June 2015 - Haskell-Cafe

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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ANN: stack-0.1.1.0
by Emanuel Borsboom 26 Jun '15

26 Jun '15

New release of stack, a build tool. Changes: https://github.com/commercialhaskell/stack/releases/tag/v0.1.1.0 General information and download links: https://github.com/commercialhaskell/stack#readme This version includes a 'stack upgrade' command, which will make to much easier to upgrade to the NEXT version (but unfortunately you'll have to get this version the old way).

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Fwd: taking over urlencoded
by Francesco Gazzetta 25 Jun '15

25 Jun '15

The package urlencoded <https://hackage.haskell.org/package/urlencoded> wasn't updated since 2012 and needs a minor modification in the .cabal file. The author was contacted half an year ago, but he didn't respond, so -according to the instructions <https://wiki.haskell.org/Taking_over_a_package> on hackage- I state my intention to take over. Or, more simply, can an hackage admin just edit the cabal file?

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Re: [Haskell-cafe] Haskell users on Chile
by Ruben Astudillo 25 Jun '15

25 Jun '15

On 24/06/15 16:18, Anupam Jain wrote: > Sure I can do that. It would help if the group was already created though. > Do you want any help setting up a mailing list or something? I set-up a mailing list on google groups here: https://groups.google.com/forum/#!forum/haskellchile If you got problems or want to also be a maintainer send me a mail. Also I should set up a channel on freenode, but that one ought to be easy. #haskell-chile should do. For the time being we should reefer to people interested to the mailing list. -- Ruben Astudillo. pgp: 0x3C332311 , usala en lo posible :-) Crear un haiku, en diecisiete silabas, es complica...

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