The semigroupoids package

[Tags: bsd3, library]

Provides a wide array of semigroupoids and operations for working with semigroupds.

A Semigroupoid is a Category without the requirement of identity arrows for every object in the category.

When working with comonads you often have the <*> portion of an Applicative, but not the pure. This was captured in Uustalu and Vene's "Essence of Dataflow Programming" in the form of the ComonadZip class in the days before Applicative. Apply provides a weaker invariant, but for the comonads used for data flow programming (found in the streams package), this invariant is preserved. Applicative function composition forms a semigroupoid.

Similarly many structures are nearly a comonad, but not quite, for instance lists provide a reasonable extend operation in the form of tails, but do not always contain a value.

Ideally the following relationships would hold:

 Traversable <---- Foldable <--- Functor ------> Alt ---------> Plus           Semigroupoid
      |               |            |                              |                  |
      v               v            v                              v                  v
 Traversable1 <--- Foldable1     Apply --------> Applicative -> Alternative      Category
                                   |               |              |                  |
                                   v               v              v                  v
                                 Bind ---------> Monad -------> MonadPlus          Arrow

Apply, Bind, and Extract give rise the Static, Kleisli and Cokleisli semigroupoids respectively.

This lets us remove many of the restrictions from various monad transformers as in many cases the binding operation or <*> operation does not require them.

Finally, to work with these weaker structures it is beneficial to have containers that can provide stronger guarantees about their contents, so versions of Traversable and Foldable that can be folded with just a Semigroup are added.


Properties

Versions1.0.0, 1.1.0, 1.1.1, 1.1.2, 1.1.3, 1.2.0, 1.2.1, 1.2.2, 1.2.2.1, 1.2.2.2, 1.2.2.3, 1.2.2.4, 1.2.4, 1.2.5, 1.2.6, 1.2.6.1, 1.2.6.2, 1.3, 1.3.1, 1.3.1.1, 1.3.1.2, 1.3.2, 1.3.2.1, 1.3.3, 1.3.4, 3.0, 3.0.0.1, 3.0.0.2, 3.0.1, 3.0.2, 3.0.3, 3.1, 4.0, 4.0.1, 4.0.2, 4.0.2.1, 4.0.3, 4.0.4, 4.2
Dependenciesbase (==4.*), comonad (>=1.1.1.5 && <1.2), containers (>=0.3 && <0.6), contravariant (>=0.2.0.1 && <0.3), semigroups (>=0.8.3.1 && <0.9), transformers (>=0.2 && <0.4)
LicenseBSD3
CopyrightCopyright (C) 2011 Edward A. Kmett
AuthorEdward A. Kmett
MaintainerEdward A. Kmett <ekmett@gmail.com>
Stabilityprovisional
CategoryControl, Comonads
Home pagehttp://github.com/ekmett/semigroupoids
Bug trackerhttp://github.com/ekmett/semigroupoids/issues
Source repositoryhead: git clone git://github.com/ekmett/semigroupoids.git
Upload dateThu Jun 28 23:05:26 UTC 2012
Uploaded byEdwardKmett
DistributionsDebian:4.2, FreeBSD:3.0.2, NixOS:4.2
Downloads90534 total (11133 in last 30 days)

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