- Haskell-Cafe - Haskell.org

ANNOUNCE: urembed-0.5.0.1 urxml-0.2.0.0
by Sergey Mironov 31 Oct '13

31 Oct '13

Hello. I'm glad to announce the release of Ur/Web[1] helper applications: urembed-0.5.0.1 and urxml-0.2.0.0 Ur is a programming language in the tradition of ML and Haskell, but featuring a significantly richer type system. Ur is functional, pure, statically-typed, and strict. Ur supports a powerful kind of metaprogramming based on row types. Ur/Web is Ur plus a special standard library and associated rules for parsing and optimization. Ur/Web supports construction of dynamic web applications backed by SQL databases. Uermbed and urxml are aimed at making Ur/Web development more pleasant. * Urembed https://github.com/grwlf/urembed Urembed embeds file or files into the Ur/Web project by generating the module which provides the programmer with functions serving the specified file as a binary. This way Ur/Web application no longer requires standalone webserver for serving static content. Also, Urembed supports generating JavaScript FFI signatures for *js files. https://github.com/grwlf/uru project uses urembed and may illustrate it's abilities. * UrXML https://github.com/grwlf/urxml UrXML is yet another XML parser/pretty-printer application. This time, it supports ur/web syntax extensions of XML. One can integrate this tool with VIM editor to indent XML parts of non-XML files like Ur/Web sources. Please, read README.md for the details. Regards, Sergey [1] - http://www.impredicative.com/ur/

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ICFP 2014: Call for Workshop & Co-located Event Proposals
by David Van Horn 31 Oct '13

31 Oct '13

CALL FOR WORKSHOP AND CO-LOCATED EVENT PROPOSALS ICFP 2014 19th ACM SIGPLAN International Conference on Functional Programming August 31 – September 6, 2014 Gothenburg, Sweden http://icfpconference.org/icfp2014/ The 19th ACM SIGPLAN International Conference on Functional Programming will be held in Gothenburg, Sweden on August 31-September 6, 2014. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for workshops (and other co-located events, such as tutorials) to be affiliated with ICFP 2014 and sponsored by SIGPLAN. These events should be less formal and more focused than ICFP itself, include sessions that enable interaction among the attendees, and foster the exchange of new ideas. The preference is for one-day events, but other schedules can also be considered. The workshops are scheduled to occur on August 31 (the day before ICFP) and September 4-6 (the three days after ICFP). ---------------------------------------------------------------------- Submission details Deadline for submission: November 15, 2013 Notification of acceptance: December 15, 2013 Prospective organizers of workshops or other co-located events are invited to submit a completed workshop proposal form in plain text format to the ICFP 2014 workshop co-chairs (Sam Tobin-Hochstadt and Tom Schrijvers), via email to icfp2014-workshops(a)ugent.be by November 15, 2013. (For proposals of co-located events other than workshops, please fill in the workshop proposal form and just leave blank any sections that do not apply.) Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by December 15, 2013, and if successful, depending on the event, they will be asked to produce a final report after the event has taken place that is suitable for publication in SIGPLAN Notices. The proposal form is available at: http://www.icfpconference.org/icfp2014/icfp14-workshops-form.txt Further information about SIGPLAN sponsorship is available at: http://acm.org/sigplan/sigplan_workshop_proposal.htm ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2014 organizing committee, together with the members of the SIGPLAN executive committee. Workshop Co-Chair: Sam Tobin-Hochstadt (Indiana University) Workshop Co-Chair: Tom Schrijvers (Ghent University) General Chair : Johan Jeuring (Utrecht University) Program Chair: Manuel Chakravarty (University of New South Wales) ---------------------------------------------------------------------- Further information Any queries should be addressed to the workshop co-chairs (Sam Tobin-Hochstadt and Tom Schrijvers), via email to icfp2014-workshops(a)ugent.be.

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Re: [Haskell-cafe] interfacing TradeKing API
by Donn Cave 30 Oct '13

30 Oct '13

I worked up a little application for Etrade's API, which is at least the same basic idea. This was some time ago and memory is pretty fuzzy, but ... I see that for some reason I modified hoauth Consumer.hs, replacing showURL with a path-to-text function I wrote myself, and I use my own version of the signRq function from that module that returns an unpacked request value. I'm sure it would be much more helpful to say what problems I was to solving there, sorry! Authentication was the hard part, naturally. Donn

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liftN
by Wvv 30 Oct '13

30 Oct '13

I try to write a function "liftN", but I'm not satisfied with result. lift :: (MonadTrans t) => Monad m => m a -> t m a liftN n | n < 1 = error "liftN: n<1" | n == 1 = lift | otherwise = lift . (liftN (n-1)) 1) I know(?), that it is impossible to write liftN now: typechecker can't decide which signature it is. 2) Main reason is finite recursive constraint 3) Let's think, it is possible to write Main candidates: promoted data and data-kinds For example, lift . lift . lift :: (Monad (t1 (t2 m)), Monad (t2 m), Monad m, MonadTrans t, MonadTrans t1, MonadTrans t2) => m a -> t (t1 (t2 m)) a My best solution looks like: data MT = M | T Int MT liftN :: forall tm. ( forall x n. Monad 'M, Monad (x :: MT), MonadTrans ('T n), ) => Int -> 'M a -> ('T 0) (tm :: MT) a liftN n | n < 1 = error "liftN: n < 1" | n == 1 = lift | otherwise = lift . (liftN (n-1)) Am I miss something? I think this function could look much prettier. But I don't know how. -- View this message in context: http://haskell.1045720.n5.nabble.com/liftN-tp5738612.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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interfacing TradeKing API
by Miro Karpis 30 Oct '13

30 Oct '13

Hi, did anybody tried to interface TradeKing API? (couldn't find anything on web) Cheers, m.

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fcntl locks, executeFile and threaded runtime
by diego souza 30 Oct '13

30 Oct '13

Hi, I'm having problems with executeFile as it seems to clear the advisory locks using the threaded runtime. Consider the following snippet (a simplification of what I'm doing): import System.IO import Control.Monad import System.Posix.IO import Control.Concurrent import System.Posix.Files import System.Posix.Process main = do let lock = (WriteLock, AbsoluteSeek, 0, 0) fd <- openFd "/tmp/foobar" ReadWrite (Just stdFileMode) defaultFileFlags {trunc=True} pid <- forkProcess $ do setLock fd lock >> putStrLn "child: ok" executeFile "/usr/bin/sleep" False ["5"] Nothing threadDelay $ 1 * 1000 * 1000 setLock fd lock >> putStrLn "parent: fail!" void $ getProcessStatus True False pid Then I consistentlty get these results: $ ghc -threaded --make test.hs; ./test child: ok parent: fail! $ ghc -rtsopts --make test.hs; ./test child: ok test: setLock: resource exhausted (Resource temporarily unavailable) Any pointers? At first I though it might be an issue with the unix package but that doesn't seem to be the case. $ ghc-pkg list | grep unix unix-2.6.0.1 $ ./test +RTS --info [("GHC RTS", "YES") ,("GHC version", "7.6.3") ,("RTS way", "rts_thr") ,("Build platform", "x86_64-unknown-linux") ,("Build architecture", "x86_64") ,("Build OS", "linux") ,("Build vendor", "unknown") ,("Host platform", "x86_64-unknown-linux") ,("Host architecture", "x86_64") ,("Host OS", "linux") ,("Host vendor", "unknown") ,("Target platform", "x86_64-unknown-linux") ,("Target architecture", "x86_64") ,("Target OS", "linux") ,("Target vendor", "unknown") ,("Word size", "64") ,("Compiler unregisterised", "NO") ,("Tables next to code", "YES") ] Thanks! ~dsouza

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ANNOUNCE: lens-family 1.0.0
by roconnor＠theorem.ca 30 Oct '13

30 Oct '13

Before there was lens there was lens-family.... I'm pleased to announce the second major release of the lens-family pacakges: lens-family-core-1.0.0 and lens-family-1.0.0. They can be found at * <http://hackage.haskell.org/package/lens-family-core> * <http://hackage.haskell.org/package/lens-family> I consider these packages to be kiddie-pool sized lens libraries for those people who are, for whatever reason, too intimidated by the lens library. I think this is a good way to get one's feet wet with lenses. The type for lenses and traversals are completely compatible with the lens library. This release brings two major developments to lens-family: * Support for traversals and folds. * The names have been all renamed to be mostly compatible with the lexicon developed by lens. With a common lexicon, I hope that users will find it easy to transition from lens-family to lens when they outgrow the kiddie pool. The lens-family-core package is a completely Haskell 98 package for those who need the compatibility. The lens-family package is a wrapper around lens-family-core that provides a few useful Rank 2 type synonyms to make using functional references a little easier. P.S. If edwardk is reading, I've used Ryan Ingram's definition from <http://twanvl.nl/blog/haskell/cps-functional-references#comment-comment0> to implement alongside so that it works for both lenses and getters. You probably want to do the same. -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

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Unwanted http-conduit buffering of chunked request body?
by Manuel Gómez 30 Oct '13

30 Oct '13

Hi list, I’ve been playing with http-conduit in an attempt to do some manual testing on a HTTP service, and I ran into something I had not expected. I was trying to set up a POST request with a chunked request body from a conduit. The following code does work: > {-# LANGUAGE OverloadedStrings #-} > > import Blaze.ByteString.Builder.ByteString (fromByteString) > import Control.Concurrent (threadDelay) > import Control.Monad.IO.Class (liftIO) > import Control.Monad.Trans.Resource (runResourceT) > import Data.ByteString (getLine) > import Data.Conduit (yield) > import Network.HTTP.Conduit (RequestBody(RequestBodySourceChunked), http, method, parseUrl, rawBody, requestBody, withManager) > > source = do say "a"; wait; say "b"; wait; say "c" > > wait = liftIO $ threadDelay 1000000 > say = yield . fromByteString > > main = runResourceT $ do > req <- parseUrl "http://localhost:12345/" > withManager $ http req > { method = "POST" > , requestBody = RequestBodySourceChunked source > } The important part is the `source` conduit: it yields a string, waits for a bit, yields another, waits for a bit, and yields again. I expected this to send chunks as soon as the source yielded them. However, it seems to be sending all the chunks together at the end, when the source finishes. Doing the same thing without `wait`, and with `forever` as opposed to just sending three bits of string, seems to work closer to my expectations: it seems to buffer for a bit, then it sends what was buffered, then it buffers some more, and so on. Is this http-conduit or Blaze doing undesired buffering? A quick run on `strace` seems to indicate it’s only doing the `send` system call every once in a while, so the buffering seems to be happening inside Haskell. I’m not even sure this is how the HTTP chunked transfer encoding is meant to be used — my actual use case has to do with sending potentially large files and hopefully using constant memory at the other end, but I’m also curious about using this to send asynchronous events and such. Is this how it’s supposed to work?

