Thanks so much for making a proposal for this, Ben!! It's great to see progress here.
I'm also glad that there is now a proposal process. I made a fairly similar proposal almost exactly 5 years ago to the libraries list - https://mail.haskell.org/pipermail/libraries/2015-April/025471.html - but without the subtlety of particular backtrace representations. Skimming the ensuing thread may still be informative. In particular, there is one thing I would like to highlight from that old proposal. I think it'd be good to have a standard way to represent a chain of exceptions, and build this into `catch` and `finally`. Python and Java both have a mechanism for this, and both refer to it as a "cause" exception. When an exception is thrown during exception handling, the exception being handled is preserved as its "cause". I find this mechanism to be incredibly useful in Java, it has made the underlying issue much clearer in many cases, and in other cases at least provides helpful context. I have no doubt such a mechanism would have saved me many hours of debugging exceptions in Haskell systems I've worked on in the past. I considered commenting about that directly on the proposal, but I figure this is a better place to suggest expanding the scope of the change :) . Totally understandable if you want to keep this proposal focused on stacktraces, but I think it'd be good to consider this as a potential future improvement. -Michael On Thu, May 7, 2020 at 3:55 PM Ben Gamari <b...@well-typed.com> wrote: > > Hi everyone, > > After a nice discussion on IRC about the unfortunate state of error > reporting in Haskell, I felt compelled to write down some long-lingering > thoughts regarding backtraces on exceptions. The result is GHC proposal > #330 [1]. I think the approach is viable and perhaps even > straightforward. I have the sketch of an implementation here [2]. > > Please have a look at the proposal and leave your comments. If there is > consensus it is possible that we could have this done for 8.12. > > Cheers, > > - Ben > > > [1] https://github.com/ghc-proposals/ghc-proposals/pull/330 > [2] https://gitlab.haskell.org/ghc/ghc/-/merge_requests/3236 > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >
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