| License | BSD-style |
|---|---|
| Maintainer | Vincent Hanquez <vincent@snarc.org> |
| Stability | experimental |
| Portability | portable |
| Safe Haskell | None |
| Language | Haskell2010 |
Basement.Compat.Base
Description
internal re-export of all the good base bits
- ($) :: (a -> b) -> a -> b
- ($!) :: (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
- (<$>) :: Functor f => (a -> b) -> f a -> f b
- not :: Bool -> Bool
- otherwise :: Bool
- fst :: (a, b) -> a
- snd :: (a, b) -> b
- id :: Category k cat => forall a. cat a a
- maybe :: b -> (a -> b) -> Maybe a -> b
- either :: (a -> c) -> (b -> c) -> Either a b -> c
- flip :: (a -> b -> c) -> b -> a -> c
- const :: a -> b -> a
- error :: HasCallStack => [Char] -> a
- and :: Foldable t => t Bool -> Bool
- undefined :: HasCallStack => a
- seq :: a -> b -> b
- class Show a where
- class Eq a => Ord a where
- class Eq a where
- class Bounded a where
- class Enum a where
- class Functor f where
- class Functor f => Applicative f where
- class Applicative m => Monad m where
- data Maybe a :: * -> *
- data Ordering :: *
- data Bool :: *
- data Int :: *
- data Integer :: *
- data Char :: *
- class Integral a where
- class Fractional a where
- class HasNegation a where
- data Int8 :: *
- data Int16 :: *
- data Int32 :: *
- data Int64 :: *
- data Word8 :: *
- data Word16 :: *
- data Word32 :: *
- data Word64 :: *
- data Word :: *
- data Double :: *
- data Float :: *
- data IO a :: * -> *
- class IsList l where
- class IsString a where
- class Generic a
- data Either a b :: * -> * -> *
- class Typeable * a => Data a where
- mkNoRepType :: String -> DataType
- data DataType :: *
- class Typeable k a
- class Monoid a where
- (<>) :: Monoid m => m -> m -> m
- class (Typeable * e, Show e) => Exception e
- throw :: Exception e => e -> a
- throwIO :: Exception e => e -> IO a
- data Ptr a :: * -> * = Ptr Addr#
- ifThenElse :: Bool -> a -> a -> a
- internalError :: [Char] -> a
Documentation
($) :: (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.
(<$>) :: Functor f => (a -> b) -> f a -> f b infixl 4 #
An infix synonym for fmap.
The name of this operator is an allusion to $.
Note the similarities between their types:
($) :: (a -> b) -> a -> b (<$>) :: Functor f => (a -> b) -> f a -> f b
Whereas $ is function application, <$> is function
application lifted over a Functor.
Examples
Convert from a Maybe IntMaybe Stringshow:
>>>show <$> NothingNothing>>>show <$> Just 3Just "3"
Convert from an Either Int IntEither IntString using show:
>>>show <$> Left 17Left 17>>>show <$> Right 17Right "17"
Double each element of a list:
>>>(*2) <$> [1,2,3][2,4,6]
Apply even to the second element of a pair:
>>>even <$> (2,2)(2,True)
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.
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.
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)".
Methods
showsPrec :: Int -> a -> ShowS #
Convert a value to a readable String.
showsPrec should satisfy the law
showsPrec d x r ++ s == showsPrec d x (r ++ s)
Derived instances of Read and Show satisfy the following:
That is, readsPrec parses the string produced by
showsPrec, and delivers the value that showsPrec started with.
