Getting started

Install

go get github.com/stablekernel/crucible/state

The kernel depends only on the Go standard library.

Your first machine, end to end

A machine is generic over three types you define: S (state), E (event), and C (context, your domain entity). Here is a toy turnstile, forged and fired from scratch.

package main

import (
  "context"
  "fmt"

  "github.com/stablekernel/crucible/state"
)

type Gate string  // S
type Signal string // E
type Turnstile struct{ Coins int } // C

const (
  Locked   Gate = "Locked"
  Unlocked Gate = "Unlocked"
)

const (
  Coin Signal = "Coin"
  Push Signal = "Push"
)

func main() {
  // Forge a builder, declare states + transitions, then Quench to freeze
  // the definition into an immutable *Machine. Quench panics on misconfig.
  m := state.Forge[Gate, Signal, Turnstile]("turnstile").
    Initial(Locked).
    Transition(Locked).On(Coin).GoTo(Unlocked).
    Transition(Unlocked).On(Push).GoTo(Locked).
    Quench()

  // Cast an instance around an entity value.
  inst := m.Cast(Turnstile{})

  // Fire advances the instance and returns a FireResult. It performs NO IO.
  // NewState is the next state, Effects is data for the caller to dispatch.
  res := inst.Fire(context.Background(), Coin)
  fmt.Println(res.NewState) // Unlocked

  res = inst.Fire(context.Background(), Push)
  fmt.Println(res.NewState) // Locked
}

That toy machine looks like this:

stateDiagram-v2
    [*] --> Locked
    Locked --> Unlocked: Coin
    Unlocked --> Locked: Push

A real machine

The same primitives scale to hierarchical and parallel statecharts. Here is the food-delivery order machine that ships as a worked example. Note the nested Active region with parallel fulfillment and watchdog sub-machines, guarded transitions, and an after(...) timer:

stateDiagram-v2
    [*] --> Placed
    state Active {
        [*] --> Active_Fulfillment__Cooking
        Active_Fulfillment__Cooking
        Active_Fulfillment__AwaitingCourier
        Active_Fulfillment__EnRoute
        Active_Fulfillment__AwaitingCourier --> Active_Fulfillment__EnRoute: PickedUp
        Active_Fulfillment__Cooking --> Active_Fulfillment__AwaitingCourier: PlatedUp
        --
        [*] --> Active_Watchdog__OnTime
        Active_Watchdog__OnTime
        Active_Watchdog__Overdue
        Active_Watchdog__Overdue --> [*]
        Active_Watchdog__OnTime --> Active_Watchdog__Overdue: after(30m0s) SLABreached
    }
    Delivered --> [*]
    Canceled --> [*]
    Rejected --> [*]
    Active --> Refunding: Cancel
    Active --> Settling: DroppedOff
    Authorizing --> Active: Authorized [or(generousOrder,and(subtotal ge 5000,priority in ["fast","express"]))]
    Authorizing --> Rejected: Declined
    Placed --> Authorizing: Submit
    Refunding --> Canceled: Refunded
    Settling --> Delivered

Next: read the foundry vocabulary to learn exactly what each lifecycle verb does.