Control.Monad.Instances

Deprecated: This module now contains no instances and will be removed in the future

This module is DEPRECATED and will be removed in the future!

Functor and Monad instances for (->) r and Functor instances for (,) a and Either a.

Documentation

class Functor f where

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.

Methods

fmap :: (a -> b) -> f a -> f b

Instances

Functor []

Functor IO

Functor Maybe

Functor ReadP

Functor ReadPrec

Functor STM

Functor Handler

Functor ZipList

Functor ArgDescr

Functor OptDescr

Functor ArgOrder

Functor ((->) r)

Functor (Either a)

Functor ((,) a)

Functor (ST s)

Functor (Proxy *)

Arrow a => Functor (ArrowMonad a)

Functor (ST s)

Monad m => Functor (WrappedMonad m)

Functor (Const m)

Arrow a => Functor (WrappedArrow a b)

class 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.

Minimal complete definition: >>= and return.

Instances of Monad should satisfy the following laws:

return a >>= k  ==  k a
m >>= return  ==  m
m >>= (\x -> k x >>= h)  ==  (m >>= k) >>= h

Instances of both Monad and Functor should additionally satisfy the law:

fmap f xs  ==  xs >>= return . f

The instances of Monad for lists, Maybe and IO defined in the Prelude satisfy these laws.

Minimal complete definition

(>>=), return

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.

return :: a -> m a

Inject a value into the monadic type.

fail :: String -> m a

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.

Instances

Monad []

Monad IO

Monad Maybe

Monad ReadP

Monad ReadPrec

Monad STM

Monad ((->) r)

Monad (Either e)

Monad (ST s)

Monad (Proxy *)

ArrowApply a => Monad (ArrowMonad a)

Monad (ST s)

Monad m => Monad (WrappedMonad m)