ghc-semigroupoids

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.

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