Instances
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
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 BigNat | |
| Eq SpecConstrAnnotation | |
| Eq Natural | |
| Eq Void | |
| Eq Constr | Equality of constructors |
| Eq DataRep | |
| Eq ConstrRep | |
| Eq Fixity | |
| Eq Version | |
| Eq CDev | |
| Eq CIno | |
| Eq CMode | |
| Eq COff | |
| Eq CPid | |
| Eq CSsize | |
| Eq CGid | |
| Eq CNlink | |
| Eq CUid | |
| Eq CCc | |
| Eq CSpeed | |
| Eq CTcflag | |
| Eq CRLim | |
| Eq Fd | |
| Eq AsyncException | |
| Eq ArrayException | |
| Eq ExitCode | |
| Eq IOErrorType | |
| Eq WordPtr | |
| Eq IntPtr | |
| 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 GeneralCategory | |
| Eq SrcLoc | |
| Eq PinnedStatus # | |
| Eq Endianness # | |
| Eq Char7 # | |
| Eq Word128 # | |
| Eq Word256 # | |
| Eq FileSize # | |
| Eq RecastDestinationSize # | |
| Eq RecastSourceSize # | |
| Eq OutOfBoundOperation # | |
| Eq Addr # | |
| Eq ValidationFailure # | |
| Eq AsciiString # | |
| Eq String # | |
| Eq Encoding # | |
| 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 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 (ZipList a) | |
| Eq (ForeignPtr 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 (IORef a) | |
| Eq a => Eq (BE a) # | |
| Eq a => Eq (LE a) # | |
| Eq (FinalPtr a) # | |
| Eq (CountOf ty) # | |
| Eq (Offset ty) # | |
| Eq a => Eq (NonEmpty a) # | |
| Eq (Zn n) # | |
| Eq (Zn64 n) # | |
| (PrimType ty, Eq ty) => Eq (Block ty) # | |
| (PrimType ty, Eq ty) => Eq (UArray ty) # | |
| Eq a => Eq (Array 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 (STRef s a) | |
| (Eq b, Eq a) => Eq (These a b) # | |
| PrimType a => Eq (BlockN n a) # | |
| 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 (f p) => Eq (M1 i c f p) | |
| (Eq a, Eq b, Eq c, Eq d) => Eq (a, b, c, d) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e) => Eq (a, b, c, d, e) | |
| (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
The Functor class is used for types that can be mapped over.
Instances of Functor should satisfy the following laws:
fmap id == id fmap (f . g) == fmap f . fmap g
The instances of Functor for lists, Maybe and IO
satisfy these laws.
Minimal complete definition
Instances
class Functor f => Applicative f where #
A functor with application, providing operations to
A minimal complete definition must include implementations of these functions satisfying the following laws:
- identity
pureid<*>v = v- composition
pure(.)<*>u<*>v<*>w = u<*>(v<*>w)- homomorphism
puref<*>purex =pure(f x)- interchange
u
<*>purey =pure($y)<*>u
The other methods have the following default definitions, which may be overridden with equivalent specialized implementations:
As a consequence of these laws, the Functor instance for f will satisfy
If f is also a Monad, it should satisfy
(which implies that pure and <*> satisfy the applicative functor laws).
Methods
Lift a value.
(<*>) :: f (a -> b) -> f a -> f b infixl 4 #
Sequential application.
(*>) :: f a -> f b -> f b infixl 4 #
Sequence actions, discarding the value of the first argument.
(<*) :: f a -> f b -> f a infixl 4 #
Sequence actions, discarding the value of the second argument.
Instances
| Applicative [] | |
| Applicative Maybe | |
| Applicative IO | |
| Applicative U1 | |
| Applicative Par1 | |
| Applicative Identity | |
| Applicative Min | |
| Applicative Max | |
| Applicative First | |
| Applicative Last | |
| Applicative Option | |
| Applicative NonEmpty | |
| Applicative ZipList | |
| Applicative Dual | |
| Applicative Sum | |
| Applicative Product | |
| Applicative First | |
| Applicative Last | |
| Applicative ((->) a) | |
| Applicative (Either e) | |
| Applicative f => Applicative (Rec1 f) | |
| Monoid a => Applicative ((,) a) | |
| Monad m => Applicative (WrappedMonad m) | |
| Arrow a => Applicative (ArrowMonad a) | |
| Applicative (Proxy *) | |
| Applicative (ST s) | |
| (Applicative f, Applicative g) => Applicative ((:*:) f g) | |
| (Applicative f, Applicative g) => Applicative ((:.:) f g) | |
| Arrow a => Applicative (WrappedArrow a b) | |
| Monoid m => Applicative (Const * m) | |
| Applicative f => Applicative (Alt * f) | |
| Monad m => Applicative (Reader r m) # | |
| Monad m => Applicative (State s m) # | |
| Applicative f => Applicative (M1 i c f) | |
| Monad state => Applicative (Builder collection mutCollection step state err) # | |
class Applicative m => Monad m where #
The Monad class defines the basic operations over a monad,
a concept from a branch of mathematics known as category theory.
