/* pete1a.pl
 *
 * CS 313
 *
 * easy version of pete's puzzle solver
 *
 * extended to try to solve all puzzles with nums 1 and 2.
 */

num(1).
num(2).
/* can add more numbers here */

solveall :-
  write_ln('pete1a.pl - all solutions for puzzles with 1 and 2 only'),
  num(A), num(B), num(C), num(D),
  write(A), write(B), write(C), write(D), write(': '),
  trysolve(A, B, C, D),
  fail.

trysolve(A, B, C, D) :-
  solve(A, B, C, D),
  !.                     /* the CUT prevents backtracking for more solns */

trysolve(_, _, _, _) :-
  write_ln('---------- no solution').

/* rest as in pete1.pl, except using =:= (equality after evaluating): */

solve(A, B, C, D) :- 
  exp2(A, B, E1),
  exp2(C, D, E2),
  E1 =:= E2,              /* replaces 'checkeq' predicate in pete1.pl */
  write_ln(E1 = E2).

exp2(A, B, A+B).
exp2(A, B, A-B).
exp2(A, B, A*B).
exp2(A, B, A/B) :- B \= 0.



/*

Sample output:

?- solveall.
pete1a.pl - all solutions for puzzles with 1 and 2 only
1111: 1+1=1+1
1112: 1+1=1*2
1121: 1+1=2*1
1122: 1-1=2-2
1211: 1*2=1+1
1212: 1+2=1+2
1221: 1+2=2+1
1222: ---------- no solution
2111: 2-1=1*1
2112: 2+1=1+2
2121: 2+1=2+1
2122: 2-1=2/2
2211: 2-2=1-1
2212: ---------- no solution
2221: 2/2=2-1
2222: 2+2=2+2
false.

*/