Implementation of Nim in R

nim.R

## Nim
next_player <- function(player) if(player == 1) 2 else 1
valid_move  <- function(board, row, num) board[row] >= num
finished    <- function(board) all(board == 0)
update      <- function(board, row, num) `[<-`(board, row, board[row] - num)
disp_row    <- function(row, num) cat(row, ":", rep("*", num), "\n")
disp_board  <- function(board) purrr::walk2(seq_along(board), board, disp_row)

nim <- function(board = 5:1, player = 1) {
  if(finished(board)) {
    cat("Game over. Player", next_player(player), "wins!")
    return(invisible())
  }

  disp_board(board)
  cat("Player", player)
  row <- as.integer(readline("Choose a row: "))
  num <- as.integer(readline("Number of stars to remove: "))

  if(!valid_move(board, row, num)) {
    cat("Not a valid move. Try again.\n")
    nim(board, player)
  } else nim(update(board, row, num), next_player(player))
}