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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">One difficulty is that I think that writing Core-to-Core passes might become a lot more challenging. It gets gnarly writing code that satisfies the type checker, depending of course on how strong
the invariants are.<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 think <a href="https://www.researchgate.net/publication/292674440_Type-safe_Runtime_Code_Generation_Accelerate_to_LLVM">
Typesafe runtime code generation</a> has some material on this.<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">TL;DR: by all means give it a try. I’m not terribly optimistic… but progress is made when we find that things we thought weren’t possible are possible after all. So I’d be happy to be proved wrong.<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>
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<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>Ari Fordsham<br>
<b>Sent:</b> 14 September 2021 13:39<br>
<b>To:</b> ghc-devs@haskell.org<br>
<b>Subject:</b> More type safety in Core?<o:p></o:p></span></p>
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<span style="font-size:9.0pt;font-family:"Segoe UI",sans-serif;color:#212121">You don't often get email from
<a href="mailto:arifordsham@gmail.com">arifordsham@gmail.com</a>. <a href="http://aka.ms/LearnAboutSenderIdentification">
Learn why this is important</a><o:p></o:p></span></p>
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<p class="MsoNormal">I don't know if this is the right forum for this, I apologise if I'm intruding...
<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Are there any plans to use the type system to enforce safety in Core, via e.g. GADTs? This would replace much of core-lint with static checking.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Conal Eliottt has done something similar in a blog post (<a href="https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fconal.net%2Fblog%2Fposts%2Foverloading-lambda%23%3A~%3Atext%3DHaskell%2520source%2520language.-%2CI%2C-originally%2520intended%2520to&data=04%7C01%7Csimonpj%40microsoft.com%7C3f5f8d3d0bc141e5a78408d9777ca375%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637672217369668112%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=6IB9AcOy%2BzMmbVU51i9IenjPVA6usmeQE87j4Z1tXlk%3D&reserved=0">http://conal.net/blog/posts/overloading-lambda#:~:text=Haskell%20source%20language.-,I,-originally%20intended%20to</a>)
and it seems relatively straightforward.<o:p></o:p></p>
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<p class="MsoNormal">This would be especially beneficial to those working at the cutting edge of GHC features, statically ensuring their Core manipulations are correct. I would be surprised if existing compiler bugs wouldn't be found while implementing this.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">What would the performance impact be? would using GADTs incur extra overhead? I'd assume you'd save something by lugging around less type information in Core.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Ari Fordsham<o:p></o:p></p>
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