Re: [Haskell-cafe] newtype is superfluous

Wolfgang Jeltsch wrote:

This is not true. With newtype, A _|_ is _|_, with data, A _|_ is not _|_.

It's probably more helpful to explain this in terms of a program that exhibits different behavior in the two cases: case error "data" of A x -> "newtype"

But as far as I know, the above newtype declaration is equivalent to this:

data A = A !Int

Nope: case A (error "data!") of A x -> "data or newtype" -- Ben