Function fib

packages/effect/test/Effect/stack-safety.test.ts:34–43

(
        n: number,
        a: BigInt = BigInt("0"),
        b: BigInt = BigInt("1")
      )

  it.effect("deep flatMap", () =>
    Effect.gen(function*() {
      const fib = (
        n: number,
        a: BigInt = BigInt("0"),
        b: BigInt = BigInt("1")
      ): Effect.Effect<BigInt, Error> => {
        return pipe(
          Effect.sync(() => ((a as any) + (b as any)) as BigInt),
          Effect.flatMap((b2) => n > 0 ? fib(n - 1, b, b2) : Effect.succeed(b2))
        )
      }
      const result = yield* (fib(1000))
      const expected = BigInt(
        "113796925398360272257523782552224175572745930353730513145086634176691092536145985470146129334641866902783673042322088625863396052888690096969577173696370562180400527049497109023054114771394568040040412172632376"