No, he is right; however, Java has the exact problem.

The place where this code will screw up is in the logic of the comparison routine. It will be difficult for the types of x and y (or a and b in the Java example) to be wrong, but it is easy to say:

    compare (length x) (length x)

or

    compare (length y) (length x)

instead of

    compare (length x) (length y)

Your tests will catch this, though.