From the perspective of a Haskell programmer, however, it is best to
think of a monad as an abstract datatype of actions.
Haskell's do expressions provide a convenient syntax for writing
monadic expressions.
Instances of Monad should satisfy the following laws:
Furthermore, the Monad and Applicative operations should relate as follows:
The above laws imply:
and that pure and (<*>) satisfy the applicative functor laws.
The instances of Monad for lists, Maybe and IO
defined in the Prelude satisfy these laws.
Minimal complete definition
Methods
(>>=) :: m a -> (a -> m b) -> m b infixl 1 #
Sequentially compose two actions, passing any value produced by the first as an argument to the second.
(>>) :: m a -> m b -> m b infixl 1 #
Sequentially compose two actions, discarding any value produced by the first, like sequencing operators (such as the semicolon) in imperative languages.
Inject a value into the monadic type.
Fail with a message. This operation is not part of the
mathematical definition of a monad, but is invoked on pattern-match
failure in a do expression.
As part of the MonadFail proposal (MFP), this function is moved
to its own class MonadFail (see Control.Monad.Fail for more
details). The definition here will be removed in a future
release.
Instances
| Monad [] | |
| Monad Maybe | |
| Monad IO | |
| Monad U1 | |
| Monad Par1 | |
| Monad Identity | |
| Monad Min | |
| Monad Max | |
| Monad First | |
| Monad Last | |
| Monad Option | |
| Monad NonEmpty | |
| Monad Dual | |
| Monad Sum | |
| Monad Product | |
| Monad First | |
| Monad Last | |
| Monad ((->) r) | |
| Monad (Either e) | |
| Monad f => Monad (Rec1 f) | |
| Monoid a => Monad ((,) a) | |
| Monad m => Monad (WrappedMonad m) | |
| ArrowApply a => Monad (ArrowMonad a) | |
| Monad (Proxy *) | |
| Monad (ST s) | |
| (Monad f, Monad g) => Monad ((:*:) f g) | |
| Monad f => Monad (Alt * f) | |
| Monad m => Monad (Reader r m) # | |
| Monad m => Monad (State r m) # | |
| Monad f => Monad (M1 i c f) | |
| Monad state => Monad (Builder collection mutCollection step state err) # | |
The Maybe type encapsulates an optional value. A value of type
Maybe aa (represented as Just aNothing). Using Maybe is a good way to
deal with errors or exceptional cases without resorting to drastic
measures such as error.
The Maybe type is also a monad. It is a simple kind of error
monad, where all errors are represented by Nothing. A richer
error monad can be built using the Either type.
Instances
| Monad Maybe | |
| Functor Maybe | |
| Applicative Maybe | |
| Foldable Maybe | |
| Generic1 Maybe | |
| Alternative Maybe | |
| MonadPlus Maybe | |
| MonadFailure Maybe # | |
| Eq a => Eq (Maybe a) | |
| Data a => Data (Maybe a) | |
| Ord a => Ord (Maybe a) | |
| Read a => Read (Maybe a) | |
| Show a => Show (Maybe a) | |
| Generic (Maybe a) | |
| Semigroup a => Semigroup (Maybe a) | |
| Monoid a => Monoid (Maybe a) | Lift a semigroup into |
| NormalForm a => NormalForm (Maybe a) # | |
| SingI (Maybe a) (Nothing a) | |
| SingKind a (KProxy a) => SingKind (Maybe a) (KProxy (Maybe a)) | |
| SingI a a1 => SingI (Maybe a) (Just a a1) | |
| From (Maybe a) (Either () a) # | |
| type Rep1 Maybe | |
| type Failure Maybe # | |
| type Rep (Maybe a) | |
| data Sing (Maybe a) | |
| type (==) (Maybe k) a b | |
| type DemoteRep (Maybe a) (KProxy (Maybe a)) | |
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.