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Getting types inside a function in ghci
by martin 30 Oct '13

30 Oct '13

Hello all, is there a way to determine types of symbols which are not toplevel but inside a function?

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Re: [Haskell-cafe] reifying based-on type of a newtype or data
by oleg＠okmij.org 30 Oct '13

30 Oct '13

Anthony Clayden wrote: > newtype Foo = Foo Int deriving (Read, Show, Typeable, Data, ...) > someFoo = Foo 7 > ... > What I want is to get the based-on type baked inside `someFoo` > -- that is: `Int` > (It would also be handy to get the name of the data constr, just in case > it's different to the type.) If we have a data type declaration data C a b = D1 a Int b | D2 a | D3 [a] we use methods of module Typeable to get information about the left-hand-side of the equation (about the type expression C a b and its structure, an application of a type constructor C to two arguments). We use methods of module Data.Data to get information about the right-hand-side of the equation (about _data_ constructors D1, D2 and D3 and their arguments). Here is an example: > {-# LANGUAGE DeriveDataTypeable, ScopedTypeVariables #-} > > import Data.Data > > data C a b = D1 a Int b | D2 a | D3 [a] deriving (Data, Typeable) A sample datum of type C > someC = undefined :: C Int Char *Main> typeOf someC C Int Char meaning someC has the type C Int Char. *Main> dataTypeOf someC DataType {tycon = "Main.C", datarep = AlgRep [D1,D2,D3]} Now we see something about the right-hand-side of the equation defining C: C a b is a data type and it has three data constructors, D1, D2 and D3. How to get information about their arguments? First, we extract constructors > getCtor :: Data a => Int -> a -> Constr > getCtor i x = case dataTypeRep $ dataTypeOf x of AlgRep cs -> cs !! i *Main> getCtor 0 someC D1 Now, we reify a data constructor by unfolding it in a particular way > newtype DTInfo a = DTInfo [TypeRep] > -- Get information about the given ctor of a given algebraic data type > -- (the data type value may be undefined -- we only need its type) > ctorInfo :: forall a. Data a => a -> Constr -> [TypeRep] > ctorInfo _ ctor = case go ctor of DTInfo reps -> reverse reps > where > go :: Constr -> DTInfo a > go = gunfold (\ (DTInfo infos :: DTInfo (b->r)) -> > DTInfo (typeOf (undefined:: b) : infos)) > (\r -> DTInfo []) *Main> ctorInfo someC $ getCtor 0 someC [Int,Int,Char] meaning that D1 of the type C Int Char has three arguments, Int, Int, Char -- in that order. *Main> ctorInfo someC $ getCtor 1 someC [Int] *Main> ctorInfo someC $ getCtor 2 someC [[Int]] It is easy to answer the original question about someFoo *Main> getCtor 0 someFoo Foo *Main> ctorInfo someFoo $ getCtor 0 someFoo [Int] -- A faster way for a defined datum *Main> ctorInfo someFoo $ toConstr someFoo [Int] So, someFoo is constructed by data constructor Foo and that data constructor has one Int argument.

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Munich Haskell Meeting
by Heinrich Hördegen 30 Oct '13

30 Oct '13

Dear all, on Thursday, 31st of October, our monthly Haskell meeting will take place in Munich. We meet at 19h30 at Cafe Puck. If you plan to join, please go to http://www.haskell-munich.de/dates and click the button. Cheers, Heinrich

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Instance deriving for Void types.
by Lyndon Maydwell 29 Oct '13

29 Oct '13

Hi Cafe. I was wondering if it's possible to have automatic deriving for some classes for the Void type. This would be classes that require a parameter of the type in its functions. This should obviously be trivial as the definition can be undefined since there's no way to supply a value of the type. I guess the obvious one would be Show. data Nada deriving Show {* instance Show Nada where show _ = undefined *} Thoughts?

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Re: [Haskell-cafe] reifying based-on type of a newtype or data
by AntC 29 Oct '13

29 Oct '13

> John Lato <jwlato <at> gmail.com> writes: > > What about Data.Typeable.typeRepArgs ? > typeRepArgs :: TypeRep -> [TypeRep] > Prelude Data.Data> typeRepArgs (typeOf Foo)[Int,Foo] Thanks John, I did look at that, and thought it returned only type args, not the 'baked in' type. Your example applies to `(typeOf Foo)` -- that is, the data constr, which is indeed a function. And `typeOf Foo` is `Int -> Foo`, as I noted in the OP. I want something that can apply to a value of type Foo. (`someFoo`, in my example.) > ... > For anything more complicated, I suspect you'll need > Data/Generic/Template Haskell. That is rather what I feared. I want to avoid TH, because that imposes on my user. Could you point to where/what in Data/Generics? > > > > newtype Foo = Foo Int deriving (Read, Show, Typeable, Data, ...) > > someFoo = Foo 7 > > > > I can ask for `typeOf someFoo` and get `Foo` OK. > > I can ask for `typeOf Foo` and get `Int -> Foo` OK. > > If I ask for `typeOf (typeOf someFoo)` I get `TypeRep`. > > `typeOf (show $ typeOf someFoo`) gets me `[Char]` (aka `String`) > > > > What I want is to get the based-on type baked inside `someFoo`

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reifying based-on type of a newtype or data
by AntC 29 Oct '13

29 Oct '13

[reposted from Beginners, where it met stoney silence.] So I have (or rather the user of my package has): > {-# LANGUAGE DeriveDataTypeable #-} > > newtype Foo = Foo Int deriving (Read, Show, Typeable, Data, ...) > someFoo = Foo 7 > Note: * the `newtype` could be `data` -- if that would help. * this is _not_ a parameterised type, but a 'baked in' `Int`. * the data constr is named same as the type -- if that would help. I can ask for `typeOf someFoo` and get `Foo` OK. I can ask for `typeOf Foo` and get `Int -> Foo` OK. If I ask for `typeOf (typeOf someFoo)` I get `TypeRep`. `typeOf (show $ typeOf someFoo`) gets me `[Char]` (aka `String`) So far very logical, but not very helpful. What I want is to get the based-on type baked inside `someFoo` -- that is: `Int` (It would also be handy to get the name of the data constr, just in case it's different to the type.) Do I need to get into `deriving (..., Generic)` ? That looks like serious machinery! Thanks AntC

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about learning haskell
by swrangsar basumatary 28 Oct '13

28 Oct '13

i know what is a monad now. but i still have problems understanding the continuation monad and arrows. Also is it necessary to know category theory to be a good haskell programmer?

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[ANN] xmobar 0.19 released
by Jose A. Ortega Ruiz 28 Oct '13

28 Oct '13

I've just released version 0.19 of xmobar, a lightweight system monitor written in Haskell. Homepage: http://xmobar.org Release notes: http://xmobar.org/releases.html As of this release, the old bug tracker at Google code is deprecated. Please use [Github's tracker] for new bugs. Details: _New features_ - New monitor `BatteryN`, a variant of `BatteryP` that lets you specify the name of the monitor in the template. - Support for configuration file living in `XDG_CONFIG_HOME` (see [github #99]). - `Com` uses safer `runInteractiveProcess` instead of spawning a shell (David McLean). If you're using shell expansion in your `Com` (e.g. "~/bin/script") here's a workaround: `Run Com "/bin/bash" ["-c", "~/bin/script"]` (cf. [github #127]). - New plugin `UnsafeStdinReader` that allows actions from stdin. Now it's possible to have clickable workspaces! (Thiago Negri, see [github #125]). - New monitor configuration option (`-x` or `--nastring`) that allows specifying what string to display when a monitor is not available (defaulting to "N/A"). Cf. [github #119]. _Bug fixes_ - Using the width options `-w`, `-m` and `-M` in battery monitors watts display ([github #118]). - Using the `-d` option in `CoreTemp` ([github #115]) - Fix for systems not supporting PCRE regular expressions: we use now BCEs, so regex-compat should be enough everywhere (see [github #117]). - Weather monitor: support for stations without name (Sergei Trofimovich, [issue #65]). [Github's tracker]: https://github.com/jaor/xmobar/issues [github #99]: https://github.com/jaor/xmobar/issues/115 [github #115]: https://github.com/jaor/xmobar/issues/115 [github #117]: https://github.com/jaor/xmobar/issues/117 [github #125]: https://github.com/jaor/xmobar/issues/125 [issue #65]: http://code.google.com/p/xmobar/issues/detail?id=65 [github #118]: https://github.com/jaor/xmobar/issues/118 [github #119]: https://github.com/jaor/xmobar/issues/119 [github #127]: https://github.com/jaor/xmobar/issues/127

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Vacancy Professor Software Technology
by Johan Jeuring 28 Oct '13

