On 14 Apr 2010, at 09:12, Jonas Almström Duregård wrote:

f,g :: Bool -> Int
f x = 6
g x = 6

We can in Haskell compute that these two functions are equal, without solving the halting problem.

what about these?
f,g :: Bool -> Int
f x = 6
g x = x `seq` 6

As pointed out on #haskell by roconnor, we apparently don't care, this is a shame... We only care that x == y => f x == g y, and x == y can't tell if _|_ == _|_.

It's a shame that we can't use this to tell if two functions are equally lazy (something I would consider part of the semantics of the function).

Bob