{-# LANGUAGE TypeOperators #-} {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE NoMonoPatBinds #-} -- | Constructor-destructor isomorphisms for some common datatypes. module Data.Piso.Common ( -- * @()@ unit, -- * @(,)@ tup, -- * @(,,)@ tup3, -- * @Maybe a@ nothing, just, -- * @[a]@ nil, cons, -- * @Either a b@ left, right, -- * @Bool@ false, true ) where import Prelude hiding (id, (.), maybe, either) import Data.Piso import Data.Piso.TH unit :: Piso t (() :- t) unit = \$(derivePisos ''()) tup :: Piso (a :- b :- t) ((a, b) :- t) tup = \$(derivePisos ''(,)) tup3 :: Piso (a :- b :- c :- t) ((a, b, c) :- t) tup3 = \$(derivePisos ''(,,)) nothing :: Piso t (Maybe a :- t) just :: Piso (a :- t) (Maybe a :- t) (nothing, just) = \$(derivePisos ''Maybe) nil :: Piso t ([a] :- t) nil = Piso f g where f t = [] :- t g ([] :- t) = Just t g _ = Nothing cons :: Piso (a :- [a] :- t) ([a] :- t) cons = Piso f g where f (x :- xs :- t) = (x : xs) :- t g ((x : xs) :- t) = Just (x :- xs :- t) g _ = Nothing left :: Piso (a :- t) (Either a b :- t) right :: Piso (b :- t) (Either a b :- t) (left, right) = \$(derivePisos ''Either) false :: Piso t (Bool :- t) true :: Piso t (Bool :- t) (false, true) = \$(derivePisos ''Bool)