- Glasgow-haskell-users

[ANNOUNCE] GHC 8.2.2 release candidate 3
by Ben Gamari 31 Oct '17

31 Oct '17

Hello everyone, The GHC team is very pleased to announce the third candidate of the 8.2.2 release of the Glasgow Haskell Compiler. Source and binary distributions are available at https://downloads.haskell.org/~ghc/8.2.2-rc3/ This is the third and last of three release candidates leading up the final 8.2.2 release. This release fixes approximately fifty bugs present in 8.2.1. These most notably include, * A correctness issue resulting in segmentation faults in some FFI-users (#13707, #14346) * A correctness issue resulting in undefined behavior in some programs using STM (#14171) * A bug which may have manifested in segmentation faults in out-of-memory condition (#14329) * clearBit of Natural no longer bottoms (#13203) * A specialisation bug resulting in exponential blowup of compilation time in some specialisation-intensive programs (#14379) * ghc-pkg now works even in environments with misconfigured NFS mounts (#13945) * GHC again supports production of position-independent executables (#13702) * Better error messages around kind mismatches (#11198, #12373, #13530, #13610) See [1] for the full list. Release candidate three contains only two patches not present in -rc2 but fixes a packaging issue which lead to unintentional downgrading the process and Cabal libraries. As always, please report any issues you encounter. Happy testing, - Ben [1] https://ghc.haskell.org/trac/ghc/query?status=closed&milestone=8.2.2&col=id…

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How does GHC's testsuite work?
by Sébastien Hinderer 31 Oct '17

31 Oct '17

Dear all, I am a member of OCaml's developement team. More specifically, I am working on a test-driver for the OCaml compiler, which will be part of OCaml's 4.06 release. I am currently writing an article to describe the tool and its principles. In this article, I would like to also talk about how other compilers' testsuites are handled and loking how things are done in GHC is natural. In OCaml, our testsuite essentially consist in whole programs that we compile and run, checking that the compilation and execution results match the expected ones. >From what I could see from GHC's testsuite, it seemed to me that it uses Python to drive the tests. I also understood that the testsuite has tests that are more kind of unit-tests, in the .T file. Am I correct here? Or do you guys also have whole program tests? If you do, how do you compile and run them? Any comment / hint on this aspect of the test harness' design would be really helpful. Many thanks in advance, Sébastien.

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Getting segmentation fault on stack/cabal -any command, including stack --install-ghc, On windows.
by Michael McCulloch 22 Oct '17

22 Oct '17

Hello. After searching around I can't find people with a similar issue (Maybe I'm looking in the wrong places?). I installed Haskell platform 8.2.1, using Stack 1.5.1, Cabal 2.0.0.0. Windows 10 Fall Creators Update( This issue was also occurring pre FCU). The issue also occurs with 8.0.2a Prior to FCU, I could run ghci directly, but now i get: Access violation in generated code when reading 00000000046710f6 Can anyone help me out? -- Michael McCulloch c: (403) 629-9645 e: michael.james.mcculloch(a)gmail.com

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GHC rewrite rule type-checking failure
by Conal Elliott 04 Oct '17

04 Oct '17

I'm running into type checking problem with GHC rewrite rules in GHC 8.0.2, illustrated in the code below. The first rule type-checks, but the second triggers the type error mentioned in the comment following the rule definition. I'd expect both rules to type-check, adding the needed constraints to the applicability condition for the rule. Is GHC's behavior intended (and perhaps necessary), or a bug? Thanks, -- Conal Code (also attached): {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# OPTIONS_GHC -Wall #-} -- Demonstrate a type checking failure with rewrite rules module RuleFail where class C k where comp' :: k b c -> k a b -> k a c instance C (->) where comp' = (.) -- Late-inlining version to enable rewriting. comp :: C k => k b c -> k a b -> k a c comp = comp' {-# INLINE [0] comp #-} morph :: (a -> b) -> k a b morph = error "morph: undefined" {-# RULES "morph/(.)" morph comp = comp #-} -- Fine class D k a where addC' :: k (a,a) a instance Num a => D (->) a where addC' = uncurry (+) -- Late-inlining version to enable rewriting. addC :: D k a => k (a,a) a addC = addC' {-# INLINE [0] addC #-} {-# RULES "morph/addC" morph addC = addC #-} -- Fail -- • Could not deduce (D k b) arising from a use of ‘addC’ -- from the context: D (->) b -- Why does GHC infer the (C k) constraint for the first rule but not (D k b) -- for the second rule?

