4.3 Unification

int PlTerm::operator =(Type)

The operator = is defined for the Types PlTerm, long, double, char * and PlAtom. It performs Prolog unification and returns TRUE if successful and FALSE otherwise.

The boolean return-value leads to somewhat unconventional-looking code as normally, assignment returns the value assigned in C. Unification however is fundamentally different to assignment as it can succeed or fail. Here is a common example.

PREDICATE(hostname, 1)
{ char buf[32];

  if ( gethostname(buf, sizeof(buf)) == 0 )
    return A1 = buf;

  return FALSE;
}