| 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
- class Functor f where
- class Applicative m => Monad m where
Documentation
class Functor f where Source #
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 Applicative m => Monad m where Source #
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 Source #
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 Source #
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 :: String -> m a Source #
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: 2.1 |
| Monad Maybe # | Since: 2.1 |
| Monad IO # | Since: 2.1 |
| Monad Par1 # | Since: 4.9.0.0 |
| Monad ReadP # | Since: 2.1 |
| Monad ReadPrec # | Since: 2.1 |
| Monad Last # | |
| Monad First # | |
| Monad Product # | Since: 4.8.0.0 |
| Monad Sum # | Since: 4.8.0.0 |
| Monad Dual # | Since: 4.8.0.0 |
| Monad STM # | Since: 4.3.0.0 |
| Monad Identity # | Since: 4.8.0.0 |
| Monad NonEmpty # | Since: 4.9.0.0 |
| Monad Option # | Since: 4.9.0.0 |
| Monad Last # | Since: 4.9.0.0 |
| Monad First # | Since: 4.9.0.0 |
| Monad Max # | Since: 4.9.0.0 |
| Monad Min # | Since: 4.9.0.0 |
| Monad Complex # | Since: 4.9.0.0 |
| Monad (Either e) # | Since: 4.4.0.0 |
| Monad (U1 *) # | Since: 4.9.0.0 |
| Monoid a => Monad ((,) a) # | Since: 4.9.0.0 |
| Monad (ST s) # | Since: 2.1 |
| Monad (Proxy *) # | Since: 4.7.0.0 |
| ArrowApply a => Monad (ArrowMonad a) # | Since: 2.1 |
| Monad m => Monad (WrappedMonad m) # | |
| Monad (ST s) # | Since: 2.1 |
| Monad f => Monad (Rec1 * f) # | Since: 4.9.0.0 |
| Monad f => Monad (Alt * f) # | |
| Monad ((->) LiftedRep LiftedRep r) # | Since: 2.1 |
| (Monad f, Monad g) => Monad ((:*:) * f g) # | Since: 4.9.0.0 |
| (Monad f, Monad g) => Monad (Product * f g) # | Since: 4.9.0.0 |
| Monad f => Monad (M1 * i c f) # | Since: 4.9.0.0 |