On Feb 4, 2006, at 1:31 PM, Jon Fairbairn wrote:
... There ought to be a list_product somewhere (I mean [1..] `list_product` [4..] == [(1,4),(2,4),(1,5),(3,4),(2,5),(1,6),...]). Is there?
Not that I know of, but here's one which handles finite lists correctly; it'd be a nice addition to Data.List: dzip :: [a] -> [b] -> [(a,b)] dzip = dzipWith (,) dzipWith :: (a -> b -> c) -> [a] -> [b] -> [c] dzipWith f [] ys = [] dzipWith f as [] = [] dzipWith f as (y:ys) = dzipK ys [y] where dzipK (b:bs) rbs = zipWith f as rbs ++ dzipK bs (b : rbs) dzipK [] rbs = dzipT as where dzipT ys@(_:yt) = zipWith f ys rbs ++ dzipT yt dzipT [] = [] -Jan-Willem Maessen
Jón
-- Jón Fairbairn Jon.Fairbairn at cl.cam.ac.uk
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