profunctor-optics

profunctor-optics-th

Template Haskell generation of profunctor optics from record types.

Overview

Automatically derive lenses, prisms, traversals, and other optics from data type declarations using Template Haskell.

Deriving lenses

Theory

A lens focuses on exactly one field of a product type. For a record with fields, each field naturally gives rise to a lens. Template Haskell automates the boilerplate.

Example 1: record lenses

{-# LANGUAGE TemplateHaskell #-}
import Data.Profunctor.Optic.TH

data Person = Person
    { _personName :: String
    , _personAge  :: Int
    }

makeFieldOptics defaultFieldRules ''Person

-- Generates:
-- personName :: Lens' Person String
-- personAge  :: Lens' Person Int

>>> view personName (Person "Alice" 30)
"Alice"
>>> set personAge 31 (Person "Alice" 30)
Person "Alice" 31

Example 2: sum type prisms

{-# LANGUAGE TemplateHaskell #-}
import Data.Profunctor.Optic.TH

data Shape
    = Circle Double
    | Rectangle Double Double
    | Triangle Double Double Double

makeFieldOptics defaultFieldRules ''Shape

-- Generates prisms for each constructor

Modules

Module	Contents
Data.Profunctor.Optic.TH	makeFieldOptics, defaultFieldRules, makePrismOptics

Dependencies

base, profunctor-optics, template-haskell, th-abstraction