Haskell Language Common GHC Language Extensions MultiParamTypeClasses
Example
It's a very common extension that allows type classes with multiple type parameters. You can think of MPTC as a relation between types.
{-# LANGUAGE MultiParamTypeClasses #-}
class Convertable a b where
convert :: a -> b
instance Convertable Int Float where
convert i = fromIntegral i
The order of parameters matters.
MPTCs can sometimes be replaced with type families.
