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docs: Document that withAsync does not propagate exceptions in the first argument #128
Description
When I wrote PRs #104 and #105, I described withAsync as equally safe as race. That is wrong.
withAsync silently swallows exceptions in the first argument, e.g.
withAsync (error "TODO") $ \_ -> do -- more codeHere, the error will not bubble up.
(I haven't actually tried it with error yet, but with a worker thread doing a forever, and was surprised that it just didn't work, when in fact a No such file or directory was silently swallowed.)
race doesn't have this issue, in particular not the common pattern bResult <- fmap (either absurd id) $ race a b.
This should be made clearer in the docs in various places.
Reacted by Julius Marozas
Activity
parsonsmatt commentedon Nov 20, 2022
I also found this confusing.
The documentation does say that "If the operation throws an exception, then that exception is re-thrown by
wait. This ensures property (1): No exception is swallowed."If you want the exception thrown as an async, then you have to use
link-will cause the exception in
ato be asynchronously passed to the parent thread.