Implementations of concurrent fibonacci numbers in vanilla asyncio and trio

trio_fib.py

import asyncio
import trio

import sys


async def fib(n: int) -> int:
    if n < 0:
        raise ValueError('boom')
    elif n in {0, 1}:
        return 1
    else:
        results = await asyncio.gather(fib(n-1), fib(n-2))
        return sum(results)


async def trio_fib(n: int) -> int:
    async with trio.open_nursery() as nursery:
        send_chan, recv_chan = trio.open_memory_channel(0)
        nursery.start_soon(fib_producer, n, send_chan)
        async with recv_chan:
            async for val in recv_chan:
                return val


async def fib_producer(n: int, out_chan):
    if n < 0:
        raise ValueError('boom')
    elif n in {0, 1}:
        async with out_chan:
            await out_chan.send(1)
    else:
        async with trio.open_nursery() as nursery:
            send_chan, recv_chan = trio.open_memory_channel(0)
            async with send_chan:
                nursery.start_soon(fib_producer, n-1, send_chan.clone())
                nursery.start_soon(fib_producer, n-2, send_chan.clone())
            nursery.start_soon(fib_receiver, recv_chan, out_chan)


async def fib_receiver(in_chan, out_chan):
    result = 0
    async with in_chan:
        async for value in in_chan:
            result += value
    async with out_chan:
        await out_chan.send(result)