package topdownop

object main {
	def main(argv:Array[String]) {
		println(parse(argv(0)))
		println(eval(argv(0)))
	}

	def parse(src:String) = {
		var str = src
		val tokens = for(i <- Stream.from(0)) yield {
			def t ():Any = {
				val num = """^([0-9]+)(.*$)""".r
				val ptn = """^([-\+*\/\=\;\:]+|[\(\)\[\]\{\}]|[^-\+*\/\(\)\[\]\{\}\s\=\;\:]+|$)(.*$)""".r
				val spc = """^[\s]+(.*$)""".r
				str match {
				case ptn(a,e) => str = e; a
				case spc(e) => str = e; t()
				case _ => throw new Error("error")
				}
			}
			t
		}


		var token:Any = null
		var t:Any = null
		var index = 0

		def advance() { token = tokens(index); index += 1 }

		// ２項演算子と優先順位
		val infixs:Map[Any,Int] = Map(
			"*" -> 20,
			"/" -> 20,
			"-" -> 10,
			"+" -> 10)

		// ２項演算子
		def infix(n:Int):Boolean = {
			val op = token
			val p = infixs(op)
			if(p <= n) {
				false
			} else {
				advance()
				t = (t, op, exp(p))
				true
			}
		}

		// 式
		def exp(n:Int):Any = {
			t = token
			advance()
			while(infixs.contains(token) && infix(n)){}
			t
		}

		advance()
		exp(0)
	}

	// 評価
	def eval(s:String):Int = eval(parse(s))

	def eval(a:Any):Int = {
		a match {
		case (a,"+",b) => eval(a) + eval(b)
		case (a,"*",b) => eval(a) * eval(b)
		case (a,"-",b) => eval(a) - eval(b)
		case (a,"/",b) => eval(a) / eval(b)
		case _ =>
			try {a.toString.toInt}catch{case _ => 0}
		}
	}
}