October 2013 - Haskell-Cafe

Munich Haskell Meeting
by Heinrich Hördegen 29 Oct '13

29 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 28 Oct '13

28 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$

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