28 Oct '13

Dear colleague, Want to teach and do research in an exciting environment, in the fourth most happy city on earth (http://www.bbc.com/travel/feature/20131022-living-in-the-worlds-happiest-pl… Or do you think a colleague might be a suitable candidate? Let us know. We have a vacancy for: Full Professor Software Technology (0.8 – 1.0 fte) The full professor directs and supervises research in the field of software technology, specifically in the design and development of formalisms and methodologies for effective program construction and program analysis. She or he develops new initiatives, aiming at research programs in software technology that are relevant for software systems in general and for the departmental focus domain of game technology. This includes the acquisition of external research funds at the national and international level, and the dissemination, of research results and its applications, to the relevant research communities. The initiatives should be developed in line with worldwide trends in software technology such as software generation, domain-specific languages, and multi-core programming. The full professor has a leading role in teaching and supervision. She or he contributes to the department’s curriculum development at all levels: BSc, MSc, and PhD. The full professor plays an active role in the leadership and administrative duties of the Division of Software Systems, the Department and/or Faculty. Profile Candidates must have an excellent track record in research, teaching and leadership, as exemplified by: Research: • A PhD degree in Computer Science or a closely related scientific field. • An excellent publication record, including papers in high-impact journals and conference proceedings. • Proven ability to obtain extramural funding for research and to provide leadership in collaborative research programs. Teaching: • Experience and enthusiasm for teaching and student supervision. • Experience and leadership in curriculum development. • Academic leadership: • An active role in leading (national and international) activities in the area of the chair and participation in academic communities. • An established international network of research partnerships with other leading research groups and institutions. • Experience in administrative roles at department or faculty level. Utrecht University employs a system of quality assessment for teaching and research with consequences for career development. This implies that, in addition to having a PhD in a relevant field of research, a successful candidate also possesses appropriate senior level academic teaching and research qualifications. The Faculty may use an assessment as an instrument in the selection procedure. We offer a permanent position as full professor at 0.8 – 1.0 fte. The gross salary depends on qualifications and experience, and ranges between € 5,003.- and € 7,285.- per month (salary scale H2, of the Collective Labour Agreement of the Dutch Universities). The salary is supplemented with a holiday bonus of 8% and an end-of-year bonus of 8.3% per year. In addition we offer: an excellent pension scheme, a partially paid parental leave, and flexible employment conditions. Conditions are based on the Collective Labour Agreement Dutch Universities. More information about terms of employment: http://www.uu.nl/EN/informationfor/jobseekers/Working-for-Utrecht-Universit… About the department:§ The Department of Information and Computing Sciences (http://www.cs.uu.nl/) has a strong national and international reputation in computer science and in information science. The department’s research activities are clustered into four divisions, viz. Software Systems, Artificial Intelligence, Virtual Worlds, and Interaction Technology. Each division is specialized in a specific research area within computer science and contributes from this area to the department’s overall focus on Game Technology. The focus area of Game Technology deals with all technological aspects of games, and of interactive virtual experiences more in general; Game Technology constitutes one of the four strategic research themes of the Faculty of Science. While the research activities of the four computer-science divisions meet in the Game Technology area, research is not restricted to games application. Through collaboration with (often external) partners, the various divisions also connect with the other strategic research themes of the university, viz. life sciences, sustainability, and youth and identity. The Department of Information and Computing Sciences offers educational bachelor programs in computer science and information science, and three (English) research master programs, viz. Computing Science, Game and Media Technology, and Business Informatics; the Department is further involved in the master program Artificial Intelligence. Three years ago the Department introduced a track on Game Technology in the bachelor program in computer science, which led to a substantial annual increase of bachelor students. The bachelor programs are the largest computer science and information science programs in the Netherlands. Utrecht University is among Europe’s largest and most prominent institutions for research and education. The Faculty of Science consists of six departments: Information & Computing Sciences, Mathematics, Physics & Astronomy, Chemistry, Biology, and Pharmaceutical Sciences. The Faculty is home to 3500 students and nearly 2000 staff members and is internationally renowned for the quality of its research and its teaching. The Faculty’s academic programs reflect the developments in science and society today. Its Undergraduate School and Graduate Schools in Natural Sciences and Life Sciences guarantee the outstanding quality of its BSc, MSc, and PhD programs. More information A more detailed description of the chair can be found here: http://www.cs.uu.nl/vacatures/auxdoc/SoftwTechn/StructReport2013WWW.pdf. For additional information and documentation please contact the Secretary of the Search Committee: Dr Marinus Veldhorst, email: M.Veldhorst(a)uu.nl, telephone +31 30 253 4450. As part of the selection procedure, the candidate is expected to give an outline of his/her research statement and an oral presentation. Applications including a letter of motivation in which the candidate’s research and teaching vision are outlined, a CV with a list of publications, a research statement, and contact details of at least three references, must be submitted before January 5, 2014. Apply before 05/01/2014 on http://ssl1.peoplexs.com/Peoplexs22/CandidatesPortalNoLogin/ApplicationForm… -------------------------------- Johan Jeuring Professor of Software Technology for Learning and Teaching Department of Information and Computing Sciences Utrecht University The Netherlands http://www.staff.science.uu.nl/~jeuri101/homepage/ J.T.Jeuring(a)uu.nl

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Ghc 7.7 and some 'missing' libraries
by Magnus Therning 27 Oct '13

27 Oct '13

After a few attempts I've finally managed to build Ghc from Git. One thing I noticed was that a few libraries seem to have gone missing on the install. Does anyone know why this is? Lib | Installed | In source | | (libraries/) -----------------+-----------+------------- haskeline | | x primitive | | x random | | x terminfo | | x vector | | x xhtml | | x /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus If our ideas of intellectual property are wrong, we must change them, improve them and return them to their original purpose. When intellectual property rules diminish the supply of new ideas, they steal from all of us. -- Andrew Brown, November 19, 2005, The Guardian

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Fwd: PhD/Postdoc in programming models for heterogeneous infrastructures
by Ivan Perez 26 Oct '13

26 Oct '13

Hoi hoi, haskellers! Our friends from UPM just sent the following PhD/Postdoc offer. Goed weekend!! Ivan -- The Universidad Politécnica de Madrid (www.upm.es/internacional) have an opening at the Ph.D. or post-doctoral levels within the 3-year POLCA (Programming Large Scale Heterogeneous Infrastructures) European project. POLCA aims at developing a methodology and tools to support a programming model to efficiently exploit heterogeneous computing infrastructures (CPUs / GPUs / ASICs / FPGAs) while reducing the burden on the programmer and the need to port code between architectures. The project will build upon the design and use of high-level source code annotations ("pragmas") which describe code properties which can then be used to perform aggressive, mathematically sound, source-to-source transformations capable to adapt the code to the target architecture. We seek applicants with a strong background in some of the following fields: * Source-to-source program transformation for optimization and parallelism. * Algebra of programming. * High-level architectural and system-design languages (such as Clash or ForSyDe). * Analysis of functional and non-functional program properties. Knowledge in the following topics will be a strong plus: - Existing compiler infrastructures (LLVM / Clang / ...). - Abstract syntax. - Embedded domain specific languages. - Meta-programming. - CPUs, GPUs, ASICs or FPGAs programming. Successful applicants are expected to actively contribute to the development of the project toolset and must have an interest to carry research at the intersection between specifications, programming languages, program transformation, and parallelism. Collaboration in usual EU research project chores is also expected. All positions are initially for one year, renewable for up to three years (in total), contingent on the availability of funds. Other mutually agreed arrangements are possible. In any case, satisfactory progress will be monitored and required for renewal. The starting date is negotiable, but preference may be given to candidates able to adapt to the project starting dates. For further information, please contact Ángel Herranz (aherranz at fi.upm.es). Applying -------- Candidates are kindly asked to send an email to Ángel Herranz (aherranz at fi.upm.es) with the following content: - A PDF (max size 5Mb) or plain text file containing their Research statement. - A PDF file containing their CV (max size: 5Mb). - A list of names and contact data of persons that can provide references about you and their work. Applications must be received by November 17th, 2013 to receive full consideration. However, applications will continue to be accepted until the positions are filled. Salary ------ An internationally competitive salary will be offered, negotiated with the candidate. Selected candidates will have access to an excellent public healthcare system. Work Environment ---------------- UPM team in the POLCA project will work in close collaboration with the IMDEA Software Institute (software.imdea.org) The School of Computer Science of the UPM and the IMDEA Software Institute are located in the vibrant area of Madrid, Spain, and offer an ideal working environment where researchers can focus on developing new ideas and projects. The working language is English. UPM is Equal Opportunity Employers and strongly encourage applications from a diverse and international community. Both comply with the European Charter for Researchers.

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Trouble installing haskeline: ExitFailure 139
by David Banas 26 Oct '13

26 Oct '13

Has anyone else hit an unexplained *ExitFailure 139* when trying to install the *haskeline* package? Thanks, -db dbanas@dbanas-lap:~/prj$ cabal install -v haskeline Reading available packages... Choosing modular solver. Resolving dependencies... Extracting /home/dbanas/.cabal/packages/ hackage.haskell.org/haskeline/0.7.0.3/haskeline-0.7.0.3.tar.gz to /tmp/haskeline-0.7.0.3-16574... creating /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/dist/setup creating /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/dist creating /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/dist/setup /usr/local/bin/ghc --make /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/Setup.hs -o /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/dist/setup/setup -odir /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/dist/setup -hidir /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/dist/setup -i -i/tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3 -package Cabal-1.16.0 [1 of 1] Compiling Main ( /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/Setup.hs, /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/dist/setup/Main.o ) Linking /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/dist/setup/setup ... /tmp/haskeline-0.7.0.3-16574/haskeline-0.7.0.3/dist/setup/setup configure --verbose=2 --ghc --prefix=/home/dbanas/.cabal --user --flags=terminfo --flags=-libiconv --flags=-legacy-encoding --constraint=unix ==2.6.0.1 --constraint=transformers ==0.3.0.0 --constraint=terminfo ==0.3.2.5 --constraint=filepath ==1.3.0.1 --constraint=directory ==1.2.0.1 --constraint=containers ==0.5.0.0 --constraint=bytestring ==0.10.0.2 --constraint=base ==4.6.0.1 --disable-tests --disable-benchmarks World file is already up to date. cabal: Error: some packages failed to install: haskeline-0.7.0.3 failed during the configure step. The exception was: ExitFailure 139 dbanas@dbanas-lap:~/prj$

5 7

Weird issue with ConstraintKinds
by Jacques Carette 26 Oct '13

26 Oct '13

Consider the following (minimal, for illustration purposes) code: {-# LANGUAGE ConstraintKinds #-} module Weird where class A a where class B b where class C c where data X a = X a data Y a = Y a -- works fine, but can be verbose when things multiply instance (A a, B a) => C (X a) where -- So use ConstraintKinds: type D a = (A a, B a) instance D a => C (Y a) where ===== and now I get Variable `a' occurs more often than in the instance head in the constraint: D a (Use -XUndecidableInstances to permit this) In the instance declaration for `C (Y a)' Why?? Since D is an abbreviation, why would it behave differently than when I hand expand it? [This is with GHC 7.6.3] Jacques

2 2

ANNOUNCE: Ajhc Haskell Compiler 0.8.0.9 Release
by Kiwamu Okabe 26 Oct '13

26 Oct '13

We are happy to announce Ajhc 0.8.0.9. This version is a point release to fix some BUGs, and support Android NDK platform. You can get Ajhc using "cabal install ajhc" command. The usage is found at Ajhc's project web site http://ajhc.metasepi.org/. The source code at https://github.com/ajhc/ajhc. Welcome sending any bugs or your ideas to https://github.com/ajhc/ajhc/issues. ## Support new platforms ### Android NDK http://developer.android.com/tools/sdk/ndk/index.html The demo movie at http://www.youtube.com/watch?v=n6cepTfnFoo. The touchable cube application is written with Haskell and compiled by Ajhc. In the demo, the application is breaked by ndk-gdb debugger when running GC. You could watch the demo source code at \url{https://github.com/ajhc/demo-android-ndk}. ## Other changes * Experimental support Mac OS X to compile Ajhc and use it. * Start to run buid test for Mac OS X on Travis CI. https://travis-ci.org/ajhc/ajhc/builds/12218394 * Depend on derive package. But near future use DrIFT again. For Haskell 98 compliant. https://github.com/ajhc/ajhc/issues/47 * Fix the bugs forgetting to clear memory. Enjoy! :) - - - Metasepi team

