- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] haskell-src-exts maintenance
by Roman Cheplyaka 01 Jul '15

01 Jul '15

Thanks for the update, Peter. Forwarding it to cafe. On 01/07/15 10:36, Peter A Jonsson wrote: > Hi Roman, > > I’ve inserted what I replied to Matthew a couple of days ago below. > Unfortunately my reply bounced from both libraries and haskell-cafe > since I’m not a subscriber. Matthew should have gotten the reply > though. > > Kind Regards, > > Peter > > > Dear Matthew, > >> I think it is important to get this work merged and update the >> parser to support modern language features introduced in GHC 7.8 >> and 7.10. > > We all agree about the importance of HSE supporting modern language > features that people actually use. The simple reason for my > inactivity lately is that I’ve been swamped at work so HSE has been > on the backburner. I just started my vacation though so I’m slowly > working through my backlog of things that I haven’t had time to do > previously. Without having looked at any patches in the bug tracker I > can say that the current state of HSE is stable so we should be able > to merge the simple things quickly and the more involved things > should be doable. Once that is done it’s probably time to make a new > yearly major release.

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Advice gfx library
by Nicholls, Mark 30 Jun '15

30 Jun '15

I am interested in writing some real code now! What i could do with is a gfx library that Can render mpeg/mov files Scale Transform etc Is simple! Runs on windows in some form Ive got hudaks book about multimedia, and understand the general reactive idea behind it....i want to build on top of that Ive nosed around gloss and grapefruit, but the mpeg piece seems missing from these Any ideas? Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage. CONFIDENTIALITY NOTICE This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited. While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data. Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us. MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

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How to Hijack stdin,err,out, thread safely?
by Hiromi ISHII 30 Jun '15

30 Jun '15

Hi, I'm currently writing a web app to check the spec of input code usging QuickCheck. quickCheck* functions writes results to stderr & stdout, but I don't want them written to the app's original stdout/err. (I'm using SafeHaskell features to avoid malicious code executed, so don't worry about that :-)) So I want to execute I/O action hijacking stdout/err in a thread-safe manner. For example, I need function like below: censorHandles :: IO a -> IO (a, String, String) censorHandles = ... or withStd :: Handle -> Handle -> Handle -> IO a -> IO a withStd = ... -- Hiromi ISHII konn.jinro(a)gmail.com

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Munich Haskell Meeting, 2015-06-30 @ 19:30
by Christian Neukirchen 29 Jun '15

29 Jun '15

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Monday, June 30 at Cafe Puck at 19h30. For details see here: http://www.haskell-munich.de/dates If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-jun-2015/ **Please note that I cannot make it tomorrow, but I'll reserve the table for you.** Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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Dealing with invertible functions
by Clinton Mead 29 Jun '15

29 Jun '15

I was trying to think of a way to deal with invertible functions, say if I want to set up a one-to-one mapping from A<->B without having to maintain two sets of functions (and worry about them getting out of sync). So I thought about making an "invertible" function. This is a function that knows it's own inverse, and you can compose them and get the inverses for free. Of course you need to set up the base functions manually, but then after that the composed functions don't have to be maintained separately both ways. Below I'm going to include some code, and I have a few questions: 1) Am I (badly) reinventing the wheel. 2) Is there otherwise something terrible with this approach. 3) I ended up wanting a function with signature "f a b -> a -> b". This feels strangly like applicative but not exactly. Am I reinventing the wheel here also or should I be doing this differently? Any advise appreciated, the ideone link is here: https://ideone.com/HlUHUd But I've also copied the code below: --- import Prelude hiding ((.)) import Control.Category ((.), (<<<), (>>>), Category) data InvertibleFunction a b = InvertibleFunction (a -> b) (b -> a) instance Category InvertibleFunction where (InvertibleFunction b_c c_b) . (InvertibleFunction a_b b_a) = InvertibleFunction (b_c . a_b) (b_a . c_b) inv (InvertibleFunction x y) = InvertibleFunction y x add :: (Num n) => n -> InvertibleFunction n n add x = InvertibleFunction (+x) (\y -> y - x) class KindaApplicative f where (<$>) :: f a b -> a -> b instance KindaApplicative InvertibleFunction where (InvertibleFunction f _) <$> x = f x main = print $ ((inv (add 2)) <$> 5)

