Alan I'm way behind with this exact-print stuff and Anchors in particular. If you and your co-workers on it are confident you know what to do, that's great - although as ever, please document the design carefully. (I volunteer as a reader of such a design overview. I know that a current draft exists.) If you want a design discussion with others less closely involved then do suggest it -- probably a synchronous meeting with a tutorial element would be helpful. thanks for working on this in such a sustained way. Simon PS: I am leaving Microsoft at the end of November 2021, at which point simonpj@microsoft.commailto:simonpj@microsoft.com will cease to work. Use simon.peytonjones@gmail.commailto:simon.peytonjones@gmail.com instead. (For now, it just forwards to simonpj@microsoft.com.) From: ghc-devs On Behalf Of Alan & Kim Zimmerman Sent: 28 October 2021 22:18 To: ghc-devs Subject: Exact Print Annotations : Anchor in a SrcSpan I have been updating the ghc-exactprint library for real world use cases on the about to be released GHC 9.2.1, and realised I need to be able to put an Anchor into every SrcSpan in the ParsedSource AST. I prepared !6854 to sort it out in master and turned to the problem of GHC 9.2.1, where I had missed the boat. And then I discovered that we have SrcSpan defined as data SrcSpan = RealSrcSpan !RealSrcSpan !(Maybe BufSpan) | UnhelpfulSpan !UnhelpfulSpanReason and the (Maybe BufSpan) is only used for attaching haddock comments after parsing. This means there is an isomorphism between the RealSrcSpan variant and an Anchor, which I take advantage of with the code in [1], by using the Maybe to encode the AnchorOperation and the BufSpan to encode the DeltaPos. And it struck me that perhaps we should make this a more official approach. The only problem is the detail of the BufSpan, to be able to play both roles cleanly. Alan [1] https://gist.github.com/alanz/5e262599ab79138606cdfcf3792ef635https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgist.github.com%2Falanz%2F5e262599ab79138606cdfcf3792ef635&data=04%7C01%7Csimonpj%40microsoft.com%7Cd10e614607c843649c4108d99a587f99%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637710527929989318%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=4KMwfrLhB7lxKPsiSJ5UobLbEul7OEvT4CiPI8NOzu4%3D&reserved=0