ExChess.Board (ExChess v0.1.0)

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Exposes a set of types and functions to work with the game's chess board.

Summary

Types

t()

A map with ExChess.Squares as keys and ExChess.Pieces as values.

Functions

empty()

Returns an empty board.

get(board, square)

Gets the piece from square of board. Returns the ExChess.Piece or nil when not found.

get_pieces_by_color(board, color)

Returns a list of all pieces of color on board.

new()

Creates a new chess board in the starting position: rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR

set(board, square, piece)

Returns an updated board with square's value set to piece.

square_empty?(board, square)

Returns true if square of board has no piece on it, otherwise false.

unset(board, square)

Returns an updated board where the square and it's piece are unset.

Types

t()

@type t() :: %{required(ExChess.Square.t()) => ExChess.Piece.t()}

A map with ExChess.Squares as keys and ExChess.Pieces as values.

If a square on the board is occupied by no piece, it should not appear in the map's keys at all.

This implementation is quite primitive and not very performant, so in later versions it will be replaced with a different board representation, probably bitboards.

Functions

empty()

@spec empty() :: t()

Returns an empty board.

Currently not very useful, but the client code should not care about the fact the board is a map.

Examples

iex> ExChess.Board.empty()
...> |> ExChess.Fen.from_board()
"8/8/8/8/8/8/8/8"

get(board, square)

@spec get(t(), ExChess.Square.t()) :: ExChess.Piece.t() | nil

Gets the piece from square of board. Returns the ExChess.Piece or nil when not found.

Examples

Piece found

iex> white_king_square = ExChess.Square.new(4, 0)
iex> ExChess.Board.new()
...> |> ExChess.Board.get(white_king_square)
%ExChess.Piece{type: :k, color: :white}

Piece not found

iex> ExChess.Board.empty()
...> |> ExChess.Board.get(ExChess.Square.new(0, 0))
nil

get_pieces_by_color(board, color)

@spec get_pieces_by_color(t(), ExChess.Piece.color()) :: [
  {ExChess.Square.t(), ExChess.Piece.t()}
]

Returns a list of all pieces of color on board.

The returned element is a list of tuples where the first element is the ExChess.Square, and the second element is the ExChess.Piece.

Examples

Empty board

iex> ExChess.Board.empty()
...> |> ExChess.Board.get_pieces_by_color(:white)
[]

Board with pieces

iex> ExChess.Fen.to_board("k7/1p6/8/8/8/8/8/8")
...> |> ExChess.Board.get_pieces_by_color(:black)
[
  {%ExChess.Square{file: 0, rank: 7}, %ExChess.Piece{type: :k, color: :black}},
  {%ExChess.Square{file: 1, rank: 6}, %ExChess.Piece{type: :p, color: :black}}
]

new()

@spec new() :: t()

Creates a new chess board in the starting position: rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR

Examples

iex> ExChess.Board.new()
...> |> ExChess.Fen.from_board()
"rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"

set(board, square, piece)

@spec set(t(), ExChess.Square.t(), ExChess.Piece.t()) :: t()

Returns an updated board with square's value set to piece.

Examples

Set piece on empty square

iex> ExChess.Board.empty()
...> |> ExChess.Board.set(ExChess.Square.new(0, 0), ExChess.Piece.new(:k, :white))
...> |> ExChess.Fen.from_board()
"8/8/8/8/8/8/8/K7"

Set piece on occupied square

iex> square = ExChess.Square.new(0, 0)
iex> board = ExChess.Board.empty()
...> |> ExChess.Board.set(square, ExChess.Piece.new(:k, :white))
iex> ExChess.Fen.from_board(board)
"8/8/8/8/8/8/8/K7"
iex> ExChess.Board.set(board, square, ExChess.Piece.new(:n, :black))
...> |> ExChess.Fen.from_board()
"8/8/8/8/8/8/8/n7"

square_empty?(board, square)

@spec square_empty?(t(), ExChess.Square.t()) :: boolean()

Returns true if square of board has no piece on it, otherwise false.

Empty

iex> ExChess.Board.empty()
...> |> ExChess.Board.square_empty?(ExChess.Square.new(0, 0))
true

Not empty

iex> white_king_square = ExChess.Square.new(4, 0)
iex> ExChess.Board.new()
...> |> ExChess.Board.square_empty?(white_king_square)
false

unset(board, square)

@spec unset(t(), ExChess.Square.t()) :: t()

Returns an updated board where the square and it's piece are unset.

Examples

Unset piece from occupied square

iex> square = ExChess.Square.new(0, 0)
iex> board = ExChess.Board.empty()
...> |> ExChess.Board.set(square, ExChess.Piece.new(:k, :white))
iex> ExChess.Fen.from_board(board)
"8/8/8/8/8/8/8/K7"
iex> ExChess.Board.unset(board, square)
...> |> ExChess.Fen.from_board()
"8/8/8/8/8/8/8/8"

Unset piece from empty square

iex> ExChess.Board.empty()
...> |> ExChess.Board.unset(ExChess.Square.new(0, 0))
...> |> ExChess.Fen.from_board()
"8/8/8/8/8/8/8/8"