- Glasgow-haskell-users

Orphan Instances with GHC 6.8
by Adrian Hey 17 Oct '07

17 Oct '07

Hello Folks, One thing different from 6.6 and 6.8 is I find that with -Wall I get a lot more warnings about orphan instances, even if the code has not changed. Has the definition of what an Orphan instance is changed? Or is this a bug? If so, is the bug in 6.6 or 6.8? I can make them go away with the -fno-warn-orphans flag, but I'm still curious as to why I didn't have to do this before. Thanks -- Adrian Hey

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Prevent optimization from tempering with unsafePerformIO
by Bernd Brassel 16 Oct '07

16 Oct '07

Hello, I am writing a compiler from the functional logic language Curry to Haskell. As the result is a real extension of Haskell, there has to be SOME side effect involved. Unfortunately, this seems to prevent me from using any of ghc's optimizations on the resulting code. I have tried for some time to invoke the no-inline pragmata, but they seem to have no effect at all. Recently at ICFP, Neil Mitchell told me that there definitely is a way to avoid this problem. But does anybody know how? Thanks for your help! Bernd Brassel

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undecidable & overlapping instances: a bug?
by Jorge Marques Pelizzoni 13 Oct '07

13 Oct '07

Hi, all! I am quite intrigued at the behaviour examplified in the attached module. It's true I am a newbie and probably don't quite get the whole consequence spectrum of -fallow-undecidable-instances, but why providing that dummy instance (commented out) get the thing to compile? By the way, I'm using GHC 6.6 on WinXP (actually, latest Visual Haskell with MS Visual Studio 2005) and the error message I get is: FooModule.hs:13:9: Could not deduce (Show a) from the context (Concrete a b) arising from use of `bar' at FooModule.hs:13:9-13 Possible fix: add (Show a) to the class or instance method `foo' In the expression: bar x In the definition of `foo': foo x = bar x In the definition for method `foo' A second question: which kinds of overlapping are covered by -fallow-overlapping-instances? It seems that the following (also in the attached module) is not allowed: instance (Show a, Abstract a b) => Concrete a b where foo x = show x instance (Abstract a b) => Concrete a b which gives me the message: FooModule.hs:17:0: Duplicate instance declarations: instance [overlap ok] (Show a, Abstract a b) => Concrete a b -- Defined at FooModule.hs:17:0 instance [overlap ok] (Abstract a b) => Concrete a b -- Defined at FooModule.hs:30:0 Thanks in advance for any pointers. Cheers, Jorge.

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Determining GHC version use to compile an executable?
by Ravi Nanavati 10 Oct '07

10 Oct '07

I was wondering if there was a clever way to determine the GHC version that was used to compile a particular executable. I looked in the RTS flags and didn't see anything obvious, but I was wondering if I missed something or if there was a clever back door. It's not a big deal if there isn't but, if there is, it might help me diagnose a problem. Thanks, - Ravi

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is -fno-monomorphism-restriction evil?
by Jorge Marques Pelizzoni 09 Oct '07

09 Oct '07

Hi, all! It may be a side-effect of being a newbie, but many times I find the -fno-monomorphism-restriction quite handy. Is it intrinsically evil? I mean, has anyone had a bad time using it or does it imply some runtime performance overhead? I guess it is not portable, is it? Thanks in advance. Cheers, Jorge.

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Re: how to build API docs from snapshot? (solved)
by Johannes Waldmann 09 Oct '07

09 Oct '07

Johan Tibell wrote: > Did you change mk/build.mk before running ./configure and make? Ah! I did change this, but I forgot to (re-)configure. Thanks a lot. -- -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- ---- http://www.imn.htwk-leipzig.de/~waldmann/ -------

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how to build API docs from snapshot?
by Johannes Waldmann 09 Oct '07

09 Oct '07

How can I build the library API docs from a (source) snapshot, e.g. ghc-6.8.0.20070921-src-extralibs.tar.bz2 ? Thanks, -- -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- ---- http://www.imn.htwk-leipzig.de/~waldmann/ -------

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bug in 6.8.1-candidate
by Serge D. Mechveliani 02 Oct '07

02 Oct '07

Dear GHC developers, this is again on the `panic' bug in ghc-6.8.1-candidate. The archive http://botik.ru/pub/local/Mechveliani/ghcBugs/bug2-6.8.0-sep28.zip presents one more report on this bug. Unzip and see install.txt. The project is built, but the test program Test.hs cannot build, ghc reports of `panic'. Further, return to the project build: in the file GBasFld.hs, comment-out the type declaration for the function b_criterion_ev, and re-build the project. Now, it reports of `panic' when compiling GBasFld. Simply speaking, docon-2.11 works under ghc-6.6.1 and does not work under ghc-6.8.0-sep28.zip. Regards, ----------------- Serge Mechveliani mechvel(a)botik.ru

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FFI Bindings to Libraries using GMP
by benedikth 01 Oct '07

01 Oct '07

Hello, I've been struggling using FFI bindings to libraries which rely on the GNU Mp Bignum library (gmp) - this is apparently a well known problem (http://hackage.haskell.org/trac/ghc/ticket/311, http://hackage.haskell.org/trac/ghc/wiki/ReplacingGMPNotes) I do rely on using such libraries, and so started to get it work on MacOsX; no solution was close to being satisfactory however, so I'd like to ask for some advice. Those two options worked to some extend: (1) Create or modify the library in question, so gmp is statically linked and its symbols are hidden. When source code is available, this is relatively easy, altough it requires modification of the build process (which can be a hassle). If a static "ar" archive is available, it is cumbersome (at least on Mac Os X I ran into a lot of troubles using nmedit), but possible. Furthermore, the resulting libraries are bloated, as each of them contains a copy of the GMP; left alone portability issues. (2) As suggested in ticket#311, I tried switching the allocator functions when switching to FFI. It worked, but not in GHCi; also, doing it manually is a lot of work, because, as far as I could figure out, it is neccessary to write a wrapper function for every C-function (indirectly) using the gmp. Furthermore, most of the libraries expose gmp datatypes (mpz_t,mpq_t) in their API. I currently use a little haskell module working on GHC.Exts, but that's propably not a good option from a maintainer's point of view. There are certainly other possibilities, but I couldn't find one which is both maintainable and portable. I would be very grateful for any advice, or some information on plans for resolving ticket #311. There are some great libraries (like the Parma Polyhedral Library, to pick an example) out there using gmp, and it would be nice if writing bindings to those libs could be simplified. Thanks, Benedikt Huber

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runhaskell rather than runghc
by Serge D. Mechveliani 30 Sep '07

30 Sep '07

Dear GHC and Cabal developers and users, I suggest to use `runhaskell' rather than `runghc'. Because it looks to have more sense, and also for political correctness. Cabal is a tool for `making' various Haskell implementations. In 2015, we may have implementations ghc, Hugs, hbc, foo_1, ..., foo_n. Does Cabal need to provide runghc, runhugs, runhbc ... runfoo_n ? Do I mistake? Regards, ----------------- Serge Mechveliani mechvel(a)botik.ru

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