type Event =

| SwitchedOn

| SwitchedOff

| Broke

type State =

| Working of CurrentState

| Broken

and CurrentState = { on: bool; remainingUses: int }

let initial = Working { on = false; remainingUses = 3 }

let private evolve s e =

match s with

| Broken -> s

| Working s ->

match e with

| SwitchedOn -> Working { on = true; remainingUses = s.remainingUses - 1 }

| SwitchedOff -> Working { s with on = false }

| Broke -> Broken

let fold = Array.fold evolve

let decideSwitch (on: bool) s = [|

match s with

| Broken -> ()

| Working { on = true } ->

if not on then

SwitchedOff

| Working { on = false; remainingUses = r } ->

if on then

if r = 0 then Broke

else SwitchedOn |]