| Safe Haskell | Safe |
|---|---|
| Language | Haskell98 |
Control.Monad.Compat
Synopsis
- module Control.Monad
- class Applicative m => Monad (m :: * -> *) where
- class (Alternative m, Monad m) => MonadPlus (m :: * -> *) where
Documentation
module Control.Monad
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 [] | Since: base-2.1 |
| Monad Maybe | Since: base-2.1 |
| Monad IO | Since: base-2.1 |
| Monad Complex | Since: base-4.9.0.0 |
| Monad Min | Since: base-4.9.0.0 |
| Monad Max | Since: base-4.9.0.0 |
| Monad First | Since: base-4.9.0.0 |
| Monad Last | Since: base-4.9.0.0 |
| Monad Option | Since: base-4.9.0.0 |
| Monad Identity | Since: base-4.8.0.0 |
| Monad STM | Since: base-4.3.0.0 |
| Monad First | |
| Monad Last | |
| Monad Dual | Since: base-4.8.0.0 |
| Monad Sum | Since: base-4.8.0.0 |
| Monad Product | Since: base-4.8.0.0 |
| Monad ReadPrec | Since: base-2.1 |
| Monad ReadP | Since: base-2.1 |
| Monad NonEmpty | Since: base-4.9.0.0 |
| Monad P | Since: base-2.1 |
| Monad (Either e) | Since: base-4.4.0.0 |
| Monoid a => Monad ((,) a) | Since: base-4.9.0.0 |
| Monad (ST s) | Since: base-2.1 |
| Monad (ST s) | Since: base-2.1 |
| Monad m => Monad (WrappedMonad m) | |
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 (Proxy :: * -> *) | Since: base-4.7.0.0 |
| Monad f => Monad (Alt f) | |
| Monad ((->) r :: * -> *) | Since: base-2.1 |
| (Monad f, Monad g) => Monad (Product f g) | Since: base-4.9.0.0 |
class (Alternative m, Monad m) => MonadPlus (m :: * -> *) where #
Monads that also support choice and failure.
Methods
The identity of mplus. It should also satisfy the equations
mzero >>= f = mzero v >> mzero = mzero
The default definition is
mzero = empty
An associative operation. The default definition is
mplus = (<|>)
Instances
| MonadPlus [] | Since: base-2.1 |
| MonadPlus Maybe | Since: base-2.1 |
| MonadPlus IO | Since: base-4.9.0.0 |
| MonadPlus Option | Since: base-4.9.0.0 |
| MonadPlus STM | Since: base-4.3.0.0 |
| MonadPlus ReadPrec | Since: base-2.1 |
| MonadPlus ReadP | Since: base-2.1 |
| MonadPlus P | Since: base-2.1 |
Defined in Text.ParserCombinators.ReadP | |
| MonadPlus (Proxy :: * -> *) | Since: base-4.9.0.0 |
| MonadPlus f => MonadPlus (Alt f) | |
| (MonadPlus f, MonadPlus g) => MonadPlus (Product f g) | Since: base-4.9.0.0 |