January 2015 - Haskell-Cafe

Typed TH
by Christopher Done 15 Feb '15

15 Feb '15

http://lpaste.net/116791 If someone feels like spending time exploring this and putting it in a library I will be interested in trying it. I saw some old work to patch GHC to do this including typed quotation of expressions, which doesn't seem to have arrived. Relatedly I made a trivial Lisp with untyped and typed quotation https://gist.github.com/chrisdone/516489f4f27846712225 It doesn't seem to be a much-explored area in the Lisp world, Haskell is treading new waters in some ways.

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Domain specific error messages
by Sean Seefried 06 Feb '15

06 Feb '15

If the list doesn't mind I'm reposting my reply to Alberto G. Corona in under the thread "Monads: external questions" as a new message since the topic has changed enough. ------------- Hi Alberto, I've been interested in domain specific error messages for years and I agree with you that it is one of the major things holding back the utility of DSLs to novice programmers. This is a shame since one of the touted benefits of DSLs is that they *can* be used by novices with a minimum of training, which is simply not true in the presence of error messages that require detailed knowledge of Haskell to understand. I'd caution against saying that there is a lack of interest in that ticket you linked to. It's still a research level problem despite the fact that some great work has been done on it already. Incidentally, the author of "Scripting the Type Inference Process" went on to do an entire PhD on the topic entitled "Top Quality Type Error Messages"[2]. I recently wrote him an email and he told me that the constraint-based type inference framework that he used in the thesis, TOP, is available on Hackage [3]. Recently I noticed that this problem is already being worked on in Idris. See "Reflect on your Mistakes!" [4] and some code on GitHub [5]. Perhaps we can get people interested in this feature again? Cheers, Sean [1] http://www.open.ou.nl/bhr/heeren-scripting.pdf [2] http://www.open.ou.nl/bhr/TopQuality.pdf [3] https://hackage.haskell.org/package/Top [4] http://www.itu.dk/people/drc/drafts/error-reflection-submission.pdf [5] https://gist.github.com/david-christiansen/8349698 On Sun Nov 23 2014 at 3:57:10 AM Alberto G. Corona <agocorona(a)gmail.com> wrote: > Michael: > > You are right, but these are minor problems I think, compared with the > huge potential advantages. > > I can not believe it when a slow immature language like Ruby could take > over web development just for one library, Rails and some buzzwords, when a > faster, safer language can do it millions of times better. Haskell can > revolutionize all the industry simply selling it not as one more language, > but as THE meta-language for building EDSLs for each domain problem. some > EDSLs so close to the domain problem that can be used by non-programmers. > > That lack of vision and effort in the side of the haskell community hurts > me. And the lack of interest in this ticket > > https://ghc.haskell.org/trac/ghc/ticket/7870 > > Is a clear display of this lack of interest. it is like the Aristocracy > of the Haskell Wondwerland fears to be hijacked by hordes of mediocre DSL > villains from the industry, so it is necessary to keep the walls high > > Haskell is a language dominated by academics that has no interest in the > success of Haskell. On the contrary. > > 2014-10-29 15:13 GMT+01:00 Michael Jones <mike(a)proclivis.com>: > >> When I took a Lambda Calculus class years ago in Silicon Valley, 90% of >> the students groaned and complained. They just wanted to learn Java and >> make money. Having a background in OO design and experience with Eiffel, I >> was intrigued and stuck with it, building some tools with ML, and later >> Haskell. >> >> In the workplace it was near impossible to avoid the .Net culture, and >> most of my code has been C#. But the factors that mattered were: >> >> - Continuity with past languages and tools >> - Availability of programmers >> - Third party libraries >> - Inter langage operability >> - Reuse of legacy code >> >> etc >> >> Best I can tell, there is no way to avoid the business context. I suggest >> that if you have freedom, you need to be multilingual. Many systems could >> benefit from applying the proper tool to the corresponding problem. >> >> But I will say this, becoming proficient at Haskell really improved my >> designs by providing an alternative conceptual framework. But, it had a >> very substantial learning curve. All I can say is trust that even if your >> core language is procedural, you will be better at that for learning a >> functional language. >> >> To make Haskell a first class citizen in the IT shops, I think focus >> would have to shift more to the business context and needs. And certainly >> more focus in the universities that are still dominated by procedural >> languages. Once that is drilled into ones head, it affects the way one >> thinks. >> >> To give an example, I have these problems: >> >> - Update