- Haskell-Cafe - Haskell.org

ANNOUNCE: haskell-src-exts 1.14.0
by Niklas Broberg 21 Aug '13

21 Aug '13

Fellow Haskelleers, I'm pleased to announce the release of haskell-src-exts-1.14.0! * On hackage: http://hackage.haskell.org/package/haskell-src-exts * Via cabal: cabal install haskell-src-exts * git repo: https://github.com/haskell-suite/haskell-src-exts<http://code.haskell.org/haskell-src-exts> There are two primary reasons for this release, and a number of smaller ones. The first primary reason is technical: haskell-src-exts 1.14 revamps the Extension datatype, among other things to allow turning extensions on and off (similar to what Cabal allows). We also introduce the concept of a Language, separate from a set of extensions. This is the only backwards-incompatible change in this release. The second reason is structural: haskell-src-exts is now part of a larger context -- the Haskell Suite. The package has a new home on github (see above), alongside its new cool friends: haskell-names and haskell-packages. There is also a really nice issue tracker there - please help me fill it, or better yet, empty it! What this release does *not* cover is support for the extensions added to GHC in recent time (with the exceptions of CApiFFI and InterruptibleFFI). Work is in progress on many of these, and there will be another major release not far off in the future. This release owes many thanks to Roman Cheplyaka in particular, as well as Erik Hesselink, Simon Meier and David Fox. Thanks a lot! Complete changelog: 1.13.6 --> 1.14.0 =============== * Modernize the Extension datatype in L.H.E.Extension, following the lead of Cabal, to allow negative and positive extension modifiers (turning features on and off). You need to worry about backwards-incompatible changes if any of the following pertains to you: 1) If you use the Extension datatype programmatically - it has changed significantly (see documentation). 2) The ParseMode record now has one more field (baseLanguage :: Language), which might give you a type error. 3) The behavior of the (extensions :: [Extension]) field has changed, which could bite you if you pass custom extensions in the ParseMode. Previously, the ParseMode defaulted to the list of extensions accepted by Haskell2010, and if you set the list explicitly you would override this. Now, the defaults are { baseLanguage = Haskell2010, extensions = [] }, and explicitly setting a list of extensions will be interpreted on top of Haskell2010. See further the documentation for L.H.E.Extension. * Add support for the 'capi' calling convention. It is enabled with the CApiFFI extension. It's been included since GHC 7.4, and advertised since 7.6. * Add support for the 'interruptible' FFI safety annotation, enabled with the InterruptibleFFI extension. * Give better error message when lexing newline fails. In particular, fix the bug when the parser would crash if the file didn't end with a newline. * Support unboxed tuple expressions and patterns. * Fix bug in lexing of primitive integer literals in hex or octal notation. * Disallow negative primitive word literals (such as W# (-0x8000000000000000##)). * Allow phase control for SPECIALIZE pragma. * Derive Foldable and Traversable instances for all annotated AST types. * Fix bug with pretty-printing WARNING and DEPRECATED pragmas. Cheers, Niklas

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ANNOUNCE: posix-paths, for faster file system operations
by Niklas Hambüchen 21 Aug '13

