Infinite loop in pow function

Question

I'm new to Haskell, and I'm getting an infinite loop here, but I don't know why.

module Main where

pow :: Int -> Int -> Int
pow x 0 = 1
pow x y = x * pow x y-1

main :: IO ()
main = print( pow 2 3 )

Any ideas?

Answer 1

pow x y = x * pow x y-1

doesn't do what you think it does. It is parsed as

pow x y = (x) * (pow x y) - (1)
                ^^^^^^^^^
               infinite loop

Now you can see the infinite loop more clearly. You need to parenthesize y-1,

pow x y = x * pow x (y-1)