[RPNCalculator] #practice

RPNCalculator.groovy

import java.util.*;

class RpnCalculator {
    static void main(String[] args) {
        Calculator calc = new Calculator()
        '4 6 3 + 9 3 - * 1 1 ^ - +'.split(' ').each {calc.enter(it)}
    }
}

class Calculator {
    Stack stack = [] as Stack
    def calculate = {action-> return { action.call(stack.pop(), stack.pop()) }}
    def actions = [
        '+': calculate {a,b -> b + a},
        '-': calculate {a,b -> b - a},
        '*': calculate {a,b -> b * a},
        '/': calculate {a,b -> b / a},
        '^': calculate {a,b -> b ** a}
    ]

    void enter(String entry) {
        def action = actions[entry]
        BigDecimal last = null
        if (action) {
            if (stack.size() > 1) {
                last = action.call()
                stack.push(last)
            } else if (stack.size() == 1) {
                last = stack.peek()
            }
        } else if (entry.isBigDecimal()) {
            stack.push(entry as BigDecimal)
            last = entry as BigDecimal
        }

        if (last != null) {
            println "$stack: $last"
        } else {
            println stack
        }
    }
}