G'day all. On Wed, Jun 05, 2002 at 08:20:03PM -0500, Jon Cast wrote:
I think you're confused about what the type declarations mean. When you say
sqrt :: Float -> Float
you're promising to operate over /all/ Floats.
That would be true of Haskell functions were constrained to be total functions. They are not. Sqrt takes values of type Float, but it just happens to be a partial function over that type.
Unfortunately, Haskell doesn't allow {x :: Float | x >= 0} as a type, nor does it provide a positive-only floating point type.
One general rule of strongly-typed programming is: A program is type correct if it is accepted by my favourite type checker. A corollary is that what you call a type, I reserve the right to call a precondition. Cheers, Andrew Bromage