If you change the code from "n `mod` n" to "n `mod` 2", and add "-O" as a compiler flag, you'll see an "and" with 1 pop up in the assembly. Without -O, what's

If you change the code from "n `mod` n" to "n `mod` 2", and add "-O" as a compiler flag, you'll see an "and" with 1 pop up in the assembly. Without -O, what's happening is that "mod" is a method from the Integral type class (for the non-haskellers: read "interface"/"abstract class"), and thus the program just reads the corresponding field from the stafically allocated copy of the Integral dictionary for Int, and subsequently calls it. Of course one should just inline this known function call, and that's precisely what -O lets ghc do.