[howling]

All these discussions of "=" are missing the point.

The notation "x = x + 1" is awful because at lhs x denotes a reference to an integer while at rhs x denotes the value hold by the reference. If you know C, it is similar to the difference between an integer pointer *x and an integer x. As an illustration, here are two programs that are doing the same thing, one in C and one in Haskell.

  #include <stdio.h>

  int main() {
    int x = 0;
    x = x + 1;
    printf("%d\n", x);
    return 0;
  }


  import Data.IORef

  main :: IO ()
  main = do
    xref <- newIORef 0
    x1 <- readIORef xref
    writeIORef xref (x1 + 1)
    x2 <- readIORef xref
    print x2

[segmondy]

We don't have such problem in Prolog. In prolog X can never be equal to X+1. X will always be X. Once X has a value, it never changes. One of the thing that gives most procedural programmers a headache.