The comonad package

[ Tags: bsd3, comonads, control, library ] [ Propose Tags ]

Comonads


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Properties

Versions 0.1.0, 0.1.1, 0.3.0, 0.4.0, 0.5.0, 0.6.0, 0.6.1, 0.6.1.1, 0.6.1.2, 0.6.2, 0.6.2.1, 0.7.0, 0.9.0, 0.9.0.1, 1.0, 1.0.1, 1.0.2, 1.0.3, 1.1.0, 1.1.0.1, 1.1.0.2, 1.1.1, 1.1.1.1, 1.1.1.2, 1.1.1.3, 1.1.1.4, 1.1.1.5, 1.1.1.6, 3.0, 3.0.0.1, 3.0.0.2, 3.0.1.1, 3.0.2, 3.0.3, 3.1, 4.0, 4.0.1, 4.2, 4.2.1, 4.2.2, 4.2.3, 4.2.4, 4.2.5, 4.2.6, 4.2.7, 4.2.7.1, 4.2.7.2, 4.3, 5, 5.0.1, 5.0.2
Change log CHANGELOG.markdown
Dependencies base (==4.*), containers (>=0.3 && <0.6), contravariant (>=0.2.0.1 && <2), distributive (>=0.2.2 && <1), semigroups (>=0.8.3.1 && <1), tagged (>=0.1 && <1), transformers (>=0.2 && <0.6), transformers-compat (>=0.3 && <1) [details]
License BSD3
Copyright Copyright (C) 2008-2014 Edward A. Kmett, Copyright (C) 2004-2008 Dave Menendez
Author Edward A. Kmett
Maintainer Edward A. Kmett <ekmett@gmail.com>
Category Control, Comonads
Home page http://github.com/ekmett/comonad/
Bug tracker http://github.com/ekmett/comonad/issues
Source repository head: git clone git://github.com/ekmett/comonad.git
Uploaded Sat Jul 29 01:21:55 UTC 2017 by ryanglscott
Updated Thu Aug 3 14:47:21 UTC 2017 by ryanglscott to revision 1
Distributions Arch:5.0.2, Debian:4.2.7.2, FreeBSD:4.2.7.2, LTSHaskell:5.0.2, NixOS:5.0.2, Stackage:5.0.2, Tumbleweed:5.0.1
Downloads 176660 total (1839 in the last 30 days)
Rating 2.5 (4 ratings) [clear rating]
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Status Docs available [build log]
Last success reported on 2017-07-29 [all 1 reports]
Hackage Matrix CI

Modules

[Index]

Flags

NameDescriptionDefaultType
test-doctestsEnabledManual
containers

You can disable the use of the containers package using -f-containers.

Disabing this is an unsupported configuration, but it may be useful for accelerating builds in sandboxes for expert users.

EnabledManual
contravariant

You can disable the use of the contravariant package using -f-contravariant.

Disabling this is an unsupported configuration, but it may be useful for accelerating builds in sandboxes for expert users.

If disabled we will not supply instances of Contravariant

EnabledManual
distributive

You can disable the use of the distributive package using -f-distributive.

Disabling this is an unsupported configuration, but it may be useful for accelerating builds in sandboxes for expert users.

If disabled we will not supply instances of Distributive

EnabledManual

Use -f <flag> to enable a flag, or -f -<flag> to disable that flag. More info

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Maintainer's Corner

For package maintainers and hackage trustees


Readme for comonad-5.0.2

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comonad

Hackage Build Status

This package provides comonads, the categorical dual of monads. The typeclass provides three methods: extract, duplicate, and extend.

class Functor w => Comonad w where
    extract :: w a -> a
    duplicate :: w a -> w (w a)
    extend :: (w a -> b) -> w a -> w b

There are two ways to define a comonad:

I. Provide definitions for extract and extend satisfying these laws:

extend extract      = id
extract . extend f  = f
extend f . extend g = extend (f . extend g)

In this case, you may simply set fmap = liftW.

These laws are directly analogous to the laws for monads. The comonad laws can perhaps be made clearer by viewing them as stating that Cokleisli composition must be a) associative and b) have extract for a unit:

f =>= extract   = f
extract =>= f   = f
(f =>= g) =>= h = f =>= (g =>= h)

II. Alternately, you may choose to provide definitions for fmap, extract, and duplicate satisfying these laws:

extract . duplicate      = id
fmap extract . duplicate = id
duplicate . duplicate    = fmap duplicate . duplicate

In this case, you may not rely on the ability to define fmap in terms of liftW.

You may, of course, choose to define both duplicate /and/ extend. In that case, you must also satisfy these laws:

extend f  = fmap f . duplicate
duplicate = extend id
fmap f    = extend (f . extract)

These implementations are the default definitions of extend andduplicate and the definition of liftW respectively.

Contact Information

Contributions and bug reports are welcome!

Please feel free to contact me through github or on the #haskell IRC channel on irc.freenode.net.

-Edward Kmett