I like John's idea with a class Strict, but I think there should also be
a second class Eval for computing whnf's:
class Strict a where
strict :: a -> Bool
class Eval a where
eval :: a -> Bool
Example: for Complex we get:
instance Strict a => Strict (Complex a) where
strict (a:+b) = strict a && strict b
instance Eval (Complex a) where
eval (a:+b) = True
Based on this we can define Miranda's "force" and "seq":
force:: Strict a => a -> a
force x | strict x = x
seq:: Eval a => a -> b -> b
seq x y | eval x = y
Stefan
