Haskell still has some boilerplate - actually quite a lot if you don't use -XGeneralizedNewtypeDeriving (which has known problems when used with other extension

Haskell still has some boilerplate - actually quite a lot if you don't use -XGeneralizedNewtypeDeriving (which has known problems when used with other extensions). With newtype deriving, this is about as simple as it gets: {-# LANGUAGE GeneralizedNewtypeDeriving #-} class Degrees deg where toK :: deg -> K fromK :: K -> deg newtype K = K { unK :: Double } deriving (Show) instance Degrees K where toK = id fromK = id newtype C = C { unC :: Double } deriving (Show) instance Degrees C where toK = K . (+ 273.16) . unC fromK = C . (flip (-) 273.16) . unK newtype F = F { unF :: Double } deriving (Show) instance Degrees F where toK = K . (+ 273.16) . (* (5/9)) . (flip (-) 32) . unF fromK = F . (+ 32) . (* (9/5)) . (flip (-) 273.16) . unK Without newtype deriving (or other generic deriving extensions), one would need to implement instances of {Num, Real, Fractional, RealFrac, Floating, RealFloat} for all three types, which do nothing but map to the Double equivalents.