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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I thought I’d sent a message about this DynFlags thing, but I can’t trace it now. So here’s a resend.<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">Currently<o:p></o:p></span></p>
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<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span style="mso-fareast-language:EN-US">The DynFlags record includes Hooks<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span style="mso-fareast-language:EN-US">Hooks in contains functions, that mention TcM, DsM etc<o:p></o:p></span></li></ul>
<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">This is bad. We should think of DynFlags as an
<b>abstract syntax tree</b>. That is, the result of parsing the flag strings, yes, but not much more. So for hooks we should have an algebraic data type representing the hook
<i>specification</i>, but it should not be the hook functions themselves. HsSyn, for example, after parsing, is just a tree with strings in it. No TyCons, Ids, etc. That comes much later.<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">So DynFlags should be a collection of algebraic data types, but should not depend on anything else.<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 that may cut a bunch of awkward loops.<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"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Simon Peyton Jones
<br>
<b>Sent:</b> 10 September 2020 14:17<br>
<b>To:</b> Sebastian Graf <sgraf1337@gmail.com>; Sylvain Henry <sylvain@haskus.fr><br>
<b>Cc:</b> ghc-devs <ghc-devs@haskell.org><br>
<b>Subject:</b> RE: Parser depends on DynFlags, depends on Hooks, depends on TcM, DsM, ...<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">And for sure the *<b>parser</b>* should not depend on the *<b>desugarer</b>* and *<b>typechecker</b>*. (Which it does, as described below.)<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">S<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"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-devs <<a href="mailto:ghc-devs-bounces@haskell.org">ghc-devs-bounces@haskell.org</a>>
<b>On Behalf Of </b>Sebastian Graf<br>
<b>Sent:</b> 10 September 2020 14:12<br>
<b>To:</b> Sylvain Henry <<a href="mailto:sylvain@haskus.fr">sylvain@haskus.fr</a>><br>
<b>Cc:</b> ghc-devs <<a href="mailto:ghc-devs@haskell.org">ghc-devs@haskell.org</a>><br>
<b>Subject:</b> Parser depends on DynFlags, depends on Hooks, depends on TcM, DsM, ...<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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Hey Sylvain,<o:p></o:p></p>
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<o:p> </o:p></p>
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In <a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fmerge_requests%2F3971&data=02%7C01%7Csimonpj%40microsoft.com%7C0c3760e72fad4200d39408d8558b3871%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637353404753453548&sdata=fVpIzJgaqFfWaJ5ppCE5daHwdETTQF03o1h0uNtDxGA%3D&reserved=0">
https://gitlab.haskell.org/ghc/ghc/-/merge_requests/3971</a> I had to fight once more with the transitive dependency set of the parser, the minimality of which is crucial for
<a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fhackage.haskell.org%2Fpackage%2Fghc-lib-parser&data=02%7C01%7Csimonpj%40microsoft.com%7C0c3760e72fad4200d39408d8558b3871%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637353404753463506&sdata=HZMaqK6t7PLifc26wf%2BqcUef4Ko%2BQcaPRx4o7XLcVq8%3D&reserved=0">
ghc-lib-parser</a> and tested by the CountParserDeps test.<o:p></o:p></p>
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<o:p> </o:p></p>
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I discovered that I need to make (parts of) `DsM` abstract, because it is transitively imported from the Parser for example through Parser.y -> Lexer.x -> DynFlags -> Hooks -> {DsM,TcM}.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
Since you are our mastermind behind the "Tame DynFlags" initiative, I'd like to hear your opinion on where progress can be/is made on that front.<o:p></o:p></p>
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<o:p> </o:p></p>
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I see there is <a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fissues%2F10961&data=02%7C01%7Csimonpj%40microsoft.com%7C0c3760e72fad4200d39408d8558b3871%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637353404753463506&sdata=sn9zv1MO8p%2FSbwsm1NDaSiUaumE%2FvTo4NkGreYOjITA%3D&reserved=0">
https://gitlab.haskell.org/ghc/ghc/-/issues/10961</a> and <a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fissues%2F11301&data=02%7C01%7Csimonpj%40microsoft.com%7C0c3760e72fad4200d39408d8558b3871%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637353404753463506&sdata=vFTEuEzIQLJTtpu7%2BuwFnOEWMPv8eY%2B%2FvgbrrV18uss%3D&reserved=0">
https://gitlab.haskell.org/ghc/ghc/-/issues/11301</a> which ask a related, but different question: They want a DynFlags-free interface, but I even want a DynFlags-free *module*.<o:p></o:p></p>
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<o:p> </o:p></p>
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Would you say it's reasonable to abstract the definition of `PState` over the `DynFlags` type? I think it's only used for pretty-printing messages, which is one of your specialties (the treatment of DynFlags in there, at least).<o:p></o:p></p>
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Anyway, can you think of or perhaps point me to an existing road map on that issue?<o:p></o:p></p>
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<o:p> </o:p></p>
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Thank you!<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
Sebastian<o:p></o:p></p>
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