The comonad package

[Tags: bsd3, library]

Comonads


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Versions0.1.0, 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
Change logCHANGELOG.markdown
Dependenciesbase (==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 && <0.5), transformers-compat (>=0.3 && <1) [details]
LicenseBSD3
CopyrightCopyright (C) 2008-2014 Edward A. Kmett, Copyright (C) 2004-2008 Dave Menendez
AuthorEdward A. Kmett
MaintainerEdward A. Kmett <ekmett@gmail.com>
Stabilityprovisional
CategoryControl, Comonads
Home pagehttp://github.com/ekmett/comonad/
Bug trackerhttp://github.com/ekmett/comonad/issues
Source repositoryhead: git clone git://github.com/ekmett/comonad.git
UploadedFri Jul 24 13:42:08 UTC 2015 by EdwardKmett
DistributionsDebian:4.2.7.2, FreeBSD:4.2.7.2, LTSHaskell:4.2.7.2, NixOS:4.2.7.2, Stackage:4.2.7.2
Downloads129441 total (1349 in last 30 days)
Votes
3 []
StatusDocs available [build log]
Last success reported on 2015-07-24 [all 1 reports]

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[Index]

Flags

NameDescriptionDefaultType
test-doctestsEnabledManual
containersYou 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
contravariantYou 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
distributiveYou 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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Maintainers' corner

For package maintainers and hackage trustees

Readme for comonad-4.2.7.2

comonad

Build Status

This package provides comonads, the categorical dual of monads.

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 and perhaps can be made clearer by viewing them as laws stating that Cokleisli composition must be associative, and has 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 are the default definitions of 'extend' and'duplicate' 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