diff -r 017f621f5835 -r 3ffe978a5664 core_templates3/postfix2.scala --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/core_templates3/postfix2.scala Fri Nov 05 16:47:55 2021 +0000 @@ -0,0 +1,69 @@ +// Shunting Yard Algorithm +// including Associativity for Operators +// ===================================== + +object C3b { + + +// type of tokens +type Toks = List[String] + +// helper function for splitting strings into tokens +def split(s: String) : Toks = s.split(" ").toList + +// left- and right-associativity +abstract class Assoc +case object LA extends Assoc +case object RA extends Assoc + + +// power is right-associative, +// everything else is left-associative +def assoc(s: String) : Assoc = s match { + case "^" => RA + case _ => LA +} + + +// the precedences of the operators +val precs = Map("+" -> 1, + "-" -> 1, + "*" -> 2, + "/" -> 2, + "^" -> 4) + +// the operations in the basic version of the algorithm +val ops = List("+", "-", "*", "/", "^") + +// (3) Implement the extended version of the shunting yard algorithm. +// This version should properly account for the fact that the power +// operation is right-associative. Apart from the extension to include +// the power operation, you can make the same assumptions as in +// basic version. + +def syard(toks: Toks, st: Toks = Nil, out: Toks = Nil) : Toks = ??? + + +// test cases +// syard(split("3 + 4 * 8 / ( 5 - 1 ) ^ 2 ^ 3")) // 3 4 8 * 5 1 - 2 3 ^ ^ / + + + +// (4) Implement a compute function that produces an Int for an +// input list of tokens in postfix notation. + +def compute(toks: Toks, st: List[Int] = Nil) : Int = ??? + + +// test cases +// compute(syard(split("3 + 4 * ( 2 - 1 )"))) // 7 +// compute(syard(split("10 + 12 * 33"))) // 406 +// compute(syard(split("( 5 + 7 ) * 2"))) // 24 +// compute(syard(split("5 + 7 / 2"))) // 8 +// compute(syard(split("5 * 7 / 2"))) // 17 +// compute(syard(split("9 + 24 / ( 7 - 3 )"))) // 15 +// compute(syard(split("4 ^ 3 ^ 2"))) // 262144 +// compute(syard(split("4 ^ ( 3 ^ 2 )"))) // 262144 +// compute(syard(split("( 4 ^ 3 ) ^ 2"))) // 4096 +// compute(syard(split("( 3 + 1 ) ^ 2 ^ 3"))) // 65536 + +}