Package Info

ghc-semigroupoids


Semigroupoids: Category sans id


Unspecified

Provides a wide array of (semi)groupoids and operations for working with them.

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

A 'Category' is any 'Semigroupoid' for which the Yoneda lemma holds.

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:

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

Apply, Bind, and Extend (not shown) 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.


License: BSD-2-Clause
URL: https://hackage.haskell.org/package/semigroupoids

Categories

Releases

Package Version Update ID Released Package Hub Version Platforms Subpackages
5.3.7-bp154.1.12 info GA Release 2022-05-09 15 SP4
  • AArch64
  • ppc64le
  • x86-64
  • ghc-semigroupoids
  • ghc-semigroupoids-devel
5.3.4-bp153.1.20 info GA Release 2021-04-08 15 SP3
  • AArch64
  • ppc64le
  • x86-64
  • ghc-semigroupoids
  • ghc-semigroupoids-devel
5.3.4-bp152.1.11 info GA Release 2020-06-16 15 SP2
  • AArch64
  • ppc64le
  • x86-64
  • ghc-semigroupoids
  • ghc-semigroupoids-devel
5.3.2-bp151.2.2 info GA Release 2019-07-17 15 SP1
  • ppc64le
  • x86-64
  • ghc-semigroupoids
  • ghc-semigroupoids-devel
5.3.2-bp151.1.10 info GA Release 2019-05-31 15 SP1
  • AArch64
  • ghc-semigroupoids
  • ghc-semigroupoids-devel
5.2-bp150.2.5 info GA Release 2018-07-31 15
  • ppc64le
  • ghc-semigroupoids
  • ghc-semigroupoids-devel
5.2-bp150.2.4 info GA Release 2018-07-30 15
  • AArch64
  • x86-64
  • ghc-semigroupoids
  • ghc-semigroupoids-devel
5.0.1-2.4 info 5585 2016-09-14 12 GA-SP5
  • ppc64le
  • ghc-semigroupoids
  • ghc-semigroupoids-devel
5.0.1-2.8 info 5585 2016-09-14 12 GA-SP5
  • AArch64
  • s390x
  • x86-64
  • ghc-semigroupoids
  • ghc-semigroupoids-devel