Instances
Invariant: Jn# and Jp# are used iff value doesn't fit in S#
Useful properties resulting from the invariants:
Instances
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 characters), 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).
Instances
| Bounded Char | |
| Enum Char | |
| Eq Char | |
| Data Char | |
| Ord Char | |
| Read Char | |
| Show Char | |
| Storable Char | |
| Subtractive Char # | |
| NormalForm Char # | |
| PrimMemoryComparable Char # | |
| PrimType Char # | |
| Functor (URec Char) | |
| Foldable (URec Char) | |
| Generic1 (URec Char) | |
| Eq (URec Char p) | |
| Ord (URec Char p) | |
| Show (URec Char p) | |
| Generic (URec Char p) | |
| data URec Char | Used for marking occurrences of |
| type Difference Char # | |
| type Rep1 (URec Char) | |
| type Rep (URec Char p) | |
Integral Literal support
e.g. 123 :: Integer 123 :: Word8
Minimal complete definition
Methods
fromInteger :: Integer -> a #
Instances
class Fractional a where #
Fractional Literal support
e.g. 1.2 :: Double 0.03 :: Float
Minimal complete definition
Methods
fromRational :: Rational -> a #
Instances
class HasNegation a where #
Negation support
e.g. -(f x)
Minimal complete definition
Instances
8-bit signed integer type
Instances
16-bit signed integer type
Instances
32-bit signed integer type
Instances
64-bit signed integer type
Instances
8-bit unsigned integer type
Instances
16-bit unsigned integer type
Instances
32-bit unsigned integer type
Instances
64-bit unsigned integer type
Instances
Instances
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.
Instances
| Eq Double | |
| Floating Double | |
| Data Double | |
| Ord Double | |
| Read Double | |
| RealFloat Double | |
| Storable Double | |
| HasNegation Double # | |
| Fractional Double # | |
| Integral Double # | |
| Additive Double # | |
| Divisible Double # | |
| Multiplicative Double # | |
| Subtractive Double # | |
| NormalForm Double # | |
| PrimType Double # | |
| Functor (URec Double) | |
| Foldable (URec Double) | |
| Generic1 (URec Double) | |
| Eq (URec Double p) | |
| Ord (URec Double p) | |
| Show (URec Double p) | |
| Generic (URec Double p) | |
| data URec Double | Used for marking occurrences of |
| type Difference Double # | |
| type Rep1 (URec Double) | |
| type Rep (URec Double p) | |
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.
Instances
| Eq Float | |
| Floating Float | |
| Data Float | |
| Ord Float | |
| Read Float | |
| RealFloat Float | |
| Storable Float | |
| HasNegation Float # | |
| Fractional Float # | |
| Integral Float # | |
| Additive Float # | |
| Divisible Float # | |
| Multiplicative Float # | |
| Subtractive Float # | |
| NormalForm Float # | |
| PrimType Float # | |
| Functor (URec Float) | |
| Foldable (URec Float) | |
| Generic1 (URec Float) | |
| Eq (URec Float p) | |
| Ord (URec Float p) | |
| Show (URec Float p) | |
| Generic (URec Float p) | |
| data URec Float | Used for marking occurrences of |
| type Difference Float # | |
| type Rep1 (URec Float) | |
| type Rep (URec Float p) | |
A value of type IO aa.
There is really only one way to "perform" an I/O action: bind it to
Main.main in your program. When your program is run, the I/O will
be performed. It isn't possible to perform I/O from an arbitrary
function, unless that function is itself in the IO monad and called
at some point, directly or indirectly, from Main.main.
