Henning Thielemann wrote:
What is the reason for implementing parallelism with 'par :: a -> b -> b'? Analogy to 'seq'?
I'd think it's actually easier to implement than par2 below; evaluating par x y "sparks" a thread evaluating x, and then returns y. The analogy to 'seq' is there, of course.
I thought parallelism would be introduced most naturally by a function which does two computations in parallel and puts together their results after completion. Say
par2 :: (a -> b -> c) -> (a -> b -> c)
to be used like
par2 (+) expensiveComputationA expensiveComputationB
I assume that par2 can be implemented this way:
par2 f x y = f x (par x y)
For this to work, f has to evaluate its second argument before the first one, or the par will be useless. Try this:
par2 f x y = x `par` y `par` f x y
(In complete analogy to using `seq` for enforcing strictness.) HTH, Bertram