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Promoting associated data types
by Kosyrev Serge 29 Jun '15

29 Jun '15

Good day! DataKinds doesn't allow promotion of type/data families. However, in the specific case of associated data families -- aren't they constrained more, and sufficiently so that the following, for example, could be made to work without stepping into dangerous territories: -- {-# LANGUAGE DataKinds #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UnicodeSyntax #-} module M where class C a where data D a ∷ * data I instance C I where data D I class C1 a (b ∷ D I) where -- ..or, maybe, perhaps even the following: class C1 a (b ∷ D) where -- respectfully, Косырев Серёга

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Re: [Haskell-cafe] Tokenizing Haskell for future A.I.
by Stefan Reich 27 Jun '15

27 Jun '15

Oops. Subject should have read "Tokenizing" of course. :-) On 6/27/15, Stefan Reich <stefan.reich.maker.of.eye(a)googlemail.com> wrote: > Hi folks! > > I've been an avid Haskell user for a couple years. > > I am now making an A.I. system that will help programming in general. > It's based on a Java variation called JavaX (javax.tinybrain.de). > > However, any language can be processed. The most important step is > tokenization which is actually the bulk effort of the parsing process. > > Thus. Anyone in the mood for contributing a Haskell tokenizer? > > Instructions here: > http://tinybrain.blog.de/2015/06/27/a-standard-system-for-tokenization-2060… > > The benefit? One day, your Haskell coding (/refactoring) can be done > by A.I. (Or a part of it...) > > Cheers, > Stefan >

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Tokeninng Haskell for future A.I.
by Stefan Reich 27 Jun '15

27 Jun '15

Hi folks! I've been an avid Haskell user for a couple years. I am now making an A.I. system that will help programming in general. It's based on a Java variation called JavaX (javax.tinybrain.de). However, any language can be processed. The most important step is tokenization which is actually the bulk effort of the parsing process. Thus. Anyone in the mood for contributing a Haskell tokenizer? Instructions here: http://tinybrain.blog.de/2015/06/27/a-standard-system-for-tokenization-2060… The benefit? One day, your Haskell coding (/refactoring) can be done by A.I. (Or a part of it...) Cheers, Stefan

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Higher Kinded Void
by Anupam Jain 27 Jun '15

27 Jun '15

Hi all, I currently have some code for which I require a uninhabitable Functor. I currently just use - data VoidF a instance Functor VoidF where fmap = undefined Is there a reason something like this is not in the package void? Perhaps we could even have Void1 with kind * -> *, Void2 with kind * -> * -> * etc. I opened a github issue a few days ago but haven't received a response from ekmett yet - https://github.com/ekmett/void/issues/9 -- Anupam

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Generalizing a library
by Geraldus 26 Jun '15

26 Jun '15

Hi Cafe! I've written very first version of GHCJS port <https://github.com/geraldus/ghcjs-perch> of Perch <https://github.com/agocorona/haste-perch> library originally designed to work with Haste compiler. Most of work is already done, though some polishing is needed. In essence Haste and GHCJS versions are very similar, the major difference is how foreign functions are defined, and in fact Perch is built using just a few low-level primitives <https://github.com/geraldus/ghcjs-perch/blob/master/src/Internal/FFI.hs>. So, as these libraries are very similar I want to generalize Perch to make it independent of compiler somehow. My initial idea was to have a Perch library and several compiler specific back-ends which user should select depending on his toolchain, but my Haskell skills are still very poor to find a proper way to do this. Can someone point me in right direction or at least give some advices? Very appreciate any help!

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