21 Aug '13

John Lato and I would like to announce our posix-paths package. https://github.com/JohnLato/posix-paths It implements a large portion of System.Posix.FilePath using ByteString based RawFilePaths instead of String based FilePaths, and on top of that provides a Traversal module with a fast replacement for `getDirectoryContents` and a recursive `allDirectoryContents`. `getDirectoryContents` is (unsurprisingly?) really slow. Our replacement is 11 times faster in the recursive use case [1], and only 20% slower than `find`. Benchmarks are at [2], code is at [3]. We hope that these improvements will eventually make it into base some day. Until then, we propose our package as a base for discussion and further improvements. Contributions are welcome: Some FilePath operations are not in it yet (especially the Windows / drive related ones), and our traversals might not work on Windows. We would also appreciate some thorough looks at their low level implementations. If you find our benchmarks against getDirectoryContents unfair or would like to add another one, please send a pull request. We have been running this on Linux production machines for a few months now, and are pleased by the speed-up. [1] For the recursive version of the original `getDirectoryContents`, we used the implementation given in Real World Haskell: http://book.realworldhaskell.org/read/io-case-study-a-library-for-searching… [2] Benchmarks: On a real file system: http://johnlato.github.io/posix-paths/usrLocal.html On tmpfs: http://johnlato.github.io/posix-paths/tmpfs.html (note that here find is slow because of process starting overhead) [3] Code: Github: https://github.com/JohnLato/posix-paths RawFilePath operations: https://github.com/JohnLato/posix-paths/blob/master/src/System/Posix/FilePa… Traversals: https://github.com/JohnLato/posix-paths/blob/master/src/System/Posix/Direct… Benchmarks: https://github.com/JohnLato/posix-paths/blob/master/benchmarks/Bench.hs

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Looking for ICFP roommate
by Conal Elliott 21 Aug '13

21 Aug '13

I'm looking for an ICFP roommate. I plan to attend Sunday through Saturday and stay the nights of Saturday the 21st through Saturday the 28th. I missed the discounted price of $225 (yipes) at the Airport Hilton (sold out). Perhaps someone already has a room reserved with two beds or could switch to one with two beds and would like to reduce their cost by room-sharing for part or all of their stay. If so, please let me know. Thanks, - Conal

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wxHaskell mailinglist
by Nathan Hüsken 20 Aug '13

20 Aug '13

Hey, Anyone knows what the proper channel for reporting bugs and asking questions about wxHaskell is? The github page https://github.com/wxHaskell/wxHaskell/wiki seems to have issues disabled, and when I post to the wxHaskell user mailinglist, it tells me that the list is moderated. But my post did not get accepted for the last 2 days. Regards, Nathan

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Re: [Haskell-cafe] Compiling stringable with GHC 7.0.4
by Ketil Malde 20 Aug '13

20 Aug '13

I took the liberty of implementing this fix and uploading stringable-0.1.1.1 to HackageDB. I tested it on GHC 7.0.4 (you know, shipped with the cutting-edge Fedora distribution one year ago, but ancient and no longer to be bothered with by Haskell standards :-) and on 7.6.2. -k Ketil Malde <ketil(a)malde.org> writes: > Hi, > > ------------------------------------------------------- > I don't think FlexibleInstances works with this GHC, I get: > > % cabal install --prefix=$G stringable > Resolving dependencies... > Configuring stringable-0.1.1... > Building stringable-0.1.1... > Preprocessing library stringable-0.1.1... > [1 of 1] Compiling Data.Stringable ( Data/Stringable.hs, dist/build/Data/Stringable.o ) > > Data/Stringable.hs:54:10: > Illegal instance declaration for `Stringable String' > (All instance types must be of the form (T t1 ... tn) > where T is not a synonym. > Use -XTypeSynonymInstances if you want to disable this.) > In the instance declaration for `Stringable String' > ------------------------------------------------------- > > I changed the first line of Data/Stringable.hs to: > > {-# LANGUAGE FlexibleInstances, TypeSynonymInstances #-} > > and then it compiled. Is there any reason not to retain the TSI pragma? > > -k -- If I haven't seen further, it is by standing in the footprints of giants

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One-element tuple
by AntC 20 Aug '13

20 Aug '13

There's an annoying inconsistency: (CustId 47, CustName "Fred", Gender Male) -- threeple (CustId 47, CustName "Fred) -- twople -- (CustId 47) -- oneple not! () -- nople (That is, it's annoying if you're trying to make typeclass instances for extensible/contractable tuples. Yes, I know I could use HLists.) I'm not happy with either approach I've tried: data Oneple a = Oneple a -- (or newtype) (Oneple $ CustId 47) -- too verbose type Oneple a = [a] [CustId 47] -- at least looks bracket-y What do you do? AntC

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llvm on macos
by Dominic Steinitz 20 Aug '13

