Question

While reading Real world Haskell I came up with this note:

ghci> :info (+)
  class (Eq a, Show a) => Num a where
  (+) :: a -> a -> a
  ...
  -- Defined in GHC.Num
  infixl 6 +

But how can Haskell define + as a non-native function? At some level you have to say that 2 + 3 will become assembler i.e. machine code.

Answer 1

The + function is overloaded and for some types, like Int and Double the definition of + is something like

instance Num Int where
    x + y = primAddInt x y

where primAddInt is a function the compiler knows about and will generate machine code for.

The details of how this looks and works depends on the Haskell implementation you’re looking at.