GHC.Exts

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

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 Prelude.minBound and Prelude.maxBound from the Prelude.Bounded class.

Constructors

I# Int#

Instances

Bounded Int

Enum Int

Eq Int

Integral Int

Data Int

Num Int

Ord Int

Read Int

Real Int

Show Int

Ix Int

Typeable Int

Generic Int

Bits Int

Storable Int

PrintfArg Int

data Word

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

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

Enum Float

Eq Float

Floating Float

Fractional Float

Data Float

Num Float

Ord Float

Read Float

Real Float

RealFloat Float

RealFrac Float

Show Float

Typeable Float

Generic Float

Storable Float

PrintfArg 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

Enum Double

Eq Double

Floating Double

Fractional Double

Data Double

Num Double

Ord Double

Read Double

Real Double

RealFloat Double

RealFrac Double

Show Double

Typeable Double

Generic Double

Storable Double

PrintfArg Double

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 Prelude.toEnum and Prelude.fromEnum from the Prelude.Enum class respectively (or equivalently ord and chr).

Constructors

C# Char#

Instances

Bounded Char

Enum Char

Eq Char

Data Char

Ord Char

Read Char

Show Char

Ix Char

Typeable Char

Generic Char

Storable Char

IsChar Char

PrintfArg Char

IsString [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 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

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, 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 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

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).

uncheckedShiftL64# :: Word# -> Int# -> Word#

uncheckedShiftRL64# :: Word# -> Int# -> Word#

uncheckedIShiftL64# :: Int# -> Int# -> Int#

uncheckedIShiftRA64# :: Int# -> Int# -> Int#

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.

Overloaded string literals

class IsString a where

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

Methods

fromString :: String -> a

Instances

IsString [Char]

Debugging

breakpoint :: a -> a

breakpointCond :: Bool -> a -> a

Ids with special behaviour

lazy :: a -> a

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

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 good chance to fire.

Transform comprehensions

newtype Down a

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]]

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]

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

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

Event logging

traceEvent :: String -> IO ()

SpecConstr annotations

data SpecConstrAnnotation

Constructors

NoSpecConstr

ForceSpecConstr

Instances

Eq SpecConstrAnnotation

Data SpecConstrAnnotation

Typeable SpecConstrAnnotation