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GHC.Exts

Portability | non-portable (GHC Extensions)
Stability | internal
Maintainer | cvs-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

Int (I#)
data Word = W# Word#
Float (F#)
Double (D#)
Char (C#)
data Ptr a = Ptr Addr#
data FunPtr a = FunPtr Addr#
maxTupleSize :: Int
module GHC.Prim
shiftL# :: Word# -> Int# -> Word#
shiftRL# :: Word# -> Int# -> Word#
iShiftL# :: Int# -> Int# -> Int#
iShiftRA# :: Int# -> Int# -> Int#
iShiftRL# :: Int# -> Int# -> Int#
uncheckedShiftL64#
uncheckedShiftRL64#
uncheckedIShiftL64#
uncheckedIShiftRA64#
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
Int (I#)

data Word | Source

A `Word` is an unsigned integral type, with the same size as `Int`.
Constructors

W# Word# |

Instances

Bounded Word
Enum Word
Eq Word
Integral Word
Data Word
Num Word
Ord Word
Read Word
Real Word
Show Word
Ix Word
Typeable Word
Bits Word
Storable Word
PrintfArg Word

Float (F#)
Double (D#)
Char (C#)

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# |

Instances

Typeable1 Ptr
Eq (Ptr a)
Typeable a => Data (Ptr a)
Ord (Ptr a)
Show (Ptr a)
Storable (Ptr a)

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# |

Instances

Typeable1 FunPtr
Eq (FunPtr a)
Ord (FunPtr a)
Show (FunPtr a)
Storable (FunPtr a)

The maximum tuple size

maxTupleSize :: Int | Source

Primitive operations
module GHC.Prim

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).
uncheckedShiftL64#
uncheckedShiftRL64#
uncheckedIShiftL64#
uncheckedIShiftRA64#
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 where | Source

Class for string-like datastructures; used by the overloaded string extension (-foverloaded-strings in GHC).
Methods

fromString :: String -> a | Source

Instances

IsString ([] Char)

Debugging

breakpoint :: a -> a | Source

breakpointCond :: Bool -> a -> a | Source

Ids with special behaviour

lazy :: a -> a | Source

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 -> a | Source

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 |

Instances

Eq a => Eq (Down a)
Ord a => Ord (Down a)

groupWith :: Ord b => (a -> b) -> [a] -> [[a]] | Source

The `groupWith` function uses the user supplied function which projects an element out of every list element in order to to first sort the input list and then to form groups by equality on these projected elements

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] -> a | Source

`the` ensures that all the elements of the list are identical and then returns that unique element
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