| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
CorePrelude
Contents
- ($) :: (a -> b) -> a -> b
- ($!) :: (a -> b) -> a -> b
- (&&) :: Bool -> Bool -> Bool
- (||) :: Bool -> Bool -> Bool
- (.) :: Category k cat => forall b c a. cat b c -> cat a b -> cat a c
- not :: Bool -> Bool
- otherwise :: Bool
- fst :: (a, b) -> a
- snd :: (a, b) -> b
- id :: Category k cat => forall a. cat a a
- maybe :: b -> (a -> b) -> Maybe a -> b
- either :: (a -> c) -> (b -> c) -> Either a b -> c
- flip :: (a -> b -> c) -> b -> a -> c
- const :: a -> b -> a
- error :: HasCallStack => [Char] -> a
- putStr :: MonadIO m => Text -> m ()
- putStrLn :: MonadIO m => Text -> m ()
- print :: (MonadIO m, Show a) => a -> m ()
- getArgs :: MonadIO m => m [Text]
- terror :: HasCallStack => Text -> a
- odd :: Integral a => a -> Bool
- even :: Integral a => a -> Bool
- uncurry :: (a -> b -> c) -> (a, b) -> c
- curry :: ((a, b) -> c) -> a -> b -> c
- swap :: (a, b) -> (b, a)
- until :: (a -> Bool) -> (a -> a) -> a -> a
- asTypeOf :: a -> a -> a
- undefined :: HasCallStack => a
- seq :: a -> b -> b
- class Eq a => Ord a where
- class Eq a where
- class Bounded a where
- class Enum a where
- class Show a
- class Read a
- class Functor f where
- class Applicative m => Monad m where
- (=<<) :: Monad m => (a -> m b) -> m a -> m b
- class IsString a where
- class Num a where
- class (Num a, Ord a) => Real a where
- class (Real a, Enum a) => Integral a where
- class Num a => Fractional a where
- class Fractional a => Floating a where
- class (Real a, Fractional a) => RealFrac a where
- class (RealFrac a, Floating a) => RealFloat a where
- data Maybe a :: * -> *
- data Ordering :: *
- data Bool :: *
- data Char :: *
- data IO a :: * -> *
- data Either a b :: * -> * -> *
- data ByteString :: *
- type LByteString = ByteString
- data Text :: *
- type LText = Text
- data Map k a :: * -> * -> *
- data HashMap k v :: * -> * -> *
- data IntMap a :: * -> *
- data Set a :: * -> *
- data HashSet a :: * -> *
- data IntSet :: *
- data Seq a :: * -> *
- data Vector a :: * -> *
- type UVector = Vector
- class (Vector Vector a, MVector MVector a) => Unbox a
- type SVector = Vector
- class Storable a
- class Hashable a where
- data Word :: *
- data Word8 :: *
- data Word32 :: *
- data Word64 :: *
- data Int :: *
- data Int32 :: *
- data Int64 :: *
- data Integer :: *
- type Rational = Ratio Integer
- data Float :: *
- data Double :: *
- (^) :: (Num a, Integral b) => a -> b -> a
- (^^) :: (Fractional a, Integral b) => a -> b -> a
- subtract :: Num a => a -> a -> a
- fromIntegral :: (Integral a, Num b) => a -> b
- realToFrac :: (Real a, Fractional b) => a -> b
- class Monoid a where
- (<>) :: Monoid m => m -> m -> m
- class Foldable t
- asum :: (Foldable t, Alternative f) => t (f a) -> f a
- class (Functor t, Foldable t) => Traversable t
- first :: Arrow a => forall b c d. a b c -> a (b, d) (c, d)
- second :: Arrow a => forall b c d. a b c -> a (d, b) (d, c)
- (***) :: Arrow a => forall b c b' c'. a b c -> a b' c' -> a (b, b') (c, c')
- (&&&) :: Arrow a => forall b c c'. a b c -> a b c' -> a b (c, c')
- bool :: a -> a -> Bool -> a
- mapMaybe :: (a -> Maybe b) -> [a] -> [b]
- catMaybes :: [Maybe a] -> [a]
- fromMaybe :: a -> Maybe a -> a
