<[EMAIL PROTECTED]> wrote: > Hi I have a bit of a dilemma.I have a list of lists, eg, > [[1,2,3],[4,5,6],[7,8,9]]. Imagine they represent a grid with 0-2 on > the x axis and 0-2 on the y axis, eg, (0,0) is 1, (1,0) is 2, (2,1) > is 6, etc and (2,3) is 9. I want to be able to put in the list of > lists, and the (x,y) coordinate, and return the value. > select x y ys = (ys !! y) !! x
> Also, I need to be able to replace a value in the list. Eg, if I > wanted to replace (2,3) with 100, then the output of the expression > would be [[1,2,3],[4,5,6],[7,8,100]]. > you can't replace it, you can only construct a new list: Your function will likely be of the type replace :: Int -> Int -> a -> [[a]] -> [[a]] I won't give the answer here, as that would spoil all of the fun and delight you'll have while browsing through the Prelude and Data.List and see how much duct tape there's around, waiting to be used, plus I'd have to open a new file as ghci doesn't support multi-line functions. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
