chess2plyrs

chess2plyrs is an R package which allows to create a chess game and add moves, verify the status of the game and list legal moves, as well as read and write FENs. It is also possible to plot the current board position. A simple chess engine based on minimax is also implemented.

Initialise a game

A new game can be created with the newgame function:

g1 <- newgame()
g1

## $board
##   a    b    c    d    e    f    g    h   
## 8 "Rb" "Nb" "Bb" "Qb" "Kb" "Bb" "Nb" "Rb"
## 7 "pb" "pb" "pb" "pb" "pb" "pb" "pb" "pb"
## 6 ""   ""   ""   ""   ""   ""   ""   ""  
## 5 ""   ""   ""   ""   ""   ""   ""   ""  
## 4 ""   ""   ""   ""   ""   ""   ""   ""  
## 3 ""   ""   ""   ""   ""   ""   ""   ""  
## 2 "pw" "pw" "pw" "pw" "pw" "pw" "pw" "pw"
## 1 "Rw" "Nw" "Bw" "Qw" "Kw" "Bw" "Nw" "Rw"
## 
## $turn
## [1] 1
## 
## $history
## NULL
## 
## $fen_history
## [1] "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w"

We can see that the object we create is a lists which contains

board: the current position
turn: 1 if it is white’s turn, -1 if it is black’s turn
history: the previous moves played (in a primitive style)
fen_history: the FEN representation of the previous moves

We can add one move using the chess_move function, which takes in input:

the game being played
the piece label (p for pawns, N for knights, B for bishops, R for rooks, Q for queens, K for kings)
the initial square of the piece to be moved
the final square

chess_move(game = g1,
            piece = "p",
            initialposition = "e2",
            finalposition = "e4")

## $board
##   a    b    c    d    e    f    g    h   
## 8 "Rb" "Nb" "Bb" "Qb" "Kb" "Bb" "Nb" "Rb"
## 7 "pb" "pb" "pb" "pb" "pb" "pb" "pb" "pb"
## 6 ""   ""   ""   ""   ""   ""   ""   ""  
## 5 ""   ""   ""   ""   ""   ""   ""   ""  
## 4 ""   ""   ""   ""   "pw" ""   ""   ""  
## 3 ""   ""   ""   ""   ""   ""   ""   ""  
## 2 "pw" "pw" "pw" "pw" ""   "pw" "pw" "pw"
## 1 "Rw" "Nw" "Bw" "Qw" "Kw" "Bw" "Nw" "Rw"
## 
## $turn
## [1] -1
## 
## $history
## [1] "pe2-e4"
## 
## $fen_history
## [1] "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w"  
## [2] "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b"

We can also make use of the pipe operator for a smoother insertion of the moves:

g2 <- newgame() |>
  chess_move("p", "e2", "e4")  |>
  chess_move("p", "e7", "e5")  |>
  chess_move("N", "g1", "f3")  |>
  chess_move("N", "b8", "c6")  |>
  chess_move("B", "f1", "b5")  |>
  chess_move("N", "g8", "f6")  |>
  chess_move("K", "e1", "0-0") |>
  chess_move("N", "f6", "e4")

If we try to add an illegal move, a note tells us that the move is not legal and the action is not performed:

x <- newgame() |>
  chess_move("p", "e2", "d5") # illegal move

## Move not valid

Chess plotting

First, we can plot the current board with the function chessplot. The style option allows for different piece styles:

style = 1 is the default option: unicode encoding is used
style = 2 plots pieces with their labels instead of the unicode. As unicode may yield an error on some platforms, here we use this option

chessplot(g2, style = 2)

Score list

We can get the moves list in scientific notation using the moves_scoresheet function

moves_scoresheet(g2)

##   n white black
## 1 1    e4    e5
## 2 2   Nf3   Nc6
## 3 3   Bb5   Nf6
## 4 4   0-0  Nxe4

Game result

The function game_result tells whether the game is still ongoing or if there is a checkmate or stalemate.

game_result(g2)

## There are still legal moves available, the game is ongoing

## To move: white

## [1] 0

We can see that in the current position there are still legal moves, hence the game is not finished.

Legal moves

All legal moves in a given position can be listed using the function legalmoves

legalmoves(g2)

##  [1] "pa2a3" "pa2a4" "Bb5e2" "Bb5d3" "Bb5c4" "Bb5a6" "Bb5a4" "Bb5c6" "pb2b3"
## [10] "pb2b4" "Nb1a3" "Nb1c3" "pc2c3" "pc2c4" "pd2d3" "pd2d4" "Qd1e1" "Qd1e2"
## [19] "Nf3e5" "Nf3d4" "Nf3g5" "Nf3h4" "Nf3e1" "Rf1e1" "pg2g3" "pg2g4" "Kg1h1"
## [28] "ph2h3" "ph2h4"

Takeback

The function takeback allows to remove the last move played. It can also be used sequentially.

takeback(g2)

## $board
##   a    b    c    d    e    f    g    h   
## 8 "Rb" ""   "Bb" "Qb" "Kb" "Bb" ""   "Rb"
## 7 "pb" "pb" "pb" "pb" ""   "pb" "pb" "pb"
## 6 ""   ""   "Nb" ""   ""   "Nb" ""   ""  
## 5 ""   "Bw" ""   ""   "pb" ""   ""   ""  
## 4 ""   ""   ""   ""   "pw" ""   ""   ""  
## 3 ""   ""   ""   ""   ""   "Nw" ""   ""  
## 2 "pw" "pw" "pw" "pw" ""   "pw" "pw" "pw"
## 1 "Rw" "Nw" "Bw" "Qw" ""   "Rw" "Kw" ""  
## 
## $turn
## [1] -1
## 
## $history
## [1] "pe2-e4"  "pe7-e5"  "Ng1-f3"  "Nb8-c6"  "Bf1-b5"  "Ng8-f6"  "Ke1_0-0"
## 
## $fen_history
## [1] "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w"            
## [2] "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b"          
## [3] "rnbqkbnr/pppp1ppp/8/4p3/4P3/8/PPPP1PPP/RNBQKBNR w"        
## [4] "rnbqkbnr/pppp1ppp/8/4p3/4P3/5N2/PPPP1PPP/RNBQKB1R b"      
## [5] "r1bqkbnr/pppp1ppp/2n5/4p3/4P3/5N2/PPPP1PPP/RNBQKB1R w"    
## [6] "r1bqkbnr/pppp1ppp/2n5/1B2p3/4P3/5N2/PPPP1PPP/RNBQK2R b"   
## [7] "r1bqkb1r/pppp1ppp/2n2n2/1B2p3/4P3/5N2/PPPP1PPP/RNBQK2R w" 
## [8] "r1bqkb1r/pppp1ppp/2n2n2/1B2p3/4P3/5N2/PPPP1PPP/RNBQ1RK1 b"