profunctor-optics

profunctor-optics-generics

Newtype-based optics via Coercible.

Overview

Provides wrapped and ala for working with newtypes through profunctor optics, using GHC’s Coercible constraint for zero-cost conversions.

Iso for newtypes

Theory

Every newtype N is isomorphic to its underlying type A. The Coercible constraint witnesses this at zero runtime cost. wrapped lifts this into an Iso:

wrapped :: (Coercible s a, Coercible t b) => Iso s t a b

Example 1: wrapping and unwrapping

import Data.Profunctor.Optic.Newtype
import Data.Profunctor.Optic
import Data.Monoid (Sum(..))

>>> view wrapped (Sum 42)
42
>>> review wrapped 42 :: Sum Int
Sum {getSum = 42}

Example 2: ala

import Data.Profunctor.Optic.Newtype
import Data.Monoid

-- ala lifts a function to work "under" a newtype:
-- ala Sum foldMap [1, 2, 3]  ≡  getSum (foldMap Sum [1, 2, 3])

>>> ala @(Sum Int) foldMap [1, 2, 3]
6
>>> ala @(Product Int) foldMap [1, 2, 3]
6

Rewrapping

rewrapped converts between two newtypes that wrap the same underlying type:

>>> review (rewrapped @(Sum Int)) (Product 42) :: Sum Int
Sum {getSum = 42}

Modules

Module	Contents
Data.Profunctor.Optic.Newtype	wrapped, rewrapped, rewrapped', ala

Dependencies

base, profunctor-optics