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{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
module Main (main) where
import GHC.Generics
infixr 1 `T`
data T a = T a a deriving Generic
instance HasFixity (T a)
data I a = a `I` a deriving Generic
instance HasFixity (I a)
class HasFixity a where
fixity :: a -> Fixity
default fixity :: (Generic a, GHasFixity (Rep a)) => a -> Fixity
fixity = gfixity . from
class GHasFixity f where
gfixity :: f a -> Fixity
instance GHasFixity f => GHasFixity (D1 d f) where
gfixity (M1 x) = gfixity x
instance Constructor c => GHasFixity (C1 c f) where
gfixity c = conFixity c
main :: IO ()
main = do
putStrLn $ show (fixity (T "a" "b")) ++ ", " ++ show (fixity ("a" `I` "b"))
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