce a FunPtr of the correct type. For example: 

 type Compare = Int -> Int -> Bool
 foreign import ccall "wrapper"
   mkCompare :: Compare -> IO (FunPtr Compare)

Calls to wrapper stubs like mkCompare allocate storage, which should be released with Foreign.Ptr.freeHaskellFunPtr when no longer required.

To convert FunPtr values to corresponding Haskell functions, one can define a dynamic stub for the specific foreign type, e.g. 

 type IntFunction = CInt -> IO ()
 foreign import ccall "dynamic" 
   mkFun :: FunPtr IntFunction -> IntFunction
Constructors
FunPtr Addr#
show/hide Instances
The maximum tuple size
maxTupleSize :: IntSource
Primitive operations
shiftL# :: Word# -> Int# -> Word#Source
Shift the argument left by the specified number of bits (which must be non-negative).
shiftRL# :: Word# -> Int# -> Word#Source
Shift the argument right by the specified number of bits (which must be non-negative).
iShiftL# :: Int# -> Int# -> Int#Source
Shift the argument left by the specified number of bits (which must be non-negative).
iShiftRA# :: Int# -> Int# -> Int#Source
Shift the argument right (signed) by the specified number of bits (which must be non-negative).
iShiftRL# :: Int# -> Int# -> Int#Source
Shift the argument right (unsigned) by the specified number of bits (which must be non-negative).
Fusion
build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]Source

A list producer that can be fused with foldr. This function is merely 

    build g = g (:) []

but GHC's simplifier will transform an expression of the form foldr k z (build g), which may arise after inlining, to g k z, which avoids producing an intermediate list.

augment :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a] -> [a]Source

A list producer that can be fused with foldr. This function is merely 

    augment g xs = g (:) xs

but GHC's simplifier will transform an expression of the form foldr k z (augment g xs), which may arise after inlining, to g k (foldr k z xs), which avoids producing an intermediate list.

Overloaded string literals
class IsString a whereSource
Class for string-like datastructures; used by the overloaded string extension (-foverloaded-strings in GHC).
Methods
fromString :: String -> aSource
show/hide Instances
Debugging
breakpoint :: a -> aSource
breakpointCond :: Bool -> a -> aSource
Ids with special behaviour
lazy :: a -> aSource
The call '(lazy e)' means the same as e, but lazy has a magical strictness property: it is lazy in its first argument, even though its semantics is strict.
inline :: a -> aSource
The call '(inline f)' reduces to f, but inline has a BuiltInRule that tries to inline f (if it has an unfolding) unconditionally The NOINLINE pragma arranges that inline only gets inlined (and hence eliminated) late in compilation, after the rule has had a god chance to fire.
Transform comprehensions
newtype Down a Source
The Down type allows you to reverse sort order conveniently. A value of type Down a contains a value of type a (represented as Down a). If a has an Ord instance associated with it then comparing two values thus wrapped will give you the opposite of their normal sort order. This is particularly useful when sorting in generalised list comprehensions, as in: then sortWith by Down x
Constructors
Down a
show/hide Instances
Eq a => Eq (Down a)
Ord a => Ord (Down a)
groupWith :: Ord b => (a -> b) -> [a] -> [[a]]Source
sortWith :: Ord b => (a -> b) -> [a] -> [a]Source
The sortWith function sorts a list of elements using the user supplied function to project something out of each element
the :: Eq a => [a] -> aSource
the ensures that all the elements of the list are identical and then returns that unique element
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