November 2015 - Haskell-Cafe

Running GHC LLVM output through LLVM bitcode linker first
by Clinton Mead 23 Nov '15

23 Nov '15

Is there a way to run the LLVM code (both generated by Haskell and provided by the user) though the LLVM bitcode linker to perform intermodule optimizations (like inlining) http://llvm.org/docs/CommandGuide/llvm-link.html Here's some example code: -- Main.hs -- {-# LANGUAGE MagicHash #-} {-# LANGUAGE UnboxedTuples #-} {-# LANGUAGE GHCForeignImportPrim #-} {-# LANGUAGE ForeignFunctionInterface #-} {-# LANGUAGE UnliftedFFITypes #-} {-# LANGUAGE BangPatterns #-} import GHC.Exts(Word(W#)) import GHC.Prim(Word#) foreign import ccall llvmid :: Word# -> Word# main = do line1 <- getLine let !(W# x1) = read line1 let !r1 = llvminc x1 print (W# r1) -- funcs.ll -- define fastcc i64 @llvminc(i64 inreg %x) { %r = add i64 %x, 1 ret i64 %r } When I compile like the following: ghc -O2 -fllvm -keep-s-files Main.hs funcs.ll I get an executable that performs correctly, but when I look at the assembly output in Main.s I get the following: callq suspendThread movq %rax, %rbp movq %rbx, %rdi callq llvminc movq %rax, %rbx movq %rbp, %rdi callq resumeThread This leads me to believe that this is being done like a c call through registers, but not inlined, though I'm not sure about this. I also suspect sending the "Main.ll" and "funcs.ll" files through the LLVM bitcode linker and then sending the resulting one bitcode to the LLVM compiler would perform these intramodule optimisations. Is there anyway to get GHC to use the LLVM bitcode linker to link all the LLVM files (both user provided and resulting from GHC compilation) though the LLVM bitcode linker first before the system linker?

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[NL-FP 2016] 2nd CFP: Dutch Functional Programming Day 2016
by Atze Dijkstra 23 Nov '15

23 Nov '15

[My apologies for multiple received copies of the same message] 2nd Call for Participation: Dear all, The next Dutch Functional Programming day (NL-FP 2016) will be held on Friday, January 8, 2016 at the Utrecht University, The Netherlands. You are invited to participate and to give a presentation. At the end of the day we will have a joint dinner. On the web page http://foswiki.cs.uu.nl/foswiki/NlFpDay2016/WebHome <http://foswiki.cs.uu.nl/foswiki/NlFpDay2016/WebHome> for the day you’ll find preliminary information which will be further filled in due time. Registration is by letting me know via email (with a subject header that begins with [NL-FP 2016]) whether you want to (1) participate, (2) join dinner, (3) give a presentation (please include title + abstract), also see the webpage for additional details. If you intend to participate, please let me know as soon as possible because we like to know how many people we can expect. Hope to meet you all in Utrecht at the next FP Day! Best regards, - Atze - Atze Dijkstra, Department of Information and Computing Sciences. /|\ Utrecht University, PO Box 80089, 3508 TB Utrecht, Netherlands. / | \ Tel.: +31-30-2534118/1454 | WWW : http://www.cs.uu.nl/~atze <http://www.cs.uu.nl/~atze> . /--| \ Fax : +31-30-2513971 .... | Email: atze(a)uu.nl <mailto:atze@uu.nl> ............... / |___\

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Is there an overview of backend technologies for Haskell?
by Joachim Durchholz 23 Nov '15

23 Nov '15

Hi to all, I'm wondering how the various backend technologies are regarded. What trade-offs are involved (e.g. spineless-tagless vs. generating machine code, seems to be very, very different), what options there might be, what the choice would be if a compiler were to be written from scratch, that kind of stuff. The first two pages of a web search for "Haskell backends" returned only references to GHC's LLVM backend. Which was interesting but not an overview :-) URLs welcome. Regards, Jo

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type operators and colon in GHC
by John Leo 22 Nov '15