1 0

Horray, a ghc bug!
by Andreas Abel 25 Oct '13

25 Oct '13

You do not get them often, but here is one... [208 of 254] Compiling Agda.TypeChecking.MetaVars.Occurs ( src/full/Agda/TypeChecking/MetaVars/Occurs.hs, dist/build/Agda/TypeChecking/MetaVars/Occurs.o ) ghc: panic! (the 'impossible' happened) (GHC version 7.4.1 for x86_64-unknown-linux): compiler/rename/RnSource.lhs:429:14-81: Irrefutable pattern failed for pattern Data.Maybe.Just (inst_tyvars, _, SrcLoc.L _ cls, _) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -- Andreas Abel <>< Du bist der geliebte Mensch. Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY andreas.abel(a)ifi.lmu.de http://www2.tcs.ifi.lmu.de/~abel/

10 15

Trouble w/ ExitFailure 139 (Segmentation Fault), during Cabal installs.
by David Banas 25 Oct '13

25 Oct '13

Hi all, Prolog: I have installed GHC v7.6.3, from source, on Ubuntu 13.0.4. I think I've made my GHC v7.6.3 installation unstable, because I'm having lots of trouble with "ExitFailure 139"s when cabal installing. And I'm wondering if this is a pertinent clue: dbanas@dbanas-lap:~/prj/plush$ cabal unpack lifted-base Unpacking to lifted-base-0.2.1.0/ dbanas@dbanas-lap:~/prj/plush$ pushd lifted-base-0.2.1.0/ ~/prj/plush/lifted-base-0.2.1.0 ~/prj/plush ~ dbanas@dbanas-lap:~/prj/plush/lifted-base-0.2.1.0$ ghc --make Setup.hs [1 of 1] Compiling Main ( Setup.hs, Setup.o ) Linking Setup ... dbanas@dbanas-lap:~/prj/plush/lifted-base-0.2.1.0$ ./Setup configure Segmentation fault (core dumped) dbanas@dbanas-lap:~/prj/plush/lifted-base-0.2.1.0$ head Setup.hs #! /usr/bin/env runhaskell {-# LANGUAGE NoImplicitPrelude, UnicodeSyntax #-} module Main (main) where ------------------------------------------------------------------------------- -- Imports ------------------------------------------------------------------------------- dbanas@dbanas-lap:~/prj/plush/lifted-base-0.2.1.0$ chmod 755 Setup.hs dbanas@dbanas-lap:~/prj/plush/lifted-base-0.2.1.0$ ./Setup.hs configure Configuring lifted-base-0.2.1.0... Setup.hs: At least the following dependencies are missing: base-unicode-symbols >=0.1.1 && <0.3, monad-control ==0.3.*, transformers-base ==0.4.* dbanas@dbanas-lap:~/prj/plush/lifted-base-0.2.1.0$ What I'm attempting to call attention too, with the above excerpt, is this: *If I compile and run "Setup configure" I get a core dump, but if I just run "Setup.hs configure" (taking advantage of the fact that Setup.hs begins with a shebang line) it works fine.* Is this a clue as to how I've horked up my ghc installation? Thanks! -db

1 0

to make a statically known sized non-empty list
by Markus Läll 25 Oct '13

25 Oct '13

Hi haskell-cafe, so for fun and profit I was trying to make a non-empty list data type, where the size of the non-empty prefix would be known for the type-system with the following code, but it fails with an error "No instance for (Functor (NonEmpty * a)) ..." for the last line. To me it seems that all should be known, but something must be missing.. data Nat = Zero | Succ Nat data family NonEmpty (n :: Nat) a data instance NonEmpty Zero a = Tail [a] data instance NonEmpty (Succ n) a = Head a (NonEmpty n a) instance Functor (NonEmpty Zero) where fmap f (Tail xs) = Tail (fmap f xs) instance Functor (NonEmpty (Succ a)) where fmap f (Head x xs) = Head (f x) (fmap f xs) -- Markus Läll

3 3

Haskell Weekly News: Issue 284
by Daniel Santa Cruz 25 Oct '13

25 Oct '13

Welcome to issue 284 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of October 13 to 19, 2013. Quotes of the Week * Polarina: Once you get something with [lens] to work correctly, all other Haskell code looks like C++ in comparison. Top Reddit Stories * The GHC October status report - a nice summary of what to expect from 7.8 Domain: ghc.haskell.org, Score: 106, Comments: 51 On Reddit: [1] http://goo.gl/ZOYHI7 Original: [2] http://goo.gl/1PM4s7 * Haskell for all: An all-atom protein search engine powered by Haskell Domain: haskellforall.com, Score: 84, Comments: 51 On Reddit: [3] http://goo.gl/TwntnD Original: [4] http://goo.gl/4WbmZp * FSF - Recognizing an inspiring woman for Ada Lovelace Day: Haskell/Perl hacker Audrey Tang Domain: fsf.org, Score: 82, Comments: 15 On Reddit: [5] http://goo.gl/XbrLS7 Original: [6] http://goo.gl/zGTnbL * Automatic SIMD Vectorization for Haskell and ICFP 2013 Domain: dorchard.wordpress.com, Score: 50, Comments: 3 On Reddit: [7] http://goo.gl/ikP8nw Original: [8] http://goo.gl/kYCQyW * A Little Lens Starter Tutorial - School of Haskell Domain: fpcomplete.com, Score: 49, Comments: 43 On Reddit: [9] http://goo.gl/RQjC2m Original: [10] http://goo.gl/LA7fUo * Abstractions for the Functional Roboticist with Anthony Cowley at NY Haskell Domain: vimeo.com, Score: 43, Comments: 13 On Reddit: [11] http://goo.gl/f4j0CP Original: [12] http://goo.gl/pSZBNR * The "magic" of "join (,)" Domain: self.haskell, Score: 42, Comments: 18 On Reddit: [13] http://goo.gl/oVjtNL Original: [14] http://goo.gl/oVjtNL * A Taste of Agda with Francesco Mazzoli at NY Haskell Domain: vimeo.com, Score: 41, Comments: 15 On Reddit: [15] http://goo.gl/anu7xJ Original: [16] http://goo.gl/vIfDNM * [Demo movie] Ajhc Haskell compiler can create Haskell Apps running on Android NDK! Domain: youtube.com, Score: 36, Comments: 22 On Reddit: [17] http://goo.gl/HM4AJ3 Original: [18] http://goo.gl/j1Gmqi * Open question: help me design a new encoding API for aeson Domain: serpentine.com, Score: 31, Comments: 30 On Reddit: [19] http://goo.gl/CE6Q0I Original: [20] http://goo.gl/ikdO5O * Made some Haskell Wallpapers, thought I'd share Domain: imgur.com, Score: 30, Comments: 27 On Reddit: [21] http://goo.gl/A1LILP Original: [22] http://goo.gl/c054gN * How to use Travis-CI with multiple GHC versions Domain: github.com, Score: 30, Comments: 6 On Reddit: [23] http://goo.gl/hsH9a7 Original: [24] http://goo.gl/K2Eja5 * A Gentle Introduction to Parsec Domain: blog.barrucadu.co.uk, Score: 29, Comments: 1 On Reddit: [25] http://goo.gl/GHUil8 Original: [26] http://goo.gl/21xyq2 * Haskell.org committee is looking for self-nominations Domain: haskell.org, Score: 28, Comments: 2 On Reddit: [27] http://goo.gl/B3pc80 Original: [28] http://goo.gl/19dZX4 * Backpropogation, Steepest Descent, and Automatic Differentiation Domain: idontgetoutmuch.wordpress.com, Score: 23, Comments: 22 On Reddit: [29] http://goo.gl/izxqMg Original: [30] http://goo.gl/F2fjNk * Anonymous records. A solution to the problems of record-system. Domain: gist.github.com, Score: 22, Comments: 24 On Reddit: [31] http://goo.gl/CjdbT3 Original: [32] http://goo.gl/UY5OqT Top StackOverflow Questions * Is there a canonical haskell type for “One or Both”? votes: 15, answers: 3 Read on SO: [33] http://goo.gl/yn8MkJ * Show progress of Haskell program votes: 14, answers: 4 Read on SO: [34] http://goo.gl/IEegAQ * Does Data.ByteString.readFile block all threads? votes: 13, answers: 3 Read on SO: [35] http://goo.gl/5X805o * Am I abusing unsafePerformIO? votes: 11, answers: 3 Read on SO: [36] http://goo.gl/SnfOcK * GHCJS: How do I import a high order javascript function using FFI? votes: 10, answers: 1 Read on SO: [37] http://goo.gl/fCbPE2 * Simulating a spring/damper system in Yampa votes: 9, answers: 1 Read on SO: [38] http://goo.gl/zQ50Ao Until next time, [39]+Daniel Santa Cruz References 1. http://ghc.haskell.org/trac/ghc/wiki/Status/Oct13 2. http://www.reddit.com/r/haskell/comments/1opw22/the_ghc_october_status_repo… 3. http://www.haskellforall.com/2013/10/an-all-atom-protein-search-engine.html 4. http://www.reddit.com/r/haskell/comments/1oc5g5/haskell_for_all_an_allatom_… 5. https://www.fsf.org/blogs/community/recognizing-an-inspiring-woman-for-ada-… 6. http://www.reddit.com/r/haskell/comments/1oj2u4/fsf_recognizing_an_inspirin… 7. http://dorchard.wordpress.com/2013/10/14/automatic-simd-vectorization-for-h… 8. http://www.reddit.com/r/haskell/comments/1og58l/automatic_simd_vectorizatio… 9. https://www.fpcomplete.com/user/tel/a-little-lens-starter-tutorial 10. http://www.reddit.com/r/haskell/comments/1obpxb/a_little_lens_starter_tutor… 11. http://vimeo.com/rickasaurus/haskell-robots 12. http://www.reddit.com/r/haskell/comments/1oo2at/abstractions_for_the_functi… 13. http://www.reddit.com/r/haskell/comments/1olk04/the_magic_of_join/ 14. http://www.reddit.com/r/haskell/comments/1olk04/the_magic_of_join/ 15. https://vimeo.com/77168227 16. http://www.reddit.com/r/haskell/comments/1oq0dt/a_taste_of_agda_with_france… 17. http://www.youtube.com/watch?v=n6cepTfnFoo 18. http://www.reddit.com/r/haskell/comments/1oq22l/demo_movie_ajhc_haskell_com… 19. http://www.serpentine.com/blog/2013/10/14/open-question-help-me-design-a-ne… 20. http://www.reddit.com/r/haskell/comments/1ohe9m/open_question_help_me_desig… 21. http://imgur.com/a/DRdNi 22. http://www.reddit.com/r/haskell/comments/1om4ie/made_some_haskell_wallpaper… 23. https://github.com/hvr/multi-ghc-travis 24. http://www.reddit.com/r/haskell/comments/1os3f6/how_to_use_travisci_with_mu… 25. http://blog.barrucadu.co.uk/2013/05/27/a-gentle-introduction-to-parsec/ 26. http://www.reddit.com/r/haskell/comments/1ojsi4/a_gentle_introduction_to_pa… 27. http://www.haskell.org/pipermail/haskell-cafe/2013-October/110997.html 28. http://www.reddit.com/r/haskell/comments/1onnab/haskellorg_committee_is_loo… 29. http://idontgetoutmuch.wordpress.com/2013/10/13/backpropogation-is-just-ste… 30. http://www.reddit.com/r/haskell/comments/1odmk1/backpropogation_steepest_de… 31. https://gist.github.com/nikita-volkov/6977841 32. http://www.reddit.com/r/haskell/comments/1oicmu/anonymous_records_a_solutio… 33. http://stackoverflow.com/questions/19413438/is-there-a-canonical-haskell-ty… 34. http://stackoverflow.com/questions/19343695/show-progress-of-haskell-program 35. http://stackoverflow.com/questions/19347907/does-data-bytestring-readfile-b… 36. http://stackoverflow.com/questions/19371636/am-i-abusing-unsafeperformio 37. http://stackoverflow.com/questions/19415306/ghcjs-how-do-i-import-a-high-or… 38. http://stackoverflow.com/questions/19461227/simulating-a-spring-damper-syst… 39. https://plus.google.com/105107667630152149014/about