- isJust :: Maybe a -> Bool
- isNothing :: Maybe a -> Bool
- listToMaybe :: [a] -> Maybe a
- maybeToList :: Maybe a -> [a]
- partitionEithers :: [Either a b] -> ([a], [b])
- lefts :: [Either a b] -> [a]
- rights :: [Either a b] -> [b]
- on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
- comparing :: Ord a => (b -> a) -> b -> b -> Ordering
- equating :: Eq a => (b -> a) -> b -> b -> Bool
- newtype Down a :: * -> * = Down a
- class Functor f => Applicative f where
- (<$>) :: Functor f => (a -> b) -> f a -> f b
- (<|>) :: Alternative f => forall a. f a -> f a -> f a
- (>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c
- lift :: MonadTrans t => forall m a. Monad m => m a -> t m a
- class Monad m => MonadIO m where
- liftIO :: MonadIO m => forall a. IO a -> m a
- class (Typeable * e, Show e) => Exception e where
- class Typeable k a
- data SomeException :: *
- data IOException :: *
- module System.IO.Error
- type FilePath = String
- (</>) :: FilePath -> FilePath -> FilePath
- (<.>) :: FilePath -> String -> FilePath
- type String = [Char]
- hash :: Hashable a => a -> Int
- hashWithSalt :: Hashable a => Int -> a -> Int
Standard
Operators
($) :: (a -> b) -> a -> b infixr 0 #
Application operator. This operator is redundant, since ordinary
application (f x) means the same as (f . However, $ x)$ has
low, right-associative binding precedence, so it sometimes allows
parentheses to be omitted; for example:
f $ g $ h x = f (g (h x))
It is also useful in higher-order situations, such as map ($ 0) xszipWith ($) fs xs
($!) :: (a -> b) -> a -> b infixr 0 #
Strict (call-by-value) application operator. It takes a function and an argument, evaluates the argument to weak head normal form (WHNF), then calls the function with that value.
Functions
maybe :: b -> (a -> b) -> Maybe a -> b #
The maybe function takes a default value, a function, and a Maybe
value. If the Maybe value is Nothing, the function returns the
default value. Otherwise, it applies the function to the value inside
the Just and returns the result.
Examples
Basic usage:
>>>maybe False odd (Just 3)True
>>>maybe False odd NothingFalse
Read an integer from a string using readMaybe. If we succeed,
return twice the integer; that is, apply (*2) to it. If instead
we fail to parse an integer, return 0 by default:
>>>import Text.Read ( readMaybe )>>>maybe 0 (*2) (readMaybe "5")10>>>maybe 0 (*2) (readMaybe "")0
Apply show to a Maybe Int. If we have Just n, we want to show
the underlying Int n. But if we have Nothing, we return the
empty string instead of (for example) "Nothing":
>>>maybe "" show (Just 5)"5">>>maybe "" show Nothing""
either :: (a -> c) -> (b -> c) -> Either a b -> c #
Case analysis for the Either type.
If the value is Left aa;
if it is Right bb.
Examples
We create two values of type Either String IntLeft constructor and another using the Right constructor. Then
we apply "either" the length function (if we have a String)
or the "times-two" function (if we have an Int):
>>>let s = Left "foo" :: Either String Int>>>let n = Right 3 :: Either String Int>>>either length (*2) s3>>>either length (*2) n6
flip :: (a -> b -> c) -> b -> a -> c #
flip ff.
const x is a unary function which evaluates to x for all inputs.
