We could always make a hyperlink to the source code as hosted on GitLab. But I actually argue not to: such links would quickly become outdated, in one of two ways: either we make a permalink, in which case the linked Note text will become outdated; or we make a link to a particular file & line, in which case the Note might move somewhere else. Instead, just by naming the Note title, we have a slightly-harder-to-use link, where you use it by grepping the source code. This is less convenient, but it will stay up-to-date. Until we have better tooling to, say, create an HTML anchor based on a Note, I think this is the best we can do.
Richard > On Dec 28, 2021, at 12:10 PM, Benjamin Redelings > <benjamin.redeli...@gmail.com> wrote: > > I was thinking about the relationship between the wiki and the notes in the > GHC source. > > Would it be possible to link directly to [compiler notes] in the GHC source > from the wiki, using hyperlinks? Right now, I'm seeing references that look > like: (See Note [Constraint flavours].) > > (I can see the motivation to include comments in the source, but I also think > that the wiki is more discoverable than the compiler source code. So, in the > interests of pursuing both approaches, it would be nice to be able to link to > notes FROM the wiki. I suppose one could include a hyperlink to the file on > github that contains the note...) > > I'm not sure how much web infrastructure would be required to make hyperlinks > for notes... > > -BenRI > > On 11/8/21 5:35 AM, Simon Peyton Jones wrote: >> Is there anywhere on the GHC wiki that explains how to interpret this >> output, and says that the type and dictionary applications ARE there, just >> not shown by '-ddump-tc'? >> >> Perhaps it would be helpful to add some basic description of what comes out >> of the typechecker to a page like this one? (below) >> >> https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/compiler/hsc-main >> <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fwikis%2Fcommentary%2Fcompiler%2Fhsc-main&data=04%7C01%7Csimonpj%40microsoft.com%7Cab59b17d2f394945ad1e08d9a2b96c81%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637719740212483767%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=WZL1VADZPUlaOACd58K1XZO5MzPOKrfLFMSuBD%2FGW44%3D&reserved=0> >> Yes it would! Would you care to start such a wiki page (a new one; don’t >> just clutter up the one you point to)? You can write down what you know. >> Don’t worry if you aren’t 100% sure – we can correct it. And if you >> outright don’t know, leave a “What should I say here?” note. >> >> "This late desugaring is somewhat unusual. It is much more common to desugar >> the program before typechecking, or renaming, because that presents the >> renamer and typechecker with a much smaller language to deal with. However, >> GHC's organisation means that >> >> This note is now slightly out of date. We are now, very carefully, doing >> some desugaring before typechecking. See >> Note [Handling overloaded and rebindable constructs] in GHC.Rename.Expr >> Note [Rebindable syntax and HsExpansion] in GHC.Hs.Expr >> >> You can and should point to these and similar Notes from the wiki page you >> write. Indeed there may be some part of what you write that would be better >> framed as Note in GHC’s source code. >> >> Thanks! >> >> Simon >> >> PS: I am leaving Microsoft at the end of November 2021, at which point >> simo...@microsoft.com <mailto:simo...@microsoft.com> will cease to work. >> Use simon.peytonjo...@gmail.com <mailto:simon.peytonjo...@gmail.com> >> instead. (For now, it just forwards to simo...@microsoft.com >> <mailto:simo...@microsoft.com>.) >> >> From: ghc-devs <ghc-devs-boun...@haskell.org> >> <mailto:ghc-devs-boun...@haskell.org> On Behalf Of Benjamin Redelings >> Sent: 08 November 2021 13:12 >> To: Richard Eisenberg <li...@richarde.dev> <mailto:li...@richarde.dev> >> Cc: ghc-devs@haskell.org <mailto:ghc-devs@haskell.org> >> Subject: Re: Output language of typechecking pass? >> >> Hi, >> >> >> Questions: >> >> 1. It seems like this separation is actually necessary, in order to apply >> generalization only to let arguments written by the programmer, and not to >> let bindings introduced during desugaring. Is that right? >> >> I don't think so. That is, if we did it all in one pass, I still think we >> could get generalization right. >> I guess I asked this question wrong. I mean to say, if we did the two >> passes in the reverse order (desugaring first, followed by typechecking), >> that would not work, right? >> >> As the wiki says: >> >> "This late desugaring is somewhat unusual. It is much more common to desugar >> the program before typechecking, or renaming, because that presents the >> renamer and typechecker with a much smaller language to deal with. However, >> GHC's organisation means that >> >> error messages can display precisely the syntax that the user wrote; and >> desugaring is not required to preserve type-inference properties. >> " >> >> >> 2. Does the output of type checking contain type lambdas? >> >> Yes. See below. >> >> >> 3. Does the type checking pass determine where to add dictionary arguments? >> >> Yes. See below. >> >> >> 4. Are there any other resources I should be looking at? >> >> Yes. You want to enable -fprint-typechecker-elaboration (and possible >> -fprint-explicit-coercions). With the former, you get to see all this stuff >> you're looking for. It's normally suppressed so that the output resembles >> the user's code. >> >> I hope this helps! >> Richard >> Hmm... so, I think I see how this works now. I don't think >> '-fprint-explicit-coercions' does anything here though. >> >> $ ghc -ddump-tc Test2.hs -fprint-typechecker-elaboration >> >> ... >> >> AbsBinds [a_a2hp] [$dNum_a2hB] >> {Exports: [g <= g_a2hz >> wrap: <>] >> Exported types: g :: forall a. Num a => a -> a -> a >> [LclId] >> Binds: g x_aYk y_aYl = (y_aYl * x_aYk) + 1 >> Evidence: [EvBinds{[W] $dNum_a2hs = $dNum_a2hq >> [W] $dNum_a2hw = $dNum_a2hq >> [W] $dNum_a2hq = $dNum_a2hB}]} >> >> ... >> >> The type and dictionary arguments are visible here (along with the evidence >> bindings), but type and dictionary applications are only visible if you use >> -ddump-tc-ast, which is a lot more verbose. (I don't think there is another >> flag that shows these applications?) Since I didn't initially know what >> "evidence" was, and there is nothing to say that a_a2hp is a type lambda >> argument, this was pretty opaque until I managed to read the tc-ast and the >> light went on. >> >> I can see now that the type and dictionary arguments are added by annotating >> the AST. >> >> Is there anywhere on the GHC wiki that explains how to interpret this >> output, and says that the type and dictionary applications ARE there, just >> not shown by '-ddump-tc'? >> >> Perhaps it would be helpful to add some basic description of what comes out >> of the typechecker to a page like this one? (below) >> >> https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/compiler/hsc-main >> <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fwikis%2Fcommentary%2Fcompiler%2Fhsc-main&data=04%7C01%7Csimonpj%40microsoft.com%7Cab59b17d2f394945ad1e08d9a2b96c81%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637719740212483767%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=WZL1VADZPUlaOACd58K1XZO5MzPOKrfLFMSuBD%2FGW44%3D&reserved=0> >> -BenRI >>
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