The core bits of the CaptionsGeneration sample project.

captions_generation_project_highlights.swift

// …in ContentView.swift in the linked sample project.

struct State: Equatable {
	var transcription = ""
	var isFetchingTranscription = false
}

enum Action {
	case onAppear
	case setTranscriptionString(String)
	case transcriptionResult(Result<String, NSError>)
	case fetchTranscription
}

let transcriptionReducer = Reducer<State, Action, Void> { state, action, _ in
	switch action {
	case .onAppear: // (1)
		return Effect.fireAndForget {
			SFSpeechRecognizer.requestAuthorization { _ in }
		}
	case .fetchTranscription:
		state.transcription.removeAll()
		state.isFetchingTranscription = true

		// (2)
		return transcriptionEffect(Bundle.main.url(forResource: "sample", withExtension: "m4a")!)
			.subscribe(on: DispatchQueue.global(qos: .userInitiated))
			.catchToEffect() // Converts an Effect<Output, Failure> to an Effect<Result<Output, Failure>, Never>.
			// https://github.com/pointfreeco/swift-composable-architecture/blob/11f215c3b6923dfcccec6d1de6a672963a0d3c6e/Sources/ComposableArchitecture/Effect.swift#L319-L336
			// This is another form of [materialization](https://jasdev.me/materialization-primer).
			.receive(on: DispatchQueue.main)
			.map(Action.transcriptionResult) // Packs the result back into an action the reducer can handle.
			.eraseToEffect()
	case let .setTranscriptionString(transcription):
		// …
	case let .transcriptionResult(result):
		// …
	}
}

// …