# free: Monads for free

Free monads are useful for many tree-like structures and domain specific languages.

If `f`

is a `Functor`

then the free `Monad`

on `f`

is the type
of trees whose nodes are labeled with the constructors of `f`

. The word
"free" is used in the sense of "unrestricted" rather than "zero-cost":
`Free f`

makes no constraining assumptions beyond those given by `f`

and the
definition of `Monad`

. As used here it is a standard term from the
mathematical theory of adjoint functors.

Cofree comonads are dual to free monads. They provide convenient ways to talk
about branching streams and rose-trees, and can be used to annotate syntax
trees. The cofree comonad can be seen as a stream parameterized by a `Functor`

that controls its branching factor.

More information on free monads, including examples, can be found in the following blog posts: http://comonad.com/reader/2008/monads-for-free/ http://comonad.com/reader/2011/free-monads-for-less/

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Change log | CHANGELOG.markdown |

Dependencies | base (>=4 && <4.8), bifunctors (==4.*), comonad (==4.*), distributive (>=0.2.1), mtl (>=2.0.1.0 && <2.2), prelude-extras (>=0.4 && <1), profunctors (==4.*), semigroupoids (==4.*), semigroups (>=0.8.3.1 && <1), template-haskell (>=2.7.0.0 && <3), transformers (>=0.2.0 && <0.4) [details] |

License | BSD-3-Clause |

Copyright | Copyright (C) 2008-2013 Edward A. Kmett |

Author | Edward A. Kmett |

Maintainer | Edward A. Kmett <ekmett@gmail.com> |

Revised | Revision 1 made by HerbertValerioRiedel at 2014-12-02T10:55:14Z |

Category | Control, Monads |

Home page | http://github.com/ekmett/free/ |

Bug tracker | http://github.com/ekmett/free/issues |

Source repo | head: git clone git://github.com/ekmett/free.git |

Uploaded | by EdwardKmett at 2014-04-20T00:30:56Z |

Distributions | Arch:5.1.7, Debian:5.0.2, Fedora:5.1.7, FreeBSD:4.12.1, LTSHaskell:5.1.7, NixOS:5.1.7, Stackage:5.1.7, openSUSE:5.1.3 |

Downloads | 235204 total (2258 in the last 30 days) |

Rating | 2.5 (votes: 5) [estimated by Bayesian average] |

Your Rating | |

Status | Docs available [build log] Successful builds reported [all 1 reports] |

## Downloads

- free-4.7.1.tar.gz [browse] (Cabal source package)
- Package description (revised from the package)

Note: This package has metadata revisions in the cabal description newer than included in the tarball. To unpack the package including the revisions, use 'cabal get'.