I've responded on the MR. Thanks for stepping up to do this! Richard

On Dec 30, 2019, at 5:53 AM, Rowan Goemans wrote:

Hello everyone,

A couple of days ago I tried to implement type level warnings [1]. I have got something now that sort of works but issues the same warning multiple times and not on the correct location. It's currently a WIP merge request [2]. I would like some help/pointers to continue the implementation

The approach I have taken is to issue the warning once TypeWarning is rewritten. However, this has severe problems since now a warning is issued multiple times and at different locations due to the rewriting happening multiple times. I don't know what the best location is to do this check and issue the warning. Prior to constraint solving isn't a good place since the TypeWarning could be nested deeply in some constraint. Afterwards also isn't doable since then the TypeWarning constraint is gone.

An alternative could be to not implement any instance in for TypeWarning similar to TypeError and special case it somehow.

Any help is appreciated!

[1] https://gitlab.haskell.org/ghc/ghc/issues/17027 https://gitlab.haskell.org/ghc/ghc/issues/17027 [2] https://gitlab.haskell.org/ghc/ghc/merge_requests/2361 https://gitlab.haskell.org/ghc/ghc/merge_requests/2361

Best regards,

Rowan Goemans _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs