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Choice

module Main where

We define add to be a function that adds its arguments unless one of its arguments is zero, in which case it returns zero. Here, we use an if statement.

add ∷ Int → Int → Int
add x y = if x == 0 || y == 0 then 0 else x + y

main ∷ IO ()
main = do
   print $ add 0 1
   print $ add 1 0
   print $ add 1 1

0
0
2

Main.hs