1 0

mavericks + xcode 5 quick fix directions
by Carter Schonwald 24 Oct '13

24 Oct '13

Hey Everyone, I've synthesized some quick fix directions that let you use a preexisting GHC install despite the Mavericks upgrade https://gist.github.com/cartazio/7131371 please share with folks who are struggling with mavericks upgrade breaking everything :) thanks! -Carter

1 0

Re: [Haskell-cafe] Why do I need UndecidableInstances?
by adam vogt 24 Oct '13

24 Oct '13

On Thu, Oct 24, 2013 at 11:23 AM, Stijn van Drongelen <rhymoid(a)gmail.com> wrote: > Hi, > > As far as I know, you're referring to the Paterson Conditions. Condition 'b' > kind of corresponds to "at least one of the types is shrinking", while > condition 'a' corresponds to "all the other are not growing", so the rules > are already formulated in the way you suggest. The Paterson Conditions are > also not the issue here; the Coverage Condition is. > >> The equivalent code using type families doesn't need >> undecidable instances in my ghc-7.6.2. > > > This is because (I think) type family instances are not subject to the > Coverage Condition. In principle, type families are to type classes as > functions are to relations. Functional dependencies may be used to make type > classes more 'function-like'. I guess(!) the Coverage Condition is trying to > capture this notion. > > I don't know why it's formulated in this way, because in Alejandro's > example, the classes really look 'function-like'. > > Kind regards, > > Stijn van Drongelen Hi Stijn, Thanks for clarifying the issue. There is an example of why the coverage condition is needed on line 512 of (github doesn't handle line numbers in lhs correctly unfortunately): https://github.com/ghc/ghc/blob/9a04e1c7257f93f0c1cadc56a5e2a177574f6871/co… It doesn't seem possible to write a type for that function with just a type family; you need a class Mul to get into an infinite loop while looking for instances. So it seems appropriate that the coverage condition does not apply to type families. Regards, Adam

1 0

Better versions of this code
by Tyson Whitehead 24 Oct '13

24 Oct '13

Hey All, I wrote some quick code to change mediawiki preformatted text (adjacent lines begining with a ' ') to nowiki blocks (first line with a ' ' and rest enclosed in <nowiki>...</nowiki> quotes). http://lpaste.net/94688 I frequently find myself pretty unsatisfied with this type of code though. Anyone have any rewrites that would help teach me how to do this more elegantly in the future. Thanks! -Tyson PS: The mediawiki text I was using the above on has no existing <nowiki>...</nowiki> blocks.

3 3

Why do I need UndecidableInstances?
by Alejandro Serrano Mena 24 Oct '13

24 Oct '13

Dear café, I'm trying to compile a set of simple examples using Functional Dependencies. One of the first ones is the case of natural numbers, which I've defined along with some operations as: data Zero data Succ a class Plus x y z | x y -> z instance Plus Zero x x instance Plus x y z => Plus (Succ x) y (Succ z) class Max x y z | x y -> z instance Max Zero y y instance Max (Succ x) Zero (Succ x) instance Max x y z => Max (Succ x) (Succ y) (Succ z) I thought the compiler would accept this only with the extensions EmptyDataDecls, MultiParamTypeClasses, FunctionalDependencies and FlexibleInstances. But, to my surprise, GHC is also asking me for UndecidableInstances. Why is this the case? Thanks in advance :)

3 2

mongoDB performance problem
by 陈灿华 24 Oct '13

24 Oct '13

hi, any also find that mongoDB package is too slow. I have two programs that are almost the same, which one dumps document to stdout, the other one insert into mongodb, and the first one is hundreds times faster than the mongodb one. any one has ideas to tune the second one ? Thanks.

2 1

Stackage with GHC 7.8 has started
by Michael Snoyman 24 Oct '13

24 Oct '13

Hi everyone, I wanted to announce that FP Complete is now running a Jenkins job to build Stackage with GHC 7.8. You can see the current results in the relevant Github issue[1]. Essentially, we're still trying to get version bounds updated so that a build can commence. I'd like to ask two things from the community: * If you have a package with a restrictive upper bound, now's a good time to start testing that package with GHC 7.8 and relaxing those upper bounds. It would be great if, when GHC 7.8 is released, a large percentage of Hackage already compiled with it. * If you have a package on Hackage that is not yet on Stackage, now's a great time to add it. We're going to be doing daily builds against three versions of GHC (7.4.2, 7.6.3, and 7.8), which will help ensure your packages continue to build consistently. Michael [1] https://github.com/fpco/stackage/issues/128

6 11

Re: [Haskell-cafe] [ANN] IHaskell -- Haskell for Interactive Computing (via IPython)
by Andrew Gibiansky 24 Oct '13

24 Oct '13

Thank you for the correction, Ivan. I've pushed that change to IHaskell.cabal so that this doesn't trip anyone up in the future. IHaskell assumes that when you run 'cabal install', your IHaskell executable will be on the $PATH. (In order to run 'IHaskell setup', both your shell and IHaskell itself must be able to detect where the IHaskell executable is, because it needs to put that information into the IPython configuration it generates.) -- Andrew On Wed, Oct 23, 2013 at 2:18 AM, Triwanto Simanjuntak < simanjuntak.triwanto(a)gmail.com> wrote: > Andrew, > > The solution from Ivan made the installation of IHaskell successful. > However when creating IPython profile by invoking, "IHaskell setup", > gave error, "IHaskell: command not found". Is it because the > installation didn't make IHaskell on $Path ? > > Triwanto > simanjuntak.triwanto(a)gmail.com > > > On Wed, Oct 23, 2013 at 2:39 PM, Ivan Lazar Miljenovic > <ivan.miljenovic(a)gmail.com> wrote: > > On 23 October 2013 16:53, Andrew Gibiansky <andrew.gibiansky(a)gmail.com> > wrote: > >> Triwanto, > >> > >> IHaskell depends on the 'uuid' package and requires version 1.2.*. > Check to > >> make sure you have uuid installed. I build it with 1.2.13, and it looks > like > >> the most recent one is 1.2.14, which should also have that module [1]. > So, > >> before building, make sure you have uuid==1.2.* installed - I'm sort of > new > >> to cabal packaging, so perhaps my dependencies are not specified quite > >> correctly, but that is the issue that message seems to point to. > >> > >> Let me know how it goes. The full list of dependencies from the *.cabal > file > >> is as follows, in case you have other problems: > >> build-depends: base ==4.6.*, > >> zeromq3-haskell ==0.5.*, > >> aeson ==0.6.*, > >> MissingH ==1.2.*, > >> basic-prelude ==0.3.*, > >> classy-prelude ==0.6.*, > >> bytestring ==0.10.*, > >> uuid ==1.2.*, > >> containers ==0.5.*, > >> haskell-src-exts ==1.14.*, > >> ghc ==7.6.*, > >> ghc-paths ==0.1.*, > >> random ==1.0.*, > >> strict ==0.3.*, > >> shelly ==1.3.*, > >> text ==0.11.* > >> > >> Note that zeromq3-haskell will require zmq3 installed, and in saucy > that is > >> provided via 'apt-get install libzmq3-dev', I think. > > > > The .V4 module only seems to have appeared in version 1.2.6; as such > > you'll need to change the appropriate line to "uuid >= 1.2.6 && < 1.3" > > (assuming you have indeed tested and found that your code won't work > > with the 1.3.x versions). > > > >> > >> Andrew > >> > >> [1] > >> > http://haddocks.fpcomplete.com/fp/7.4.2/20130922-179/uuid/Data-UUID-V4.html > >> > >> > >> On Tue, Oct 22, 2013 at 10:11 PM, Triwanto Simanjuntak > >> <simanjuntak.triwanto(a)gmail.com> wrote: > >>> > >>> Andrew, > >>> > >>> I tried to install IHaskell on Ubuntu 13.10 (Saucy 64 bit) and recieved > >>> the following error > >>> > >>> Resolving dependencies... > >>> Configuring IHaskell-0.1.0.0... > >>> Building IHaskell-0.1.0.0... > >>> Preprocessing executable 'IHaskell' for IHaskell-0.1.0.0... > >>> > >>> IHaskell/Message/UUID.hs:10:8: > >>> Could not find module `Data.UUID.V4' > >>> Perhaps you meant > >>> Data.UUID.V1 (from uuid-1.2.3) > >>> Data.UUID.V3 (from uuid-1.2.3) > >>> Data.UUID.V5 (from uuid-1.2.3) > >>> Use -v to see a list of the files searched for. > >>> Failed to install IHaskell-0.1.0.0 > >>> cabal: Error: some packages failed to install: > >>> IHaskell-0.1.0.0 failed during the building phase. The exception was: > >>> ExitFailure 1 > >>> > >>> Any idea how to solve it? > >>> > >>> Thanks, > >>> > >>> Triwanto > >>> > >>> > >>> On Tuesday, October 22, 2013 4:32:10 AM UTC+7, Andrew Gibiansky wrote: > >>>> > >>>> Hey everyone! > >>>> > >>>> I'm excited to announce the initial release of IHaskell, a Haskell > >>>> language kernel for IPython: > >>>> > >>>> http://gibiansky.github.io/IHaskell > >>>> > >>>> IHaskell allows IPython to communicate with the kernel and evaluate > >>>> Haskell code. This enables using IPython interfaces such as console, > >>>> qtconsole, and most importantly, IPython notebook with Haskell. The > IPython > >>>> Notebook supports image, HTML, and LaTeX output, which enables things > such > >>>> as Javascript viewers for complex data structures or embedded graphs > and > >>>> makes it a great platform for interactive computing. > >>>> > >>>> You can take a look at the code and install instructions here: > >>>> > >>>> https://github.com/gibiansky/IHaskell > >>>> > >>>> A general overview of the architecture is available as well: > >>>> > >>>> http://andrew.gibiansky.com/blog/ipython/ipython-kernels/ > >>>> > >>>> Contributing: IHaskell is a very young project, but one that I think > >>>> would make a great contribution to the Haskell community. There's > still tons > >>>> and tons left to do before it's on par with what IPython notebook is > capable > >>>> of, so if you're at all interested in contributing, please get in > touch! > >>>> I've tried to keep everything well-documented and readable, but I > will also > >>>> be happy to answer questions about the code myself. > >>>> > >>>> If you find any bugs or edge cases or installation difficulties, > please > >>>> send me an email or create a Github issue for it! > >>>> > >>>> Thanks, > >>>> -- Andrew Gibiansky > >>>> > >>>> > >> > >> > >> _______________________________________________ > >> Haskell-Cafe mailing list > >> Haskell-Cafe(a)haskell.org > >> http://www.haskell.org/mailman/listinfo/haskell-cafe > >> > > > > > > > > -- > > Ivan Lazar Miljenovic > > Ivan.Miljenovic(a)gmail.com > > http://IvanMiljenovic.wordpress.com >

