import { Channel } from "https://deno.land/x/async_channels@v1.0.0-rc8/mod.ts";
flatMap returns a receiver channel that contains the flattened (1 level)
results of applying fn to each value of this channel.
The receiver channel will close, when the original channel closes (or if the provided signal is triggered).
Parameters
optional
pipeOpts: ChannelPipeOptions