(x,y) = (10,20)
(z:zs) = 0 : [1..]

prelude> x
10
prelude> z
0
prelude> takeN 3 zs
[1,2,3]

(x,y) = (10,20)
(z:zs) = 0 : [1..]
True = False -- HERE

prelude> x
10
prelude> 4
4
prelude> True
True

module Main where
         -- ^^^^^

x, y :: Int
(x, y) = undefined

main :: IO ()
main = putStrLn "hello!"