20 Aug '13

I am trying to use llvm but am being told I don't have llvm installed. Dominics-MacBook-Pro:Laplace dom$ ghc src-repa/Main.hs -rtsopts -threaded -eventlog -Odph -fllvm -optlo-O3 -fno-liberate-case -isrc-repa [1 of 3] Compiling SolverStencil ( src-repa/SolverStencil.hs, src-repa/SolverStencil.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package pretty-1.1.1.0 ... linking ... done. Loading package array-0.4.0.1 ... linking ... done. Loading package deepseq-1.3.0.1 ... linking ... done. Loading package containers-0.5.0.0 ... linking ... done. Loading package old-locale-1.0.0.5 ... linking ... done. Loading package time-1.4.0.1 ... linking ... done. Loading package random-1.0.1.1 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package QuickCheck-2.5.1.1 ... linking ... done. Loading package bytestring-0.10.0.2 ... linking ... done. Loading package primitive-0.5.0.1 ... linking ... done. Loading package vector-0.10.0.1 ... linking ... done. Loading package repa-3.2.3.1 ... linking ... done. <no location info>: Warning: Couldn't figure out LLVM version! Make sure you have installed LLVM ghc: could not execute: opt The ghc documentation (http://www.haskell.org/ghc/docs/7.6.1/html/users_guide/code-generators.html) says that llvm and clang are installed by default for 10.6 and later. I am on 10.8.3. Indeed Dominics-MacBook-Pro:Laplace dom$ llvm- llvm-cpp-4.2 llvm-g++ llvm-g++-4.2 llvm-gcc llvm-gcc-4.2 And Dominics-MacBook-Pro:Laplace dom$ clang clang clang++ But ghc-info tells me Dominics-MacBook-Pro:Laplace dom$ ghc --info [("Project name","The Glorious Glasgow Haskell Compilation System") ,("GCC extra via C opts"," -fwrapv") ,("C compiler command","/usr/bin/gcc") ,("C compiler flags"," -m64 -fno-stack-protector -m64") ,("ar command","/usr/bin/ar") ,("ar flags","clqs") ,("ar supports at file","@ArSupportsAtFile@") ,("touch command","touch") ,("dllwrap command","/bin/false") ,("windres command","/bin/false") ,("perl command","/usr/bin/perl") ,("target os","OSDarwin") ,("target arch","ArchX86_64") ,("target word size","8") ,("target has GNU nonexec stack","False") ,("target has .ident directive","True") ,("target has subsections via symbols","True") ,("LLVM llc command","llc") ,("LLVM opt command","opt") ,("Project version","7.6.2") ,("Booter version","7.4.2") ,("Stage","2") ,("Build platform","x86_64-apple-darwin") ,("Host platform","x86_64-apple-darwin") ,("Target platform","x86_64-apple-darwin") ,("Have interpreter","YES") ,("Object splitting supported","YES") ,("Have native code generator","YES") ,("Support SMP","YES") ,("Unregisterised","NO") ,("Tables next to code","YES") ,("RTS ways","l debug thr thr_debug thr_l thr_p dyn debug_dyn thr_dyn thr_debug_dyn") ,("Leading underscore","YES") ,("Debug on","False") ,("LibDir","/usr/local/lib/ghc-7.6.2") ,("Global Package DB","/usr/local/lib/ghc-7.6.2/package.conf.d") ,("Gcc Linker flags","[\"-m64\"]") ,("Ld Linker flags","[\"-arch\",\"x86_64\"]") ] But I don't have either llc or opt Dominics-MacBook-Pro:Laplace dom$ llc -bash: llc: command not found Dominics-MacBook-Pro:Laplace dom$ opt -bash: opt: command not found Dominics-MacBook-Pro:Laplace dom$ What is the solution? Thanks, Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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Categories with associated constraints?
by Conal Elliott 19 Aug '13

19 Aug '13

Has anyone given a go at a Category class and friends (including cartesian and closed) with associated constraints (presumably using the ConstraintKinds language extension)? I gave it a try a while back and wasn't able to keep the signatures from getting very complicated. Thanks, -- Conal

