Finite state machine

A simple finite state machine implementation written in Kotlin. Added jvm compiler hooks for better semantics when using this library in java.

Add it to your project

Library can obtained in gradle using jitpack

repositories {
    // ...
    maven { url 'https://jitpack.io' }
    // ...
}


dependencies {
    // ...
    implementation 'com.github.codergoblin:fsm:0.0.1-SNAPSHOT'
    // ...
}

Simple state machine example

Implementation for the following diagram

+------- +------+ -----COIN-----> +--------+ <-COIN-+
|        |LOCKED|                 |UNLOCKED|        |
+-PUSH-> +------+ <---PUSH------- +--------+ -------+

Kotlin

Java

import codegoblin.fsm.TransitionBuilder.Companion.match fun main() { val coinMachine: FiniteStateMachine<State, Action> = FiniteStateMachine.create { put(LOCKED, match { match(COIN).thenReturn(UNLOCKED) }) put(UNLOCKED, match { match(PUSH).thenReturn(LOCKED) }) } val newState = coinMachine(LOCKED, PUSH) // Still locked } enum class Action { PUSH, COIN } enum class State { LOCKED, UNLOCKED }

import static codegoblin.fsm.TransitionBuilder.match; public class CoinMachine { public static void main(String[] args) { FiniteStateMachine<State, Action> coinMachine = FiniteStateMachine.create( transitions -> { transitions.put( LOCKED, match(matcher -> matcher.match(COIN).thenReturn(UNLOCKED)) ); transitions.put( UNLOCKED, match(matcher -> matcher.match(PUSH).thenReturn(LOCKED)) ); } ); State newState = coinMachine.invoke(LOCKED, PUSH); // Still locked } enum Action { PUSH, COIN } enum State { LOCKED, UNLOCKED } }

Semantics

fun main() {

    val walkingSimulation = FiniteStateMachine.create<String, Request> {
        put("running",
            match {
                // Override default behavior of returning existing state in case no transitions are found 
                withDefaultTransformation { "stand" }
                    // Match exact value
                    .match(Request("stop")).thenReturn("standing")
                    // Match value with a qualifier
                    .match { it -> it.action == "duck" }.thenReturn("ducking")
                    // Apply matchers to namespaced properties for simpler semantcs
                    .extracting { it.action }
                    .match {
                        match("jump").thenReturn("in the air")
                    }
            })
        //...
    }

}
data class Request(val action: String)

Build it yourself

git clone https://github.com/codergoblin/fsm.git
cd fsm
./gradlew jar

Executable is located under build/libs