free-functors: Free functors, adjoint to functors that forget class constraints.

[ bsd3, data, library, math ] [ Propose Tags ]

A free functor is a left adjoint to a forgetful functor. It used to be the case that the only category that was easy to work with in Haskell was Hask itself, so there were no interesting forgetful functors.

But the new ConstraintKinds feature of GHC provides an easy way of creating subcategories of Hask. That brings interesting opportunities for free (and cofree) functors.

The examples directory contains an implementation of non-empty lists as free semigroups, and automata as free actions. The standard example of free higher order functors is free monads, and this definition can be found in Data.Functor.HFree.

Versions [faq] 0, 0.1, 0.1.1, 0.1.2, 0.2, 0.3, 0.4, 0.4.1, 0.5, 0.6, 0.6.1,, 0.6.2, 0.6.3,,,, 0.6.4,, 0.6.5, 0.7, 0.7.1, 0.7.2, 0.8, 0.8.1, 0.8.2, 0.8.3, 0.8.4, 0.9, 1.0, 1.0.1
Change log CHANGELOG
Dependencies algebraic-classes (==0.9.*), base (==4.12.*), bifunctors (==5.*), comonad (==5.*), contravariant (==1.5.*), profunctors (==5.*), template-haskell (==2.14.*), transformers (==0.5.*) [details]
License BSD-3-Clause
Author Sjoerd Visscher
Category Data, Math
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Source repo head: git clone git://
Uploaded by SjoerdVisscher at Mon Sep 24 20:34:36 UTC 2018
Distributions NixOS:1.0.1
Downloads 15017 total (730 in the last 30 days)
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