ShogibanKit

Shogi, or Japanese Chess, is based on very complex rules, and it is hard to implement all basic rules. This ShogibanKit aims to implement such complex algorithm to find valid move or action, or to find out whether it is checkmate or not. I also would like to state that ShogibanKit does not provide:

• Any Graphical User Interface
• Any Artificial Intelligence

Status: Under Development

• Now, Swift 5 ready

Coding Experiment

It would be controversial for sure, I tried using Japanese for class names, variable names, and others. It is part of my experiment to see if coding with non English name would work or not, or impact of maintaining the code. For example, all type of pieces is expressed as follows using Japanese. It would be natural and easier to read code or Shogi player programmers.

enum 駒型 : Int8 {
	case 歩, 香, 桂, 銀, 金, 角, 飛, 王
	// ...
}

Since there are no Capitalization in Japanese, Swift complains using the same name for type and variables.

enum Koma { ... }
var koma = Koma(...) // OK: no problem!

enum 駒 { ... }
var 駒 = 駒(...) // Error: variable name cannot be same as type name

So suffix 型 to be added for Japanese type names.

enum 駒型 { ... }
var 駒 = 駒型(...) // OK: no problem!

Common classes and types

Here is the list of common classes or types.

Name	Type	Description
筋型	enum	Column (right to left)
段型	enum	Row
位置型	enum	Position (row and column)
駒型	enum	Type of piece (no front/back)
駒面型	enum	Type of piece (cares front/back)
持駒型	struct	Captured pieces
先後型	enum	Which player
升型	enum	State of board position (which players which piece, or empty?)
指手型	enum	Describe the one movement
局面型	class	Snapshot of the state of game-board

Describing position

Here are some example of describe the location of the board. The column order is from right to left, same as Shogi official. Although columns and rows is 1 based index, actual rawValue is 0 based index.

let col = 筋.４  // Zenkaku (全角)
let row = 段.七  // Zenkaku (全角)
let position1 = 位置.５五  // Zenkaku (全角)
let position2 = 位置(筋: col, 段: row)

Describing Player

I am not sure how to describe 先手, 後手 in English. Black and White may be OK for Go (碁), but not Shogi. It does not describe the detail of individual, just describe which player.

enum 先後型 {
	case 先手, 後手
}

Describing Pieces

駒型 and 駒面型 describe the pieces. 駒型 does not have state of front and back, on the other hand 駒面型 cares about the state of front and back, or promoted or not.

let fu = 駒型.歩
let to = 駒面型.と

For the formatting purpose, promoted pieces of 香, 桂, 銀 are expressed as 杏, 圭, 全 rather than 成香, 成桂, 成銀. They are not official way to describe it, but commonly used for computer scene.

enum 駒面型 {
	case 歩, 香, 桂, 銀, 金, 角, 飛, 王
	case と, 杏, 圭, 全, 馬, 竜
}

Describing Captured Pieces

持駒型 describe the state of captured pieces. It knows which 駒型 is captured and its number. By the way, even though promoted pieces are captured, they cannot be used as state of promoted so are managed as 駒型.

You find number of captured 駒 as follows.

let 先手持駒: 持駒型 = ...
let 銀の持ち駒数 = 先手持駒[.銀]

Describing the state of game-borad

局面型 describes the snapshot of a game-board. And each cell is described as 升型.

let 局面 = 局面型(string:
			"▽持駒:なし\r" +
			"|▽香|▽桂|▽銀|▽金|▽王|▽金|▽銀|▽桂|▽香|\r" +
			"|　　|▽飛|　　|　　|　　|　　|　　|▽角|　　|\r" +
			"|▽歩|▽歩|▽歩|▽歩|▽歩|▽歩|▽歩|▽歩|▽歩|\r" +
			"|　　|　　|　　|　　|　　|　　|　　|　　|　　|\r" +
			"|　　|　　|　　|　　|　　|　　|　　|　　|　　|\r" +
			"|　　|　　|　　|　　|　　|　　|　　|　　|　　|\r" +
			"|▲歩|▲歩|▲歩|▲歩|▲歩|▲歩|▲歩|▲歩|▲歩|\r" +
			"|　　|▲角|　　|　　|　　|　　|　　|▲飛|　　|\r" +
			"|▲香|▲桂|▲銀|▲金|▲王|▲金|▲銀|▲桂|▲香|\r" +
			"▲持駒:なし\r",
		手番: .先手)

Or you may provide 指手型 to execute to create the next game-borad state.

let 前の局面: 局面型  = ...
let 指手 = ...
let 次の局面 = 局面型.指手を実行(指手)

You can also print() or .string property to extract string representation. And this string can be used for 局面型(_,手番:).

let ある局面: = ...
print("\(ある局面)")
let stringRepresentaion = ある局面.string
let 手番 = ある局面.手番
let 再現局面 = 局面(stringRepresentaion, 手番: 手番)

