org.occurrent.dsl.decider.arrow.Decider.kt Maven / Gradle / Ivy
/*
*
* Copyright 2023 Johan Haleby
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.occurrent.dsl.decider.arrow
import arrow.core.Either
/**
* Decider implementation that uses `Either` from the Arrow library
*/
interface Decider {
fun initialState(): S
fun decide(command: C, state: S): Either>
fun evolve(state: S, event: E): S
fun isTerminal(state: S): Boolean = false
}
/**
* Create a new decider
*/
fun decider(initialState: S, decide: (C, S) -> Either>, evolve: (S, E) -> S, isTerminal: (S) -> Boolean = { false }): Decider =
object : Decider {
override fun initialState(): S = initialState
override fun evolve(state: S, event: E): S = evolve(state, event)
override fun decide(command: C, state: S): Either> = decide(command, state)
override fun isTerminal(state: S): Boolean = isTerminal(state)
}