Nice! That’s a really cool solution, and probably scales well! It fails the first requirement though, the input should be piped in. Reading from a file is faster than reading from stdin in general (eg replace IO.binstream with File.read and it runs faster) and gives you much more control, like you show in your code.
You can speed up your version quite a bit if you switch to iolists, instead of printing line by line.
I actually ended up writing an article about this script, with my final version single threaded (13 lines of code) running in 13 seconds Elixir String Processing Optimization | jola.dev
and compared performance as well as some words on the downsides
