count:: [a] -> Int
count [] = 0
count (x:xs) = 1 + count xs

_count:: Num b => b -> [a] -> b
_count b [] = b
_count b (x:xs) = _count (b + 1) xs

count:: [a] -> Int
count = _count 0

myfold:: (b -> a -> b) -> b -> [a] -> b
myfold f b [] = b
myfold f b (x:xs) = myfold f (f b x) xs

count = myfold incr 0
   where incr c _ = c + 1

myfoldr:: (a -> b -> b) -> b -> [a] -> b
myfoldr f b [] = b
myfoldr f b (x:xs) = f x (myfoldr f b xs)