deep_copy_bug.nim

import terminal, os
type Board = array[-1 .. 40, array[-1 .. 20, bool]]

proc initBoard: Board =
  result[20][8] = true
  result[21][9] = true
  result[19][10] = true
  result[20][10] = true
  result[21][10] = true

proc countLives(board: Board, x, y: int): int =
  result = if board[x][y]: -1 else: 0
  for nx in (x - 1) .. (x + 1):
    for ny in (y - 1) .. (y + 1):
      if board[nx][ny]: inc result

proc tick(board: var Board) =
  var copy = board
  deepCopy(copy, board) # REMOVE THIS TO GET A WORKING VERSION
  for x in 0..<board.high:
    for y in 0..<board[0].high:
      let neighbours = countLives(copy, x, y)
      let alive = copy[x][y]
      if not alive and neighbours == 3:
        board[x][y] = true
      elif alive and neighbours in {0 .. 8} - {2, 3}:
        board[x][y] = false

proc draw(board: Board) =
  stdout.eraseScreen()
  for x in 0..<board.high:
    for y in 0..<board[0].high:
      setCursorPos(stdout, x, y)
      if board[x][y]:
        stdout.write "●"
      else:
        stdout.write " "
  stdout.flushFile

var board = initBoard()
while true:
  board.draw()
  board.tick()

  sleep(200)