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bgamari / ghc-pretty-errors

Design planning for prettier error messages from GHC
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Errors-as-values proposal #5

Closed alpmestan closed 4 years ago

alpmestan commented 4 years ago

@bgamari @goldfirere Here's a first shot at a proposal for representing errors as values of good old ADTs, the first part of the plan to get where we want.

(The second will be a proposal for enriching the document representations , Doc and SDoc. The errors would then be able to take advantage of this by emitting documents that contain expressions/types/etc as annotations, therefore reaching our goal.)

alpmestan commented 4 years ago

@goldfirere In light of your reaction to the open error types hierarchy, I switched to the closed, simpler one. I thought the several .hs-boot files would be frowned upon a lot more than that, and Ben considers this less of an annoyance than he used to, in light of all the discussions we've had so far.

Feedback welcome!

alpmestan commented 4 years ago

For the sake of minimalism, I think it's best to leave the error codes out of this proposal. But I definitely love the idea, and it would be pretty straightforward to implement, once the categories are figured out. It's precisely because of the potential for bikeshedding around the bins that I suggest that we leave them out.

I can definitely mention them though, as a rather straightforward extension of this proposal. The educational value of such an "error manual" would be massive.

goldfirere commented 4 years ago

OK. I see the value of minimalism here: this proposal is only an internal refactoring, with nothing visible to users. That's a very nice property and one worth maintaining.

alpmestan commented 4 years ago

@goldfirere I did my best to address your feedback in the latest commit. The error code idea is now mentioned in the "Effects and interactions" section, I clarified that the cost of implementing this proposal is mostly a short-term one and fixed the type signature of errorMessage.

Let me know what you think. :-)

goldfirere commented 4 years ago

I think this is ready for public consumption. I'm sure there will be more to improve, but l think it's ready to post to ghc-proposals. Thanks!

alpmestan commented 4 years ago

@goldfirere It's now up, at https://github.com/ghc-proposals/ghc-proposals/pull/306