8 Queen solver

eightqueen.pro

% eightqueen.pro
%

nocheck(_,[]).
nocheck(X/Y, [X1/Y1 | Rest]) :- X=\=X1,Y=\=Y1,
                                abs(Y1-Y) =\= abs(X1-X),
                                nocheck(X/Y,Rest).

legal([]).
legal([X/Y | Rest]) :-
    legal( Rest),
%    member(X,[1,2,3,4,5,6,7,8]),
    member(X,[1,2,3,4,5,6,7,8]),
    nocheck(X/Y,Rest).


if(Test,Then) :- Test,!,Then.
if(_,_,Else) :- Else.


manual(X) :- write('ls:  list the solutions
cn:  output the number of solutions
mp;  display mapping on the board for solutions
\n
Enter Command:'),
            read(X),
            write('You enter:'), write(X), nl.

eightqueens :- manual(CMD),
                  eightqueens_body(CMD).

eightqueens_body(CMD) :- 
                  CMD == 'mp',findall( X, eightqueens_map(X), L),
                  len(L,N),write('There are '),write(N),write(' solutions.').

eightqueens_body(CMD) :-
                  CMD == 'ls',findall( X, eightqueens_list(X), L),
                  showlist3(L,1), len(L,N),write('There are '),write(N),write(' solutions.').
                  
eightqueens_body(CMD) :-
                  CMD == 'cn',findall( X, eightqueens_cnt(X), L),
                  len(L,N),write('There are '),write(N),write(' solutions.').

eightqueens_map(X) :- 
                  X = [_/1,_/2,_/3,_/4,_/5,_/6,_/7,_/8],
                  legal(X),
                  showlist(X),
                  write('['),tab(1),
                  showlist2(X).

eightqueens_list(X) :- 
                  X = [_/1,_/2,_/3,_/4,_/5,_/6,_/7,_/8],
                  legal(X).

                  %legal(X),
                  %write('['),
                  %showlist3(X).

eightqueens_cnt(X) :- 
                  X = [_/1,_/2,_/3,_/4,_/5,_/6,_/7,_/8],
                  legal(X).

showlist([]) :- nl.
showlist([X|Y]) :- X = C/_, showboard(C,8), showlist(Y). 

showlist2([]) :- write(']\n\n\n').
showlist2([X|Y]) :- write(X), tab(1), showlist2(Y). 

                  
showlist3([],0) :- nl.
showlist3([X|Y],N) :- N1 is N + 1, write(N), tab(1), write('['), showlist2(X), showlist3(Y,N1). 

showboard(X,N) :- X = 0, write('Q|'), N1 is N -1, showboard2(N1).
showboard(X,N) :- X > 0, write(' |'), X1 is X - 1, N1 is N -1, showboard(X1,N1). 

showboard2(N) :- N < 0, write('\n').
showboard2(N) :- N = 0, write(' |'),N1 is N -1, showboard2(N1).
showboard2(N) :- N > 0, write(' |'),N1 is N - 1, showboard2(N1).

len([],0) :- nl.
len([_|T], N) :- len(T, N1), N is 1 + N1.