Bas van Dijk: > For my own exercise I'm writing a function 'weave' that "weaves" a > list of lists together. For example: > > weave [[1,1,1], [2,2,2], [3,3]] ==> [1,2,3,1,2,3,1,2] > weave [[1,1,1], [2,2], [3,3,3]] ==> [1,2,3,1,2,3,1] > > Note that 'weave' stops when a list is empty.
This *almost* does what you want: > weave' = concat . transpose Perhaps you could look at implementations of transpose for inspiration. The following two sources show implementations which behave differently when given ragged matrices. You seem to be looking for something between these two extremes. http://darcs.haskell.org/libraries/base/Data/List.hs http://www.soi.city.ac.uk/~ross/papers/Applicative.html Here's a modification of the latter to give the termination behaviour you show above: > weave = concat . foldr zipWeave [] where > zipWeave (x:xs) (ys:yss) = (x:ys) : zipWeave xs yss > zipWeave xs [] = map (:[]) xs > zipWeave [] ys = [] _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
