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 |

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`

.

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.

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

(<$) :: a -> f b -> f a infixl 4 Source

Replace all locations in the input with the same value. The default definition is `fmap . const`

, but this may be overridden with a more efficient version.

Functor [] | |

Functor IO | |

Functor Maybe | |

Functor ReadP | |

Functor ReadPrec | |

Functor Last | |

Functor First | |

Functor STM | |

Functor Handler | |

Functor ZipList | |

Functor Identity | |

Functor ArgDescr | |

Functor OptDescr | |

Functor ArgOrder | |

Functor ((->) r) | |

Functor (Either a) | |

Functor ((,) a) | |

Functor (ST s) | |

Functor (Proxy *) | |

Arrow a => Functor (ArrowMonad a) | |

Monad m => Functor (WrappedMonad m) | |

Functor (Const m) | |

Functor (ST s) | |

Functor f => Functor (Alt * f) | |

Arrow a => Functor (WrappedArrow a b) |

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.

(>>=) :: 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 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.

© The University of Glasgow and others

Licensed under a BSD-style license (see top of the page).

https://downloads.haskell.org/~ghc/7.10.3/docs/html/libraries/base-4.8.2.0/Control-Monad-Instances.html