IO is a monad, so IO actions can be combined using either the do-notation
or the >> and >>= operations from the Monad class.
The IsList class and its methods are intended to be used in
conjunction with the OverloadedLists extension.
Since: 4.7.0.0
Associated Types
The Item type function returns the type of items of the structure
l.
Methods
The fromList function constructs the structure l from the given
list of Item l
fromListN :: Int -> [Item l] -> l #
The fromListN function takes the input list's length as a hint. Its
behaviour should be equivalent to fromList. The hint can be used to
construct the structure l more efficiently compared to fromList. If
the given hint does not equal to the input list's length the behaviour of
fromListN is not specified.
The toList function extracts a list of Item l from the structure l.
It should satisfy fromList . toList = id.
Instances
| IsList CallStack | Be aware that 'fromList . toList = id' only for unfrozen Since: 4.9.0.0 |
| IsList Version | Since: 4.8.0.0 |
| IsList AsciiString # | |
| IsList String # | |
| IsList [a] | |
| IsList (NonEmpty a) | |
| IsList c => IsList (NonEmpty c) # | |
| PrimType ty => IsList (Block ty) # | |
| PrimType ty => IsList (UArray ty) # | |
| IsList (Array ty) # | |
Class for string-like datastructures; used by the overloaded string extension (-XOverloadedStrings in GHC).
Minimal complete definition
Methods
fromString :: String -> a #
Representable types of kind *. This class is derivable in GHC with the DeriveGeneric flag on.
Instances
data Either a b :: * -> * -> * #
The Either type represents values with two possibilities: a value of
type Either a bLeft aRight b
The Either type is sometimes used to represent a value which is
either correct or an error; by convention, the Left constructor is
used to hold an error value and the Right constructor is used to
hold a correct value (mnemonic: "right" also means "correct").
Examples
The type Either String IntString or an Int. The Left constructor can be used only on
Strings, and the Right constructor can be used only on Ints:
>>>let s = Left "foo" :: Either String Int>>>sLeft "foo">>>let n = Right 3 :: Either String Int>>>nRight 3>>>:type ss :: Either String Int>>>:type nn :: Either String Int
The fmap from our Functor instance will ignore Left values, but
will apply the supplied function to values contained in a Right:
>>>let s = Left "foo" :: Either String Int>>>let n = Right 3 :: Either String Int>>>fmap (*2) sLeft "foo">>>fmap (*2) nRight 6
The Monad instance for Either allows us to chain together multiple
actions which may fail, and fail overall if any of the individual
steps failed. First we'll write a function that can either parse an
Int from a Char, or fail.
>>>import Data.Char ( digitToInt, isDigit )>>>:{let parseEither :: Char -> Either String Int parseEither c | isDigit c = Right (digitToInt c) | otherwise = Left "parse error">>>:}
The following should work, since both '1' and '2' can be
parsed as Ints.
>>>:{let parseMultiple :: Either String Int parseMultiple = do x <- parseEither '1' y <- parseEither '2' return (x + y)>>>:}
>>>parseMultipleRight 3
But the following should fail overall, since the first operation where
we attempt to parse 'm' as an Int will fail:
>>>:{let parseMultiple :: Either String Int parseMultiple = do x <- parseEither 'm' y <- parseEither '2' return (x + y)>>>:}
>>>parseMultipleLeft "parse error"
Instances
| Bifunctor Either | |
| Monad (Either e) | |
| Functor (Either a) | |
| Applicative (Either e) | |
| Foldable (Either a) | |
| Generic1 (Either a) | |
| MonadFailure (Either a) # | |
| From (Maybe a) (Either () a) # | |
| (Eq b, Eq a) => Eq (Either a b) | |
| (Data a, Data b) => Data (Either a b) | |
| (Ord b, Ord a) => Ord (Either a b) | |
| (Read b, Read a) => Read (Either a b) | |
| (Show b, Show a) => Show (Either a b) | |
| Generic (Either a b) | |
| Semigroup (Either a b) | |
| (NormalForm l, NormalForm r) => NormalForm (Either l r) # | |
| From (Either a b) (These a b) # | |
| type Rep1 (Either a) | |
| type Failure (Either a) # | |
| type Rep (Either a b) | |
| type (==) (Either k k1) a b | |
class Typeable * a => Data a where #
The Data class comprehends a fundamental primitive gfoldl for
folding over constructor applications, say terms. This primitive can
be instantiated in several ways to map over the immediate subterms
of a term; see the gmap combinators later in this class. Indeed, a
generic programmer does not necessarily need to use the ingenious gfoldl
primitive but rather the intuitive gmap combinators. The gfoldl
primitive is completed by means to query top-level constructors, to
turn constructor representations into proper terms, and to list all
possible datatype constructors. This completion allows us to serve
generic programming scenarios like read, show, equality, term generation.
