free (original) (raw)

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 Functorthat controls its branching factor.

More information on free monads, including examples, can be found in the following blog posts:https://ekmett.github.io/reader/2008/monads-for-free/ https://ekmett.github.io/reader/2011/free-monads-for-less/

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Change log CHANGELOG.markdown
Dependencies base (>=4.9 && <5), bifunctor-classes-compat (>=0.1 && <0.2), comonad (>=5.0.8 && <6), containers (>=0.5.7.1 && <0.9), distributive (>=0.5.2 && <1), exceptions (>=0.10.4 && <0.11), indexed-traversable (>=0.1.1 && <0.2), mtl (>=2.2.2 && <2.4), profunctors (>=5.6.1 && <6), semigroupoids (>=5.3.5 && <7), template-haskell (>=2.11 && <2.24), th-abstraction (>=0.4.2.0 && <0.8), transformers (>=0.5 && <0.7), transformers-base (>=0.4.5.2 && <0.5) [details]
Tested with ghc ==8.0.2, ghc ==8.2.2, ghc ==8.4.4, ghc ==8.6.5, ghc ==8.8.4, ghc ==8.10.7, ghc ==9.0.2, ghc ==9.2.6, ghc ==9.4.4, ghc ==9.6.1
License BSD-3-Clause
Copyright Copyright (C) 2008-2015 Edward A. Kmett
Author Edward A. Kmett
Maintainer Edward A. Kmett ekmett@gmail.com
Revised Revision 7 made by ryanglscott at 2025-03-03T10:16:41Z
Category Control, Monads
Home page http://github.com/ekmett/free/
Bug tracker http://github.com/ekmett/free/issues
Source repo head: git clone https://github.com/ekmett/free.git
Uploaded by ryanglscott at 2023-03-12T18:42:24Z
Distributions Arch:5.2, Debian:5.1.3, Fedora:5.2, FreeBSD:4.12.1, LTSHaskell:5.2, NixOS:5.2, Stackage:5.2, openSUSE:5.2
Reverse Dependencies 207 direct, 8213 indirect [details]
Downloads 261772 total (103 in the last 30 days)
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Status Docs available [build log]Last success reported on 2023-03-12 [all 1 reports]