Assignments

ARCHITECTURE test1 OF
test_mux IS
    SIGNAL a : BIT := '1';
    SIGNAL b : BIT := '0';
BEGIN

...more statements...
   a <= b;
   b <= a;
...more statements...

END test1;   

ARCHITECTURE test2 OF test_mux IS BEGIN
PROCESS (result)
   VARIABLE a : BIT := '1';
   VARIABLE b : BIT := '0';
BEGIN
...more statements...
   a := b;
   b := a;
...more statements...
   END PROCESS;
END test2;