Sage is a cross-platform chess library for Swift.

Development happens in the develop branch.

• Features
• Installation
  • Compatibility
  • Swift Package Manager
  • Manually
• Usage
  • Game Management
  • Move Execution
  • Move Generation
  • Move Validation
  • Undo and Redo Moves
  • Promotion Handling
  • Pretty Printing
  • Forsyth–Edwards Notation
  • Iterating Through a Board
  • Squares to Moves
  • Playground Usage
    • Board Quick Look
• Donation
• License

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Features

• Chess game management
• Chess board structuring
• Move generation / validation
• En passant and castling
• Pawn promotions
• FEN for games and boards
• PGN parsing and exporting
• Documentation

Installation

Compatibility

• Platforms:
  • macOS 10.9+
  • iOS 8.0+
  • watchOS 2.0+
  • tvOS 9.0+
  • Linux
• Xcode 10.2.1
• Swift 4.2 (Swift 5 compatibility coming soon)

Install Using Swift Package Manager

The Swift Package Manager is a decentralized dependency manager for Swift.

1. Add the project to your Package.swift.

   import PackageDescription
   
   let package = Package(
       name: "MyAwesomeProject",
       dependencies: [
           .Package(url: "https://github.com/SuperGeroy/Sage.git",
                    majorVersion: 2)
       ]
   )

2. Import the Sage module.

   import Sage

Install Manually

1. Download and drop the /Sources folder into your project.

2. Congratulations!

Usage

Game Management

Running a chess game can be as simple as setting up a loop.

import Sage

let game = Game()

while !game.isFinished {
    let move = ...
    try game.execute(move: move)
}

Move Execution

Moves for a Game instance can be executed with execute(move:) and its unsafe (yet faster) sibling, execute(uncheckedMove:).

The execute(uncheckedMove:) method assumes that the passed move is legal. It should only be called if you absolutely know this is true. Such a case is when using a move returned by availableMoves(). Otherwise use execute(move:), which checks the legality of the passed move.

Move Generation

Sage is capable of generating legal moves for the current player with full support for special moves such as en passant and castling.

• availableMoves() will return all moves currently available.

• movesForPiece(at:) will return all moves for a piece at a square.

• movesBitboardForPiece(at:) will return a Bitboard containing all of the squares a piece at a square can move to.

Move Validation

Sage can also validate whether a move is legal with the isLegal(move:) method for a Game state.

The execute(move:) family of methods calls this method, so it would be faster to execute the move directly and catch any error from an illegal move.

Undo and Redo Moves

Move undo and redo operations are done with the undoMove() and redoMove() methods. The undone or redone move is returned.

To just check what moves are to be undone or redone, the moveToUndo() and moveToRedo() methods are available.

Promotion Handling

The execute(move:promotion:) method takes a closure that returns a promotion piece kind. This allows for the app to prompt the user for a promotion piece or perform any other operations before choosing a promotion piece kind.

try game.execute(move: move) {
    ...
    return .queen
}

The closure is only executed if the move is a pawn promotion. An error is thrown if the promotion piece kind cannot promote a pawn, such as with a king or pawn.

A piece kind can also be given without a closure. The default is a queen.

try game.execute(move: move, promotion: .queen)

Pretty Printing

The Board and Bitboard types both have an ascii property that can be used to print a visual board.

let board = Board()

board.ascii
//   +-----------------+
// 8 | r n b q k b n r |
// 7 | p p p p p p p p |
// 6 | . . . . . . . . |
// 5 | . . . . . . . . |
// 4 | . . . . . . . . |
// 3 | . . . . . . . . |
// 2 | P P P P P P P P |
// 1 | R N B Q K B N R |
//   +-----------------+
//     a b c d e f g h

board.occupiedSpaces.ascii
//   +-----------------+
// 8 | 1 1 1 1 1 1 1 1 |
// 7 | 1 1 1 1 1 1 1 1 |
// 6 | . . . . . . . . |
// 5 | . . . . . . . . |
// 4 | . . . . . . . . |
// 3 | . . . . . . . . |
// 2 | 1 1 1 1 1 1 1 1 |
// 1 | 1 1 1 1 1 1 1 1 |
//   +-----------------+
//     a b c d e f g h

Forsyth–Edwards Notation

The Game.Position and Board types can both generate a FEN string.

let game = Game()

game.position.fen()
// rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1

game.board.fen()
// rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR

They can also be initialized from a FEN string.

assert(Board(fen: game.board.fen()) == game.board)

assert(Game.Position(fen: game.position.fen()) == game.position)

Iterating Through a Board

The Board type conforms to Sequence, making iterating through its spaces seamless.

for space in Board() {
    if let piece = space.piece {
        print("\(piece) at \(space.square)")
    }
}

Squares to Moves

Sequence and Square have two methods that return an array of moves that go from/to self to/from the parameter.

[.a1, .h3, .b5].moves(from: .b4)
// [b4 >>> a1, b4 >>> h3, b4 >>> b5]

[.c3, .d2, .f1].moves(to: .a6)
// [c3 >>> a6, d2 >>> a6, f1 >>> a6]

Square.d4.moves(from: [.c2, .f8, .h2])
// [c2 >>> d4, f8 >>> d4, h2 >>> d4]

Square.a4.moves(to: [.c3, .d4, .f6])
// [a4 >>> c3, a4 >>> d4, a4 >>> f6]

Playground Usage

To use Sage.playground, first open Sage.xcodeproj and build the OS X target. You can then use the playground from within the project.

Board Quick Look

Board conforms to the CustomPlaygroundDisplayConvertible protocol.

Donation

I work on this in my free time and do my best to make it as great as it can be. If you want to help me keep pushing out awesome libraries like this, a donation would be greatly appreciated. 😄

License

Sage and its modifications are published under version 2.0 of the Apache License.