/* File: LIB.PRO, Mohsin Ahmed,     1988
 * SYNOPSIS: misc prolog predicates.
 * GPL(C) Mohsin Ahmed, http://www.cs.albany.edu/~mosh
*/

/* List of Predicates:                    */
/*    member(L,L)                         */
/*    islist(T)                           */
/*    append(L,L,L)                       */
/*    pp(T)                               */
/*    last(T,L)                           */
/*    reverse(L,L)                        */
/*    efface(E,L,L)                       */
/*    delete(E,L,L)                       */
/*    subst(E,L,E,L)                      */
/*    subset(E,L)                         */
/*    intersecion(L,L,L)                  */
/*    union(L,L,L)                        */
/*    hanoi(N)                            */
/*    replace(T,T,T,T)                    */
/* Where: T term, L list,                 */
/*        N number, E element             */

member(X,[X|_]).
member(X,[_|Y]) :-
        member(X,Y).

islist(X) :-
        var(X), !, fail.
islist([A|B]) :-
        islist(B).
islist([]).

append([],L,L).
append([X|L1],L2,[X|L3]) :-
        append(L1,L2,L3).

pp(X) :-
        pp(X,0).
pp([H|T],I) :-
        !, J is I+3,
        pp(H,J),
        ppx(T,J),
        nl.
pp(X,I)     :-
        tab(I), write(X), nl.
ppx([],_).
ppx([H|T],I) :-
        pp(H,I),
        ppx(T,I).

last(X,[X]).
last(X,[_|Y]) :-
        last(X,Y).

reverse( L1, L2 ) :-
	reverse( L1, [], L2 ).
reverse( [], Stack, Stack ).
reverse( [H|T], Stack, Out ) :-
	reverse( T, [H|Stack], Out ).
/*
reverse([],[]).
reverse([H|T],L) :-
	reverse(T,Z),
	append(Z,[H],L).
*/

efface(_,[],[]).
efface(A,[A|L],L)     :-  !.
efface(A,[B|L],[B|M]) :-
        efface(A,L,M).

delete(_,[],[]).
delete(X,[X|L],M) :-
        !, delete(X,L,M).
delete(X,[Y|L1],[Y|L2]) :-
        delete(X,L1,L2).

subst(_,[],_,[]).
subst(X,[X|L],A,[A|M]) :-
        !, subst(X,L,A,M).
subst(X,[Y|L],A,[Y|M]) :-
        subst(X,L,A,M).

subset([A|X],Y) :-
        member(A,Y), subset(X,Y).
subset([],Y).

intersection([],X,[]).
intersection([X|R],Y,[X|Z]) :-
        member(X,Y),
        !,
        intersection(R,Y,Z).
intersection([X|R],Y,Z) :-
        intersection(R,Y,Z).

union([],X,X).
union([X|R],Y,Z) :-
        member(X,Y),
        !,
        union(R,Y,Z).
union([X|R],Y,[X|Z]) :-
        union(R,Y,Z).

hanoi(N) :-
        hanoi1(N,1,2,3).
hanoi1(0,_,_,_) :-  !.
hanoi1(N,A,B,C) :-
        M is N-1,
        hanoi1(M,A,C,B),
        write([A,' -> ',B]), nl,
        hanoi1(M,C,B,A).

/* replace_var(var,var_value,old,new) */
replace(I,V,I,V)   :-  !.
replace(_,_,I,I)   :-
       atomic(I), !.
replace(_,_,[],[]) :-  !.
replace(I,V,[H|T],[NH|NT]) :-
       replace(I,V,H,NH),
       replace(I,V,T,NT),
       !.
replace(I,V,F,N_F) :-
       F =.. [C|P],
       replace(I,V,C,N_C),
       replace(I,V,P,N_P),
       N_F =.. [N_C|N_P],
       !.
replace(_,_,Z,Z) :- !.
/*----------------------------------------------------------------
	reverse( list-in:i, list-out:o ). No Append reqd.
	reverse( list-in:i, stack-to-push-list-in:i, list-out:o ).
----------------------------------------------------------------*/
reverse( L1, L2 ):- reverse( L1, [], L2 ).
reverse( [], Stack, Stack ).
reverse( [H|T], Stack, Out ):- reverse( T, [H|Stack], Out ).