22 Nov '15

According to sections 7.4.3 and 7.4.4 of the latest Haskell documentation https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/data-type-e… you can define (7.4.3) an infix type constructor as long as it begins with a colon, for example data a :*: b = Foo a b and furthermore (7.4.4) you can define an infix operator without having to use a colon if you enable the TypeOperators extension: data a * b = Foo a b However if I try the former without using TypeOperators I get this compiler error in 7.10.2: Illegal declaration of a type or class operator ‘:*:’ Use TypeOperators to declare operators in type and declarations Using TypeOperators fixes this, but then * without colon also works so I don't see the point of using colon anymore. My guess is this was some some kind of historical distinction which is no longer valid and the documentation needs to be updated. Is this true, or am I missing something? John

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ANN: prefix-units 0.2.0
by Iustin Pop 22 Nov '15

22 Nov '15

Hi all, New version of my small library prefix-units (for parsing and formatting things like "10K"). Changes: * Incompatible API change to cleanup some initial design decisions: the two level `FormatOption`/`FormatMode` model is removed, the fixed unit of `FormatOption` is moved to a new constructor `FormatMode`, and `FormatOption` is removed entirely. This should be a simpler API, at the cost of breaking compatibility. * Fixed issue #3 (No support for negative numbers). * Worked around issue #1 (Add 'base' unit) by adding a mode that disables scaling; it should have the same effect without introducing an artificial unit. Feedback welcome, either via email or at https://github.com/iustin/prefix-units. happy hacking, iustin

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Warning: Tab Character
by Jeon-Young Kang 21 Nov '15

21 Nov '15

Hello everyone. I am a newbie of Haskell, using Textmate on mac. I got the following warning. How can I fix it? Warning: Tab character Ok, modules loaded: Main. Sincerely, Young

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NNOUNCE: Haskell Communities and Activities Report (29th ed., November 2015)
by Mihai Maruseac 21 Nov '15

21 Nov '15

On behalf of all the contributors, we are pleased to announce that the Haskell Communities and Activities Report (29th edition, November 2015) is now available, in PDF and HTML formats: http://haskell.org/communities/11-2015/report.pdf http://haskell.org/communities/11-2015/html/report.html Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. We hope you will find it as interesting a read as we did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline) to the call. The editors collect all the contributions into a single report and feed that back to the community. When we try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ======================================== End of March 2015: target deadline for contributions to the May 2015 edition of the HCAR Report ======================================== Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editors for a simple e-mail reminder in March (you could point us to them as well, and we can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Mihai Maruseac <hcar at haskell.org> -- Mihai Maruseac (MM) "If you can't solve a problem, then there's an easier problem you can solve: find it." -- George Polya

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RDF with Haskell
by Jeon-Young Kang 21 Nov '15

21 Nov '15

I am a newbie learning Haskell. I'd like to import RDF in Haskell as well as to do SPARQL. I went through RDF4H, Swish, and so on. But it is still difficult to understand them for me. Anyone can suggest me to learn that? or recommend any kinds of books or tutorials? Sincerely, Jeon-Young -- Department of Geography State University of New York at Buffalo jykang22(a)gmail.com Jeon-Young Kang

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Re: [Haskell-cafe] AMP - how do you motivate this in teaching?
by Olaf Klinke 21 Nov '15

21 Nov '15

Albert's explanation is the best so far, IMHO. liftA2 is by far the most useful and reasonable function in Control.Applicative. Realizing that it can be made the definition of Applicative is what made me friends with that typeclass. As an algebraicist, to me Control.Monad.join is what distinguishes Monad from Applicative, although Albert's explanation is more accessible new programmers. I tend to explain monads by example of container monads mimicking powerset features, and join has a natural interpretation there. -- Olaf

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ANN: cacophony 0.4.0, pipes-cacophony 0.1.2
by John Galt 20 Nov '15

20 Nov '15

cacophony[1] is a library which implements the Noise[2] protocol. Noise is a framework for cryptographic protocols based on ECDH key agreement authored by Trevor Perrin. pipes-cacophony[3] builds on cacophony to provide pipes that facilitate key agreement and secure messaging (in conjunction with, for example, pipes-network). -- John [1] http://hackage.haskell.org/package/cacophony [2] https://github.com/trevp/noise/blob/master/noise.md [3] http://hackage.haskell.org/package/pipes-cacophony

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