G'day all.
Quoting Patty Fong
I also understand how to write my own fold function. What i don't understand quite is how to use them. given this data type and this fold function i wrote:
data Music = Note Pitch Octave Duration | Silence Duration | PlayerPar Music Music | PlayerSeq Music Music | Tempo (Ratio Int) Music data Pitch = Cf | C | Cs type Octave = Int type Duration = Ratio Int
I know this doesn't answer your question, but for this example, it might be easier to use some kind of iterator. In this example: getNotes :: Music -> [Music] getNotes n@(Note _ _ _) = [n] getNotes (PlayerPar m1 m2) = getNotes m1 ++ getNotes m2 -- etc etc count_notes = length . getNotes See http://haskell.org/hawiki/IterationPattern for some ideas. Cheers, Andrew Bromage