G'day all. On Fri, Oct 19, 2001 at 02:30:59PM +0100, Ian Lynagh wrote:
Also, the prelude definition of zipWith has LVL whereas the following definition has LVV. Why is something like the following not used?
zipWith :: (a->b->c) -> [a] -> [b] -> [c] zipWith f (a:as) (b:bs) = f a b : zipWith f as bs zipWith _ _ [] = [] zipWith _ _ _ = []
Generally speaking, Haskell programmers don't like inserting more code with the only effect being to make the function less lazy. This goes double for standard library code. I say "generally" because occasionally there's a good reason (e.g. forcing evaluation can make a program more space-efficient). Is there a good reason behind your version of zipWith other than the strictness signature being more symmetrical? :-) If you really need a reason which doesn't involve bottom, consider a (fairly common) call such as: zipWith f xs [1..] If xs is finite, your version of zipWith would evaluate the infinite list [1..] one place beyond that which was really needed. Cheers, Andrew Bromage