The combinators gmapT, gmapQ, gmapM, etc are all provided with
default definitions in terms of gfoldl, leaving open the opportunity
to provide datatype-specific definitions.
(The inclusion of the gmap combinators as members of class Data
allows the programmer or the compiler to derive specialised, and maybe
more efficient code per datatype. Note: gfoldl is more higher-order
than the gmap combinators. This is subject to ongoing benchmarking
experiments. It might turn out that the gmap combinators will be
moved out of the class Data.)
Conceptually, the definition of the gmap combinators in terms of the
primitive gfoldl requires the identification of the gfoldl function
arguments. Technically, we also need to identify the type constructor
c for the construction of the result type from the folded term type.
In the definition of gmapQx combinators, we use phantom type
constructors for the c in the type of gfoldl because the result type
of a query does not involve the (polymorphic) type of the term argument.
In the definition of gmapQl we simply use the plain constant type
constructor because gfoldl is left-associative anyway and so it is
readily suited to fold a left-associative binary operation over the
immediate subterms. In the definition of gmapQr, extra effort is
needed. We use a higher-order accumulation trick to mediate between
left-associative constructor application vs. right-associative binary
operation (e.g., (:)). When the query is meant to compute a value
of type r, then the result type withing generic folding is r -> r.
So the result of folding is a function to which we finally pass the
right unit.
With the -XDeriveDataTypeable option, GHC can generate instances of the
Data class automatically. For example, given the declaration
data T a b = C1 a b | C2 deriving (Typeable, Data)
GHC will generate an instance that is equivalent to
instance (Data a, Data b) => Data (T a b) where
gfoldl k z (C1 a b) = z C1 `k` a `k` b
gfoldl k z C2 = z C2
gunfold k z c = case constrIndex c of
1 -> k (k (z C1))
2 -> z C2
toConstr (C1 _ _) = con_C1
toConstr C2 = con_C2
dataTypeOf _ = ty_T
con_C1 = mkConstr ty_T "C1" [] Prefix
con_C2 = mkConstr ty_T "C2" [] Prefix
ty_T = mkDataType "Module.T" [con_C1, con_C2]This is suitable for datatypes that are exported transparently.
Minimal complete definition
Methods
gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> a -> c a #
Left-associative fold operation for constructor applications.
The type of gfoldl is a headache, but operationally it is a simple
generalisation of a list fold.
The default definition for gfoldl is const id
gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c a #
Unfolding constructor applications
Obtaining the constructor from a given datum. For proper terms, this is meant to be the top-level constructor. Primitive datatypes are here viewed as potentially infinite sets of values (i.e., constructors).
dataTypeOf :: a -> DataType #
The outer type constructor of the type
dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c a) #
Mediate types and unary type constructors.
In Data instances of the form T a, dataCast1 should be defined
as gcast1.
The default definition is const Nothing
dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a) #
Mediate types and binary type constructors.
In Data instances of the form T a b, dataCast2 should be
defined as gcast2.
