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ANNOUNCE: monad-levels
by Ivan Lazar Miljenovic 02 Feb '15

02 Feb '15

I'm pleased to announce the first release of my new monad-levels library (aka Yet Another Monad Transformer Library ;-) http://hackage.haskell.org/package/monad-levels I've written more about the motivations of the library here: https://ivanmiljenovic.wordpress.com/2015/02/02/monadic-yak-shaving/ -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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parallelism and purity
by Kazu Yamamoto 02 Feb '15

02 Feb '15

Hi cafe, I received questions about parallelism in Haskell. I'm familiar with concurrency but not with parallelism. So, let me ask: Q1) Are there any *applications* using Haskell parallelism? Q2) What kind of parallelism is used in the application? - Task parallel - Data parallel - Data-flow paralle? - etc Q3) Does Haskell purity contribute for the application in the parallelism point of view? I'm one of the translators of "Parallel and Concurrent Programming in Haskell" into Japanese. So, please don't say read the book. :-) --Kazu

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cpp question
by S. Doaitse Swierstra 01 Feb '15

01 Feb '15

With the new version of GHC (7.8.3) I am running into problems with cpp. The header of one of the files of my uu-parsinglib library reads as follows: {-# LANGUAGE NoMonomorphismRestriction, RankNTypes, FlexibleContexts, CPP #-} #define DEMO(p,i) demo "p" i p #define DEMOG(p,i) demo "p" i (mkP (p)) module Text.ParserCombinators.UU.Demo.MergeAndPermute where ... However when I try to compile this file I get error messages like: Text/ParserCombinators/UU/Demo/Demo.hs:88:17: Not in scope: data constructor ‘DEMOG’ So it seems that the cpp is no longer called at all. Any hints? I am running: MacBook-Doaitse:src doaitse$ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.8.3 MacBook-Doaitse:src doaitse$ gcc --version Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1 Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn) Target: x86_64-apple-darwin14.1.0 Thread model: posix MacBook-Doaitse:src doaitse$ Any help is appreciated, Doaitse Swierstra

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Side conditions on Data.Profunctor.Choice?
by David Turner 31 Jan '15

31 Jan '15

Hi, I was expecting to see coherence conditions for instances of Data.Profunctor.Choice along the lines of: dimap (either (Left . f) Right) id . right' === dimap id (either (Left . f) Right) . right' and similarly for left', but there's nothing like that in the docs. Does anyone know whether (a) those conditions aren't true in general, or (b) they are true but provable from other theorems so not worth mentioning? Many thanks, David

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ANN: processor-creative-kit
by Takenobu Tani 31 Jan '15

31 Jan '15

Dear Haskellers, I am pleased to announce the first release of processor-creative-kit package for playing processors. You can create your processors with your own instruction set. It simulates a simple microprocessor(cpu) with some development tools. https://hackage.haskell.org/package/processor-creative-kit https://github.com/takenobu-hs/processor-creative-kit feature: * easy try, easy modify * a purely functional CPU core (without IO) * including a very simple prototype assembler * including a very simple prototype profiler * including a very simple prototype debugger Thank you, Takenobu

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Using m4 as a preprocessor
by Francesco Ariis 30 Jan '15

30 Jan '15

Hello, today I tried to compile a Haskell program using m4 as preprocessor, with the {-# OPTIONS_GHC -F -pgmF m4 #-} pragma on top of a .hs file. I didn't add anything else, there are no ''' or '`' in the source. Upon compiling, ghc (7.8.3) complains: m4: cannot open `/tmp/ghc10655_0/ghc10655_1.hspp': No such file or directory I searched the net for a solution, but no dice (apparently there are no Haskell programs using -F -pgmF m4?), so I am writing here. Any ideas on what is wrong?

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Creating a list with do notation
by Cody Goodman 30 Jan '15

30 Jan '15

List is a monad, does that mean i can create a list with do notation? My intuition led me to believe this would work: main = do x <- return $ do 1 2 3 print (x :: [Int]) However it didn't. Is this possible?

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Compiling Setup.hs with -threaded
by Michael Orlitzky 29 Jan '15

29 Jan '15

I found a weird bug at, https://bugs.gentoo.org/show_bug.cgi?id=537500 There is an awesome tool called shellcheck: git clone https://github.com/koalaman/shellcheck.git and we want to run its test suite. Basically: * If you run the test suite using runghc, then it works fine. * If you compile Setup.hs to setup, then the test suite hangs. * But if you compile Setup.hs to setup using -threaded, it works? Normally I would blabber on about what I think the problem could be, but the WTF factor here is just too high. Should we (always?) be compiling Setup.hs with -threaded? Or is this a bug in the runtime or a library or REALITY ITSELF?

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Pure functional and pure logical language at the same time
by Timotej Tomandl 29 Jan '15

29 Jan '15

This question was bugging me for quite a long time. Can we have a language which uses the functional logic while being both pure functional and pure logical? Do we get any advantages from maintaining both both of this purities at the same time? P.S.: I have feeling the answer is no, but I am not sure.

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Fwd: Announcing a solution to the records problem
by Christopher Done 29 Jan '15

29 Jan '15

Forwarding to Haskell-cafe because not as many people read libraries@. ---------- Forwarded message ---------- From: Nikita Volkov <nikita.y.volkov(a)gmail.com> Date: 19 January 2015 at 05:54 Subject: Announcing a solution to the records problem To: Haskell Libraries <libraries(a)haskell.org> This thing seems to be going viral on social networks already, nonetheless here's a link for those of you, who aren't yet informed: http://nikita-volkov.github.io/record/ _______________________________________________ Libraries mailing list Libraries(a)haskell.org http://www.haskell.org/mailman/listinfo/libraries

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