On: Let the Type System do the Work

[jweese]

That's why you want

    newtype Kilogram = Kilogram Double

which has no runtime overhead but does enforce the fact the Kilogram is a distinct type.

[sparkie → jweese]

We probably wanna add to it to make it useful

    {-# LANGUAGE GeneralizedNewtypeDeriving #-}
   
    newtype Kilogram = Kilogram Double deriving (Show, Eq, Ord, Num, Real, Fractional, Floating, ...)

And remind ourselves that Haskell is really quite expressive.

[dllthomas → sparkie]

Though unfortunately can't handle (mass * accel :: Newton) without swapping out the Prelude.