July 2014 - Haskell-Cafe

Retrieving information about type families
by Alejandro Serrano Mena 27 Jul '14

27 Jul '14

Dear Café, My quest for obtaining information about type families continues. Now I have a simple question: how should I access the information about "type instance"s via the GHC API? My aim is to do so after type checking, that is, to get that information from a TypecheckedModule. However, I haven't yet been able to touch the right buttons to make it work ;( Thanks in advance, Alejandro

3 6

HTTP/2 implementation?
by Ben Bangert 26 Jul '14

26 Jul '14

Has anyone started a HTTP/2 implementation in Haskell? I see there's a HPACK-08 Haskell implementation, but I haven't seen an actual HTTP/2 impl. I've been looking at starting some work on this and didn't want to replicate effort elsewhere that I may have missed. Cheers, Ben

3 5

ANNOUNCE: hplayground: haskell client-side web framework
by Alberto G. Corona 26 Jul '14

26 Jul '14

hplayground [1] is a haskell framework that compiles to JavaScript with the haste [5] compiler. It handles reactive effects under a applicative-monad that controls the modifications of the user interface. It is quite easy to create dynamic, composable applications using ordinary, beatiful, idiomatic haskell without special constructions. Rather than a framework, it is an EDSL. Full reinversion of control avoid spagetty event handlers and the monad confines the events and their effects to the subtree where they appear avoiding the problems of declarative reactive frameworks. There are examples running[4] the source code is in [1] And there is a todo reference application [3] running [2] too. There is also a blog post about that[7] Additionally, the syntax is almost identical to the formlet widgets in MFlow[6]. So most of the hplaygroud code could run also in a server if javascript is disabled. But MFlow and hplayground are completely independent projects. I hope that you enjoy it as much as I enjoyed the development of it. A big thanks to Anton Ekblad for his wonderful Haste compiler. [1] https://github.com/agocorona/hplayground [2] http://mflowdemo.herokuapp.com/todo.html [3] https://github.com/agocorona/hplay-todo [4] http://mflowdemo.herokuapp.com/noscript/wiki/browserwidgets [5] http://http://haste-lang.org/ [6] http://hackage.haskell.org/package/MFlow [7] http://haskell-web.blogspot.com.es/2014/07/hplayground-translate-your-conso… -- Alberto.

1 0

support request
by Закиров Марат 25 Jul '14

25 Jul '14

Hi All! I need to convince group of managers that Haskell is cool. Could you please share some links, presentations, data and maybe experience? Thanks in advance... -- Regards, Marat. С уважением Марат.

7 7

callCC inside expression
by martin 25 Jul '14

25 Jul '14

Hello all I recently saw a video on call/cc in Scheme, where call/cc was used inside an expression and call/cc faithfully figured out the rest of the computation. I tried the same in haskell, but was bitten badly. Then I looked at the type signature and learned that call/cc only works inside a continuation monad (if I am not mistaken). Is this correct and why is that so? Are scheme's call/cc and haskell's callCC semantically different?

3 2

what is basic Haskell?
by Johan Larson 25 Jul '14

25 Jul '14

What does a programmer need to know to be proficient in "basic Haskell"? For my money, basic programming skills are those that are required to write programs for simple tasks in the common idioms of the language. This means the practitioner should be able to read input from the terminal or files, select/combine/reformat data, and output a result. At this point, efficiency isn't really the point; only getting to a correct answer without writing anything really weird matters. In LYAH, I'd put the boundary at the end of chapter 9, which covers the IO monad. At that point the reader has studied functions, lists, tuples, types, recursion, higher order functions, four major modules, and algebraic data types. Actually, some of the later topics in chapter 8 (functors, kinds, recursive data structures) seem more like intermediate material. Thoughts? -- Johan Larson -- Toronto, Canada

6 8

Markov Text Generator & Randomness
by Charles-Pierre Astolfi 24 Jul '14

24 Jul '14

Hi -cafe, I'm coding a Markov Text Generator (of order 1). Basically, you have a source text, and knowing the frequencies of pairs of consecutive words, you generate a somewhat syntactically correct text from this. Here's the link to my code and to a source text you can use as example. test.txt http://lpaste.net/raw/4004174907431714816 code http://lpaste.net/4147715261379641344 The kickers is that this code generates sentences with consecutive words that never appears next to each other in the source text. For example, the code generated "They sat over at because old those the lighted.", but "over at" never occurs in the source text, so it shouldn't occur in a generated sentence. The makeDb function gives is correct, so my problem actually lies in generate and/or in draw. I think there's something about RVar that I messed up, but I don't see the problem. Any ideas? Cheers, -- Charles-Pierre

