99 questions/Solutions/4

(*) Find the number of elements of a list.

myLength           :: [a] -> Int
myLength []        =  0
myLength (_:xs)    =  1 + myLength xs

myLength'     =  foldl (\n _ -> n + 1) 0
myLength''    =  foldr (\_ n -> n + 1) 0
myLength'''   =  foldr (\_ -> (+1)) 0
myLength''''  =  foldr ((+) . (const 1)) 0
myLength''''' =  foldr (const (+1)) 0

myLength' xs = snd $ last $ zip xs [1..] -- Just for fun
myLength''   = snd . last . (flip zip [1..]) -- Because point-free is also fun

myLength = sum . map (\x -> 1)

This is length in Prelude.