2009/10/20 satorisanitarium <satorisanitar...@gmail.com>: > > I just started learning haskell and I just came to my first wtf moment. > > I'm trying to do something like this: > > calling: > foo 3 [1,2,3,2,4,1,6,3,6,2,3,5,2,5,2,1,6,4] > > returns: > [[1,2,3],[2,4,1,6,3],[2,3]] > > but i have no idea how to put something into a sublist. > > How to make a list of sublists out of a list, whether they be a list of > numbers or a string.
Hi, Here is a function f that looks like a recursive implementation of the function length. f is the identity for lists but shows clearly how you can build the list again. ghci> let f [] = [] ; f (x:xs) = x : f xs ghci> f "hello" "hello" But here is what happen if we change it slightly so that each element is turned into a list (which is still viewed as an element from the point of view of the enclosing list). ghci> let f [] = [] ; f (x:xs) = [x] : f xs ghci> f "hello" ["h","e","l","l","o"] If it's not clear, try to write down the type of each version of f. Now back to your original problem. Can you write a function g such that g [1,2,3,2,4,1,6,3,6,2,3,5,2,5,2,1,6,4] returns ([1,2,3],[2,4,1,6,3,6,2,3,5,2,5,2,1,6,4]) g [2,4,1,6,3,6,2,3,5,2,5,2,1,6,4] returns: ([2,4,1,6,3],[6,2,3,5,2,5,2,1,6,4]) and so on ? Then you should be able to build what you wanted by using g in a modified version of f. Yell if something doesn't make sense. Cheers, Thu _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
