--- a/pre_templates3/postfix.scala Thu Nov 04 12:20:12 2021 +0000
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,81 +0,0 @@
-// Shunting Yard Algorithm
-// by Edsger Dijkstra
-// ========================
-
-object CW8a {
-
-// type of tokens
-type Toks = List[String]
-
-// the operations in the basic version of the algorithm
-val ops = List("+", "-", "*", "/")
-
-// the precedences of the operators
-val precs = Map("+" -> 1,
- "-" -> 1,
- "*" -> 2,
- "/" -> 2)
-
-// helper function for splitting strings into tokens
-def split(s: String) : Toks = s.split(" ").toList
-
-
-// (1) Implement below the shunting yard algorithm. The most
-// convenient way to this in Scala is to implement a recursive
-// function and to heavily use pattern matching. The function syard
-// takes some input tokens as first argument. The second and third
-// arguments represent the stack and the output of the shunting yard
-// algorithm.
-//
-// In the marking, you can assume the function is called only with
-// an empty stack and an empty output list. You can also assume the
-// input os only properly formatted (infix) arithmetic expressions
-// (all parentheses will be well-nested, the input only contains
-// operators and numbers).
-
-// You can implement any additional helper function you need. I found
-// it helpful to implement two auxiliary functions for the pattern matching:
-//
-
-def is_op(op: String) : Boolean = ???
-def prec(op1: String, op2: String) : Boolean = ???
-
-
-def syard(toks: Toks, st: Toks = Nil, out: Toks = Nil) : Toks = ???
-
-
-// test cases
-//syard(split("3 + 4 * ( 2 - 1 )")) // 3 4 2 1 - * +
-//syard(split("10 + 12 * 33")) // 10 12 33 * +
-//syard(split("( 5 + 7 ) * 2")) // 5 7 + 2 *
-//syard(split("5 + 7 / 2")) // 5 7 2 / +
-//syard(split("5 * 7 / 2")) // 5 7 * 2 /
-//syard(split("9 + 24 / ( 7 - 3 )")) // 9 24 7 3 - / +
-
-//syard(split("3 + 4 + 5")) // 3 4 + 5 +
-//syard(split("( ( 3 + 4 ) + 5 )")) // 3 4 + 5 +
-//syard(split("( 3 + ( 4 + 5 ) )")) // 3 4 5 + +
-//syard(split("( ( ( 3 ) ) + ( ( 4 + ( 5 ) ) ) )")) // 3 4 5 + +
-
-
-// (2) Implement a compute function that evaluates an input list
-// in postfix notation. This function takes a list of tokens
-// and a stack as argumenta. The function should produce the
-// result as an integer using the stack. You can assume
-// this function will be only called with proper postfix
-// expressions.
-
-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
-
-}
-
-