Yes, that's right, I forgot to add that tricky semicolon. Thanks for this one. The second problem that I'm facing now, is that I've problem with implementing the design on the Basys 2 board. I mapped the two 4 bit vectors on the 8 switches, the 4 bit sum outputs on 4 LEDs and 1 LED for the carry with the first carry, if there's one coming into in the first full adder, on one of the 4 buttons. However, none of the LEDs turn on whenever I make any addition. It's off all the time.
Edit: OK, now it works fine and dandy. These ISE tools are complicated and tricky. It's easy to fall into simple errors that can take you hours to solve until you notice how easy it's, and sometimes just by deleting and adding the UCF file again!