zonble · August 5, 2019 15:53 · Aug 5, 2019
diff --git a/calc.swift b/calc.swift
@@ -0,0 +1,78 @@
+enum Token {
+	case num(Int)
+	case op(String)
+}
+
+func tokenize(_ s: String) -> [Token] {
+	let scanner = Scanner(string: s)
+	scanner.charactersToBeSkipped = CharacterSet.whitespaces
+	var tokens = [Token]()
+	while !scanner.isAtEnd {
+		if let c = scanner.scanCharacters(from: CharacterSet(charactersIn: "+-*/")) {
+			tokens.append(.op(String(c)))
+		}
+		else if let int = scanner.scanInt() {
+			tokens.append(.num(int))
+		}
+	}
+	return tokens
+}
+
+enum MyError : Error {
+	case invalidToken
+}
+
+func calc(_ tokens: [Token]) throws -> Int {
+	if tokens.count == 0 {
+		return 0
+	}
+	guard case let .num(x) = tokens[0] else {
+		throw MyError.invalidToken
+	}
+	var v = x
+	var currentToken: Token = tokens[0]
+	for token in tokens[1...] {
+		switch token {
+		case .num(let i):
+			switch currentToken {
+			case .num(_):
+				throw MyError.invalidToken
+			case .op(let c):
+				switch c {
+				case "+":
+					v += i
+				case "-":
+					v -= i
+				case "*":
+					v *= i
+				case "/":
+					v /= i
+				default:
+					throw MyError.invalidToken
+				}
+				currentToken = token
+			}
+		case .op(_):
+			switch currentToken {
+			case .op(_):
+				throw MyError.invalidToken
+			case .num(_):
+				currentToken = token
+			}
+			break
+		}
+	}
+	return v
+}
+
+//let t = tokenize("1 / 1 * 2 + 100 - 80")
+let t = tokenize("1 + 100 * 200")
+
+print(t)
+t
+do {
+	let result = try calc(t)
+	result
+} catch {
+	error
+}