Towards Optic-Based Algebraic Theories: the Case of Lenses
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Towards Optic-Based Algebraic Theories

This repository contains the supplementary material associated to the article Towards Optic-Based Algebraic Theories: the Case of Lenses (J. López-González and Juan M. Serrano), submitted to Trends in Functional Programming 2018. In essence, it contains Coq definitions and theories revolving around very well-behaved lenses and MonadState. They are summarized in the following figure.

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Broadly, we show that:

  1. MonadState generalizes lens. Particularly, MonadState A (state S) is isomorphic to lens S A. Given this situation, we will refer to MonadState as lens algebra (lensAlg).
  2. A monad morphism state A ~> state S is isomorphic to lens S A.
  3. We can abstract away state S from the aforementioned monad morphism, obtaining lensAlg' as a result. In other words, natLens S A is exactly lensAlg' (state S) A.
  4. lensAlg is isomorphic to lensAlg', and hence MonadState.
  5. We can also abstract away state A from lensAlg', obtaining lensAlgHom. In other words, lensAlg' p A is exactly lensAlgHom p (state A) A.
  6. lensAlgHom p q A induces a lawful lensAlg A p.