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Haskell.org outage
by Ben Gamari 18 Apr '22

18 Apr '22

Hello everyone, Unfortunately Haskell.org, downloads.haskell.org, and hoogle.haskell.org are currently down. We are currently investigating the cause. Updates will be posted as they are available. Cheers, - Ben

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how to build Haddock documentation for a single module?
by Norman Ramsey 15 Apr '22

15 Apr '22

I'm fine-tuning the Haddock documentation for just one module that sits in the $GHC/compiler/GHC subtree. Is there a way I can get Hadrian to build the documentation for just that module? Norman

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Markup language/convention for Notes?
by Sebastian Graf 14 Apr '22

14 Apr '22

Hi Devs, When writing Notes, I find myself using markdown-inspired or haddock-inspired features. The reason is that I keep telling myself > In 5 years time, we'll surely have an automated tool that renders Notes referenced under the cursor in a popup in our IDE And I might not be completely wrong about that, after all the strong conventions about Note declaration syntax allow me to do jump-to-definition on Note links in my IDE already (thanks to a shell script written by Zubin!). Still, over the years I kept drifting between markdown and haddock syntax, sometimes used `backticked inline code` or haddock 'ticks' to refer to functions in the compiler (sometimes even 'GHC.Fully.Qualified.ticks') and for code blocks I used all of the following forms: Haddock "code quote" > id :: a -> a > id x = x Markdown triple backticks ```hs id :: a -> a id x = x ``` Indentation by spaces id :: a -> a id x = x And so on. I know that at least Simon was thrown off in the past about my use of "tool-aware markup", perhaps also because I kept switching the targetted tool. I don't like that either. So I wonder Do you think it is worth optimising Notes for post-processing by an external tool?I think it's only reasonable if we decide for a target syntax. Which syntax should it be? Cheers, Sebastian

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Re: Run-time absence info
by David Feuer 13 Apr '22

13 Apr '22

> > Date: Wed, 13 Apr 2022 08:59:06 +0200 > From: Andreas Klebinger <klebinger.andreas(a)gmx.at> > To: ghc-devs(a)haskell.org > Subject: Re: Absence info at run-time > Message-ID: <a577aa9c-6c96-945d-85f6-eb207f88b5b3(a)gmx.at> > Content-Type: text/plain; charset=UTF-8; format=flowed > > W/W should transform such a function into one who takes one less > argument removing any runtime overhead at least for fully applied > functions. > Fully applied functions are definitely not what I'm talking about. I suppose your suggestion is then if we an expression`f x` where bar > takes multiple arguments, but doesn't use the current argument then GHC > should: > > * Inspect f, check if the first argument to f is used > * If we can determine it isn't used instead of creating a PAP capturing > `f` and `x` instead only capture `f` and record this in the PAP closure > somehow. > * Once the PAP is fully applied pass a dummy argument instead of `x` to f. > Yes, that's the idea. The "somehow" is described below. If f is a known call that seems doable, although adding a bitmap to paps > might require us to increase the size of all PAP closures, making this > optimization less useful. > Every PAP has to carry its arity. I just looked it up: typedef struct { StgHeader header; StgHalfWord arity; // number of arguments left to apply, if zero this is an AP closure StgHalfWord n_args; // number of applied arguments StgClosure *fun; // guaranteed to point to a FUN closure StgClosure *payload[]; } StgPAP; On a 64-bit machine, we can combine arity and absence info for functions of up to 31 arguments into half a word. Specifically, set the lowest bit to indicate whether the first argument is used, etc. Then bitwise-or that with 1 `shiftL` arity. Each partial application performed shifts right by the number of arguments applied; if the result is 1, we know it's fully applied. (Any idea why we need the number of arguments that have been applied in the PAP? If that's actually only need for AP, then we might be able to make things a little more compact.) > If `f` is a unknown function there is currently no way to get > absent/used info for it's arguments at runtime. And changing that would > be a major change which seems unlikely to pay off. > I described a mechanism for encoding this concisely above. The same encoding could be used for functions that haven't been partially applied. I don't know where their arities are stashed. In their info tables? > So I think this would be theoretically possible, but it would rarely pay > off. > I'm not sure it's so rare. We end up having to work around this issue in libraries, with varying levels of effort and success. > Also do you have an example where `(const a) b` leads to stupid thunks? > It seems to me const should always be inlined in such a case, avoiding a > PAP allocation. > There won't be a PAP allocation if const inlines. The stupid thunk is a thunk to apply (\ _ -> a) to b. Suppose we define `fmap` for plain arrays (I know; probably not the best example), and let <$ take its default implementation: (<$) a = fmap (const a) If we calculate x <$ arr, that will fill an array with thunks, each of them retaining an element of the original array which will never be used. > Am 12/04/2022 um 23:02 schrieb David Feuer: > > Suppose `f` doesn't use its first argument. When forming the thunk (or > > partial application) `f a`, we don't need to record `a`. What if > > instead of arity, we store a bitmap used/absent arguments, terminated > > by a 1 bit? Could we then get rid of "stupid thunks" like `(const a) b`? > > > > _______________________________________________ > > ghc-devs mailing list > > ghc-devs(a)haskell.org > > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > > > ------------------------------ > > Message: 3 > Date: Wed, 13 Apr 2022 08:21:25 +0000 > From: "Sebastian Graf" <sgraf1337(a)gmail.com> > To: "GHC Devs" <ghc-devs(a)haskell.org> > Subject: Markup language/convention for Notes? > Message-ID: <eme97afb2c-f674-4ed3-9d50-52c6482169d0@sebastian-pc> > Content-Type: text/plain; charset="utf-8"; Format="flowed" > > Hi Devs, > > When writing Notes, I find myself using markdown-inspired or > haddock-inspired features. The reason is that I keep telling myself > > > In 5 years time, we'll surely have an automated tool that renders > Notes referenced under the cursor in a popup in our IDE > > And I might not be completely wrong about that, after all the strong > conventions about Note declaration syntax allow me to do > jump-to-definition on Note links in my IDE already (thanks to a shell > script written by Zubin!). > Still, over the years I kept drifting between markdown and haddock > syntax, sometimes used `backticked inline code` or haddock 'ticks' to > refer to functions in the compiler (sometimes even > 'GHC.Fully.Qualified.ticks') and for code blocks I used all of the > following forms: > > Haddock "code quote" > > > id :: a -> a > > id x = x > > Markdown triple backticks > > ```hs > id :: a -> a > id x = x > ``` > > Indentation by spaces > > id :: a -> a > id x = x > > And so on. > > I know that at least Simon was thrown off in the past about my use of > "tool-aware markup", perhaps also because I kept switching the targetted > tool. I don't like that either. So I wonder > Do you think it is worth optimising Notes for post-processing by an > external tool?I think it's only reasonable if we decide for a target > syntax. Which syntax should it be? > Cheers, > Sebastian >