The default definition is const Nothing
gmapT :: (forall b. Data b => b -> b) -> a -> a #
A generic transformation that maps over the immediate subterms
The default definition instantiates the type constructor c in the
type of gfoldl to an identity datatype constructor, using the
isomorphism pair as injection and projection.
gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r #
A generic query with a left-associative binary operator
gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r #
A generic query with a right-associative binary operator
gmapQ :: (forall d. Data d => d -> u) -> a -> [u] #
A generic query that processes the immediate subterms and returns a list of results. The list is given in the same order as originally specified in the declaration of the data constructors.
gmapQi :: Int -> (forall d. Data d => d -> u) -> a -> u #
A generic query that processes one child by index (zero-based)
gmapM :: Monad m => (forall d. Data d => d -> m d) -> a -> m a #
A generic monadic transformation that maps over the immediate subterms
The default definition instantiates the type constructor c in
the type of gfoldl to the monad datatype constructor, defining
injection and projection using return and >>=.
gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> a -> m a #
Transformation of at least one immediate subterm does not fail
gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> a -> m a #
Transformation of one immediate subterm with success
Instances
mkNoRepType :: String -> DataType #
Constructs a non-representation for a non-representable type
Representation of datatypes. A package of constructor representations with names of type and module.
The class Typeable allows a concrete representation of a type to
be calculated.
Minimal complete definition
The class of monoids (types with an associative binary operation that has an identity). Instances should satisfy the following laws:
mappend mempty x = x
mappend x mempty = x
mappend x (mappend y z) = mappend (mappend x y) z
mconcat =
foldrmappend mempty
The method names refer to the monoid of lists under concatenation, but there are many other instances.
Some types can be viewed as a monoid in more than one way,
e.g. both addition and multiplication on numbers.
In such cases we often define newtypes and make those instances
of Monoid, e.g. Sum and Product.
Methods
Identity of mappend
An associative operation
Fold a list using the monoid.
For most types, the default definition for mconcat will be
used, but the function is included in the class definition so
that an optimized version can be provided for specific types.
Instances
| Monoid Ordering | |
| Monoid () | |
| Monoid All | |
| Monoid Any | |
| Monoid AsciiString # | |
| Monoid String # | |
| Monoid [a] | |
| Monoid a => Monoid (Maybe a) | Lift a semigroup into |
| Monoid a => Monoid (IO a) | |
| Ord a => Monoid (Max a) | |
| Ord a => Monoid (Min a) | |
| Monoid a => Monoid (Identity a) | |
| (Ord a, Bounded a) => Monoid (Min a) | |
| (Ord a, Bounded a) => Monoid (Max a) | |
| Monoid m => Monoid (WrappedMonoid m) | |
| Semigroup a => Monoid (Option a) | |
| Monoid a => Monoid (Dual a) | |
| Monoid (Endo a) | |
| Num a => Monoid (Sum a) | |
| Num a => Monoid (Product a) | |
| Monoid (First a) | |
| Monoid (Last a) | |
| Monoid (CountOf ty) # | |
| PrimType ty => Monoid (Block ty) # | |
| PrimType ty => Monoid (UArray ty) # | |
| Monoid (Array a) # | |
| Monoid b => Monoid (a -> b) | |
| (Monoid a, Monoid b) => Monoid (a, b) | |
| Monoid (Proxy k s) | |
| (Monoid a, Monoid b, Monoid c) => Monoid (a, b, c) | |
| Monoid a => Monoid (Const k a b) | |
| Alternative f => Monoid (Alt * f a) | |
| (Monoid a, Monoid b, Monoid c, Monoid d) => Monoid (a, b, c, d) | |
| (Monoid a, Monoid b, Monoid c, Monoid d, Monoid e) => Monoid (a, b, c, d, e) | |
class (Typeable * e, Show e) => Exception e #
Any type that you wish to throw or catch as an exception must be an
instance of the Exception class. The simplest case is a new exception
type directly below the root:
data MyException = ThisException | ThatException
deriving (Show, Typeable)
instance Exception MyExceptionThe default method definitions in the Exception class do what we need
