Understanding Service Implementations and Effect Composition in Effect Typescript

class A extends Effect.Service<A>()("A", {
    effect: Effect.gen(function*() {
        return Effect.succeed('')
    })
}) {}

class B extends Effect.Service<B>()("B", {
    effect: Effect.gen(function*() {
        return Effect.succeed(true)
    })
}) {}

const doA = pipe(
    A,
    Effect.flatMap((a) => a)
)

const doB = pipe(
    B, 
    Effect.flatMap((b) => b)
)

class Test extends Effect.Service<Test>()("Testy", {
    effect: Effect.gen(function*() {
        return {
            doA,
            doB
        }
    }),
}) {}

const LettersLayer = Layer.merge(A.Default, B.Default)

const test = Effect.gen(function*() { // Effect.Effect<Test, never, never>
    const derp = yield* Test
    return derp // Test
}).pipe(Effect.provide(Layer.merge(Test.Default, LettersLayer)))

const test2 = Effect.gen(function*() { //  Effect.Effect<void, never, A | B>
    const derp2 = yield* test
    const here = derp2.doA // Effect.Effect<string, never, A>
    const here2 = derp2.doB // Effect.Effect<boolean, never, B>
    const blah = yield* here
    const blah2 = yield* here2
})