JavaScript で Sudoku を解いてみる (2)

前回の続きで、塗り分けの時にモナド的に書きたいなと言っていたところを、無い知恵を絞ってモナドもどきを作ってみた。

        var Result = {
            False: {
                bind: function() {
                    return this;
                },
                get: function() {
                    return false;
                }
            },
            True: {
                bind: function(f) {
                    return f();
                },
                get: function() {
                    return true;
                }
            },
            Undefined: {
                bind: function(f) {
                    var result = f();
                    if(result.get() === false) {
                        return result;
                    }
                    return Result.Undefined;
                },
                get: function() {
                    return undefined;
                }
            }
        }

これを使うと、「与えられた要素が全て互いに異なる」という条件はこう書ける。
モナドを使いつつも、あまり関数型っぽくない書き方だが、実行効率を踏まえつつハイブリッドなやり方と言うことで

        function AllNotEqual() {
            return allNotEqual(arguments, arguments.length-2);
        }
        function allNotEqual(items, iter) {
            var result = (function(j) {
                var callee = arguments.callee;
                if(j <= iter + 1) return NotEqual(items[iter], items[j]);
                return NotEqual(items[iter], items[j]).bind(function() { return callee(j-1); });
            })(items.length - 1);
            if(iter <= 0) {
                return result;
            }
            return result.bind(function() { return allNotEqual(items, iter-1); });
        }
        function NotEqual(x, y) {
            var tmp_x = x.get(), tmp_y = y.get();
            if(tmp_x === undefined || tmp_y === undefined)
                return Result.Undefined;
            if(tmp_x != tmp_y)
                return Result.True;
            return Result.False;
        }

Sudoku の条件である、「各行、各列、各3x3のブロックで同じ数字を使わない」は、関数型言語の勉強の時に作った do 記法もどきを利用してこう書ける。
ちとながいが、よく見れば単にルールをべた書きしただけの記述。

        var MonaDo = function(fs) {
            var monado = function(funcs) {
                if(funcs.length > 1) {
                    var inner = monado(funcs.slice(1));
                    return function(a) {
                        return funcs[0](a).bind(inner);
                    }
                }
                return funcs[0];
            }
            return monado(fs)();
        }

        function RowNotEqual(cells, row) {
            return AllNotEqual.apply(this, cells[row]);
        }
        function ColNotEqual(cells, col) {
            return AllNotEqual.apply(this, cells.map(function(row) {
                return row[col];
            }));
        }
        function BlkNotEqual(cells, row, col) {
            return AllNotEqual(
                cells[row][col],  cells[row][col+1],  cells[row][col+2],
                cells[row+1][col],cells[row+1][col+1],cells[row+1][col+2],
                cells[row+2][col],cells[row+2][col+1],cells[row+2][col+2]);
        }
        var Condition = function() {
            return MonaDo([
                function() {return RowNotEqual(Cells, 0); },
                function() {return RowNotEqual(Cells, 1); },
                function() {return RowNotEqual(Cells, 2); },
                function() {return RowNotEqual(Cells, 3); },
                function() {return RowNotEqual(Cells, 4); },
                function() {return RowNotEqual(Cells, 5); },
                function() {return RowNotEqual(Cells, 6); },
                function() {return RowNotEqual(Cells, 7); },
                function() {return RowNotEqual(Cells, 8); },
                function() {return ColNotEqual(Cells, 0); },
                function() {return ColNotEqual(Cells, 1); },
                function() {return ColNotEqual(Cells, 2); },
                function() {return ColNotEqual(Cells, 3); },
                function() {return ColNotEqual(Cells, 4); },
                function() {return ColNotEqual(Cells, 5); },
                function() {return ColNotEqual(Cells, 6); },
                function() {return ColNotEqual(Cells, 7); },
                function() {return ColNotEqual(Cells, 8); },
                function() {return BlkNotEqual(Cells, 0, 0); },
                function() {return BlkNotEqual(Cells, 0, 3); },
                function() {return BlkNotEqual(Cells, 0, 6); },
                function() {return BlkNotEqual(Cells, 3, 0); },
                function() {return BlkNotEqual(Cells, 3, 3); },
                function() {return BlkNotEqual(Cells, 3, 6); },
                function() {return BlkNotEqual(Cells, 6, 0); },
                function() {return BlkNotEqual(Cells, 6, 3); },
                function() {return BlkNotEqual(Cells, 6, 6); }
            ]).get()
        };