3 5

Haskell on JVM (using LLVM backend)
by Wojciech Danilo 24 Jul '14

24 Jul '14

Hello! I was recently discussing with some frients possibilities of running Haskell programs on JVM. I belive such possibility could be a breakdown for the popularity of Haskell and could be very interesting for new people and new usage-scenarios. I have seen some topics, like these: http://stackoverflow.com/questions/7261039/haskell-on-jvm http://www.haskell.org/haskellwiki/GHC/FAQ#Why_isn.27t_GHC_available_for_.N… http://www.haskell.org/pipermail/haskell-cafe/2009-June/063454.html but are a little old and do NOT mention the LLVM backend. If we've got the LLVM backend in GHC right now, why cannot we just use something like LLJVM to convert the LLVMIR into JVM bytecode? I understand that the LLVM bytecode (optained from GHC) has all the optimizations applied (including tail recursion expansion) so it **could** be possible to just run it on JVM? All the best, Wojciech Daniło

2 1

Re: [Haskell-cafe] determining the origin of imported symbols
by Erik Rantapaa 24 Jul '14

24 Jul '14

Thanks, everyone, for all of the suggestions! On Thursday, July 24, 2014 5:53:59 AM UTC-5, Eyal Lotem wrote: > > There's also ghc's -ddump-minimal-imports which might help you. > > > On Thu, Jul 24, 2014 at 12:06 PM, JP Moresmau <jpmor...(a)gmail.com > <javascript:>> wrote: > >> BuildWrapper doesn't do the transformation, but it resolves all symbols >> to build a usage map, so it would tell you that Data.List.sort is used at >> line xxx, using the GHC API. So have a look at around >> https://github.com/JPMoresmau/BuildWrapper/blob/master/src/Language/Haskell…. >> BuildWrapper takes the GHC AST, transforms it into a JSON structure, and >> extracts all usage information. There is also an import reorganization >> function that may be useful. >> >> JP >> >> >> On Thu, Jul 24, 2014 at 10:29 AM, Erik Rantapaa <eran...(a)gmail.com >> <javascript:>> wrote: >> >>> Hi everyone, >>> >>> I looking for a way to analyze Haskell source to determine which module >>> each imported symbol comes from. My goal is to transform source code like >>> this: >>> >>> import Data.List >>> ... >>> main = do >>> nums <- fmap (map read . words) getLine :: IO [Int] >>> print $ sort nums >>> >>> to code like this: >>> >>> import qualified Prelude as B >>> import qualified Data.List as A >>> ... >>> main = do >>> nums <- B.fmap (B.map B.read B.. B.words) B.getLine :: B.IO >>> [B.Int] >>> B.print B.$ A.sort nums >>> >>> That is, I want to qualify all imported symbols with a module alias. >>> >>> Can anyone suggest modules or programs I should look at? >>> >>> Thanks, >>> ER >>> >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskel...(a)haskell.org <javascript:> >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >>> >> >> >> -- >> JP Moresmau >> http://jpmoresmau.blogspot.com/ >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Haskell-cafe" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to haskell-cafe...(a)googlegroups.com <javascript:>. >> To post to this group, send email to haskel...(a)googlegroups.com >> <javascript:>. >> Visit this group at http://groups.google.com/group/haskell-cafe. >> For more options, visit https://groups.google.com/d/optout. >> > > > > -- > Eyal >

1 0

determining the origin of imported symbols
by Erik Rantapaa 24 Jul '14

24 Jul '14

Hi everyone, I looking for a way to analyze Haskell source to determine which module each imported symbol comes from. My goal is to transform source code like this: import Data.List ... main = do nums <- fmap (map read . words) getLine :: IO [Int] print $ sort nums to code like this: import qualified Prelude as B import qualified Data.List as A ... main = do nums <- B.fmap (B.map B.read B.. B.words) B.getLine :: B.IO [B.Int] B.print B.$ A.sort nums That is, I want to qualify all imported symbols with a module alias. Can anyone suggest modules or programs I should look at? Thanks, ER

3 2