4 4

What's wrong with Hackage lately?
by Nikita Volkov 24 Oct '13

24 Oct '13

Recently two bugs settled on Hackage: 1. Page not found<http://hackage.haskell.org/package/base-4.6.0.1/docs/GHC-IO-Exception.html> for definitely existing pages. 2. Links starting with "file:///". Try any link on this page<http://hackage.haskell.org/package/pipes-network-0.6.0/docs/Pipes-Network-T…>, for example. Since it hasn't gotten fixed in at least a week, I am now wondering: why and where to report this?

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HackChi #1 - Nov 9 @ 1PM
by Jeremy Shaw 23 Oct '13

23 Oct '13

Hello, We are pleased to announce the first ever(?) Chicago Haskell Hackathon. There is a G+ invite here: https://plus.google.com/u/0/events/cc4njkf8kh5aho6soboisv6c7rc?authkey=CJD9… Hopefully I have the permissions set correctly. The contents of the invite are duplicated below. - jeremy Sat, November 9, 1:00 PM 1834 Ridge Ave #124, Evanston, IL 60201 We are please to announce the first Chicago Area Haskell Hackathon. What is as Hackathon? A Hackathon is basically just a bunch of people getting together and hacking on the Haskell code of their choice. It’s a great chance to meet other local Haskell hackers, discuss ideas, or just hack on code without other distractions. The Hackathon is open to people of all ages, experience, genders, races, orientations, etc. Never used Haskell before? We are going to kick things off with a ‘Get Started with Haskell’ session. Bring your laptop, and we’ll help you get Haskell installed and working and get your started on ‘Learn You a Haskell’ and other Haskell learning resources. Jeremy Shaw has volunteered to host this Hackathon at his place. This means we can bring our own food and drink and not have to worry about staying at a coffee house or other business for too long. You are highly encouraged to bring food, drinks, beer, etc. You can use the stove, oven, fridge, and propane grill if needed. The address is: 1834 Ridge Ave #124 Evanston, IL 60201 Dial 124 on the callbox to get in. You can also send email to jeremy(a)n-heptane.com or call 619-301-7429. The callbox sometimes fails to get through on the first try, so call more than once if you get sent to voicemail. Easily accessible via public transportation. Take the Purple Line or Metra and get off at the Davis stop. Head west towards Ridge. Cross over ridge and then head north 2-3 blocks on Ridge.

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Re: [Haskell-cafe] [ANN] IHaskell -- Haskell for Interactive Computing (via IPython)
by Andrew Gibiansky 23 Oct '13

23 Oct '13

Triwanto, IHaskell depends on the 'uuid' package and requires version 1.2.*. Check to make sure you have uuid installed. I build it with 1.2.13, and it looks like the most recent one is 1.2.14, which should also have that module [1]. So, before building, make sure you have uuid==1.2.* installed - I'm sort of new to cabal packaging, so perhaps my dependencies are not specified quite correctly, but that is the issue that message seems to point to. Let me know how it goes. The full list of dependencies from the *.cabal file is as follows, in case you have other problems: build-depends: base ==4.6.*, zeromq3-haskell ==0.5.*, aeson ==0.6.*, MissingH ==1.2.*, basic-prelude ==0.3.*, classy-prelude ==0.6.*, bytestring ==0.10.*, uuid ==1.2.*, containers ==0.5.*, haskell-src-exts ==1.14.*, ghc ==7.6.*, ghc-paths ==0.1.*, random ==1.0.*, strict ==0.3.*, shelly ==1.3.*, text ==0.11.* Note that zeromq3-haskell will require zmq3 installed, and in saucy that is provided via 'apt-get install libzmq3-dev', I think. Andrew [1] http://haddocks.fpcomplete.com/fp/7.4.2/20130922-179/uuid/Data-UUID-V4.html On Tue, Oct 22, 2013 at 10:11 PM, Triwanto Simanjuntak < simanjuntak.triwanto(a)gmail.com> wrote: > Andrew, > > I tried to install IHaskell on Ubuntu 13.10 (Saucy 64 bit) and recieved > the following error > > Resolving dependencies... > Configuring IHaskell-0.1.0.0... > Building IHaskell-0.1.0.0... > Preprocessing executable 'IHaskell' for IHaskell-0.1.0.0... > > IHaskell/Message/UUID.hs:10:8: > Could not find module `Data.UUID.V4' > Perhaps you meant > Data.UUID.V1 (from uuid-1.2.3) > Data.UUID.V3 (from uuid-1.2.3) > Data.UUID.V5 (from uuid-1.2.3) > Use -v to see a list of the files searched for. > Failed to install IHaskell-0.1.0.0 > cabal: Error: some packages failed to install: > IHaskell-0.1.0.0 failed during the building phase. The exception was: > ExitFailure 1 > > Any idea how to solve it? > > Thanks, > > Triwanto > > > On Tuesday, October 22, 2013 4:32:10 AM UTC+7, Andrew Gibiansky wrote: >> >> Hey everyone! >> >> I'm excited to announce the initial release of IHaskell, a Haskell >> language kernel for IPython: >> >> http://gibiansky.github.io/**IHaskell<http://gibiansky.github.io/IHaskell> >> >> IHaskell allows IPython to communicate with the kernel and evaluate >> Haskell code. This enables using IPython interfaces such as console, >> qtconsole, and most importantly, IPython notebook with Haskell. The IPython >> Notebook supports image, HTML, and LaTeX output, which enables things such >> as Javascript viewers for complex data structures or embedded graphs and >> makes it a great platform for interactive computing. >> >> You can take a look at the code and install instructions here: >> >> https://github.com/gibiansky/**IHaskell<https://github.com/gibiansky/IHaskell> >> >> A general overview of the architecture is available as well: >> >> http://andrew.gibiansky.com/**blog/ipython/ipython-kernels/<http://andrew.gibiansky.com/blog/ipython/ipython-kernels/> >> >> Contributing: IHaskell is a very young project, but one that I think >> would make a great contribution to the Haskell community. There's still >> tons and tons left to do before it's on par with what IPython notebook is >> capable of, so if you're at all interested in contributing, please get in >> touch! I've tried to keep everything well-documented and readable, but I >> will also be happy to answer questions about the code myself. >> >> If you find any bugs or edge cases or installation difficulties, please >> send me an email or create a Github issue for it! >> >> Thanks, >> -- Andrew Gibiansky >> >> >>

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[ANN] IHaskell -- Haskell for Interactive Computing (via IPython)
by Andrew Gibiansky 22 Oct '13

22 Oct '13

Hey everyone! I'm excited to announce the initial release of IHaskell, a Haskell language kernel for IPython: http://gibiansky.github.io/IHaskell IHaskell allows IPython to communicate with the kernel and evaluate Haskell code. This enables using IPython interfaces such as console, qtconsole, and most importantly, IPython notebook with Haskell. The IPython Notebook supports image, HTML, and LaTeX output, which enables things such as Javascript viewers for complex data structures or embedded graphs and makes it a great platform for interactive computing. You can take a look at the code and install instructions here: https://github.com/gibiansky/IHaskell A general overview of the architecture is available as well: http://andrew.gibiansky.com/blog/ipython/ipython-kernels/ Contributing: IHaskell is a very young project, but one that I think would make a great contribution to the Haskell community. There's still tons and tons left to do before it's on par with what IPython notebook is capable of, so if you're at all interested in contributing, please get in touch! I've tried to keep everything well-documented and readable, but I will also be happy to answer questions about the code myself. If you find any bugs or edge cases or installation difficulties, please send me an email or create a Github issue for it! Thanks, -- Andrew Gibiansky

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Extract text from PDF file: need testers
by Yuras Shumovich 21 Oct '13

21 Oct '13

Hello, I just uploaded new version of pdf-toolbox suite. Now it supports text extraction, see http://hackage.haskell.org/package/pdf-toolbox-document-0.0.2.0/docs/Pdf-To… New library, pdf-toolbox-content, contains low level tools for text extraction. For example, one can extract glyphs with exact positions. It can be used e.g. to implement text selection in PDF viewer (see screenshots). Is anybody interested in that functionality? I tested it on all PDF files in my ~/Downloads, but there is a number of corner cases that are not handled because I never saw them in the wild. So, if you are interested, please try it out and report any issue. The easiest way is to install pdf-toolbox-viewer (not on Hackage, see https://github.com/Yuras/pdf-toolbox/tree/master/viewer , it depends on gtk2hs) and run it with path to PDF file as an argument. Or you can just use pageExtractText function directly: import System.IO import Pdf.Toolbox.Document main = withBinaryFile "input.pdf" ReadMode $ \handle -> runPdfWithHandle handle knownFilters $ do pdf <- document catalog <- documentCatalog pdf rootNode <- catalogPageNode catalog count <- pageNodeNKids rootNode liftIO $ print count -- the first page of the document page <- pageNodePageByNum rootNode 0 txt <- pageExtractText page liftIO $ print txt Few screenshots (please let me know if you can't access them): - render via ImageMagick: https://docs.google.com/file/d/0B0K_fl2fc1ZgcnVtZXhFTUx5ekE/edit?usp=sharing - render extracted text with correct positions: https://docs.google.com/file/d/0B0K_fl2fc1ZgZE52X0hMcVNnaG8/edit?usp=sharing - combined image: https://docs.google.com/file/d/0B0K_fl2fc1ZgaUE5Qkt6S19VQlE/edit?usp=sharing On Hackage: - pdf-toolbox-document: http://hackage.haskell.org/package/pdf-toolbox-document - pdf-toolbox-core: http://hackage.haskell.org/package/pdf-toolbox-core - pdf-toolbox-content: http://hackage.haskell.org/package/pdf-toolbox-content Thanks, Yuras