For instance,
>>>map (const 42) [0..3][42,42,42,42]
error :: HasCallStack => [Char] -> a #
error stops execution and displays an error message.
terror :: HasCallStack => Text -> a Source #
error applied to Text
Since 0.4.1
uncurry :: (a -> b -> c) -> (a, b) -> c #
uncurry converts a curried function to a function on pairs.
until :: (a -> Bool) -> (a -> a) -> a -> a #
until p ff until p holds.
undefined :: HasCallStack => a #
The value of seq a b is bottom if a is bottom, and
otherwise equal to b. seq is usually introduced to
improve performance by avoiding unneeded laziness.
A note on evaluation order: the expression seq a b does
not guarantee that a will be evaluated before b.
The only guarantee given by seq is that the both a
and b will be evaluated before seq returns a value.
In particular, this means that b may be evaluated before
a. If you need to guarantee a specific order of evaluation,
you must use the function pseq from the "parallel" package.
Type classes
The Ord class is used for totally ordered datatypes.
Instances of Ord can be derived for any user-defined
datatype whose constituent types are in Ord. The declared order
of the constructors in the data declaration determines the ordering
in derived Ord instances. The Ordering datatype allows a single
comparison to determine the precise ordering of two objects.
Minimal complete definition: either compare or <=.
Using compare can be more efficient for complex types.
Methods
compare :: a -> a -> Ordering #
(<) :: a -> a -> Bool infix 4 #
(<=) :: a -> a -> Bool infix 4 #
(>) :: a -> a -> Bool infix 4 #
Instances
| Ord Bool | |
| Ord Char | |
| Ord Double | |
| Ord Float | |
| Ord Int | |
| Ord Int8 | |
| Ord Int16 | |
| Ord Int32 | |
| Ord Int64 | |
| Ord Integer | |
| Ord Ordering | |
| Ord Word | |
| Ord Word8 | |
| Ord Word16 | |
| Ord Word32 | |
| Ord Word64 | |
| Ord TypeRep | |
| Ord () | |
| Ord TyCon | |
| Ord BigNat | |
| Ord Void | |
| Ord Version | |
| Ord AsyncException | |
| Ord ArrayException | |
| Ord ExitCode | |
| Ord BufferMode | |
| Ord Newline | |
| Ord NewlineMode | |
| Ord CChar | |
| Ord CSChar | |
| Ord CUChar | |
| Ord CShort | |
| Ord CUShort | |
| Ord CInt | |
| Ord CUInt | |
| Ord CLong | |
| Ord CULong | |
| Ord CLLong | |
| Ord CULLong | |
| Ord CFloat | |
| Ord CDouble | |
| Ord CPtrdiff | |
| Ord CSize | |
| Ord CWchar | |
| Ord CSigAtomic | |
| Ord CClock | |
| Ord CTime | |
| Ord CUSeconds | |
| Ord CSUSeconds | |
| Ord CIntPtr | |
| Ord CUIntPtr | |
| Ord CIntMax | |
| Ord CUIntMax | |
| Ord All | |
| Ord Any | |
| Ord Fixity | |
| Ord Associativity | |
| Ord SourceUnpackedness | |
| Ord SourceStrictness | |
| Ord DecidedStrictness | |
| Ord ErrorCall | |
| Ord ArithException | |
| Ord SomeNat | |
| Ord SomeSymbol | |
| Ord ByteString | |
| Ord ByteString | |
| Ord IntSet | |
| Ord a => Ord [a] | |
| Ord a => Ord (Maybe a) | |
| Integral a => Ord (Ratio a) | |
| Ord (Ptr a) | |
| Ord (FunPtr a) | |
| Ord (V1 p) | |
| Ord (U1 p) | |
| Ord p => Ord (Par1 p) | |
| Ord (ForeignPtr a) | |
| Ord a => Ord (Identity a) | |
| Ord a => Ord (Min a) | |
| Ord a => Ord (Max a) | |
| Ord a => Ord (First a) | |
