- Haskell-Cafe - Haskell.org

10 open roles in expanding team at Standard Chartered
by Don Stewart 03 Jun '16

03 Jun '16

I have another ten open roles in the growing Strats team at Standard Chartered. https://donsbot.wordpress.com/2016/06/03/multiple-haskell-developer-roles-i… These are full time or contract Haskell developer positions in London or Singapore. Details in the post .

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how to reify an API?
by Johannes Waldmann 03 Jun '16

03 Jun '16

Dear Cafe, I wanted to benchmark (part of) an API of a package, by enumerating all possible (nested) calls by size of their AST, much as smallcheck does it for data. So I made this straightforward AST representation and (generically) got its Serial instances. That last part has been in smallcheck for a long time, and works nicely. But I do wonder if there is a way to get the AST (and corresponding interpreter) with less boilerplate code (than this: https://github.com/jwaldmann/pretty-test/blob/master/src/Lib.hs#L29 ) If you read the code: it also has a type for "AST contexts" because I wanted to iterate them (to produce larger trees). Again - easy to write down, but boring. - J.

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Re: [Haskell-cafe] Is there any way to use somethig like global backtrack with parsec
by Erik Rantapaa 01 Jun '16

01 Jun '16

If don't have to use Parsec, you can use a parser library like ReadP / ReadS. For example: import Text.ParserCombinators.ReadP abc = (choice [ string "a", string "ab" ] ) >> char 'c' >> eof run p s = case (readP_to_S p) s of [] -> Left "no parse" ((a,_):_) -> Right a test1 = run abc "ac" test2 = run abc "abc" test3 = run abc "ab" -- should fail On Monday, May 30, 2016 at 1:15:25 PM UTC-5, Petr Sokolov wrote: > > For example this parser doesn't parse "abc" > > test :: Parser String > test = ((try $ string "a") <|> (string "ab")) *> (string "c") > > I can rewrite it so it would parse "abc", but is there any general > approach to force parser to return and try other branches? > > (try a <|> b) *> c > > Something like > > (tryOtherBranchesIfFail (try a <|> b)) *> c > > So if it cannot parse "abc" with (try a *> c) it could return and try (b > *> c) > Or it isn't possible? > >

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SIGPLAN Programming Languages Mentoring Workshop @ ICFP
by Lindsey Kuper 01 Jun '16

01 Jun '16

SIGPLAN Programming Languages Mentoring Workshop @ ICFP Nara, Japan (co-located with ICFP 2016) Sunday, September 18th, 2016 http://conf.researchr.org/track/icfp-2016/PLMW-ICFP-2016/ We are pleased to invite students interested in functional programming research to the programming languages mentoring workshop at ICFP. The goal of this workshop is to introduce senior undergraduate and early graduate students to research topics in functional programming as well as provide career mentoring advice. We have recruited leaders from the functional programming community to provide overviews of current research topics and give students valuable advice about how to thrive in graduate school, search for a job, and cultivate habits and skills that will help them in research careers. This workshop is part of the activities surrounding ICFP, the International Conference on Functional Programming, and takes place the day before the main conference. One goal of the workshop is to make the ICFP conference more accessible to newcomers and we hope participants will stay through the entire conference. Through the generous donation of our sponsors, we are able to provide travel scholarships to fund student participation. These travel scholarships will cover reasonable travel expenses (airfare and hotel) for attendance at both the workshop and the main three days of the ICFP conference. The workshop is open to all. Students with alternative sources of funding for their travel and registration fees are welcome. In particular, many student attendance programs provide full or partial travel funding for students to attend ICFP 2016, including the ACM Student Research Competition. More information about student attendance programs at ICFP is available: http://conf.researchr.org/home/icfp-2016 Application for Travel Support: The travel funding application is available from the PLMW webpage. The deadline for full consideration of funding is July 1st, 2016. Selected participants will be notified by July 15th. Organizers: Amal Ahmed, Northeastern University Robby Findler, Northwestern University Atsushi Igarashi, Kyoto University

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Does the GHC GC handle const application?
by David Feuer 31 May '16

31 May '16

If I create a thunk representing const x y will the garbage collector be sure to replace this with x? I'm just wondering if I have to be concerned about the fact that Data.Sequence defines update in terms of adjust, with update x = adjust (const x)

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JSON parser that returns the rest of the string that was not used
by Ryan Newton 31 May '16

31 May '16

As someone who spent many years putting data in S-expression format, it seems natural to me to write multiple S-expressions (or JSON objects) to a file, and expect a reader to be able to read them back one at a time. This seems comparatively uncommon in the JSON world. Accordingly, it looks like the most popular JSON parsing lib, Aeson, doesn't directly provide this functionality. Functions like decode just return a "Maybe a", not the left-over input, meaning that you would need to somehow split up your multi-object file before attempting to parse, which is annoying and error prone. It looks like maybe you can get Aeson to do what I want by dropping down to the attoparsec layer and messing with IResult. But is there a better way to do this? Would this be a good convenience routine to add to aeson in a PR? I.e. would anyone else use this? Thanks, -Ryan

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Quantum Programming EDSLs other than Quipper
by Nicola Gigante 30 May '16

30 May '16

Hi all, Quipper [1] is a well-known library that provides an EDSL for writing and simulating quantum algorithms in Haskell. I was wondering if there was any other attempt to design an EDSL in Haskell to express quantum algorithms. In particular, Quipper is not able to statically ensure that the algorithm written is physically meaningful, as one could violate the "non-cloning property", for example (a qubit cannot be copied, for those who do not speak quantumly). Violations like this are detected at runtime when simulating the algorithm or when producing the corresponding circuit as output. Authors of Quipper already said that some of those properties could be possible to check “if Haskell had linear types”. The point is that Haskell's support for dependently typed programming has grown quite a lot in the last years, and I think that, at least theoretically, something better can now be achieved. So do anyone know any more recent attempt to express quantum computations in an Haskell EDSL that leverages cutting-edge type-level features to statically check for physically meaningful programs? Greetings, Nicola [1]: http://www.mathstat.dal.ca/~selinger/quipper/

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configurable mapping between data declarations and given XML schema?
by Johannes Waldmann 30 May '16

30 May '16

Dear Cafe, I have a legacy XML schema, and some Haskell data declarations. I want to map bidirectionally between XML documents and data. I absolutely cannot change the schema. I could change the data declarations, but it would not help much, since I don't think there is any form of declaring data that would allow me to derive the transformations generically. So, I have a mess of ad-hoc transformations. What could be done about this? I think I need "generic with customization". More detail: https://github.com/jwaldmann/haskell-tpdb/issues/16 Comments appreciated. - J.W.

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Mobile Development
by Justin Wood 30 May '16

30 May '16

I'm wondering if anyone has any experience they can share, know of any blog posts or anything else documenting the use of Haskell when developing a mobile application. Ideally, I would like something along the lines of having a native UI, a language bridge, and use Haskell for the core logic. My main focus would be getting this to work on Android and iOS. If this would also work on Blackberry and Windows Phone it would be a plus. I have successfully done this using C++ in place of Haskell in the past, but would really be interested in getting something working using Haskell. Thanks, Justin

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Testing for different dependency versions?
by Christopher Howard 29 May '16

29 May '16

Hi, I was wondering: what is the most practical way to go about testing or otherwise determining if your packaged library works with other dependency versions? E.g., cabal init specified base 4.6 because that is what happens to be installed on my Debian Jessie system, but that wouldn't even build on hackage. -- http://justonemoremathproblem.com To protect my privacy, please use PGP encryption. It's free and easy to use! My public key ID is 0x340EA95A (pgp.mit.edu)

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