/* File:      ptq_utils.P
** Author(s): David S. Warren
** Contact:   xsb-contact@cs.sunysb.edu
** 
** Copyright (C) The Research Foundation of SUNY, 1986, 1993-1998
** 
** XSB is free software; you can redistribute it and/or modify it under the
** terms of the GNU Library General Public License as published by the Free
** Software Foundation; either version 2 of the License, or (at your option)
** any later version.
** 
** XSB is distributed in the hope that it will be useful, but WITHOUT ANY
** WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
** FOR A PARTICULAR PURPOSE.  See the GNU Library General Public License for
** more details.
** 
** You should have received a copy of the GNU Library General Public License
** along with XSB; if not, write to the Free Software Foundation,
** Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
**
** $Id: ptq_utils.P,v 1.1.1.1 1998/11/05 17:00:57 sbprolog Exp $
** 
*/


/****** Utility Functions for PTQ grammar ******/

:- export delete/3, delete_some/3, not_occurs_in/2, commatolist/2.

delete(X,[X|L],L).
delete(X,[Y|L0],[Y|L1]) :- delete(X,L0,L1).

delete_some(_,[],[]).
delete_some(X,[X|L0],L) :- delete_some(X,L0,L).
delete_some(X,[Y|L0],[Y|L]) :- delete_some(X,L0,L).

not_occurs_in(X,T) :- X==T,!,fail.
not_occurs_in(_X,T) :- var(T),!.
not_occurs_in(_X,T) :- atomic(T),!.
not_occurs_in(X,T) :- functor(T,_F,A),not_occurs_in(X,T,A).

not_occurs_in(_X,_T,0) :- !.
not_occurs_in(X,T,A) :- arg(A,T,Y),not_occurs_in(X,Y),
        A1 is A-1, not_occurs_in(X,T,A1).

commatolist(A,[A]) :- var(A),!.
commatolist((A,B),[A|B1]) :- !, commatolist(B,B1).
commatolist(A,[A]).