-- Carsten Schuermann
-- Lecture 4 : Lists / Functions / Lazyness

module Lists where

-- a non-terminating function

run :: Float -> Float
run x = run x


-- two lists

x :: [Float]
x = run 4.0 : 7.11 : []

x' :: [Float]
x' = [4.0, 7.11]


y :: [Float]
y = 5.0 : 5.0 : []


hx = head x
tx = tail x

-- append

z = x ++ y


-- adding elements of a list

add x =
  case x  of
    [] -> 0.0
    h : t -> h + (add t)

-- using functions.

add' = \x ->
  case x  of
    [] -> 0.0
    h : t -> h + (add' t)


-- making it even more abstract

fold' = \l -> \c -> \f ->
  case l  of
    [] -> c
    h : l' -> f (h,  fold' l' c f) 


-- where is the mistake

fold = \l -> \c -> \f ->
  case l  of
    [] -> c
    h : l' -> f h (fold l' c f)