1 0

Is Cabal ignoring "-with-rtsopts"?
by Alfredo Di Napoli 20 Oct '13

20 Oct '13

Hello guys, I'm integrating EKG in my webserver and I've stumbled upon a peculiar behaviour: Putting this inside my cabal manifest seems to not trigger any effect (EKG shows flat lines): GHC-Options: -Wall -threaded -Werror -fwarn-tabs -with-rtsopts=-T Whereas, if I run my webserver with "blablabla [...] +RTS -T" everything works as expected. What am I missing? I am on GHC 7.6.3, Cabal 1.18 and Mac OS X 64 bit. Alfredo

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Building GHC from source: where is libffi-tarballs.git?
by Magnus Therning 20 Oct '13

20 Oct '13

I thought I'd attempt a build of GHC from source. Following the instructions at [1], [2] and [3]. Unfortunately I get stuck: % ./sync-all --testsuite get == running git clone /home/magnus/Private/arch/archhaskell/ghc-git/libffi-tarballs.git libffi-tarballs fatal: repository '/home/magnus/Private/arch/archhaskell/ghc-git/libffi-tarballs.git' does not exist git failed: 32768 at ./sync-all line 120. How do I get past this point? /M [1]: https://github.com/ghc/ghc [2]: http://ghc.haskell.org/trac/ghc/wiki/Building/GettingTheSources [3]: http://ghc.haskell.org/trac/ghc/wiki/Building/QuickStart -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus The early bird may get the worm, but the second mouse gets the cheese.

1 1

[ZipList Monad] Final answer?
by Etsuji Nakai 19 Oct '13

19 Oct '13

Hi, I found a few interesting discussions on how to construct ZipList Monad in the past (around 2009). For example, http://www.haskell.org/pipermail/haskell-cafe/2009-April/059079.html But there seems no final answer to it. After a good discussion with one of my Haskell friends, we finally came up with the following one: import Control.Monad newtype MyZipList a = MyZipList [a] deriving (Show) getBase :: MyZipList a -> [a] getBase (MyZipList xs) = xs instance Monad MyZipList where return x = MyZipList $ repeat x m >>= f = MyZipList $ bind (getBase m) (fmap getBase f) where bind :: [a] -> (a -> [b]) -> [b] bind [] f = [] bind (x:xs) f = case f x of [] -> [] y:_ -> y : bind xs (fmap tailOrNil f) tailOrNil :: [b] -> [b] tailOrNil [] = [] tailOrNil (x:xs) = xs This is fairly simple and looks to work with variable length lists. Do you think this could be the final answer? - Etsuji

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Building examples with Cabal
by Sven Panne 18 Oct '13

18 Oct '13

Is there a way to build examples in a Haskell package with Cabal without actually running them? "cabal test" and "cabal benchmark" don't really do what I want, I just want to check if e.g. all GLUT examples in https://github.com/haskell-opengl/GLUT/tree/master/examples still build after some API changes. Another requirement would be parallel builds, I want to actually use the 32 cores I have under my desk. ;-) Currently I use a recursive "make" infrastructure (https://github.com/haskell-opengl/GLUT/blob/master/examples/Makefile) which works OK, but it is quite a hack, is partly incorrect and, well, needs "make".

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Re: [Haskell-cafe] Xcode 5 support for GHC iOS
by Luke Iannini 18 Oct '13

18 Oct '13

Hi Dominick! Yes, this should work swimmingly on the 5S in 32bit mode. We'll have to wait for Apple to merge their Arm64 patches [1] before we can add full 64-bit support (I can do the 64bit simulator right now though : )). (though I just saw this! [2]) Cheers Luke [1] http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-September/065480.html [2] http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-September/065913.html On Wed, Oct 16, 2013 at 8:16 AM, Dominick Samperi <djsamperi(a)gmail.com>wrote: > Will this work with the new iPhone 5 S (64 bit ARM)? I assume that > it will work by running in 32 bit mode (requiring both 64 and 32 bit > libs to be loaded), but I'm not sure... > > Thanks, > Dominick > > > On Mon, Oct 14, 2013 at 3:48 PM, Luke Iannini <lukexipd(a)gmail.com> wrote: > >> Hi all, >> >> Just wanted to let you know I've finished updating GHC iOS to support >> Xcode 5. The new scripts are at >> https://github.com/ghc-ios/ghc-ios-scripts/tree/xcode5 and you'll find >> updated instructions at >> http://ghc.haskell.org/trac/ghc/wiki/Building/CrossCompiling/iOS . >> >> Please let me know if you have any trouble! >> Cheers >> Luke >> >> _______________________________________________ >> ghc-devs mailing list >> ghc-devs(a)haskell.org >> http://www.haskell.org/mailman/listinfo/ghc-devs >> >> >

3 3

installing glib-0.12.4 on Mac
by Kazu Yamamoto 17 Oct '13

17 Oct '13

Hi, When I tried to install glib-0.12.3 on OS X 10.8.5 with GHC 7.6.3, I got the following error: ---- 1 of 2] Compiling Gtk2HsSetup ( Gtk2HsSetup.hs, dist/setup-wrapper/Gtk2HsSetup.o ) [2 of 2] Compiling Main ( SetupMain.hs, dist/setup-wrapper/Main.o ) Linking dist/setup-wrapper/setup ... Configuring glib-0.12.4... Building glib-0.12.4... Preprocessing library glib-0.12.4... gtk2hsC2hs: Error in C header file. /usr/include/dirent.h:147: (column 10) [FATAL] >>> Syntax error! The symbol `^' does not fit here. Failed to install glib-0.12.4 ---- I believe I could install it on 31 July 2013 and I don't think I changed anything. Does anyone know how to fix this? --Kazu

2 1

Haskell.org committee self-nomination time
by Jason Dagit 17 Oct '13

17 Oct '13

Dear Haskellers, Another year of the haskell.org committee is drawing to a close and it is therefore time to seek replacements for those members whose term is expiring. This year three members are retiring, Edward Z. Yang, Vo Minh Thu, and Mark Lentczner. The rest of the committee would like to thank them for their excellent service. To nominate yourself, please send an e-mail to committee at haskell.org by 29 October 2013. The retiring members are eligible to re-nominate themselves. Please feel free to include any information about yourself that you think will help us to make a decision. Being a member of the committee does not require a significant amount of time, but committee members should aim to be responsive during discussions when the committee is called upon to make a decision. Strong leadership, communication, and judgement are very important characteristics for committee members. The role is about setting policy, providing direction/guidance for the Haskell.org infrastructure, planning for the long term, and being fiscally responsible with the Haskell.org funds (and donations). As overseers for policy regarding the open source side of Haskell, committee members must also be able to set aside personal or business related bias and make decisions with the good of the open source Haskell community in mind. More details about the committee's roles and responsibilities are on http://www.haskell.org/haskellwiki/Haskell.org_committee If you have any questions about the process, please feel free to e-mail us at committee at haskell.org or to contact one of us individually. Regards, Jason

1 0

Eternal Compatibility in Theory
by Corentin Dupont 17 Oct '13

17 Oct '13

Hi Café, I've read the Eternal Compatibility in Theory article [1], is anyone actually using it? I don't see it discussed very much on the internet. My biggest concern about it is that it would be a real pollution in the code, because you must import every module with its version number, i.e. * * *import Data.Maybe_1* instead of * **import Data.Maybe* Thus poluting a lot with version numbers, which are not relevant to what the source code should aim at: help the reader understand it. Secondly, does it means that, as the developper of a package, I have to leave all the previous versions of a module in that package? I.e: Maybe_1.hs, Maybe_2.hs would have to stay in my package? This seems to be very polluting and redundant. So the proposition seems to be "versionning and dependency management are a problem, so let's remove the problem by leaving all previous versions in the package". Did I misunderstood something? Cheers, Corentin [1] http://www.haskell.org/haskellwiki/The_Monad.Reader/Issue2/EternalCompatibi…

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Embarrassed Haskeller -- why is Read so bad? What are alternatives?
by Ryan Newton 17 Oct '13

17 Oct '13

We have great tools for [de]serializing both to binary and to JSON (binary, cereal, json, aeson, etc). But we have rather weak support for [de]serializing to human readable Haskell-ish external formats. Read instances are both (1) slow, because they take Strings, and (2) they don't allow sensible error messages! (Historical decision choosing Maybe rather than Either.) Right now I'm working on a project with a Racketeer who is trying to read a 6000 line file as a single list data structure. The derived Read instance is just telling him it won't parse, with NO error information, line number etc. To someone used to Scheme readers, that's rather poor. I wish I had something better to tell him! I am not aware of a library to recommend other than switching to JSON format on disk. OR manually kludging together a parsing hack that, for example, puts one element of the list on each line and makes much smaller calls to "read". Argh!, -Ryan

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Haskell Weekly News: Issue 283
by Daniel Santa Cruz 17 Oct '13

