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{-# LANGUAGE AllowAmbiguousTypes, FunctionalDependencies, ScopedTypeVariables, PolyKinds, TypeApplications, DataKinds #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE OverloadedRecordDot #-}
class HasField x r a | x r -> a where
hasField :: r -> (a -> r, a)
getField :: forall x r a . HasField x r a => r -> a
getField = snd . hasField @x -- Note: a.x = is getField @"x" a.
setField :: forall x r a . HasField x r a => r -> a -> r
setField = fst . hasField @x -- Note : a{x = b} is setField @"x" a b.
-- 'Corge' has a '&&&' field of type 'Int'
data Corge = Corge { (&&&) :: Int } deriving (Show, Eq)
instance HasField "&&&" Corge Int where
hasField r = (\x -> case r of Corge { .. } -> Corge { (&&&) = x, .. }, (&&&) r)
main = do
let b = Corge { (&&&) = 12 };
print $ (b.(&&&))
-- Syntax error: Dot notation is not available for fields with
-- operator names
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