| Ord a => Ord (Last a) | |
| Ord m => Ord (WrappedMonoid m) | |
| Ord a => Ord (Option a) | |
| Ord a => Ord (NonEmpty a) | |
| Ord a => Ord (ZipList a) | |
| Ord a => Ord (Dual a) | |
| Ord a => Ord (Sum a) | |
| Ord a => Ord (Product a) | |
| Ord a => Ord (First a) | |
| Ord a => Ord (Last a) | |
| Ord a => Ord (Down a) | |
| Ord a => Ord (IntMap a) | |
| Ord a => Ord (Seq a) | |
| Ord a => Ord (ViewL a) | |
| Ord a => Ord (ViewR a) | |
| Ord a => Ord (Set a) | |
| Ord a => Ord (Hashed a) | |
| Ord a => Ord (Array a) | |
| Ord a => Ord (Vector a) | |
| (Storable a, Ord a) => Ord (Vector a) | |
| (Prim a, Ord a) => Ord (Vector a) | |
| (Ord b, Ord a) => Ord (Either a b) | |
| Ord (f p) => Ord (Rec1 f p) | |
| Ord (URec Char p) | |
| Ord (URec Double p) | |
| Ord (URec Float p) | |
| Ord (URec Int p) | |
| Ord (URec Word p) | |
| Ord (URec (Ptr ()) p) | |
| (Ord a, Ord b) => Ord (a, b) | |
| Ord a => Ord (Arg a b) | |
| Ord (Proxy k s) | |
| (Ord k, Ord v) => Ord (Map k v) | |
| (Ord1 m, Ord a) => Ord (MaybeT m a) | |
| (Ord1 m, Ord a) => Ord (ListT m a) | |
| Ord c => Ord (K1 i c p) | |
| (Ord (g p), Ord (f p)) => Ord ((:+:) f g p) | |
| (Ord (g p), Ord (f p)) => Ord ((:*:) f g p) | |
| Ord (f (g p)) => Ord ((:.:) f g p) | |
| (Ord a, Ord b, Ord c) => Ord (a, b, c) | |
| Ord a => Ord (Const k a b) | |
| Ord (f a) => Ord (Alt k f a) | |
| Ord ((:~:) k a b) | |
| (Ord w, Ord1 m, Ord a) => Ord (WriterT w m a) | |
| (Ord w, Ord1 m, Ord a) => Ord (WriterT w m a) | |
| (Ord1 f, Ord a) => Ord (IdentityT * f a) | |
| (Ord e, Ord1 m, Ord a) => Ord (ExceptT e m a) | |
| (Ord e, Ord1 m, Ord a) => Ord (ErrorT e m a) | |
| Ord (f p) => Ord (M1 i c f p) | |
| (Ord a, Ord b, Ord c, Ord d) => Ord (a, b, c, d) | |
| (Ord1 f, Ord1 g, Ord a) => Ord (Sum * f g a) | |
| (Ord1 f, Ord1 g, Ord a) => Ord (Product * f g a) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e) => Ord (a, b, c, d, e) | |
| (Ord1 f, Ord1 g, Ord a) => Ord (Compose * * f g a) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f) => Ord (a, b, c, d, e, f) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g) => Ord (a, b, c, d, e, f, g) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h) => Ord (a, b, c, d, e, f, g, h) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i) => Ord (a, b, c, d, e, f, g, h, i) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j) => Ord (a, b, c, d, e, f, g, h, i, j) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k) => Ord (a, b, c, d, e, f, g, h, i, j, k) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l) => Ord (a, b, c, d, e, f, g, h, i, j, k, l) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l, Ord m) => Ord (a, b, c, d, e, f, g, h, i, j, k, l, m) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l, Ord m, Ord n) => Ord (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l, Ord m, Ord n, Ord o) => Ord (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | |
The Eq class defines equality (==) and inequality (/=).
All the basic datatypes exported by the Prelude are instances of Eq,
and Eq may be derived for any datatype whose constituents are also
instances of Eq.