17 Oct '13

Welcome to issue 283 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of October 06 to 12, 2013. Quotes of the Week * elliott: haskell programs allocate a lot because they can't do much else * spj: [on pointfree style] It has a certain eccentric charm all of its own. * acowley: When we pick a random number, we stick to it. Top Reddit Stories * Simon Peyton Jones on Lenses at the Haskell eXchange Skillscast now available! Domain: skillsmatter.com, Score: 127, Comments: 107 On Reddit: [1] http://goo.gl/V6J6dR Original: [2] http://goo.gl/Kc1zEf * Why I don’t like the lens library Domain: fvisser.nl, Score: 99, Comments: 104 On Reddit: [3] http://goo.gl/Xz6p6C Original: [4] http://goo.gl/ZzxSOU * Cartesian Closed Comic #23: Picking a lens library Domain: ro-che.info, Score: 85, Comments: 8 On Reddit: [5] http://goo.gl/mXXUQw Original: [6] http://goo.gl/Bi2UIW * The core flaw of pipes and conduit Domain: yesodweb.com, Score: 45, Comments: 101 On Reddit: [7] http://goo.gl/tfSZ2Z Original: [8] http://goo.gl/5CpF2I * How to reimplement the conduit parsing API in pipes Domain: haskellforall.com, Score: 43, Comments: 16 On Reddit: [9] http://goo.gl/xQ9f93 Original: [10] http://goo.gl/iqFxfs * pipes resource problems Domain: yesodweb.com, Score: 40, Comments: 74 On Reddit: [11] http://goo.gl/9FpIwz Original: [12] http://goo.gl/tj0LbW * Beginners cheatsheet to the lens library Domain: haskell.org, Score: 40, Comments: 59 On Reddit: [13] http://goo.gl/I2i2or Original: [14] http://goo.gl/Y8znDQ * Demo: Ariadne, go-to-definition for Haskell Domain: youtube.com, Score: 39, Comments: 35 On Reddit: [15] http://goo.gl/KC1D5m Original: [16] http://goo.gl/0lqLPh * Do Extraterrestrials Use Functional Programming? Domain: justtesting.org, Score: 39, Comments: 39 On Reddit: [17] http://goo.gl/FZos1f Original: [18] http://goo.gl/RaIEZF * Haskell for all: Manual proofs for the `pipes` laws Domain: haskellforall.com, Score: 37, Comments: 55 On Reddit: [19] http://goo.gl/rhLmBC Original: [20] http://goo.gl/cmiDln * Unique PDFs linked in #haskell Domain: ircbrowse.net, Score: 36, Comments: 13 On Reddit: [21] http://goo.gl/mNNkM7 Original: [22] http://goo.gl/7Sj2si * Andres Löh on free monads Domain: skillsmatter.com, Score: 36, Comments: 15 On Reddit: [23] http://goo.gl/2sRcxC Original: [24] http://goo.gl/fvLiRn * Simpler conduit core (aka part 3 of 3) Domain: fpcomplete.com, Score: 36, Comments: 23 On Reddit: [25] http://goo.gl/V3FutZ Original: [26] http://goo.gl/4qYkRj * Proposal for Applicative do-notation Domain: ghc.haskell.org, Score: 36, Comments: 50 On Reddit: [27] http://goo.gl/skxmph Original: [28] http://goo.gl/st8iOp * So I (kind of) made a Haskell clone of the business card Ray Tracer Domain: github.com, Score: 35, Comments: 14 On Reddit: [29] http://goo.gl/tZZMnH Original: [30] http://goo.gl/G1hzjt * Call to Action - Fay FFI Bindings for AngularJS Domain: haskell.org, Score: 35, Comments: 16 On Reddit: [31] http://goo.gl/en6th1 Original: [32] http://goo.gl/g5T8TJ * The Haxl project at Facebook: concise, efficient access to diverse data sources Domain: skillsmatter.com, Score: 34, Comments: 9 On Reddit: [33] http://goo.gl/vEKNKb Original: [34] http://goo.gl/HKaMmn * Rethinking Supercompilation [PDF] Domain: community.haskell.org, Score: 34, Comments: 17 On Reddit: [35] http://goo.gl/IVwvdi Original: [36] http://goo.gl/BuaaXW * Musings on Lens Domain: gist.io, Score: 31, Comments: 9 On Reddit: [37] http://goo.gl/akld2Z Original: [38] http://goo.gl/CdPtlT Top StackOverflow Questions * Functions of possibly cyclic data structures votes: 12, answers: 1 Read on SO: [39] http://goo.gl/SBPV2t * How can I improve my understanding of the Haskell Type system? votes: 11, answers: 2 Read on SO: [40] http://goo.gl/HLsynN * Haskell: how to tell hlint not to: `Warning: Use string literal` votes: 7, answers: 1 Read on SO: [41] http://goo.gl/pf5d5O * How are uncurry and fanin related in category theory? votes: 7, answers: 1 Read on SO: [42] http://goo.gl/mo9150 * Haskell Iterate over 2d list, filter, output 1d list votes: 7, answers: 6 Read on SO: [43] http://goo.gl/h47C9e * Haskell why does “Num x” require “Show x”? votes: 7, answers: 3 Read on SO: [44] http://goo.gl/ORddsf * How to avoid creating an orphan FromJSON instance for Data.Tree votes: 7, answers: 1 Read on SO: [45] http://goo.gl/5MAI2k * State Monad with multiple state values votes: 6, answers: 3 Read on SO: [46] http://goo.gl/iuutId * Difference between Print and putStrLn in Haskell votes: 6, answers: 2 Read on SO: [47] http://goo.gl/GqUunm Until next time, [48]+Daniel Santa Cruz References 1. http://skillsmatter.com/podcast/scala/lenses-compositional-data-access-and-… 2. http://www.reddit.com/r/haskell/comments/1o1z8x/simon_peyton_jones_on_lense… 3. http://fvisser.nl/post/2013/okt/11/why-i-dont-like-the-lens-library.html 4. http://www.reddit.com/r/haskell/comments/1o6iqs/why_i_dont_like_the_lens_li… 5. http://ro-che.info/ccc/23 6. http://www.reddit.com/r/haskell/comments/1obeom/cartesian_closed_comic_23_p… 7. http://www.yesodweb.com/blog/2013/10/core-flaw-pipes-conduit 8. http://www.reddit.com/r/haskell/comments/1o1ink/the_core_flaw_of_pipes_and_… 9. http://www.haskellforall.com/2013/10/how-to-reimplement-conduit-parsing-api… 10. http://www.reddit.com/r/haskell/comments/1o3viw/how_to_reimplement_the_cond… 11. http://www.yesodweb.com/blog/2013/10/pipes-resource-problems 12. http://www.reddit.com/r/haskell/comments/1nw7ji/pipes_resource_problems/ 13. http://www.haskell.org/haskellwiki/LensBeginnersCheatsheet 14. http://www.reddit.com/r/haskell/comments/1oa9qx/beginners_cheatsheet_to_the… 15. https://www.youtube.com/watch?v=-sbGijbhxAc 16. http://www.reddit.com/r/haskell/comments/1nvauj/demo_ariadne_gotodefinition… 17. http://justtesting.org/post/63457249417/here-is-the-video-of-my-yow-lambda-… 18. http://www.reddit.com/r/haskell/comments/1nz5j5/do_extraterrestrials_use_fu… 19. http://www.haskellforall.com/2013/10/manual-proofs-for-pipes-laws.html 20. http://www.reddit.com/r/haskell/comments/1nw7yt/haskell_for_all_manual_proo… 21. http://ircbrowse.net/pdfs/haskell/unique 22. http://www.reddit.com/r/haskell/comments/1o23nf/unique_pdfs_linked_in_haske… 23. http://skillsmatter.com/podcast/scala/monads-for-free 24. http://www.reddit.com/r/haskell/comments/1o38fa/andres_l%C3%B6h_on_free_mon… 25. https://www.fpcomplete.com/user/snoyberg/blog-posts/simpler-conduit-core 26. http://www.reddit.com/r/haskell/comments/1o494w/simpler_conduit_core_aka_pa… 27. http://ghc.haskell.org/trac/ghc/wiki/ApplicativeDo 28. http://www.reddit.com/r/haskell/comments/1o7lpm/proposal_for_applicative_do… 29. https://github.com/RommelVR/RayTracer 30. http://www.reddit.com/r/haskell/comments/1nuhze/so_i_kind_of_made_a_haskell… 31. http://www.haskell.org/pipermail/haskell-cafe/2013-October/218522.html 32. http://www.reddit.com/r/haskell/comments/1o4x3m/call_to_action_fay_ffi_bind… 33. http://skillsmatter.com/podcast/home/simon-marlow 34. http://www.reddit.com/r/haskell/comments/1o2mqe/the_haxl_project_at_faceboo… 35. http://community.haskell.org/~ndm/temp/supero.pdf 36. http://www.reddit.com/r/haskell/comments/1o8ksw/rethinking_supercompilation… 37. http://gist.io/6923187 38. http://www.reddit.com/r/haskell/comments/1o63ww/musings_on_lens/ 39. http://stackoverflow.com/questions/19337153/functions-of-possibly-cyclic-da… 40. http://stackoverflow.com/questions/19247753/how-can-i-improve-my-understand… 41. http://stackoverflow.com/questions/19237695/haskell-how-to-tell-hlint-not-t… 42. http://stackoverflow.com/questions/19262581/how-are-uncurry-and-fanin-relat… 43. http://stackoverflow.com/questions/19308845/haskell-iterate-over-2d-list-fi… 44. http://stackoverflow.com/questions/19327792/haskell-why-does-num-x-require-… 45. http://stackoverflow.com/questions/19336569/how-to-avoid-creating-an-orphan… 46. http://stackoverflow.com/questions/19227418/state-monad-with-multiple-state… 47. http://stackoverflow.com/questions/19288652/difference-between-print-and-pu… 48. https://plus.google.com/105107667630152149014/about

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Sublime Text
by Graham Berks 16 Oct '13

16 Oct '13

Anyone using sublime haskell with sublime repl and have the cabal integration working ? >From what I understand, you can get ghci loaded with the modules / reps from the cabal file. But I can't seem to get this to work. Thanks

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Announce: HDBI-1.3 and friends
by Alexey Uimanov 16 Oct '13

16 Oct '13

Hello haskellers! HDBI is the fork of HDBC but reworked. It supports SQlite3 and Postgresql for now. It also supports streaming with coduits. There is TH deriving mechanism to map database rows to Haskell structures and back. HDBI is trying to become simple but still powerfull and flexible database interface. It must be suitable to become the common RDBMS interface for higher level interfaces like persistent or haskelldb. The documentation is not very good, while I have no enough time to make some. In this version changed typeclass signatures of Connection and Statement. Now methods `run` and `execute` get any instance of `ToRow` and method `fetch` return an instance of `FromRow`. Note that [SqlValue] is also an instance of `FromRow` and `ToRow` typeclasses so you do not loose the control. Methods `fromRow` and `toRow` for [SqlValue] are just `id`. SQlite and Postgresql drivers are fixed as well as hdbi-conduit. There is also new helper functions, like `onei :: Integer -> [SqlValue]` which helps you to execute queries with one parameter or execute many queries consistinf of one parameter. Prelude Database.HDBI Database.HDBI.SQlite> :set -XScopedTypeVariables Prelude Database.HDBI Database.HDBI.SQlite> :set -XOverloadedStrings Prelude Database.HDBI Database.HDBI.SQlite> c <- connectSqlite3 ":memory:" Prelude Database.HDBI Database.HDBI.SQlite> runRaw c "create table test(val integer)" Prelude Database.HDBI Database.HDBI.SQlite> withTransaction c $ runMany c "insert into test(val) values (?)" $ map one [1..1000] <interactive>:7:76: Warning: Defaulting the following constraint(s) to type `Integer' ......... Prelude Database.HDBI Database.HDBI.SQlite> r :: (Maybe Integer) <- runFetchOne c "select sum(val) from test" () Prelude Database.HDBI Database.HDBI.SQlite> r Just 500500 Note here that the empty set is used as a parameter of query in `runFetchOne`. Empty set is an instance of `FromRow` and `ToRow` and return an empty list of [SqlValue]. Use empty list as a parameters is bad idea, because we could instantiate some another list of things, suppose the [Integer] as `FromRow` and `ToRow` instance. So it would lead to ambigous type because [SqlValue] is also a list instantiating `FromRow` and `ToRow`.

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