-- https://bitemyapp.com/blog/instance-local-fundeps/ {-# LANGUAGE TypeFamilies, FlexibleInstances #-} data Bytes = B | KB | MB instance (b ~ Double) => Num (Bytes -> b) where fromInteger i B = fromInteger i fromInteger i KB = fromInteger $ i * 1024 fromInteger i MB = fromInteger $ i * 1024 * 1024 instance (b ~ Double) => Fractional (Bytes -> b) where fromRational r B = fromRational r fromRational r KB = fromRational $ r * 1024 fromRational r MB = fromRational $ r * 1024 * 1024 main = print $ 100 KB