Missing error mechanism for StdStream

[pcrockett]

I have a standard hello world program that I'm using to start learning the language, and I'm trying to introduce an error by redirecting the output to a device that doesn't have any free space:

./hello-pony > /dev/full

(Inspired by https://blog.sunfishcode.online/bugs-in-hello-world/)

This (and other similar scenarios) should cause an error, however I see no way to detect it. Looking at the implementation of StdStream.flush() I see this comment:

  """
  Flush any data out to the os (ignoring failures).
  """

This seems like an important gap in the builtin library.

For what it's worth, from a non-Pony developer's perspective, the FileStream error mechanism (requiring a person to check File.errno()) seems less than ideal as well. Maybe that's just a difference in style / preference.

I'd follow the RFP process to suggest a general error mechanism for OutStream, but I'm afraid I don't have the bandwidth for that right now. Apologies.

[SeanTAllen]

Thanks. I'm closing this in favor of ponylang/rfcs#205.