GHC spits out errors as SDocs, which makes it hard for clients of the GHC API to respond sensibly to them. (Parsing error message strings seems ... sub-optimal.) This ticket tracks progress towards improving the situation.

Key resources

• The errors-as-values GHC proposal 306 describes the problem, and the proposed solution
• The errors-as-values wiki page describes the high level design for how we propose to implement it in GHC.
• This WIP merge request 3691 is our work in progress.

For design discussion, use this ticket. For code review, use the MR !3691.