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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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Multiple C threads -> one unthreaded GHC RTS
by Albert Y. C. Lai 28 Sep '17

28 Sep '17

Suppose I have a C program with multiple C threads calling Haskell functions, maybe the same Haskell function too, and the GHC RTS used is the unthreaded one. What will go wrong? I ask because Cabal/cabal-install has recently added building of export-to-C shared libraries, i.e., the "foreign-library" section. It sees to all the technical details, very nice, I'm very happy about this addition, but it chooses the unthreaded GHC RTS. Thanks.

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How to get a heap visualization
by Yitzchak Gale 20 Sep '17

20 Sep '17

I need a simple heap visualization for debugging purposes. I'm using GHC 8.0.2 to compile a large and complex yesod-based web app. What's the quickest and easiest way? Vacuum looks simple and nice. But it has some long-outstanding PRs against it to support GHC 7.10 and GHC 8.0 that were never applied. https://github.com/thoughtpolice/vacuum/issues/9 Getting ghc-vis to compile looks hopeless, for a number of reasons. The dependencies on gtk and cairo are huge. It hasn't been updated on Hackage for a year and a half. It requires base < 4.9. I need to run the visualizer either on a headless Ubuntu 16.04 server, or locally on Windows. And anyway, the fancy GUI in ghc-vis is way overkill for me. The heap scraper backend for ghc-vis, ghc-heap-view, looks usable, and better supported than vacuum. But is there a quick and simple visualizer for its output, without ghc-vis? Is there anything else? Is the best option to fork vacuum and and try to apply the PRs?

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Spurious recompilations when using a compiler plugin
by Conal Elliott 19 Sep '17

19 Sep '17

It appears that use of GHC plugins causes client code to get needlessly recompiled. (See Trac issues 12567 <https://ghc.haskell.org/trac/ghc/ticket/12567> and 7414 <https://ghc.haskell.org/trac/ghc/ticket/7414>.) It’s becoming more of a problem for usability of the plugin <http://conal.net/papers/compiling-to-categories> I’ve been developing, and I’m wondering what can be done. Some questions: - Is there any work in progress on fixing this situation? - Are there serious obstacles to fixing it? - Do plugin writers or users have any workarounds? Other insights appreciated. – Conal

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Inhibiting the specialiser?
by Conal Elliott 15 Sep '17

15 Sep '17

Is there a GHC flag for inhibiting the specializer (but not all optimizations)? I'm seeing huge output from the Specialise phase killed at 4GB and growing. The output starts as follows: Result size of Specialise = {terms: 29,639, types: 10,921,552, coercions: 4,425,185} Sounds like a lot to me. Is it?. I get this behavior with -O2 and with -O. -- Conal

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TH Show instance not working.
by David Banas 20 Aug '17

20 Aug '17

Hi all, Does anyone know why this code: module Language.P4.UtilTest where import Language.P4.Util (mkShow) data Dummy = Bogus Char | Nonsense Int $(mkShow ''Dummy) is producing this error: Davids-Air-2:P4 dbanas$ stack ghc -- UtilTest.hs -ddump-splices [1 of 1] Compiling Language.P4.UtilTest ( UtilTest.hs, UtilTest.o ) UtilTest.hs:24:3-16: Splicing declarations mkShow ''Dummy ======> instance Show Dummy where show (Bogus x) = show x show (Nonsense x) = show x UtilTest.hs:24:3: error: Conflicting definitions for ‘show’ Bound at: UtilTest.hs:24:3-16 UtilTest.hs:24:3-16 | 24 | $(mkShow ''Dummy) | ^^^^^^^^^^^^^^ ? The TH splice expansion looks correct to me. If I comment out the second constructor (Nonsense Int), the code compiles without error. Thanks, -db

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