Another fold question

[Thomas L. Bevan]

patty,

what you have written is not a fold. A fold operates over a list. There is no 
list in your code, only some sort of tree structure.

> foldMusic :: (Pitch -> Octave -> Duration -> a)
> 	-> (Duration -> a)
> 	-> (a -> a -> a)
> 	-> (a -> a -> a)
> 	-> (Ratio Int -> a -> a)
> 	-> Music
> 	-> a
>

> I understand that when i use the foldMusic function i need to pass it 5
> parameters.  given the type signiature, why can i pass (+) as a parameter
> for p1 but not for n, what determines what can be passed as a parameter,
> because they all have the return type a??
 The first argument of your function is of type, (Duration -> a)
(+) has the type, a -> a -> a, so it is nothing like the first argument.

countNotes :: Music -> Int

countNotes Silence _ =  0 
countNotes Note_ =  1
countNotes PlayerPar m1 m2 =  (countNotes m1) + (countNotes m2)
countNotes PlayerSeq m1 m2 =   (countNotes m1) + (countNotes m2)
countNotes Tempo _ m =  countNotes m

Tom