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FSM DSL in Kotlin
tomoya0x00
Kotlin Developers Meetup
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About me
tomoya0x00
Twitter, GitHub, Qiita
Android, Embedded system, BLE/BT, iOS
DeNA Co., Ltd.
Automotive Business Unit.
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Everyone
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You want to make DSL by yourself?
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I want to FSM DSL in Kotlin
FSM is nite state machine.
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Why FSM?
Avoid confusion caused by multiple ag management
Easy to test
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And, I want to support composite
states
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Example
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Simple smart lock for bike sharing
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I am developing a Proof-of-Concept
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DSL Example
val sm = stateMachine(initial = MyState.NotLoaned) {
state(MyState.NotLoaned) {
edge(MyEvent.PressRental, next = MyState.Lock)
}
state(MyState.OnLoan,
entry = { println("turnOnRentalLed") },
exit = { println("turnOffRentalLed") }) {
state(MyState.Lock) {
edge(MyEvent.PressReturn, next = MyState.NotLoaned)
edge(MyEvent.PressUnLock, next = MyState.UnLock)
}
state(MyState.UnLock) {
edge(MyEvent.PressLock, next = MyState.Lock)
}
}
}
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Let's run!
val next = sm.dispatch(MyEvent.PressRental)
assert(next).isEqualTo(MyState.Lock)
result:
turnOnRentalLed
next == MyState.Lock
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Internal
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Generate the tree of states
DSL Tree of states
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DSL internal
fun stateMachine(
initial: BaseState,
init: StateMachine.() -> Unit
): StateMachine = StateMachine(initial = initial)
.apply(init)
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Problem
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Search processing is executed for each
dispatch
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When press return in Lock state
Find route to NotLoaned state from Lock state
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When press return in Lock state
Find route to NotLoaned state from Lock state
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When press return in Lock state
Find route to NotLoaned state from Lock state
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When press return in Lock state
Find route to NotLoaned state from Lock state
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When press return in Lock state
Find route to NotLoaned state from Lock state
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When press return in Lock state
Execute entry/exit on route
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Solution
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StateMachine.Builder
fun stateMachine(
initial: BaseState,
init: StateMachine.Builder.() -> Unit
): StateMachine = StateMachine.Builder(initial = initial)
.apply(init).build()
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Generate transition map in build()
state event actions next
NotLoaned PressRental [OnLoan.entry] Lock
Lock PressReturn [OnLoan.exit] NotLoaned
Lock PressUnLock [] UnLock
UnLock PressLock [] Lock
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But, not implemented yet...
to be available soon!
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Any Idea?
Tree search algorithm when creating transition map, if you have any
good idea, please let me know!
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Waiting for your suggestions︕
https://github.com/tomoya0x00/fsm-dsl-
kotlin-poc
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Thank you!