January 2019 - ghc-devs

How to use Data.Compact.Serialize
by Christopher Done 07 Jan '19

07 Jan '19

Hi, On the docs for Data.Compact.Serialize it says: http://hackage.haskell.org/package/compact-0.1.0.1/docs/Data-Compact-Serial… > Our binary representation contains direct pointers to the info tables > of objects in the region. This means that the info tables of the > receiving process must be laid out in exactly the same way as from the > original process; in practice, this means using static linking, using > the exact same binary and turning off ASLR. It seems to me that in order to use this module in any practical way (i.e. write to file from one process, and then a later run of the process reads it), you need to know a special way to build your binary which isn't fully described here. What flags, for example, should be passed to GHC to make this viable? * Turning off ASLR on Linux is done by writing 0 to /proc/sys/kernel/randomize_va_space, which applies to all programs. That's not the most isolated way to deploy an app, but I discovered that you can set this per process here: https://askubuntu.com/a/507954 * To compile GHC programs statically, use -optl-static -optl-pthread. So in total the example would be: $ stack build compact compact-0.1.0.1: download compact-0.1.0.1: configure compact-0.1.0.1: build compact-0.1.0.1: copy/register Example file from docs: $ cat main.hs {-# LANGUAGE TypeApplications #-} import System.Environment import Data.Compact import Data.Compact.Serialize main = do arg:_ <- getArgs case arg of "write" -> do orig_c <- compact ("I want to serialize this", True) writeCompact @(String, Bool) "somefile" orig_c "read" -> do res <- unsafeReadCompact @(String, Bool) "somefile" case res of Left err -> fail err Right c -> print (getCompact c) Compiling statically: $ stack ghc -- -optl-static -optl-pthread main.hs [1 of 1] Compiling Main ( main.hs, main.o ) Linking main ... [...hundred more warnings like this ...] Check that it's static: $ ldd main not a dynamic executable Write the file: $ setarch `uname -m` -R ./main write Read the file: $ setarch `uname -m` -R ./main read ("I want to serialize this",True) Can a GHC dev confirm that this is the proper way to do this? If so, I'll contribute this little example as documentation to the compact package. Cheers

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GitLab CI for patches across submodules
by Simon Jakobi 07 Jan '19

07 Jan '19

Hi, I just tried to use GitLab CI to validate a GHC patch including changes to Haddock: https://gitlab.haskell.org/sjakobi/ghc/pipelines/842 The problem is that the CI script tries to find my Haddock commit at https://gitlab.haskell.org/ghc/haddock. But that repo doesn't even allow merge request. Should the submodule origin for util/haddock maybe point at https://github.com/haskell/haddock instead? Cheers, Simon

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RE: Glasgow Haskell Compiler | Fix #16133 by checking for TypeApplications in rnExpr (!77)
by Simon Peyton Jones 07 Jan '19

07 Jan '19

I am now getting lots of email from GitLab, and I’m trying to figure out what they all mean. They come in various forms. Here’s one puzzler: * what does the email below mean? Is it a new merge request? * what is the “!77”? * What does “RyanGlScott/ghc:wip/T16133 → ghc/ghc:master” mean? Simon From: Ryan Scott <gitlab(a)gitlab.haskell.org> Sent: 05 January 2019 17:46 To: Simon Peyton Jones <simonpj(a)microsoft.com> Subject: Glasgow Haskell Compiler | Fix #16133 by checking for TypeApplications in rnExpr (!77) Project:Branches: RyanGlScott/ghc:wip/T16133 → ghc/ghc:master We had a validity check, typeAppErr, for visible kind applications (in rnHsTyKi), but didn't extend the same treatment to visible type applications (in rnExpr). Easily fixed by also invoking typeAppErr from rnExpr. Fixes https://ghc.haskell.org/trac/ghc/ticket/16133<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fghc.haske…>. — View it on GitLab<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.ha…>. You're receiving this email because of your account on gitlab.haskell.org. If you'd like to receive fewer emails, you can unsubscribe<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.ha…> from this thread or adjust your notification settings.

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Failure to catch C++ exception in Haskell on OS X
by Bas van Dijk 06 Jan '19

06 Jan '19

Dear GHC Devs, I'm debugging an issue in our haskell-opencv library where a C++ exception that is thrown by the OpenCV C++ library isn't caught by the C++ try...catch block we have inlined in our Haskell code using inline-c-cpp. This results in the process terminating by SIGABRT. Note that this only happens on OS X. In Linux the exception is caught correctly. I wrote a minimal isolated test case (which doesn't use OpenCV) at: https://github.com/basvandijk/darwin-cxx-exception-bug I wrote some instructions in the README on how to reproduce this and included some debugging notes. I'm not sure the bug is caused by a mis-configuration in my code or if it's a bug in nixpkgs, Cabal or GHC. Any idea what could be causing this? Bas

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Status of downloads.haskell.org/~ghc/master/
by Artem Pelenitsyn 06 Jan '19

06 Jan '19

Hello devs, What is the status of this directory [1]? It doesn't seem to be the tip of the master branch in the repo. In the documentation [2] it says: > GHC 8.5.20180424 User's Guide I'm asking because it has broken links to the base haddocks in it (here [3] try clicking on any link to the library docs, e.g. GHC.Conc.par), and Google happily indexes and spits out as results of search queries everything laying here and there, including these pages. Broken links could lead “outsiders” to a somewhat underwhelming impression of the state of infrastructure. [1]: http://downloads.haskell.org/~ghc/master/ [2]: http://downloads.haskell.org/~ghc/master/users-guide/index.html [3]: http://downloads.haskell.org/~ghc/master/users-guide/runtime_control.html#r… -- Best wishes, Artem

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GitLab cross-posting to Trac?
by Richard Eisenberg 06 Jan '19

06 Jan '19

Hi devs, With our new GitLab workflow, will commit messages still be posted to Issues (once the migration is complete)? That's been really useful with Trac. Thanks, Richard

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The GHC Proposals Process
by Ara Adkins 05 Jan '19

05 Jan '19

Hey All, Now we have our own git instance in GitLab, are there any plans to move the proposals process from GitHub? _ara

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GitLab: Cmd+Enter considered harmful on reviews
by Richard Eisenberg 05 Jan '19

05 Jan '19

PSA: When reviewing an MR on GitLab, every comment has two buttons: (1) add to review, and (2) add comment now. Cmd+Enter (on my machine at least), does option (2), even though option (1) is bold and green. This is not what I wanted. (By the way, "comments" actually open these things called "discussions", which can be resolved. But that's another matter.) I've now removed all my comments and added them to my review. But I wanted you all to know about this in case you stumble across the same problem. Richard

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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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Type family equation violates injectivity?
by Dominick Samperi 04 Jan '19

04 Jan '19

When I use v8.6.3 of GHC under Ubuntu to install the inline-r package I get the error "Type family equation violates injectivity annotation," and a type variable on the LHS cannot be inferred from the RHS, due to the lack of injectivity (I suppose). On the other hand, v8.0.2 of GHC (shipped with Haskell Platform under Ubuntu) does not have this problem (it has other problems). Has something changed in the latest version of the compiler that might cause this? Possible work-around? FYI, the line that triggers the error is: type instance G.Mutable (W t ty s) = Mutable.W t ty The variable that cannot be inferred is 's'. Thanks, Dominick

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