module Inductive where

-- Lists of integers.

data MyListZ = Nil | Node Integer MyListZ
    deriving Show

example_MyListZ = Node 4 (Node 1 (Node 6 Nil))

-- Structural recursion. It's foldr but different argument order.
srec_MyListZ :: forall r. MyListZ -> r -> (Integer -> r -> r) -> r
srec_MyListZ xs ifNil ifNode = go xs
  where
    go Nil = ifNil
    go (Node x xt) = ifNode x (go xt)

mySum :: MyListZ -> Integer
mySum xs = srec_MyListZ xs 0 (+)