Initiate project

chess.pl

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+color(white).
+color(black).
+
+files([a, b, c, d, e, f, g, h]).
+
+file(X) :-
+  files(Files),
+  member(X, Files).
+
+file_index(File, Index) :-
+  files(Files),
+  nth0(Index, Files, File).
+
+rank(X) :-
+  between(1, 8, X).
+
+piece(X) :-
+  member(X, [ queen, king, rook, bishop, knight, pawn ]).
+
+valid_coor(coor(File, Rank)) :-
+  file(File),
+  rank(Rank).
+
+piece(Piece, Color) :-
+  color(Color),
+  piece(Piece).
+
+piece(Piece, Color, Coor) :-
+  piece(Piece, Color),
+  valid_coor(Coor).
+
+valid_piece(piece(Piece, Color, Coor)) :-
+  piece(Piece, Color, Coor).
+
+% Movement
+
+direction(diagonal, ne,  1,  1).
+direction(diagonal, nw, -1,  1).
+direction(diagonal, se,  1, -1).
+direction(diagonal, sw, -1, -1).
+direction(straight, e,   1,  0).
+direction(straight, w,  -1,  0).
+direction(straight, n,   0,  1).
+direction(straight, s,   0, -1).
+pawn_direction(black, diagonal, se).
+pawn_direction(black, diagonal, sw).
+pawn_direction(black, straight, s).
+pawn_direction(white, diagonal, ne).
+pawn_direction(white, diagonal, nw).
+pawn_direction(white, straight, n).
+
+jump(Angle, Direction, Coor, To) :-
+  move(Angle, Direction, Coor, To);
+  move(Angle, Direction, Coor, B),
+  jump(Angle, Direction, B, To).
+
+move(Angle, Direction, coor(File, Rank), coor(ToFile, ToRank)) :-
+  direction(Angle, Direction, FileOffset, RankOffset),
+  plus(Rank, RankOffset, ToRank),
+  rank(ToRank),
+  file_index(File, Index),
+  plus(Index, FileOffset, ToIndex),
+  file_index(ToFile, ToIndex).
+
+move(Moves, From, To) :-
+  todo(Moves, From, To). % We have to check if a pawn has moved. It can jump two squares whenever that is not the case.
+
+move(piece(pawn, C, From), piece(pawn, C, To)) :-
+  pawn_direction(C, straight, D),
+  move(_, D, From, To).
+
+move(piece(rook, C, From), piece(rook, C, To)) :-
+  jump(straight, _, From, To).
+
+move(piece(bishop, C, From), piece(bishop, C, To)) :-
+  jump(diagonal, _, From, To).
+
+move(piece(king, C, From), piece(king, C, To)) :-
+  move(_, _, From, To).
+
+% The thing with the king and the rook.
+move(Moves, MovesOut) :-
+  board(Moves, Board),
+  todo(Board).
+
+% captures
+
+capture(piece(pawn, C, From), piece(pawn, C, To)) :-
+  pawn_direction(C, diagonal, D),
+  move(_, D, From, To).
+
+% Also allow capturing a piece when it tries to jump past you.
+capture(piece(pawn, C, From), piece(pawn, C, To)) :-
+  todo(Moves, From, To).
+
+capture(piece(queen, C, From), piece(queen, C, To)) :-
+  jump(_, _, From, To).
+
+capture(piece(rook, C, From), piece(rook, C, To)) :-
+  jump(straight, _, From, To).
+
+capture(piece(bishop, C, From), piece(bishop, C, To)) :-
+  jump(diagonal, _, From, To).
+
+capture(piece(king, C, From), piece(king, C, To)) :-
+  move(_, _, From, To).
+
+valid_option(Piece, capture(Option)) :-
+  capture(Piece, Option).
+
+valid_option(Piece, move(Option)) :-
+  move(Piece, Option).