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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Alan<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I’m way behind with this exact-print stuff and Anchors in particular.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">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.)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">thanks for working on this in such a sustained way.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:8.0pt">PS: I am leaving Microsoft at the end of November 2021, at which point
<a href="mailto:simonpj@microsoft.com"><span style="color:#0563C1">simonpj@microsoft.com</span></a> will cease to work. Use
<a href="mailto:simon.peytonjones@gmail.com"><span style="color:#0563C1">simon.peytonjones@gmail.com</span></a> instead. (For now, it just forwards to simonpj@microsoft.com.)<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-devs <ghc-devs-bounces@haskell.org>
<b>On Behalf Of </b>Alan & Kim Zimmerman<br>
<b>Sent:</b> 28 October 2021 22:18<br>
<b>To:</b> ghc-devs <ghc-devs@haskell.org><br>
<b>Subject:</b> Exact Print Annotations : Anchor in a SrcSpan<o:p></o:p></span></p>
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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.<o:p></o:p></p>
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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.<o:p></o:p></p>
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And then I discovered that we have SrcSpan defined as<o:p></o:p></p>
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data SrcSpan =<br>
RealSrcSpan !RealSrcSpan !(Maybe BufSpan)<br>
| UnhelpfulSpan !UnhelpfulSpanReason<o:p></o:p></p>
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and the (Maybe BufSpan) is only used for attaching haddock comments after parsing.<o:p></o:p></p>
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<o:p> </o:p></p>
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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.<o:p></o:p></p>
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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.<o:p></o:p></p>
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Alan<o:p></o:p></p>
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[1] <a href="https://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">
https://gist.github.com/alanz/5e262599ab79138606cdfcf3792ef635</a><o:p></o:p></p>
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