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Absence info at run-time
by David Feuer 13 Apr '22

13 Apr '22

Suppose `f` doesn't use its first argument. When forming the thunk (or partial application) `f a`, we don't need to record `a`. What if instead of arity, we store a bitmap used/absent arguments, terminated by a 1 bit? Could we then get rid of "stupid thunks" like `(const a) b`?

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Windows rework merged ; fresh build necessary on Windows
by Ben Gamari 08 Apr '22

08 Apr '22

Hi all, A few minutes ago I merged !7448 and the associated MRs, moving GHC to use the msys2 Clang64 toolchain on Windows. This work improves compilation time, maintainability, and fixes a numerous long-standing bugs affecting Windows and other platforms. However, as a result you may find that in an existing tree `configure` will fail with an error complaining that `clang` can not be found. This is due to the fact that the toolchain tarballs are stale and be fixed with: rm -R _build inplace/mingw win32-tarballs ./boot ./configure --enable-tarballs-autodownload Do let me know if you see any other issues; I'm a bit under the weather at the moment but I'll try to keep an eye on email. Cheers, - Ben

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Warning about glomming
by Gergő Érdi 08 Apr '22

08 Apr '22

Using -DDEBUG, I see a warning about glomming from OccurAnal. Having read the relevant Note, the situation is exactly what's described here: since I'm using cross-module specializations, the specializer will generate rewrite rules that replace external references with local forward references. But the one thing the Note doesn't explicitly state is why this is reported as a warning. It sounds like OccurAnal is well equipped to fix this problem. So is glomming a sign of a problem or is it not? If I see that warning, does that point to a problem in how I use the GHC API, a problem in the code that I'm trying to compile, or neither?

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RE: Re: Shadowing in toIface* output
by Erdi, Gergo 08 Apr '22

08 Apr '22

PUBLIC OK, I must be doing something wrong then. I am now looking at Tidy (not Prep) output, and I see Core like this: showsPrec :: forall a. Show a => Int -> a -> ShowS [GblId[ClassOp], Arity=1, Caf=NoCafRefs, Str=<S!P(SL,A,A)>, RULES: Built in rule for showsPrec: "Class op showsPrec"] showsPrec = \ (@a_a1G3) (v_B1 :: Show a_a1G3) -> case v_B1 of v_B1 { C:Show v_B2 v_B3 v_B4 -> v_B2 } so if I'm reading this right, these vs are still shadowing. I am using tidyProgram on the output of hscSimplify, and then taking the cg_binds of its result. What else should I do to get tidy (heh) Tidy output? From: ghc-devs <ghc-devs-bounces(a)haskell.org> On Behalf Of Simon Peyton Jones Sent: Monday, April 4, 2022 4:28 PM To: Gergő Érdi <gergo(a)erdi.hu> Cc: GHC Devs <ghc-devs(a)haskell.org> Subject: [External] Re: Shadowing in toIface* output ATTENTION: This email came from an external source. Do not open attachments or click on links from unknown senders or unexpected emails. Always report suspicious emails using the Report As Phishing button in Outlook to protect the Bank and our clients. So does that mean Tidy produces unique `occNameFS`s, and then `Prep` breaks them? Tidy does not produce unique OccNames. Rather, it avoids shadowing, so that if you delete all the uniques and print out the program (which is precisely what happens in an .hi file) you'll still get something sensible. I'm not sure whether or not Prep maintains this invariant. There is no particular reason it should. It might, but it is not (currently) a goal. Simon On Sat, 2 Apr 2022 at 04:35, Gergő Érdi <gergo(a)erdi.hu<mailto:gergo@erdi.hu>> wrote: So does that mean Tidy produces unique `occNameFS`s, and then `Prep` breaks them? On Fri, Apr 1, 2022 at 10:35 PM Josh Meredith <joshmeredith2008(a)gmail.com<mailto:joshmeredith2008@gmail.com>> wrote: > > Hi, > > I encountered this when we used that for Plutus. I'll have to dig up the details, but IIRC `toIfaceExpr` expects GHC to have already tidied the output, which deals with this issue of overlapping variable names. > > Cheers, > Josh > > On Sat, 2 Apr 2022 at 01:26, ÉRDI Gergő <gergo(a)erdi.hu<mailto:gergo@erdi.hu>> wrote: >> >> Hi, >> >> I'm trying to save (Prep'd) Core bindings right next to the serialized >> `ModIface` (so basically `put_`ing them into the same bytestream, after the >> `ModIface`), and that's exactly what the functions in `GHC.CoreToIface` >> seem to be for, so I expected it to Just Work. However, I noticed that I >> very frequently get problems with shadowing. For example, Core that looks >> like `\v{u1} v{u2} -> v{u1}` would get translated to `\v v -> v`, which is >> disastrous since these locally bound `Var`s are represented as just their >> `getOccFS` (i.e. the `FastString` `"v"`). >> >> But this can't be right: if `toIfaceExpr` &c. would fail this blatently, >> then the unfoldings couldn't be saved & restored, which is something GHC >> itself does as part of normal `.hi` file handling. So clearly I must be >> doing something wrong. >> >> So I guess my question could be, what could be causing `toIfaceExpr` (a >> pure function!) to behave this way for my Cores? But then, if I look at >> the implementation of `toIface*`, I can see that it really doesn't do >> anything smarter than just storing `getOccFS` in the interface (no >> uniques in sight)-- so maybe my *real* question is, what is GHC itself >> doing so that it doesn't have this same problem? >> >> Thanks, >> Gergo >> _______________________________________________ >> ghc-devs mailing list >> ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs<https://clicktime.symantec.com/3BestP7qr2g6Y7xBfCxdDwr6xU?u=http%3A%2F%2Fma…> > > _______________________________________________ > ghc-devs mailing list > ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org> > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs<https://clicktime.symantec.com/3BestP7qr2g6Y7xBfCxdDwr6xU?u=http%3A%2F%2Fma…> _______________________________________________ ghc-devs mailing list ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs<https://clicktime.symantec.com/3BestP7qr2g6Y7xBfCxdDwr6xU?u=http%3A%2F%2Fma…> This email and any attachments are confidential and may also be privileged. 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Release Updates - 9.4.1 and 9.2.3
by Matthew Pickering 07 Apr '22

07 Apr '22

Hi all, We have now forked the 9.4 branch. There are a few outstanding patches which have not yet been finished but which are essential to the release. * (#21019) Windows Toolchain Updates - Ben * (#20405) Partial Register Stall - Ben/Andreas * (!7812) Syntactic Unification - Sam The target date for the first alpha for 9.4.1 is 1st May. We have started preparing the 9.2.3 release in order to fix issues discovered in the 9.2.2 release. I will post separately to the list shortly when the schedule for this release is confirmed. The release manager for this release is Zubin. Cheers, Matt

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Git problem
by Simon Peyton Jones 07 Apr '22

07 Apr '22

Friends I see this bash$ git status On branch wip/romes/ttg-splices-improvements Your branch is up to date with 'origin/wip/romes/ttg-splices-improvements'. Changes not staged for commit: (use "git add <file>..." to update what will be committed) (use "git restore <file>..." to discard changes in working directory) (commit or discard the untracked or modified content in submodules) modified: libraries/Cabal (modified content) modified: libraries/unix (modified content) But I don't want those library changes, whatever they are. They look like Unstaged changes (2) modified libraries/Cabal @@ -1 +1 @@ -Subproject commit d638e33dbc056048b393964286c7fe394b2730d7 +Subproject commit d638e33dbc056048b393964286c7fe394b2730d7-dirty modified libraries/unix @@ -1 +1 @@ -Subproject commit 1f72ccec55c1b61299310b994754782103a617f5 +Subproject commit 1f72ccec55c1b61299310b994754782103a617f5-dirty *But using git submodule update does nothing.* How can I get my submodules in sync with this branch? Thanks Simon

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