How to propagate errors with Lwt streams?

[foretspaisibles]

Consider a stream created of a Lwt_stream.from or Lwt_stream.from_direct. How are exceptions raised by the function creating stream's elements handled? How can the stream consumer arrange to be noticed about them?

I guess or would expect that the exception is conveyed by a failed thread returned by Lwt_stream.get, but the API-documentation does not go into these details.

Consider a stream created with Let_stream.create() how can the producer notify an error to the stream consumer? It seems that there is no provision for this and the creator and consumer must use a separate line to communicate the error – which is not very convenient!

Thanks!

[aantron]

I guess or would expect that the exception is conveyed by a failed thread returned by Lwt_stream.get, but the API-documentation does not go into these details.

This is correct, though a subsequent get can cause a subsequent call to the function f passed to from/from_direct, and that call to f might not fail.

Consider a stream created with Let_stream.create() how can the producer notify an error to the stream consumer? It seems that there is no provision for this and the creator and consumer must use a separate line to communicate the error – which is not very convenient!

Indeed, a separate channel has to be used.

I've documented and written tests for the current behavior in the attached commit. Fixing the quirk with push-streams, or deciding what is the correct way to deal with exceptions, is left for #250. This issue is linked from there as well.