Sage : a cross-platform chess library for Swift

by iOS Example

Deprecated

This project is no longer in development. I am currently developing a chess
engine, Hexe. It is written in Rust, which is very similar to Swift in many
ways. There also exists Hexe.swift, a
Swift wrapper for Hexe.

Sage is not a chess engine; it’s a move generator. Hexe, on the other hand,
is able to both generate moves and evaluate them.

Sage is a cross-platform chess library for Swift.

Development happens in the develop branch.

Build Status

Branch Status
master
develop

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 7.3 and 8.0
  • Swift 2.2 and 3.0

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/nvzqz/Sage.git",
                 majorVersion: 2)
    ]
)

  2. Import the Sage module.

    import Sage

Install Using CocoaPods

CocoaPods is a centralized dependency manager for
Objective-C and Swift. Go here
to learn more.

  1. Add the project to your Podfile.

    use_frameworks!

pod 'Sage', '~> 2.0.0'

    If you want to be on the bleeding edge, replace the last line with:

    pod 'Sage', :git => 'https://github.com/nvzqz/Sage.git'

  2. Run pod install and open the .xcworkspace file to launch Xcode.

  3. Import the Sage framework.

    import Sage

Install Using Carthage

Carthage is a decentralized dependency
manager for Objective-C and Swift.

  1. Add the project to your Cartfile.

    github "nvzqz/Sage"

  2. Run carthage update and follow the additional steps
    in order to add Sage to your project.

  3. Import the Sage framework.

    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 CustomPlaygroundQuickLookable protocol.

License

Sage is published under version 2.0 of the Apache License.

GitHub

View Github