Prolog code

Posted on February 23, 2007

Example of how to draw NxM board in Prolog. Usefull when you need to show the state of a chess board or for games like wolves and sheep. Code from Simon Colton’s tutorial page.

127 cell(A,B) :-
128     L = [1,2,3,4,5,6,7,8],
129     member(A,L),
130     member(B,L).
131 
132 draw_board(Board) :-
133     write(‘  12345678\n‘),
134     write(‘ +——–+‘),
135     findall(_,
136         (cell(A,B), draw_newline(A,B),
              draw_cell(A,B,Board),draw_endline(B)),
137         _),
138     write(‘\n +——–+\n\n‘).
139 
140 draw_newline(A,1) :-
141     write(‘\n‘),
142     write(A),
143     write(‘|‘).
144 draw_newline(_,X) :-
145     X=\=1.
146 
147 
148 draw_cell(A,B,[Wolves, _]) :-
149     member(A/B,Wolves),
150     write(‘w‘), !.
151 draw_cell(A,B,[_, Sheep]) :-
152     member(A/B,Sheep),
153     write(‘r‘), !.
154 draw_cell(_,_,[_, _]) :-
155     write(‘ ‘).
156 
157 
158 draw_endline(8) :-
159     write(‘|‘).
160 draw_endline(X) :-
161     X=\=8.
162

Pass the state as a parameter
draw_board([[1/1,1/3,1/5,1/7],[2/4]]).
and it will display the board:

12345678
+——–+
1|w w w w |
2|   r    |
3|        |
4|        |
5|        |
6|        |
7|        |
8|        |
+——–+

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