Instances
| Eq Bool | |
| Eq Char | |
| Eq Double | |
| Eq Float | |
| Eq Int | |
| Eq Int8 | |
| Eq Int16 | |
| Eq Int32 | |
| Eq Int64 | |
| Eq Integer | |
| Eq Ordering | |
| Eq Word | |
| Eq Word8 | |
| Eq Word16 | |
| Eq Word32 | |
| Eq Word64 | |
| Eq TypeRep | |
| Eq () | |
| Eq TyCon | |
| Eq Handle | |
| Eq BigNat | |
| Eq SpecConstrAnnotation | |
| Eq Void | |
| Eq Version | |
| Eq AsyncException | |
| Eq ArrayException | |
| Eq ExitCode | |
| Eq IOErrorType | |
| Eq BufferMode | |
| Eq Newline | |
| Eq NewlineMode | |
| Eq CChar | |
| Eq CSChar | |
| Eq CUChar | |
| Eq CShort | |
| Eq CUShort | |
| Eq CInt | |
| Eq CUInt | |
| Eq CLong | |
| Eq CULong | |
| Eq CLLong | |
| Eq CULLong | |
| Eq CFloat | |
| Eq CDouble | |
| Eq CPtrdiff | |
| Eq CSize | |
| Eq CWchar | |
| Eq CSigAtomic | |
| Eq CClock | |
| Eq CTime | |
| Eq CUSeconds | |
| Eq CSUSeconds | |
| Eq CIntPtr | |
| Eq CUIntPtr | |
| Eq CIntMax | |
| Eq CUIntMax | |
| Eq All | |
| Eq Any | |
| Eq Fixity | |
| Eq Associativity | |
| Eq SourceUnpackedness | |
| Eq SourceStrictness | |
| Eq DecidedStrictness | |
| Eq MaskingState | |
| Eq IOException | |
| Eq ErrorCall | |
| Eq ArithException | |
| Eq SomeNat | |
| Eq SomeSymbol | |
| Eq SrcLoc | |
| Eq ByteString | |
| Eq ByteString | |
| Eq IntSet | |
| Eq CodePoint | |
| Eq DecoderState | |
| Eq UnicodeException | |
| Eq a => Eq [a] | |
| Eq a => Eq (Maybe a) | |
| Eq a => Eq (Ratio a) | |
| Eq (Ptr a) | |
| Eq (FunPtr a) | |
| Eq (V1 p) | |
| Eq (U1 p) | |
| Eq p => Eq (Par1 p) | |
| Eq (ForeignPtr a) | |
| Eq a => Eq (Identity a) | |
| Eq a => Eq (Min a) | |
| Eq a => Eq (Max a) | |
| Eq a => Eq (First a) | |
| Eq a => Eq (Last a) | |
| Eq m => Eq (WrappedMonoid m) | |
| Eq a => Eq (Option a) | |
| Eq a => Eq (NonEmpty a) | |
| Eq a => Eq (Complex a) | |
| Eq a => Eq (ZipList a) | |
| Eq a => Eq (Dual a) | |
| Eq a => Eq (Sum a) | |
| Eq a => Eq (Product a) | |
| Eq a => Eq (First a) | |
| Eq a => Eq (Last a) | |
| Eq a => Eq (Down a) | |
| Eq a => Eq (IntMap a) | |
| Eq a => Eq (Seq a) | |
| Eq a => Eq (ViewL a) | |
| Eq a => Eq (ViewR a) | |
| Eq a => Eq (Set a) | |
| Eq a => Eq (Hashed a) | Uses precomputed hash to detect inequality faster |
| Eq a => Eq (Array a) | |
| Eq a => Eq (HashSet a) | |
| Eq a => Eq (Vector a) | |
| (Storable a, Eq a) => Eq (Vector a) | |
| (Prim a, Eq a) => Eq (Vector a) | |
| (Eq b, Eq a) => Eq (Either a b) | |
| Eq (f p) => Eq (Rec1 f p) | |
| Eq (URec Char p) | |
| Eq (URec Double p) | |
| Eq (URec Float p) | |
| Eq (URec Int p) | |
| Eq (URec Word p) | |
| Eq (URec (Ptr ()) p) | |
| (Eq a, Eq b) => Eq (a, b) | |
| Eq a => Eq (Arg a b) | |
| Eq (Proxy k s) | |
| (Eq k, Eq a) => Eq (Map k a) | |
| Eq (MutableArray s a) | |
| (Eq1 m, Eq a) => Eq (MaybeT m a) | |
| (Eq1 m, Eq a) => Eq (ListT m a) | |
| (Eq v, Eq k) => Eq (Leaf k v) | |
| (Eq k, Eq v) => Eq (HashMap k v) | |
| Eq c => Eq (K1 i c p) | |
| (Eq (g p), Eq (f p)) => Eq ((:+:) f g p) | |
| (Eq (g p), Eq (f p)) => Eq ((:*:) f g p) | |
| Eq (f (g p)) => Eq ((:.:) f g p) | |
