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-- Deriving instances for a "functor-functor"-style record.
-- (https://www.benjamin.pizza/posts/2017-12-15-functor-functors.html)
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
import Control.Applicative (Alternative)
import Data.Coerce
import Data.Functor.Classes
import Data.Semigroup
import Data.Monoid (Alt(..))
import Text.Read
import Generic.Data
import Generic.Data.Orphans ()
data MyRecord f = MyRecord
{ _field1 :: f Int
, _field2 :: f Bool
} deriving Generic
instance Read1 f => Read (MyRecord f) where
readPrec = coerce (greadPrec @(MyRecord (Id1 f)))
readListPrec = readListPrecDefault
instance Show1 f => Show (MyRecord f) where
showsPrec = coerce (gshowsPrec @(MyRecord (Id1 f)))
instance Eq1 f => Eq (MyRecord f) where
(==) = coerce (geq @(MyRecord (Id1 f)))
instance Ord1 f => Ord (MyRecord f) where
compare = coerce (gcompare @(MyRecord (Id1 f)))
instance Alternative f => Semigroup (MyRecord f) where
(<>) = coerce (gmappend @(MyRecord (Alt f)))
instance Alternative f => Monoid (MyRecord f) where
mempty = coerce (gmempty @(MyRecord (Alt f)))
mappend = (<>)
main :: IO ()
main = return () -- Just make this compile
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