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Re: [Haskell-cafe] Errors in non-monadic code
by Donn Cave 19 Aug '13

19 Aug '13

jabolopes(a)google.com, MIME-Version: 1.0 Content-type: text/plain; charset=UTF-8 In-Reply-To: <CAKFCL4VfY-Dz3Xo9ZUZ_SmfRQ2nLGDLbovU%3DSuF1-sSnqVS8Hw(a)mail.gmail.com> References: <CAKFCL4VfY-Dz3Xo9ZUZ_SmfRQ2nLGDLbovU%3DSuF1-sSnqVS8Hw(a)mail.gmail.com> quoth Brandon Allbery, > Even in IO, exceptions should be reserved for truly exceptional conditions > (of the "program cannot safely continue" variety), not merely for error > checking when this can be described as a normal flow of evaluation. > Exceptions are not simply alternative flow of control, even in procedural > languages; they are *disruptions* of flow of control. I think that would be debatable, especially as applied to procedural languages in general. It's very common to use exceptions in routine flow of control in Python programs, if I remember right. Meanwhile, the Haskell library in my opinion somewhat weakens your case by making ordinary conditions into exceptions, for example end-of-file. In the end it's a large grey area. Ideally, what the program has to do, or whether it can even continue at all, is determined by the program using information reported by the function that encounters the error. If there's a good reason why exceptions should be used only when the program won't be able to continue, it must be that the language's exception handling facililty isn't very robust. Donn

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GHC and backwards compatibility
by Ketil Malde 19 Aug '13

19 Aug '13

I recently encountered the following problem: -------------------------------------------------------------------------------- $ cabal install Resolving dependencies... Configuring array-0.4.0.1... Building array-0.4.0.1... Preprocessing library array-0.4.0.1... Data/Array/IArray.hs:1:14: Unsupported extension: Trustworthy cabal: Error: some packages failed to install: array-0.4.0.1 failed during the building phase. The exception was: ExitFailure 1 asmeval-0 depends on array-0.4.0.1 which failed to install. binary-0.7.1.0 depends on array-0.4.0.1 which failed to install. biocore-0.3.1 depends on array-0.4.0.1 which failed to install. biofasta-0.0.3 depends on array-0.4.0.1 which failed to install. biopsl-0.4 depends on array-0.4.0.1 which failed to install. biosff-0.3.3 depends on array-0.4.0.1 which failed to install. bytestring-0.10.2.0 depends on array-0.4.0.1 which failed to install. containers-0.5.2.1 depends on array-0.4.0.1 which failed to install. deepseq-1.3.0.1 depends on array-0.4.0.1 which failed to install. hashable-1.2.0.10 depends on array-0.4.0.1 which failed to install. stringable-0.1.1 depends on array-0.4.0.1 which failed to install. system-filepath-0.4.7 depends on array-0.4.0.1 which failed to install. text-0.11.3.1 depends on array-0.4.0.1 which failed to install. unordered-containers-0.2.3.1 depends on array-0.4.0.1 which failed to install. -------------------------------------------------------------------------------- The installed GHC is 7.0.4, and yes, that's many major versions ago, but then again, it's only two years old, and from what I understand, it is shipped by some conservative Linux distributions. The problems here are that: a) the installation tries to install array, but current array requires the "Trustworthy" extension, which appeared in 7.2.1. Ideally, packages should try to be backwards compatible, e.g. by using conditional sections. b) the output isn't very helpful in tracking down the cause of this problem, it claims that all these packages depend on array-0.4.0.1, which is a lie. Somewhere, somehow, somethings depends on this (or at least a newer version), but I have no clue how to figure out which, except examining each of these packages and their dependencies manually. It is also possible that array shouldn't be upgraded like this, but then that needs to be made clear to cabal somehow, so that I don't spend ages trying to. Are there any solutions to this? Advice on how to proceed? -k -- If I haven't seen further, it is by standing in the footprints of giants

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