Lots of changes

Sources/Engine/Square.swift

@@ -8,7 +8,34 @@ public struct Square: Equatable {
 			guard (rank > 0 && rank < 9) && (file > 0 && file < 9) else {
 				return nil
 			}
-			return Int(8*(8-rank)+file-1)
+			return Int(8 * (8 - rank) + file - 1)
+		}
+
+		public init(rank r: Int8, file f: Int8) {
+			rank = r
+			file = f
+		}
+
+		public enum File: String, CustomStringConvertible {
+			case a, b, c, d, e, f, g, h
+
+			public static subscript(_ f: Int8) -> Self? {
+				return switch f {
+				case 1: Self.a
+				case 2: Self.b
+				case 3: Self.c
+				case 4: Self.d
+				case 5: Self.e
+				case 6: Self.f
+				case 7: Self.g
+				case 8: Self.h
+				default: nil
+				}
+			}
+
+			public var description: String {
+				self.rawValue.uppercased()
+			}
 		}
 
 		public static func == (lhs: Position, rhs: Position) -> Bool {
@@ -34,7 +61,7 @@ public struct Square: Equatable {
 
 	public let position: Position
 	public let index: Int
-	var piece: Piece? = nil
+	public internal(set) var piece: Piece? = nil
 	public let color: Color
 
 	public static func == (lhs: Square, rhs: Square) -> Bool {