in this case. You can now throw and catch ThisException and
ThatException as exceptions:
*Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
Caught ThisException
In more complicated examples, you may wish to define a whole hierarchy of exceptions:
---------------------------------------------------------------------
-- Make the root exception type for all the exceptions in a compiler
data SomeCompilerException = forall e . Exception e => SomeCompilerException e
deriving Typeable
instance Show SomeCompilerException where
show (SomeCompilerException e) = show e
instance Exception SomeCompilerException
compilerExceptionToException :: Exception e => e -> SomeException
compilerExceptionToException = toException . SomeCompilerException
compilerExceptionFromException :: Exception e => SomeException -> Maybe e
compilerExceptionFromException x = do
SomeCompilerException a <- fromException x
cast a
---------------------------------------------------------------------
-- Make a subhierarchy for exceptions in the frontend of the compiler
data SomeFrontendException = forall e . Exception e => SomeFrontendException e
deriving Typeable
instance Show SomeFrontendException where
show (SomeFrontendException e) = show e
instance Exception SomeFrontendException where
toException = compilerExceptionToException
fromException = compilerExceptionFromException
frontendExceptionToException :: Exception e => e -> SomeException
frontendExceptionToException = toException . SomeFrontendException
frontendExceptionFromException :: Exception e => SomeException -> Maybe e
frontendExceptionFromException x = do
SomeFrontendException a <- fromException x
cast a
---------------------------------------------------------------------
-- Make an exception type for a particular frontend compiler exception
data MismatchedParentheses = MismatchedParentheses
deriving (Typeable, Show)
instance Exception MismatchedParentheses where
toException = frontendExceptionToException
fromException = frontendExceptionFromExceptionWe can now catch a MismatchedParentheses exception as
MismatchedParentheses, SomeFrontendException or
SomeCompilerException, but not other types, e.g. IOException:
*Main> throw MismatchedParenthesescatche -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses)) Caught MismatchedParentheses *Main> throw MismatchedParenthesescatche -> putStrLn ("Caught " ++ show (e :: SomeFrontendException)) Caught MismatchedParentheses *Main> throw MismatchedParenthesescatche -> putStrLn ("Caught " ++ show (e :: SomeCompilerException)) Caught MismatchedParentheses *Main> throw MismatchedParenthesescatche -> putStrLn ("Caught " ++ show (e :: IOException)) *** Exception: MismatchedParentheses
Instances
throw :: Exception e => e -> a #
Throw an exception. Exceptions may be thrown from purely
functional code, but may only be caught within the IO monad.
throwIO :: Exception e => e -> IO a #
A variant of throw that can only be used within the IO monad.
Although throwIO has a type that is an instance of the type of throw, the
two functions are subtly different:
throw e `seq` x ===> throw e throwIO e `seq` x ===> x
The first example will cause the exception e to be raised,
whereas the second one won't. In fact, throwIO will only cause
an exception to be raised when it is used within the IO monad.
The throwIO variant should be used in preference to throw to
raise an exception within the IO monad because it guarantees
ordering with respect to other IO operations, whereas throw
does not.
A value of type Ptr aa.
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.
Instances
| Eq (Ptr a) | |
| Data a => Data (Ptr a) | |
| Functor (URec (Ptr ())) | |
| Ord (Ptr a) | |
| Show (Ptr a) | |
| Foldable (URec (Ptr ())) | |
| Generic1 (URec (Ptr ())) | |
| Storable (Ptr a) | |
| NormalForm (Ptr a) # | |
| Eq (URec (Ptr ()) p) | |
| Ord (URec (Ptr ()) p) | |
| Generic (URec (Ptr ()) p) | |
| type Rep1 (URec (Ptr ())) | |
| data URec (Ptr ()) | Used for marking occurrences of |
| type Rep (URec (Ptr ()) p) | |
ifThenElse :: Bool -> a -> a -> a #
for support of if .. then .. else
internalError :: [Char] -> a #
Only to use internally for internal error cases