後手持駒:桂
|▽香|▲龍|　　|　　|　　|　　|　　|　　|▽香|
|　　|　　|▲金|　　|▲龍|　　|　　|　　|　　|
|▽歩|▲全|　　|　　|▽金|　　|▽歩|▽桂|▽歩|
|　　|▽歩|　　|　　|▽王|　　|▽銀|　　|　　|
|　　|　　|　　|▲金|▲角|　　|　　|　　|　　|
|　　|　　|▽香|▲歩|▲歩|▲銀|▲桂|　　|　　|
|▲歩|▲歩|　　|　　|　　|▲歩|▲銀|　　|▲歩|
|　　|　　|　　|▲金|　　|　　|　　|▲歩|　　|
|▲香|　　|　　|▲玉|　　|　　|　　|▽馬|　　|
先手持駒:桂,歩7

Describing moves and actions

A move can be described with 指手型. 指手型 three cases. 動 describes a piece move from one place to the other. 打 describes place captured piece on the game-board at specific location. 投了 describes the checkmate or equivalent.

enum 指手型 {
	case 動(先後: 先後型, 移動前の位置: 位置型, 移動後の位置: 位置型, 移動後の駒面: 駒面型)
	case 打(先後: 先後型, 位置:位置型, 駒:駒型)
	case 終(終局理由: 終局理由型, 勝者: 先後型?)
}

You may construct hand written 指手型, but it has to be legitimate valid move. Invalid 指手型 will be rejected by 局面型's 指手を実行() method.

var 局面 = 局面(string: 手合割型.平手初期盤面, 手番: .先手)
局面 = 局面.指手を実行(指手型.動(先後: .先手, 移動前の位置: .７七, 移動後の位置: .７六, 移動後の駒面: .歩))
局面 = 局面.指手を実行(指手型.動(先後: .後手, 移動前の位置: .３三, 移動後の位置: .３四, 移動後の駒面: .歩))

For professional player, this 投了 state may be sufficient, but for amateur, 王 may be captured by careless mistake. Therefore, extra end state should be added later on.

局面型 provides 全可能指手列() method to find all possible legitimate moves. So you may iterate through each candidate to examine all moves. You may also call 指手を実行() for each moves, but it is not suitable for creating millions of instances recursively.

let 局面: 局面型 = ...
let 全可能指手 = 局面.全可能指手列()
for 候補指手 in 全可能指手 {
	if let 次の局面 = 局面(候補指手) {
		// find one you like
	} 
}

Some advanced methods and properties

• Iterate all positions in 局面型

let 局面: 局面型 = ...
for 位置 in 局面 {
	let マス = 局面[位置]
	let 駒面 = マス.駒面
}

• All positions that a piece at location can make move

let 局面: 局面型 = ...
let 位置列 = 局面.指定位置の駒の移動可能位置列(.５五) // only location
let 指手列 = 局面.指定位置の駒の移動可能指手列(.５五)

• Find all positions of where specified type of piece are located

let 局面: 局面型 = ...
let 先手の桂の位置 = 局面.駒の位置列(.桂, 先後: .先手)

• Which pieces on game-board can make move to specified location?

let 局面: 局面型 = ...
let 味方の駒の位置列 = 局面.指定位置へ移動可能な全ての駒の位置列(.７六, 先後: .先手)
let 敵味方双方の駒の位置列 = 局面.指定位置へ移動可能な全ての駒の位置列(.７六, 先後: nil)
let 後手の移動指手列 = 局面.指定位置へ移動可能な全ての駒を移動させる指手列(.７六, .後手)

• Find all movies that can capture 王 (King).

let 局面: 局面型 = ...
let 王手列 = 局面.王手列(.先手)

• Checkmate? (needs more test)

let 局面: 局面型 = ...
if 局面.詰みか() {
	// checkmate!
}

• Find opponent player

let 局面: 局面型 = ...
let 手番の敵方 = 局面.手番.敵方

• Is 先手's 王 is on the same line of 後手's 角? (English!!)

let 局面: 局面型 = ...
let 後手の角の位置 = ...
for (vx, vy) in 駒面.角.移動可能なベクトル {
	var (x, y) = (後手の角の位置.筋 + vx, 後手の角の位置.段 + vy)
	while let x = x, let y = y {
		if let マス = 局面[x, y] where マス.駒面　== .王 && マス.先後 == .先手 {
			// King is on the line
		}
		(x, y) = (x + vx, y + vy)
	}
}

Generating Image

局面型 provides extension to generate image.

extension 局面型 {
	func imageForSize(size: CGSize) -> CGImage
}

Here is the code sample of how to generate an image from 局面型, and a sample image that generated by this feature.

let image = 局面.imageForSize(CGSizeMake(300, 300))

Some Tips

In ShoogibanKit, textual expression for position can be used, and also, positions also can be printed on debug console in textual expression. If you simply use Menlo, or Hiragino, it would not be a good experiences for programmers after all.

I recommend Source Han Code JP font from Adobe. It is free to use. By using this font, Shogi's textual expression will be look like in source code and in debugger log.

You can get the font from following URLs and try. https://github.com/adobe-fonts/source-han-code-jp

TO DO's

• Test for Check mate
• 打ち歩詰め and other special cases
• 千日手 and other rules
• 局面 compaction to save and load
• UnitTest - removed because it crashes (not sure may be Xcode issue)
• may be some more

Other consideration

• String representation of 局面型 does not include 手番. If 手番 is included, it is simple to go back and forth between 局面型 and String.

Environment

• Xcode Version 13.3.1
• Apple Swift version 5.6

Feedback

Please give me your feedback to kaz.yoshikawa@gmail.com.