March 2013 - Glasgow-haskell-users

Does GHC on cygwin have an I/O manager?
by kudah 08 Apr '13

08 Apr '13

I've been desperate to get any semblance of I/O performance from Haskell on Windows. Does ghc still build under cygwin, and if so, does the cygwin build have a working I/O manager? Also, is it possible yet to build a ghc cross-compiler targeting windows?

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Problems installing 7.6.2 on MACOS
by Dominic Steinitz 07 Apr '13

07 Apr '13

Hi, I followed the instructions pointed to from here: http://www.haskell.org/ghc/download_ghc_7_6_2#macosx_x86_64 > bash-3.2$ ./configure --prefix=/Library/Haskell > bash-3.2$ sudo make install But sadly I get: > bash-3.2$ ghc-pkg list > ghc-pkg: missing --global-package-db option, location of global package database unknown and > bash-3.2$ ghc --make nnClassifier.lhs -O2 > ghc: missing -B<dir> option Any advice on how to get 7.6.2 working would be much appreciated. Dominic. Here's some more information: > bash-3.2$ which ghc-pkg > /Library/Haskell/lib/ghc-7.6.2/ghc-pkg > bash-3.2$ which ghc > /Library/Haskell/lib/ghc-7.6.2/ghc 7.4.1 still works fine: > bash-3.2$ ghc-pkg-7.4.1 list > /Library/Frameworks/GHC.framework/Versions/7.4.1-x86_64/usr/lib/ghc-7.4.1/package.conf.d: > Cabal-1.14.0 > GLUT-2.1.2.1 > bash-3.2$ ghc-7.4.1 --make nnClassifier.lhs -O2 -fforce-recomp > [1 of 6] Compiling MatrixPlus ( MatrixPlus.hs, MatrixPlus.o ) > [2 of 6] Compiling NeuralNet ( NeuralNet.hs, NeuralNet.o ) > [3 of 6] Compiling Backprop ( Backprop.hs, Backprop.o ) > [4 of 6] Compiling MarineExplore ( MarineExplore.hs, MarineExplore.o ) > [5 of 6] Compiling Runner ( Runner.hs, Runner.o ) > [6 of 6] Compiling Main ( nnClassifier.lhs, nnClassifier.o ) > Linking nnClassifier ... > ld: warning: directory not found for option '-L/opt/local/lib/' > bash-3.2$ ./nnClassifier > Reading training labels... > Read 100 labels[(1,0),(2,1),(3,0),(4,1),(5,0),(6,0),(7,1),(8,0),(9,1),(10,0)] > Reading training images... > 9:9 > 9:9

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Allowing (Char ~ Bool => Void)?
by Shachaf Ben-Kiki 05 Apr '13

05 Apr '13

Is there a good reason that GHC doesn't allow any value of type (Char ~ Bool => Void), even undefined? There are various use cases for this. It's allowed indirectly, via GADT pattern matches -- "foo :: Is Char Bool -> Void; foo x = case x of {}" (with EmptyCase in HEAD) -- but not directly. One thing this prevents, for instance, is CPSifying GADTs: data Foo a = a ~ Char => A | a ~ Bool => B -- valid newtype Bar a = Bar { runBar :: forall r. (a ~ Char => r) -> (a ~ Bool => r) -> r } -- unusable Trying to use a type like the latter in practice runs into problems quickly because one needs to provide an absurd value of type (Char ~ Bool => r), which is generally impossible (even if we're willing to cheat with ⊥!). It seems that this sort of thing should be doable. Shachaf

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ImplicitParams and MonoLocalBinds
by Roman Cheplyaka 03 Apr '13

03 Apr '13

The value of the following expression let ?y = 2 in let p = ?y in let ?y = 1 in p depends on whether the second binding is generalised. MonomorphismRestriction makes it not generalise, hence the value is 2. What surprises me is that MonoLocalBinds doesn't have this effect. Prelude> :set -XImplicitParams -XNoMonomorphismRestriction -XMonoLocalBinds Prelude> let ?y = 2 in let p = ?y in let ?y = 1 in p 1 What's going on here? Roman

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ghc and aarch64?
by Jens Petersen 26 Mar '13

26 Mar '13

I am curious if anyone has started or is planning to work on porting GHC to the new ARM 64bit architecture AArch64 for Linux? Jens

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Re: Libffi errors while cross-compiling GHC 7.6.2 (Stage 1)
by Nikita Karetnikov 23 Mar '13

23 Mar '13

> Is /usr/bin/gcc a MIPS cross-compiler? If not, how do you expect it > to work? Right, I wasn't using a cross-compiler. That's the problem. I haven't succeeded in cross-building yet. I'm using a distro with a non-common directory structure and I still have to figure out how to specify both GCCs. But it has nothing to do with the ticket. So I've just closed it. I apologize for the noise.

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Compiled code
by migmit 22 Mar '13

22 Mar '13

Suppose I compiled some module and kept it's .hi and .o files. Is it possible to use this module in my program if the source code was deleted for some reason? Seems like the answer is "yes" — by creating a fake .hs file (with no real content) and touch-in .hi and .o files I tricked ghc so that it didn't attempt to recompile the module, so the information in .hi and .o files is sufficient. But ghc insists on having the .hs file around, and I didn't find a way to turn it off. Is there any? Or there is a specific reason not to have it?

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Release plans
by Ian Lynagh 21 Mar '13

21 Mar '13

Hi all, Thank you to everyone who gave us feedback on when we should release 7.8.1, and on future release plans in general. We've looked at all the responses, and we think that the best plan is to continue to make major releases annually, with minor "patch-level" releases between them. Additionally, we may recommend particular snapshots, and provide binary builds for all tier-1 platforms, for people who wish to test new features etc in HEAD. There is more detail on how all this will work here: http://hackage.haskell.org/trac/ghc/wiki/WorkingConventions/Releases We will therefore aim for a 7.8.1 release in October. We do not currently expect to make a 7.6.3 release, although that may change if serious bugs in 7.6.2 are discovered. Would a 7.7.x recommended snapshot be useful to you? Tell us if you want one. Compared to 7.6 it would contain: * polykinded Typeable library * major improvements in DPH (vectorisation avoidance, new vectoriser) * type holes * rebindable list syntax * major changes to the type inference engine * type level natural numbers * overlapping type families * the new code generator * support for vector (SSE/AVX) instructions * Scheduler changes to the RTS to improve latency Is it worth us putting out a preview, or are you happy to work from the nightly snapshots and wait for the full release in October? Thanks Ian

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Polymorphic implicit parameters
by Roman Cheplyaka 21 Mar '13

21 Mar '13

I'm curious as to why GHC doesn't accept the following (contrived) module: {-# LANGUAGE ImplicitParams, RankNTypes #-} f :: (?g :: (forall a . a -> a)) => a -> a f = ?g The error message is: Illegal polymorphic or qualified type: forall a. a -> a In the type signature for `f': f :: ?g :: (forall a. a -> a) => a -> a It's not a big deal since one can wrap the polymorphism in a newtype, but it's somewhat unexpected. Roman

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ANNOUNCE: GHC 7.6.2 Release Candidate 1
by Ian Lynagh 20 Mar '13

20 Mar '13

We are pleased to announce the first release candidate for GHC 7.6.2: http://www.haskell.org/ghc/dist/7.6.2-rc1/ This includes the source tarball, installers for Windows, and bindists for Windows, Linux, OS X and FreeBSD, on x86 and x86_64. We plan to make the 7.6.2 release early in 2013. Please test as much as possible; bugs are much cheaper if we find them before the release! Thanks Ian, on behalf of the GHC team

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