| (Eq a, Eq b, Eq c) => Eq (a, b, c) | |
| Eq a => Eq (Const k a b) | |
| Eq (f a) => Eq (Alt k f a) | |
| Eq ((:~:) k a b) | |
| (Eq w, Eq1 m, Eq a) => Eq (WriterT w m a) | |
| (Eq w, Eq1 m, Eq a) => Eq (WriterT w m a) | |
| (Eq1 f, Eq a) => Eq (IdentityT * f a) | |
| (Eq e, Eq1 m, Eq a) => Eq (ExceptT e m a) | |
| (Eq e, Eq1 m, Eq a) => Eq (ErrorT e m a) | |
| Eq (f p) => Eq (M1 i c f p) | |
| (Eq a, Eq b, Eq c, Eq d) => Eq (a, b, c, d) | |
| (Eq1 f, Eq1 g, Eq a) => Eq (Sum * f g a) | |
| (Eq1 f, Eq1 g, Eq a) => Eq (Product * f g a) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e) => Eq (a, b, c, d, e) | |
| (Eq1 f, Eq1 g, Eq a) => Eq (Compose * * f g a) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f) => Eq (a, b, c, d, e, f) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g) => Eq (a, b, c, d, e, f, g) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h) => Eq (a, b, c, d, e, f, g, h) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i) => Eq (a, b, c, d, e, f, g, h, i) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j) => Eq (a, b, c, d, e, f, g, h, i, j) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k) => Eq (a, b, c, d, e, f, g, h, i, j, k) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l) => Eq (a, b, c, d, e, f, g, h, i, j, k, l) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l, Eq m) => Eq (a, b, c, d, e, f, g, h, i, j, k, l, m) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l, Eq m, Eq n) => Eq (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l, Eq m, Eq n, Eq o) => Eq (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | |
The Bounded class is used to name the upper and lower limits of a
type. Ord is not a superclass of Bounded since types that are not
totally ordered may also have upper and lower bounds.
The Bounded class may be derived for any enumeration type;
minBound is the first constructor listed in the data declaration
and maxBound is the last.
Bounded may also be derived for single-constructor datatypes whose
constituent types are in Bounded.
Instances
Class Enum defines operations on sequentially ordered types.
The enumFrom... methods are used in Haskell's translation of
arithmetic sequences.
Instances of Enum may be derived for any enumeration type (types
whose constructors have no fields). The nullary constructors are
assumed to be numbered left-to-right by fromEnum from 0 through n-1.
See Chapter 10 of the Haskell Report for more details.
For any type that is an instance of class Bounded as well as Enum,
the following should hold:
- The calls
succmaxBoundpredminBound fromEnumandtoEnumshould give a runtime error if the result value is not representable in the result type. For example,toEnum7 ::BoolenumFromandenumFromThenshould be defined with an implicit bound, thus:
enumFrom x = enumFromTo x maxBound
enumFromThen x y = enumFromThenTo x y bound
where
bound | fromEnum y >= fromEnum x = maxBound
| otherwise = minBoundMethods
the successor of a value. For numeric types, succ adds 1.
the predecessor of a value. For numeric types, pred subtracts 1.
