Tic Tac Toe in Ruby

ttt.rb

# NOT FINISHED!

class Board

  HORIZONTAL_ROWS = (0..8).each_slice(3).to_a
  VERTICAL_ROWS = HORIZONTAL_ROWS.transpose
  DIAGONAL_ROWS = [
    HORIZONTAL_ROWS.each_with_index.map {|a, i| a[i] },
    HORIZONTAL_ROWS.each_with_index.map {|a, i| a[2-i] },
  ]

  def initialize
    @board = Array.new(9)
  end

  def set_pos(pos, sym)
    idx = pos - 1
    if @board[idx].nil?
      @board[idx] = sym
    else
      raise 'Position already taken'
    end
  end

  def three_in_a_row?(sym)
    (HORIZONTAL_ROWS + VERTICAL_ROWS + DIAGONAL_ROWS) \
      .any? {|x| elems_eq_sym?(x, sym) }
  end

  def elems_eq_sym?(idxs, sym)
    idxs
      .map {|i| @board.at(i) }
      .all? {|e| e == sym }
  end

  def to_s
    hr = "+---+---+---+\n"
    str = @board
      .each_with_index.map {|x, i| x.nil? ? "#{i+1}  " : " #{x.to_s.upcase} " }
      .each_slice(3).map {|a| "|#{a.join('|')}|\n" }
      .join(hr)
    hr + str + hr
  end
end

module TicTacToe

  Player = Struct.new(:name, :symbol)

  PLAYERS = [
    Player.new('Player 1 (X)', :x),
    Player.new('Player 2 (O)', :o),
  ]

  def self.play
    board = Board.new
    PLAYERS.cycle do |p|
      puts board
      print "#{p.name}, choose a position: "
      pos = gets.to_i
      board.set_pos(pos, p.symbol)
      # ...
      if board.three_in_a_row?(p.symbol)
        puts "#{p.name} won!"
        break
      end
    end
  end
end

TicTacToe.play