public override void visit(MinusExp n)
 {
     n.Scope = Scope;
     n.e1.accept(this);
     n.e2.accept(this);
 }
 public void visit(MinusExp n)
 {
     throw new NotImplementedException();
 }
 public ASTType visit(MinusExp n)
 {
     return CheckTypes(n);
 }