#8809: Prettier error messages? -------------------------------------+------------------------------------- Reporter: joelteon | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): #8809,#10073,#10179 | Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): I'm delighted to see activity on the "better error messages" front. Thank you! There are two separate lines of thought here: 1. Using colour etc in `SDoc`, in a way that is portable across platforms. This seems to be non-trivial (comment:33 and comment:34), but it's non- controversial and it'd be great to have. I think Phab:D2716 and Phab:D2717 are about this. 2. Some infrastructure to allow more info to be displayed in error messages. That's what Phab:D2718 is about. I suggest we split (2) into a separate ticket. On (1) let's just do it. On the (2) front, I confess that I'm not keen on the approach shown in Phab:D2718, which allows an `SDoc` to contain an I/O action. It smells wrong in principle to me; it would fork GHC away from our goal of using the Hackage `pretty` library (#10735); and I think we can do better. I would love to make progress on adopting David Christiansen's idea for pretty printing, which he calls "A pretty printer that says what it means": * [https://www.youtube.com/watch?v=m7BBCcIDXSg Video], * [https://hackerfall.com/story/a-pretty-printer-that-says-what-it-means Blog post] * [https://wiki.haskell.org/wikiupload/4/4c/Hiw-2015-david- christiansen.pdf Slides] * [https://github.com/david-christiansen/hindent Git repo for hindent, an extensible Haskell pretty printer] That's what Ben is alluding to in comment:31. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8809#comment:35 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler