July 2017 - ghc-devs - Haskell.org

GHC's module hierarchy
by Simon Peyton Jones 02 Oct '19

02 Oct '19

Dear ghc-devs hsyl20 proposes a radical overhaul of the module structure of GHC itself. He or she suggested it six months ago in https://ghc.haskell.org/trac/ghc/ticket/13009 and has now offered a monster patch https://phabricator.haskell.org/D3647 It's clearly the result of a lot of work, but I was the only one who responded on the original ticket, and it'll affect all of your lives in a very immediate way. So, would you like to * consider the idea * look at the actual re-mapping of modules hsyl20 proposals * express an opinion about whether to go ahead Probably the ticket, rather than Phab, is the best place to comment on the general idea. I'd like to thank hsyl20. GHC's rather flat module structure has grown incrementally over years. But still, there are pros and cons. Simon

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Default options for -threaded
by lonetiger＠gmail.com 04 Jan '19

04 Jan '19

Hi All, A user on https://ghc.haskell.org/trac/ghc/ticket/11054 has asked why -N -qa isn’t the default for -threaded. I’m afraid I don’t know a good reason why it’s not. Can anyone help shed some light on this? If there is no good reason, Would anyone object to making it the default? Thanks, Tamar

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Bringing back #ghc IRC logging
by Niklas Hambüchen 25 Oct '17

25 Oct '17

Hi, as you may have noticed, #ghc IRC logging has been broken for months (though the channel topic still says "Logs: http://ircbrowse.net/ghc"). Logs being unavailable is bad because many problems and topics that were googleable before are no longer googleable. We have discussed in the last 2 days on #ghc whether we should just join #ghc with a 0-effort-on-our-side public logging service like botbot.me. This one in particular doesn't have the best UI but I found it to be very googleable, and many open-source projects use it successfully. Is anybody opposed to this? Niklas

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[ANNOUNCE] GHC 8.2.1 release candidate 1
by Ben Gamari 03 Oct '17

03 Oct '17

Hello everyone, The GHC team is very pleased to announce the first candidate of the 8.2.1 release of the Glasgow Haskell Compiler. Source and binary distributions are available at https://downloads.haskell.org/~ghc/8.2.1-rc1/ This is the first of a few release candidates leading up the final 8.2.1 release. This release will feature, * A new type-indexed Typeable implementation * The long awaited Backpack * Deriving strategies for disambiguating DeriveAnyClass, GeneralizedNewtypeDeriving, and stock mechanisms * Overloaded record fields * Improved compiler performance * Better code generation through more robust tracking of join points * Compact regions for more efficient garbage collection and serialization * Better support for machines with non-uniform memory architectures * More robust support for levity (e.g. RuntimeRep) polymorphism * A simple interface for streaming eventlog data from live processes * Further refinement of DWARF support Unfortunately there are still a few known issues in this release, including a few compiler panics (#13233, #13509) and a memory leak in the simplifier (#13426) which may adversely affect heap sizes and compilation time for some modules. This memory leak unfortunately made it impossible to provide a 32-bit Windows distribution for this candidate; this will be resolved in -rc2. As always, please let us know if you have difficulty. Thanks to everyone who has contributed to this release! Happy testing, - Ben

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Crossreferenced GHC 8.0.2
by Robin Palotai 29 Aug '17

29 Aug '17

Hello GHC devs, I ran haskell-indexer [1] on the GHC 8.0.2 tarball, partly because I find myself reading GHC source from time to time while working on the indexer, and partly since it's fun. First, here you can click around [2] and find where beloved functions are called from: http://stuff.codereview.me/#ghc/compiler/hsSyn/HsBinds.hs?corpus&signature (scroll down a bit, imports are not linked yet). Second, the way I indexed was pretty simple. I took the output of `make`, replaced the ghc used with the ghc_kythe_wrapper, and filtered the lines which included '-c', since I noticed that those duplicate previous large compile lines. This only indexes the stage1 compilation AFAIU. Feel free to suggest a better way to tap into the compilations to get everything properly indexed (and possibly only once). Any comments welcome! Robin [1]: https://github.com/google/haskell-indexer [2]: TLDR UI quirks: - Click the :: in top-left to navigate file tree - Ctrl-Click (on linux) to go directly to definition (otherwise click stuff from bottom pane) - Bottom pane often hides content, close it if stuck.

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Operating on HsSyn
by Simon Peyton Jones 31 Jul '17

31 Jul '17

Devs, Shayan is working away on "Trees that grow"... do keep it on your radar: To: ghc-devs Sent: 25 May 2017 23:49 Do take a look at this: * We propose to re-engineer HsSyn itself. This will touch a lot of code. * But it's very neat, and will bring big long-term advantages * And we can do it a bit at a time The wiki page https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow has the details. It's entirely an internal change, not a change to GHC's specification, so it's independent of the GHC proposals process. But I'd value the opinion of other GHC devs Meanwhile I have a question. When pretty-printing HsSyn we often have a situation like this: data Pass = Parsed | Renamed | Typechecked data HsExpr (p :: Pass) = HsVar (IdP p) | .... type famliy IdP p where IdP Parsed = RdrName IdP Renamed = Name IdP Typechecked = Id instance (Outputable (IdP p)) => Outputable (HsExpr p) where ppr (HsVar v) = ppr v The (ppr v) requires (Outputable (IdP p)), hence the context. Moreover, and more seriously, there are things we just can't pretty-print right now. For example, HsExpr has this data constructor: data HsExpr p = ... | OpApp (LHsExpr p) (LHsExpr p) (PostRn p Fixity) (LHsExpr p) To pretty-print the third argument, we'd need to add instance (Outputable (IdP p), Outputable (PostRn p Fixity)) -- New => Outputable (HsExpr p) where ppr (HsVar v) = ppr v and that gets onerous. So today we never print these annotations, to avoid bloating the instance contexts, which can be painful. It bit me yesterday. We have bitten that bullet for the Data class: look at HsExtension.DataId, which abbreviates the long list of dictionaries: type DataId p = ( Data p , ForallX Data p , Data (NameOrRdrName (IdP p)) , Data (IdP p) , Data (PostRn p (IdP p)) , Data (PostRn p (Located Name)) , Data (PostRn p Bool) , Data (PostRn p Fixity) ,..and nine more... ) Let me note in passing that [wiki:QuantifiedContexts<https://ghc.haskell.org/trac/ghc/wiki/QuantifiedContexts>] would make this somewhat shorter type DataId p = ( Data p , ForallX Data p , Data (NameOrRdrName (IdP p)) , Data (IdP p) , forall t. Data t => Data (PostRn p t)) But we still need one item in this list for each type function, and I am worried about how this scales to the [wiki:ImplementingTreesThatGrow<https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow>] story, when we have a type function for each data constructor -- and there are a lot of data constructors. So I have four questions 1. I think we should probably use a superclass instead of a type synonym class (Data p, ForallX Data p, ....) => DataId p where {} Why? Only one argument to pass, and to pass on to successive calls. I see no downside. 1. Shall we treat Outputable like Data? (I.e. make an abbreviation for a long list of Outputable instances and use it everywhere) 2. I thought of another way to do it (pass a token); see below 1. Are there any other ways? Token passing idea. Perhaps instead of passing lots of functions, we pass a singleton token that encodes the pass, like this: instance (PassC p) => Outputable (HsExpr p) where ppr (HsVar v) = case getPass :: IsPass p of IsParsed -> ppr v IsRenamed -> ppr v IsTypechecked -> ppr v The three ppr's are at different types, of course; that's the point. The infrastructure is something like class PassC p where getPass :: IsPass p data IsPass p where IsParsed :: IsPass Parsed IsRenamed :: IsParsed Renamed IsTypechecked :: IsParsed Typechecked instance PassC Parsed where getPass = IsParsed ...etc... Now we could sweep away all those OutputableX classes, replacing them with dynamic tests on the singletons IsParsed etc. This would have advantages: - Probably faster: there's a dynamic test, but many fewer dictionary arguments and higher-order function dispatch - Only one dictionary to pass; programming is easier. The big downside is that it's not extensible: it works only because we know the three cases. But the "Trees that Grow" story really doesn't scale well to pretty-printing: so maybe we should just give up on that?

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8.2.1: Ord TyCon is gone?
by Levent Erkok 29 Jul '17

29 Jul '17

I'm trying to port some plugin code from GHC 8.0.2 to GHC 8.2.1; alas I'm getting an error suggesting that TyCon is no longer an instance of Ord: Data/SBV/Plugin/Analyze.hs:580:33: error: • No instance for (Ord TyCon) arising from a use of ‘M.lookup’ There are instances for similar types: instance Ord GHC.Types.TyCon -- Defined in ‘GHC.Classes’ • In the expression: k `M.lookup` tcMap In the expression: case k `M.lookup` tcMap of Just knd -> return knd Nothing -> unknown In a case alternative: Just k -> case k `M.lookup` tcMap of Just knd -> return knd Nothing -> unknown | 580 | Just k -> case k `M.lookup` tcMap of | ^^^^^^^^^^^^^^^^^^ I was using TyCon's as a key in a map, but that code is no longer compiling. I've looked through the release notes but couldn't find what the new mechanism is. I'd appreciate if someone can point me in the right direction regarding how to use TyCon as a map key.. Thanks, -Levent.

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[ANNOUNCE] GHC 8.2.1 available
by Ben Gamari 27 Jul '17

27 Jul '17

=============================================== The Glasgow Haskell Compiler -- version 8.2.1 =============================================== The GHC developers are very happy to announce the long-awaited 8.2.1 release of Glasgow Haskell Compiler. Binary and source distributions can be found at https://downloads.haskell.org/~ghc/8.2.1/ This is the second release in the 8.0 series. As such, the focus of this release is performance, stability, and consolidation. Consequently numerous cleanups can be seen throughout the compiler including, * Significant improvements in compiler performance * More robust support for levity polymorphism * Reliable DWARF debugging information * Improved runtime system performance on NUMA systems * Retooling of the cost-center profiler, including support for live streaming of profile data via the GHC event log * Interface file determinism * More robust treatment of join points, enabling significantly better code generation in many cases * Numerous improvements in robustness on Windows * and the resolution of over 500 other tickets In addition, there are a number of new features, * A new, more type-safe type reflection mechanism * The long-awaited Backpack module system * Deriving strategies to disambiguate between GHC's various instance deriving mechanisms * Unboxed sum types, for efficient unpacked representation of sum data types * Compact regions, allowing better control over garbage collection in the presence of large heaps containing many long-lived objects. * Colorful messages and caret diagnostics for more legible errors A more thorough list of the changes in this release can be found in the release notes, https://haskell.org/ghc/docs/8.2.1/docs/html/users_guide/8.2.1-notes.html There are a few changes in release-engineering that should be noted, * Binary distributions for 32-bit CentOS 6.7 have been dropped. Moreover, there are no dedicated CentOS 7.0 distributions as CentOS 7 can use can use Debian 8 binaries. If you would like us to continue to produce 32-bit CentOS 6.7 distributions please let us know. * GHC HQ now builds FreeBSD and OpenBSD distributions for amd64; this comes after many years of these distributions being faithfully provided by Karel Gardas and Pali Gabor Janos, who we should heartily thank for their contributions. GHC HQ building these distributions ourselves will allow us to more quickly ship distributions to users by eliminating the need for a long lag time between source release availability and having all binary distributions available. * There is a technology-preview of an AArch64 Linux binary distribution, as well as an ARM Linux build. AArch64 support is quite preliminary but should be stable in 8.4 thanks to further linker fixes by Moritz Angerman. ARM should be stable. * GHC now tries to use the gold and lld linkers by default. These linkers are significantly faster than the BFD linker implementation that most Linux distributions use by default. If gold or lld are not available GHC will use the system's default linker. GHC can be forced to use the default linker by passing --disable-ld-override to configure. This release has been the result of over a year of hard work by over 150 code contributors. Thanks to everyone who has helped in writing patches, testing, reporting bugs, and offering feedback over the last year. This release cycle was admittedly quite drawn out, significantly longer than expected or desired. While we are confident that the result is worth the wait, we have been steadily working on infrastructure which should help shrink future release cycles and give us better testing between releases. More details on this coming soon. As always, let us know if you encounter trouble. How to get it ~~~~~~~~~~~~~ The easy way is to go to the web page, which should be self-explanatory: http://www.haskell.org/ghc/ We supply binary builds in the native package format for many platforms, and the source distribution is available from the same place. Packages will appear as they are built - if the package for your system isn't available yet, please try again later. Background ~~~~~~~~~~ Haskell is a standard lazy functional programming language. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating efficient code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces. GHC is distributed under a BSD-style open source license. A wide variety of Haskell related resources (tutorials, libraries, specifications, documentation, compilers, interpreters, references, contact information, links to research groups) are available from the Haskell home page (see below). On-line GHC-related resources ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Relevant URLs on the World-Wide Web: GHC home page http://www.haskell.org/ghc/ GHC developers' home page http://ghc.haskell.org/trac/ghc/ Haskell home page http://www.haskell.org/ Supported Platforms ~~~~~~~~~~~~~~~~~~~ The list of platforms we support, and the people responsible for them, is here: http://ghc.haskell.org/trac/ghc/wiki/Contributors Ports to other platforms are possible with varying degrees of difficulty. The Building Guide describes how to go about porting to a new platform: http://ghc.haskell.org/trac/ghc/wiki/Building Developers ~~~~~~~~~~ We welcome new contributors. Instructions on accessing our source code repository, and getting started with hacking on GHC, are available from the GHC's developer's site run by Trac: http://ghc.haskell.org/trac/ghc/ Mailing lists ~~~~~~~~~~~~~ We run mailing lists for GHC users and bug reports; to subscribe, use the web interfaces at http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-tickets There are several other haskell and ghc-related mailing lists on www.haskell.org; for the full list, see https://mail.haskell.org/cgi-bin/mailman/listinfo Some GHC developers hang out on #haskell on IRC, too: http://www.haskell.org/haskellwiki/IRC_channel Please report bugs using our bug tracking system. Instructions on reporting bugs can be found here: http://www.haskell.org/ghc/reportabug

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Harbormaster update
by Ben Gamari 27 Jul '17

27 Jul '17

Hello everyone, Note that the Harbormaster builders now bootstrap with GHC 8.2.1 and LLVM 3.9. I'll be on the lookout for any failures but ping me if you see Harbormaster fail to build your otherwise perfectly good patch. Cheers, - Ben

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RE: [commit: ghc] master: Improve error messages around kind mismatches. (8e15e3d)
by Simon Peyton Jones 27 Jul '17

27 Jul '17

| typecheck/should_fail/T7368) Solution: track the provenance of | Derived constraints and refuse to float out a constraint that has | an insoluble Derived. For the record, that's not the solution that the patch implements. Instead we just don’t float heterogeneous equalities. I think Richard just forgot to update the commit message. Simon | -----Original Message----- | From: ghc-commits [mailto:ghc-commits-bounces@haskell.org] On Behalf | Of git(a)git.haskell.org | Sent: 27 July 2017 12:50 | To: ghc-commits(a)haskell.org | Subject: [commit: ghc] master: Improve error messages around kind | mismatches. (8e15e3d) | | Repository : ssh://git@git.haskell.org/ghc | | On branch : master | Link : | https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fghc.ha | skell.org%2Ftrac%2Fghc%2Fchangeset%2F8e15e3d370e9c253ae0dbb330e25b72cb | 00cdb76%2Fghc&data=02%7C01%7Csimonpj%40microsoft.com%7C9993301a429e467 | e29b008d4d4e6350f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C6363675 | 32584262688&sdata=bY%2Bruj0hhXfC23hfMA1ivuAs2Av2%2BY4%2BJK2yyCoPzbA%3D | &reserved=0 | | >--------------------------------------------------------------- | | commit 8e15e3d370e9c253ae0dbb330e25b72cb00cdb76 | Author: Richard Eisenberg <rae(a)cs.brynmawr.edu> | Date: Thu Jun 1 17:27:14 2017 -0400 | | Improve error messages around kind mismatches. | | Previously, when canonicalizing (or unifying, in uType) a | heterogeneous equality, we emitted a kind equality and used the | resulting coercion to cast one side of the heterogeneous equality. | | While sound, this led to terrible error messages. (See the bugs | listed below.) The problem is that using the coercion built from | the emitted kind equality is a bit like a wanted rewriting a | wanted. | The solution is to keep heterogeneous equalities as irreducible. | | See Note [Equalities with incompatible kinds] in TcCanonical. | | This commit also removes a highly suspicious switch to | FM_SubstOnly | when flattening in the kinds of a type variable. I have no idea | why this was there, other than as a holdover from pre-TypeInType. | I've not left a Note because there is simply no reason I can | conceive | of that the FM_SubstOnly should be there. | | One challenge with this patch is that the emitted derived | equalities | might get emitted several times: when a heterogeneous equality is | in an implication and then gets floated out from the implication, | the Derived is present both in and out of the implication. This | causes a duplicate error message. (Test case: | typecheck/should_fail/T7368) Solution: track the provenance of | Derived constraints and refuse to float out a constraint that has | an insoluble Derived. | | Lastly, this labels one test (dependent/should_fail/RAE_T32a) | as expect_broken, because the problem is really #12919. The | different handling of constraints in this patch exposes the error. | | This fixes bugs #11198, #12373, #13530, and #13610. | | test cases: | typecheck/should_fail/{T8262,T8603,tcail122,T12373,T13530,T13610} | | | >--------------------------------------------------------------- | | 8e15e3d370e9c253ae0dbb330e25b72cb00cdb76 | compiler/typecheck/TcCanonical.hs | 296 | ++++++++++++--------- | compiler/typecheck/TcErrors.hs | 75 ++++-- | compiler/typecheck/TcEvidence.hs | 8 +- | compiler/typecheck/TcFlatten.hs | 31 ++- | compiler/typecheck/TcRnTypes.hs | 30 ++- | compiler/typecheck/TcSimplify.hs | 34 ++- | compiler/typecheck/TcType.hs | 10 +- | compiler/typecheck/TcUnify.hs | 28 +- | compiler/types/Type.hs | 4 +- | testsuite/tests/dependent/should_fail/T11471.hs | 2 +- | .../tests/dependent/should_fail/T11471.stderr | 11 +- | testsuite/tests/dependent/should_fail/all.T | 2 +- | testsuite/tests/gadt/gadt7.stderr | 6 +- | .../tests/ghci.debugger/scripts/break012.stdout | 14 +- | .../indexed-types/should_fail/ExtraTcsUntch.stderr | 6 +- | .../tests/indexed-types/should_fail/T5934.stderr | 13 - | testsuite/tests/polykinds/T12593.stderr | 56 ++++ | testsuite/tests/polykinds/T13555.stderr | 21 +- | testsuite/tests/polykinds/T7438.stderr | 6 +- | testsuite/tests/polykinds/T8566.stderr | 2 +- | testsuite/tests/polykinds/T9017.stderr | 10 +- | testsuite/tests/typecheck/should_fail/T12373.hs | 10 + | .../tests/typecheck/should_fail/T12373.stderr | 8 + | testsuite/tests/typecheck/should_fail/T13530.hs | 11 + | .../tests/typecheck/should_fail/T13530.stderr | 7 + | testsuite/tests/typecheck/should_fail/T13610.hs | 11 + | .../tests/typecheck/should_fail/T13610.stderr | 14 + | testsuite/tests/typecheck/should_fail/T5691.stderr | 10 +- | testsuite/tests/typecheck/should_fail/T7368.stderr | 6 +- | .../tests/typecheck/should_fail/T7368a.stderr | 2 +- | testsuite/tests/typecheck/should_fail/T7453.stderr | 48 +--- | testsuite/tests/typecheck/should_fail/T7696.stderr | 4 +- | testsuite/tests/typecheck/should_fail/T8262.stderr | 6 +- | testsuite/tests/typecheck/should_fail/T8603.hs | 4 + | testsuite/tests/typecheck/should_fail/T8603.stderr | 13 +- | testsuite/tests/typecheck/should_fail/all.T | 3 + | .../tests/typecheck/should_fail/tcfail090.stderr | 4 +- | .../tests/typecheck/should_fail/tcfail122.stderr | 8 +- | .../tests/typecheck/should_fail/tcfail123.stderr | 13 +- | .../tests/typecheck/should_fail/tcfail200.stderr | 6 +- | 40 files changed, 537 insertions(+), 316 deletions(-) | | Diff suppressed because of size. To see it, use: | | git diff-tree --root --patch-with-stat --no-color --find-copies- | harder --ignore-space-at-eol --cc | 8e15e3d370e9c253ae0dbb330e25b72cb00cdb76 | _______________________________________________ | ghc-commits mailing list | ghc-commits(a)haskell.org | https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmail.h | askell.org%2Fcgi-bin%2Fmailman%2Flistinfo%2Fghc- | commits&data=02%7C01%7Csimonpj%40microsoft.com%7C9993301a429e467e29b00 | 8d4d4e6350f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C6363675325842 | 62688&sdata=JkrPJNfzdjx2Rz%2FfcMq2HlIP%2BlsFIE%2FT68a%2FSUae%2Fzo%3D&r | eserved=0

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