Convert from an Int.
Convert to an Int.
It is implementation-dependent what fromEnum returns when
applied to a value that is too large to fit in an Int.
Used in Haskell's translation of [n..].
enumFromThen :: a -> a -> [a] #
Used in Haskell's translation of [n,n'..].
enumFromTo :: a -> a -> [a] #
Used in Haskell's translation of [n..m].
enumFromThenTo :: a -> a -> a -> [a] #
Used in Haskell's translation of [n,n'..m].
Instances
| Enum Bool | |
| Enum Char | |
| Enum Int | |
| Enum Int8 | |
| Enum Int16 | |
| Enum Int32 | |
| Enum Int64 | |
| Enum Integer | |
| Enum Ordering | |
| Enum Word | |
| Enum Word8 | |
| Enum Word16 | |
| Enum Word32 | |
| Enum Word64 | |
| Enum () | |
| Enum CChar | |
| Enum CSChar | |
| Enum CUChar | |
| Enum CShort | |
| Enum CUShort | |
| Enum CInt | |
| Enum CUInt | |
| Enum CLong | |
| Enum CULong | |
| Enum CLLong | |
| Enum CULLong | |
| Enum CFloat | |
| Enum CDouble | |
| Enum CPtrdiff | |
| Enum CSize | |
| Enum CWchar | |
| Enum CSigAtomic | |
| Enum CClock | |
| Enum CTime | |
| Enum CUSeconds | |
| Enum CSUSeconds | |
| Enum CIntPtr | |
| Enum CUIntPtr | |
| Enum CIntMax | |
| Enum CUIntMax | |
| Enum Associativity | |
| Enum SourceUnpackedness | |
| Enum SourceStrictness | |
| Enum DecidedStrictness | |
| Integral a => Enum (Ratio a) | |
| Enum a => Enum (Identity a) | |
| Enum a => Enum (Min a) | |
| Enum a => Enum (Max a) | |
| Enum a => Enum (First a) | |
| Enum a => Enum (Last a) | |
| Enum a => Enum (WrappedMonoid a) | |
| Enum (Proxy k s) | |
| Enum a => Enum (Const k a b) | |
| Enum (f a) => Enum (Alt k f a) | |
| (~) k a b => Enum ((:~:) k a b) | |
Conversion of values to readable Strings.
Derived instances of Show have the following properties, which
are compatible with derived instances of Read:
- The result of
showis a syntactically correct Haskell expression containing only constants, given the fixity declarations in force at the point where the type is declared. It contains only the constructor names defined in the data type, parentheses, and spaces. When labelled constructor fields are used, braces, commas, field names, and equal signs are also used. - If the constructor is defined to be an infix operator, then
showsPrecwill produce infix applications of the constructor. - the representation will be enclosed in parentheses if the
precedence of the top-level constructor in
xis less thand(associativity is ignored). Thus, ifdis0then the result is never surrounded in parentheses; ifdis11it is always surrounded in parentheses, unless it is an atomic expression. - If the constructor is defined using record syntax, then
showwill produce the record-syntax form, with the fields given in the same order as the original declaration.
For example, given the declarations
infixr 5 :^: data Tree a = Leaf a | Tree a :^: Tree a
the derived instance of Show is equivalent to
instance (Show a) => Show (Tree a) where
showsPrec d (Leaf m) = showParen (d > app_prec) $
showString "Leaf " . showsPrec (app_prec+1) m
where app_prec = 10
showsPrec d (u :^: v) = showParen (d > up_prec) $
showsPrec (up_prec+1) u .
showString " :^: " .
showsPrec (up_prec+1) v
where up_prec = 5Note that right-associativity of :^: is ignored. For example,
show(Leaf 1 :^: Leaf 2 :^: Leaf 3)"Leaf 1 :^: (Leaf 2 :^: Leaf 3)".
Instances