andrewcoppin:
OK, so this is a fairly basic question about list processing.
Several times now, I have found myself wanting to process a list to produce a new list. However, the way later elements are processed depends on what the earlier elements are - in other words, this isn't a simple "map".
What is the best way to handle this?
According to the theory, anything that consumes a list and produces a value is some kind of fold. [Assuming it traverses the list in a sensible order!] So it looks like you could implement this as a fold. But should that be a LEFT-fold or a RIGHT-fold? (I always get confused between the two!)
Sounds like a mapAccum, a combination of map and fold, http://haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html#v%3Ama... If you gave a concrete example it would be easier to diagnose. -- Don