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
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