| Haskell Hierarchical Libraries (base package) | Source code | Contents | Index

GHC.Exts |

Portability | non-portable (GHC Extensions)
Stability | internal
Maintainer | cvs-ghc@haskell.org

Contents

Representations of some basic types
Primitive operations
Fusion
Linear implicit parameter support
Debugging
Ids with special behaviour

Description
GHC Extensions: this is the Approved Way to get at GHC-specific extensions.
Synopsis

data Int = I# Int#
data Word = W# Word#
data Float = F# Float#
data Double = D# Double#

data Integer

= S# Int#
| J# Int# ByteArray#

data Char = C# Char#
data Ptr a = Ptr Addr#
data FunPtr a = FunPtr Addr#
module GHC.Prim
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 Splittable t where

split :: t -> (t, t)

breakpoint :: a -> a
lazy :: a -> a
inline :: a -> a

Representations of some basic types
data Int

A fixed-precision integer type with at least the range `[-2^29 .. 2^29-1]`. The exact range for a given implementation can be determined by using `minBound` and `maxBound` from the `Bounded` class.
Constructors

I# Int# |

Instances

Bits Int
Bounded Int
Data Int
Enum Int
Eq Int
Integral Int
Ix Int
NFData Int
NFDataIntegral Int
NFDataOrd Int
Num Int
Ord Int
PrintfArg Int
Random Int
Read Int
Real Int
Show Int
Storable Int
Typeable Int
IArray UArray Int
MArray IOUArray Int IO
IArray (IOToDiffArray IOUArray) Int
MArray (STUArray s) Int (ST s)
(Ix ix, Show ix) => Show (DiffUArray ix Int)

data Word

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

W# Word# |

Instances

Bits Word
Bounded Word
Data Word
Enum Word
Eq Word
Integral Word
Ix Word
Num Word
Ord Word
Read Word
Real Word
Show Word
Storable Word
Typeable Word
IArray UArray Word
MArray IOUArray Word IO
IArray (IOToDiffArray IOUArray) Word
MArray (STUArray s) Word (ST s)
(Ix ix, Show ix) => Show (DiffUArray ix Word)

data Float

Single-precision floating point numbers. It is desirable that this type be at least equal in range and precision to the IEEE single-precision type.
Constructors

F# Float# |

Instances

Data Float
Enum Float
Eq Float
Floating Float
Fractional Float
NFData Float
Num Float
Ord Float
PrintfArg Float
Random Float
Read Float
Real Float
RealFloat Float
RealFrac Float
Show Float
Storable Float
Typeable Float
IArray UArray Float
MArray IOUArray Float IO
IArray (IOToDiffArray IOUArray) Float
MArray (STUArray s) Float (ST s)
(Ix ix, Show ix) => Show (DiffUArray ix Float)

data Double

Double-precision floating point numbers. It is desirable that this type be at least equal in range and precision to the IEEE double-precision type.
Constructors

D# Double# |

Instances

Data Double
Enum Double
Eq Double
Floating Double
Fractional Double
NFData Double
Num Double
Ord Double
PrintfArg Double
Random Double
Read Double
Real Double
RealFloat Double
RealFrac Double
Show Double
Storable Double
Typeable Double
IArray UArray Double
MArray IOUArray Double IO
IArray (IOToDiffArray IOUArray) Double
MArray (STUArray s) Double (ST s)
(Ix ix, Show ix) => Show (DiffUArray ix Double)

data Integer

Arbitrary-precision integers.
Constructors

S# Int# |
J# Int# ByteArray# |

Instances

Bits Integer
Data Integer
Enum Integer
Eq Integer
Integral Integer
Ix Integer
NFData Integer
Num Integer
Ord Integer
PrintfArg Integer
Random Integer
Read Integer
Real Integer
Show Integer
Typeable Integer

data Char

The character type `Char` is an enumeration whose values represent Unicode (or equivalently ISO/IEC 10646) characters (see http://www.unicode.org/ for details). This set extends the ISO 8859-1 (Latin-1) character set (the first 256 charachers), which is itself an extension of the ASCII character set (the first 128 characters). A character literal in Haskell has type `Char`.

To convert a `Char` to or from the corresponding `Int` value defined by Unicode, use `toEnum` and `fromEnum` from the `Enum` class respectively (or equivalently `ord` and `chr`).

Constructors

C# Char# |

Instances

Bounded Char
Data Char
Enum Char
Eq Char
IsChar Char
Ix Char
NFData Char
Ord Char
PrintfArg Char
Random Char
Read Char
Show Char
Storable Char
Typeable Char
IArray UArray Char
MArray IOUArray Char IO
IArray (IOToDiffArray IOUArray) Char
MArray (STUArray s) Char (ST s)
(Ix ix, Show ix) => Show (DiffUArray ix Char)

data Ptr a

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 `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
IArray UArray (Ptr a)
MArray IOUArray (Ptr a) IO
Typeable a => Data (Ptr a)
Eq (Ptr a)
Ord (Ptr a)
Show (Ptr a)
Storable (Ptr a)
IArray (IOToDiffArray IOUArray) (Ptr a)
MArray (STUArray s) (Ptr a) (ST s)

data FunPtr a

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`, `Double`, `Float`, `Bool`, `Int8`, `Int16`, `Int32`, `Int64`, `Word8`, `Word16`, `Word32`, `Word64`, ``Ptr` a`, ``FunPtr` a`, ``StablePtr` a` or a renaming of any of these using `newtype`.
- the return type is either a marshallable foreign type or has the form ``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 `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
IArray UArray (FunPtr a)
MArray IOUArray (FunPtr a) IO
Eq (FunPtr a)
Ord (FunPtr a)
Show (FunPtr a)
Storable (FunPtr a)
IArray (IOToDiffArray IOUArray) (FunPtr a)
MArray (STUArray s) (FunPtr a) (ST s)

Primitive operations
module GHC.Prim
shiftL# :: Word# -> Int# -> Word#
Shift the argument left by the specified number of bits (which must be non-negative).
shiftRL# :: Word# -> Int# -> Word#
Shift the argument right by the specified number of bits (which must be non-negative).
iShiftL# :: Int# -> Int# -> Int#
Shift the argument left by the specified number of bits (which must be non-negative).
iShiftRA# :: Int# -> Int# -> Int#
Shift the argument right (signed) by the specified number of bits (which must be non-negative).
iShiftRL# :: Int# -> Int# -> Int#
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]
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]
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.
Linear implicit parameter support
class Splittable t where

Methods

split :: t -> (t, t)

Debugging
breakpoint :: a -> a
Ids with special behaviour
lazy :: a -> a
The `lazy` function restrains strictness analysis a little. The call `(lazy e)` means the same as `e`, but `lazy` has a magical property so far as strictness analysis is concerned: it is lazy in its first argument, even though its semantics is strict. After strictness analysis has run, calls to `lazy` are inlined to be the identity function.

This behaviour is occasionally useful when controlling evaluation order. Notably, `lazy` is used in the library definition of `Control.Parallel.par`:

    par :: a -> b -> b

    par x y = case (par# x) of _ -> lazy y

If `lazy` were not lazy, `par` would look strict in `y` which would defeat the whole purpose of `par`.

Like `seq`, the argument of `lazy` can have an unboxed type.

inline :: a -> a
The call `(inline f)` arranges that f is inlined, regardless of its size. More precisely, the call `(inline f)` rewrites to the right-hand side of `f`'s definition. This allows the programmer to control inlining from a particular call site rather than the definition site of the function (c.f. `INLINE` pragmas in User's Guide, Section 7.10.3, "INLINE and NOINLINE pragmas").

This inlining occurs regardless of the argument to the call or the size of `f`'s definition; it is unconditional. The main caveat is that `f`'s definition must be visible to the compiler. That is, `f` must be `let`-bound in the current scope. If no inlining takes place, the `inline` function expands to the identity function in Phase zero; so its use imposes no overhead.

If the function is defined in another module, GHC only exposes its inlining in the interface file if the function is sufficiently small that it might be inlined by the automatic mechanism. There is currently no way to tell GHC to expose arbitrarily-large functions in the interface file. (This shortcoming is something that could be fixed, with some kind of pragma.)

Produced by Haddock version 0.8