instruction demo

Instruction.kt

import java.lang.RuntimeException

sealed class InstructionPart
data class Add(val argument: Int): InstructionPart()
data class Subtract(val argument: Int): InstructionPart()
data class Multiply(val argument: Int): InstructionPart()
data class Divide(val argument: Int): InstructionPart()
data class Apply(val argument: Int): InstructionPart()

typealias Instruction = List<InstructionPart>


fun String.parse() = "(add|subtract|multiply|divide|apply) ([0-9]*)".toRegex().findAll(this)
        .fold(emptyList<InstructionPart>()) { instruction, part ->
            val parts = part.groupValues
            val operator = parts[1]
            val argument = parts[2].toInt()

            val instructionPart = when(operator) {
                "add" -> Add(argument)
                "subtract" -> Subtract(argument)
                "multiply" -> Multiply(argument)
                "divide" -> Divide(argument)
                "apply" -> Apply(argument)
                 else -> throw RuntimeException("unknown instruction")
            }
            instruction + instructionPart
        }


fun Instruction.apply(): Int {
    val initialResult = when(val ip = last()) {
        is Apply -> ip.argument
        else -> throw RuntimeException("unknown order of instruction")
    }

    return fold(initialResult) { r, i ->
        when(i){
            is Add -> r + i.argument
            is Subtract -> r - i.argument
            is Multiply -> r * i.argument
            is Divide -> r / i.argument
            is Apply -> r
        }
    }
}

fun main() {
    println("add 2 multiply 3 apply 3".parse().apply())
}