to GHC 7.8.3 from 7.6 caused run time behavior changes breaking >> USB application >> - Sandboxes are not completely isolated from the core library and often >> builds break >> - Most new grads don’t even know what a functional language is >> - Documentation gets out of sync with releases (where documentation means >> Wiki and web) >> - FFI is difficult to use and debug >> - Lack of books, user groups, etc >> >> Mike >> >> On Oct 29, 2014, at 3:48 AM, Alberto G. Corona <agocorona(a)gmail.com> >> wrote: >> >> I know that I'm using a different language when talking about monads. The >> language of the IT industry. >> >> Many haskellers use the language for toy programming. Others are >> professional academics. The few that use the language for commercial >> purposes are too busy developing practical applications rather than >> thinking deep about how to apply the haskell concepts to their problems. >> As a result many of such problems remains essentially unsolved. These busy >> developers try to transcode solutions from other languages that lack the >> deep and expressiveness of Haskell. >> >> This lack of interest in one side and the lack of time in the other is >> disappointing. The symptoms are everywhere. Particularly, I find it in the >> lack of support and interests for this ticket: >> >> https://ghc.haskell.org/trac/ghc/ticket/7870 >> >> I though that there was definitively a shift from "avoid success at all >> costs" a few years ago, for a commitment for the success, but still there >> are many minds to change, especially the brilliant ones. >> >> 2014-10-26 2:02 GMT+01:00 Alberto G. Corona <agocorona(a)gmail.com>: >> >>> >>> >>> 2014-10-26 1:23 GMT+02:00 Jeffrey Brown <jeffbrown.the(a)gmail.com>: >>> >>>> As opposed to the internal logic of monads, how they work, I hope to >>>> start a discussion about their external logic: how and why to use monads. >>>> >>>> design >>>> ------ >>>> How do monads change the way one >>>> * thinks about a problem? >>>> * structures data? >>>> * refactors? >>>> * tests? >>>> Should I always be giving the monads a lot of cognitive bandwidth, >>>> because they reorder the way everything should be, or is it an investment >>>> with a high initial cognitive cost but requiring little maintenance >>>> thereafter? >>>> >>>> what is their common framework? >>>> ------------------------------- >>>> Monads let data reach farther than it otherwise would. Subjectively, >>>> they feel like a controlled way of violating encapsulation. >>>> >>>> Are there other, deeper or more specific, commonalities that explain >>>> why monads are a good way to implement exceptions, output, state, and >>>> perhaps other services? >>>> >>> >>> I made monads for execution state recovery, web navigation.. workflows, >>> long running transactions, backtracking, traceback and event chaining in >>> web browser applications. >>> >>> I´m confident that the perspectives for monads to solve real IT problems >>> are very promising. And when I mean monad I mean all the associated stuff : >>> applicative, alternative etc. >>> >>> I´m confident that there will be a cloud monad (for chaining jobs and >>> work distribution) an orchestration monad for orchestration of web services >>> etc. >>> >>> There are problems that are intrinsically procedural among them, almost >>> all problems in IT. instead of using ad-hoc data/control structures like >>> events, handlers, configurations, routes, exceptions, logs, transaction >>> compensations, promises ....the list goes on and on , the monad is the >>> common control structure that can subsume all of them inside his >>> programmable semicolon >>> >>> So, once the monad is set up, the user of the monad code the solution >>> for the domain problem in a clean EDSL with absolutely no plumbing, at the >>> level of the problem. so anyone that know the problem can understand the >>> code. >>> >>> Is the monad instance, and the applicative etc the ones that subsume >>> under the hood the special data/control structure necessary for the domain >>> problem. >>> >>> >>> Often if your code is general enough, it can be used in any monad. So >>> you benefit from this. I think that in th future there will be a lot of >>> surprises about the shareability of code between monads when the IT >>> industry start to use them seriously. I think that we are just at the >>> beginning. >>> >>> I hope that some others of your questions are also answered here >>> >> >> >> >> -- >> Alberto. >> >>

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Cabal config file - default install flags?
by Lucas Paul 02 Feb '15

02 Feb '15

I'd like to have cabal automatically use -j8 when I cabal install something. Is there something I can put into the .cabal/config file that will accomplish this? More generally, where can I find documentation on that config file? - Lucas Paul

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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 30 Jan '15

30 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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