January 2013 - Haskell-Cafe

DIY vs as-a-Service with MemCachier
by Kazu Yamamoto 17 Jan '13

17 Jan '13

Hello, The following blog post by Joyent is worth reading: http://joyent.com/blog/diy-vs-as-a-service-with-memcachier "We don't really believe in Node.js (Go & Haskell are our choices), so that is a small concern to us, but everyone has their failings." --Kazu

3 2

ANN: hoodle-0.1.1
by Ian-Woo Kim 16 Jan '13

16 Jan '13

Hi, hoodle lovers :-) I am pleased to announce hoodle v0.1.1. In this version, I added the following functionality and made several improvement. * context (popup) menu support : after you select, you will see a context menu for the selected items (make pdf, make svg, cut, copy, delete ...) You can also make your own context menu by scripting $HOME/.hoodle.d/start.hs. I will explain this later in this email. * text input support : text can be entered. currently font cannot be changed yet. * SVG import support : SVG can be imported as vector graphics * JPG import support : in addition to PNG, now JPG can be imported * embedding image : by default, hoodle now embed image in the file. It can be turned off by checking off in option menu. * full screen mode support * color picker support * rendering engine is improved much I have added the following experimental functions. * LaTeX input support (more precisely itex and MathML) : using lasem library ( https://live.gnome.org/Lasem git repository : http://git.gnome.org/cgit/lasem/ ), mathematical expression input is supported. * smooth scrolling Internally, hoodle generates SVG image from text (and latex input), so that it can be viewed exactly the same for any computer and font configuration. Hoodle has a scripting support like xmonad. If you have $HOME/.hoodle.d/start.hs , then the script will be automatically compiled using dyre and you can customize your hoodle. There are not so many hooks available yet, but I will add more and more hooks as time goes. Currently, I use file name suggestion hook (using current date/time) and custom context menu. (using this, I automatically generate png image from selected items and put it on my dropbox folder. This turned out extremely useful.) See my example start.hs : https://gist.github.com/4551914 Installation is always simple :-) after > cabal update you can install hoodle without poppler (pdf rendering support) > cabal install hoodle or with poppler (pdf rendering support) : recommended > cabal install -fpoppler hoodle-render hoodle-core hoodle If you have previous version of hoodle on your system, to uninstall previous version > ghc-pkg unregister coroutine-object --force > ghc-pkg unregister hoodle-types --force > ghc-pkg unregister xournal-types --force then install using cabal as above. Please give it a try. Hope that you will enjoy the new version. best, Ian-Woo Kim p.s. if you are interested in hoodle development and any questions about using hoodle, please subscribe to hoodle google group ( https://groups.google.com/forum/?fromgroups#!forum/hoodle ) . Issuing at http://github.com/wavewave/hoodle is also very welcome. