GHC.Exts

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

data Word

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

Constructors

W# Word#

Instances

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 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 Integer

Arbitrary-precision integers.

Constructors

S# Int#
J# Int# ByteArray#

Instances

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

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

Typeable a => Data (Ptr a)

Eq (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, 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

Eq (FunPtr a)

Ord (FunPtr a)

Show (FunPtr a)

Storable (FunPtr a)

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).

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 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

Source

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.)

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