Felipe Lessa wrote: (snip )
Although we can't have a pointer to the middle of a list [a], we can have another data struture that behaves sort of as if we had that pointer: a zipper. For example,
http://hackage.haskell.org/packages/archive/ListZipper/1.1.1.0/doc/html/Data...
To understand a list zipper you could think of it as something like
struct zipper { list left, right; }
So we track our "position" by tracking what's on the left and what's on the right. By using the API of the link above you could have something similar to what you wanted:
lpred :: Zipper a -> a lpred = focus . left
lsucc :: Zipper a -> a lsucc = focus . right
-- Felipe.
Hi Felipe - Thanks very much for that! That's very handy to know. I think that I'll base my lpred and lsucc on this approach. Bye for now - - Andy