| Copyright | (c) The University of Glasgow 2001 |
|---|---|
| License | BSD-style (see the file libraries/base/LICENSE) |
| Maintainer | libraries@haskell.org |
| Stability | provisional |
| Portability | portable |
| Safe Haskell | Safe |
| Language | Haskell2010 |
Control.Monad.Instances
Description
Documentation
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
| Functor [] # | Since: base-2.1 |
| Functor Maybe # | Since: base-2.1 |
| Functor IO # | Since: base-2.1 |
| Functor Par1 # | Since: base-4.9.0.0 |
| Functor NonEmpty # | Since: base-4.9.0.0 |
| Functor ReadP # | Since: base-2.1 |
| Functor ReadPrec # | Since: base-2.1 |
| Functor Down # | Since: base-4.11.0.0 |
| Functor Product # | Since: base-4.8.0.0 |
| Functor Sum # | Since: base-4.8.0.0 |
| Functor Dual # | Since: base-4.8.0.0 |
| Functor Last # | Since: base-4.8.0.0 |
| Functor First # | Since: base-4.8.0.0 |
| Functor STM # | Since: base-4.3.0.0 |
| Functor Handler # | Since: base-4.6.0.0 |
| Functor Identity # | Since: base-4.8.0.0 |
| Functor ZipList # | Since: base-2.1 |
| Functor ArgDescr # | Since: base-4.6.0.0 |
| Functor OptDescr # | Since: base-4.6.0.0 |
| Functor ArgOrder # | Since: base-4.6.0.0 |
| Functor Option # | Since: base-4.9.0.0 |
| Functor Last # | Since: base-4.9.0.0 |
| Functor First # | Since: base-4.9.0.0 |
| Functor Max # | Since: base-4.9.0.0 |
| Functor Min # | Since: base-4.9.0.0 |
| Functor Complex # | Since: base-4.9.0.0 |
| Functor (Either a) # | Since: base-3.0 |
| Functor (V1 :: Type -> Type) # | Since: base-4.9.0.0 |
| Functor (U1 :: Type -> Type) # | Since: base-4.9.0.0 |
| Functor ((,) a) # | Since: base-2.1 |
| Functor (ST s) # | Since: base-2.1 |
| Functor (Proxy :: Type -> Type) # | Since: base-4.7.0.0 |
| Arrow a => Functor (ArrowMonad a) # | Since: base-4.6.0.0 |
Defined in Control.Arrow Methods fmap :: (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b # (<$) :: a0 -> ArrowMonad a b -> ArrowMonad a a0 # | |
| Monad m => Functor (WrappedMonad m) # | Since: base-2.1 |
Defined in Control.Applicative Methods fmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b # (<$) :: a -> WrappedMonad m b -> WrappedMonad m a # | |
| Functor (ST s) # | Since: base-2.1 |
| Functor (Arg a) # | Since: base-4.9.0.0 |
| Functor f => Functor (Rec1 f) # | Since: base-4.9.0.0 |
| Functor (URec Char :: Type -> Type) # | Since: base-4.9.0.0 |
| Functor (URec Double :: Type -> Type) # | Since: base-4.9.0.0 |
| Functor (URec Float :: Type -> Type) # | Since: base-4.9.0.0 |
| Functor (URec Int :: Type -> Type) # | Since: base-4.9.0.0 |
| Functor (URec Word :: Type -> Type) # | Since: base-4.9.0.0 |
| Functor (URec (Ptr ()) :: Type -> Type) # | Since: base-4.9.0.0 |
| Functor f => Functor (Alt f) # | Since: base-4.8.0.0 |
| Functor f => Functor (Ap f) # | Since: base-4.12.0.0 |
| Functor (Const m :: Type -> Type) # | Since: base-2.1 |
| Arrow a => Functor (WrappedArrow a b) # | Since: base-2.1 |
Defined in Control.Applicative Methods fmap :: (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 # (<$) :: a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 # | |
| Functor ((->) r :: Type -> Type) # | Since: base-2.1 |
| Functor (K1 i c :: Type -> Type) # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (f :+: g) # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (f :*: g) # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (Sum f g) # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (Product f g) # | Since: base-4.9.0.0 |
| Functor f => Functor (M1 i c f) # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (f :.: g) # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (Compose f g) # | Since: base-4.9.0.0 |
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
(>>=) :: forall a b. 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.
(>>) :: forall a b. 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 [] # | Since: base-2.1 |
| Monad Maybe # | Since: base-2.1 |
| Monad IO # | Since: base-2.1 |
| Monad Par1 # | Since: base-4.9.0.0 |
| Monad NonEmpty # | Since: base-4.9.0.0 |
| Monad ReadP # | Since: base-2.1 |
| Monad ReadPrec # | Since: base-2.1 |
| Monad Down # | Since: base-4.11.0.0 |
| Monad Product # | Since: base-4.8.0.0 |
| Monad Sum # | Since: base-4.8.0.0 |
| Monad Dual # | Since: base-4.8.0.0 |
| Monad Last # | Since: base-4.8.0.0 |
| Monad First # | Since: base-4.8.0.0 |
| Monad STM # | Since: base-4.3.0.0 |
| Monad Identity # | Since: base-4.8.0.0 |
| Monad Option # | Since: base-4.9.0.0 |
| Monad Last # | Since: base-4.9.0.0 |
| Monad First # | Since: base-4.9.0.0 |
| Monad Max # | Since: base-4.9.0.0 |
| Monad Min # | Since: base-4.9.0.0 |
| Monad Complex # | Since: base-4.9.0.0 |
| Monad (Either e) # | Since: base-4.4.0.0 |
| Monad (U1 :: Type -> Type) # | Since: base-4.9.0.0 |
| Monoid a => Monad ((,) a) # | Since: base-4.9.0.0 |
| Monad (ST s) # | Since: base-2.1 |
| Monad (Proxy :: Type -> Type) # | Since: base-4.7.0.0 |
| ArrowApply a => Monad (ArrowMonad a) # | Since: base-2.1 |
Defined in Control.Arrow Methods (>>=) :: ArrowMonad a a0 -> (a0 -> ArrowMonad a b) -> ArrowMonad a b # (>>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b # return :: a0 -> ArrowMonad a a0 # fail :: String -> ArrowMonad a a0 # | |
| Monad m => Monad (WrappedMonad m) # | Since: base-4.7.0.0 |
Defined in Control.Applicative Methods (>>=) :: WrappedMonad m a -> (a -> WrappedMonad m b) -> WrappedMonad m b # (>>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b # return :: a -> WrappedMonad m a # fail :: String -> WrappedMonad m a # | |
| Monad (ST s) # | Since: base-2.1 |
| Monad f => Monad (Rec1 f) # | Since: base-4.9.0.0 |
| Monad f => Monad (Alt f) # | Since: base-4.8.0.0 |
| Monad f => Monad (Ap f) # | Since: base-4.12.0.0 |
| Monad ((->) r :: Type -> Type) # | Since: base-2.1 |
| (Monad f, Monad g) => Monad (f :*: g) # | Since: base-4.9.0.0 |
| (Monad f, Monad g) => Monad (Product f g) # | Since: base-4.9.0.0 |
| Monad f => Monad (M1 i c f) # | Since: base-4.9.0.0 |