I'm curious - what other technologies/libraries/APIs, including in other languages, did you draw on for inspiration, or would you say are similar to Rill?

The short answer would be: I kept writing a code that spawns goroutines, that read from a channel, do some processing and write results to another channel. Add some wait/err groups to this and we'll get a lot of boilerplate repeated all over the place. I viewed this as "channel transformations" and wanted to abstract it away. When generics came out it became technically possible.

Surprisingly, part of my inspiration came from scala (which I haven't touched since 2014). Back then Scala had transformable streams and the "Try" typethen.

The channel-focused approach to stream processing reminds me of Heka [0]. It was a contemporary of Samza and Heron, and it was fairly prominent in the early Go ecosystem (maybe 10 years ago). As I recall it, quite foggily and quite a long while later, one of the final nails in Heka's coffin was that channel throughput didn't scale well. Do you have benchmarks for Rill, or is it not intended for high-throughput use cases?

[0]: https://github.com/mozilla-services/heka