Created
July 20, 2015 10:23
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def ifn(str: String): Int = expr(str.split(" ").toList)._1 | |
// expr := term ["+"|"-" term]* | |
def expr(src: List[String]): (Int, List[String]) = { | |
//println(s"[expr] src: $src") | |
val (v1, src2) = term(src) | |
def expr2(v1: Int, src: List[String]): (Int, List[String]) = src match { | |
case "+"::src3 => { | |
val (v2, src4) = term(src3) | |
expr2(v1 + v2, src4) | |
} | |
case "-"::src3 => { | |
val (v2, src4) = term(src3) | |
expr2(v1 - v2, src4) | |
} | |
case _ => (v1, src) | |
} | |
expr2(v1, src2) | |
} | |
// term := factor ["*"|"/" factor]* | |
def term(src: List[String]): (Int, List[String]) = { | |
//println(s"[term] src: $src") | |
val (v1, src2) = factor(src) | |
def term2(v1: Int, src: List[String]): (Int, List[String]) = src match { | |
case "*"::src3 => { | |
val (v2, src4) = factor(src3) | |
term2(v1 * v2, src4) | |
} | |
case "/"::src3 => { | |
val (v2, src4) = factor(src3) | |
term2(v1 / v2, src4) | |
} | |
case _ => (v1, src) | |
} | |
term2(v1, src2) | |
} | |
// factor := Int | |
def factor(src: List[String]): (Int, List[String]) = { | |
(src.head.toInt, src.tail) | |
} | |
def test(src: String) = println(src + " = " + ifn(src)) | |
test("1") | |
test("1 + 2") | |
test("1 + 2 + 3 + 4") | |
test("1 * 2 * 3") | |
test("1 + 2 * 3") | |
test("1 * 2 + 3") | |
test("2 * 3 * 4") | |
test("2 + 3 * 4") | |
test("2 * 3 + 4") | |
test("5 - 2") | |
test("1 - 2 - 3") | |
test("2 * 3 - 4 * 5 * 6 - 7 * 8") | |
test("100 / 10 / 5") |
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