In the Point-Free series on application architecture and state management, they define a series of ways to compose reducers. Sometimes, however, it seems that the signature of reducers can complicate the signature of these different compositions. I found creating a typealias for reducers separated the concern of understanding the concept of redu…

PointFreeStateManagement.swift

// In the Point-Free series on application architecture and state management,
// they define a series of ways to compose reducers. Sometimes, however, it seems
// that the signature of reducers can complicate the signature of these different 
// compositions. I found creating a typealias for reducers separated the concern of
// understanding the concept of reducers and understanding their higher order
// constructions, especially when starting to write my own.

// Adding a typealias for Reducer can make certain parts a bit more readable
typealias Reducer<Value, Action> = (inout Value, Action) -> Void

func combine<Value, Action>(
  _ reducers: Reducer<Value, Action>...
) -> Reducer<Value, Action> {
  return { value, action in
    for reducer in reducers {
      reducer(&value, action)
    }
  }
}

final class Store<Value, Action>: ObservableObject {
  let reducer: Reducer<Value, Action>
  @Published private(set) var value: Value

  init(initialValue: Value, reducer: @escaping Reducer<Value, Action>) {
    self.reducer = reducer
    self.value = initialValue
  }

  func send(_ action: Action) {
    self.reducer(&self.value, action)
  }
}

func pullback<LocalValue, GlobalValue, LocalAction, GlobalAction>(
  _ reducer: @escaping Reducer<LocalValue, LocalAction>,
  value: WritableKeyPath<GlobalValue, LocalValue>,
  action: WritableKeyPath<GlobalAction, LocalAction?>
) -> Reducer<GlobalValue, GlobalAction> {
  return { globalValue, globalAction in
    guard let localAction = globalAction[keyPath: action] else { return }
    reducer(&globalValue[keyPath: value], localAction)
  }
}

func logging<Value, Action>(
  _ reducer: @escaping Reducer<Value, Action>
) -> Reducer<Value, Action> {
  return { value, action in
    reducer(&value, action)
    print("Action: \(action)")
    print("Value:")
    dump(value)
    print("---")
  }
}