Ejemplo n.º 1
0
 /**
  * var unification.
  *
  * <p>First, verify the Term eventually already unified with the same Var if the Term exist, unify
  * var with that term, in order to handle situation as (A = p(X) , A = p(1)) which must produce
  * X/1.
  *
  * <p>If instead the var is not already unified, then:
  *
  * <p>if the Term is a var bound to X, then try unification with X so for example if A=1, B=A then
  * B is unified to 1 and not to A (note that it's coherent with chronological backtracking: the
  * eventually backtracked A unification is always after backtracking of B unification.
  *
  * <p>if are the same Var, unification must succeed, but without any new bindings (to avoid cycles
  * for extends in A = B, B = A)
  *
  * <p>if the term is a number, then it's a success and new link is created (retractable by means
  * of a code)
  *
  * <p>if the term is a compound, then occur check test is executed: the var must not appear in the
  * compound ( avoid X=p(X), or p(X,X)=p(Y,f(Y)) ); if occur check is ok then it's success and a
  * new link is created (retractable by a code)
  */
 boolean unify(List vl1, List vl2, Term t) {
   Term tt = getTerm();
   if (tt == this) {
     t = t.getTerm();
     if (t instanceof Var) {
       if (this == t) {
         try {
           vl1.add(this);
         } catch (NullPointerException e) {
           /* vl1==null mean nothing intresting for the caller */
         }
         return true;
       }
     } else if (t instanceof Struct) {
       // occur-check
       if (occurCheck(vl2, (Struct) t)) {
         return false;
       }
     } else if (!(t instanceof Number)) {
       return false;
     }
     link = t;
     try {
       vl1.add(this);
     } catch (NullPointerException e) {
       /* vl1==null mean nothing intresting for the caller */
     }
     // System.out.println("VAR "+name+" BOUND to "+link+" - time: "+time+" - mark: "+mark);
     return true;
   } else {
     return (tt.unify(vl1, vl2, t));
   }
 }
Ejemplo n.º 2
0
 @Override
 public boolean unify(Term t1) {
   // used to be implemented using recursion but caused stack overflow problems with long lists
   Term t2 = this;
   do {
     TermType tType = t1.getType();
     if (tType == TermType.LIST) {
       if (t2.getArgument(0).unify(t1.getArgument(0)) == false) {
         return false;
       }
       t1 = t1.getArgument(1);
       t2 = t2.getArgument(1);
     } else if (tType.isVariable()) {
       return t1.unify(t2);
     } else {
       return false;
     }
   } while (t2.getType() == TermType.LIST);
   return t2.unify(t1);
 }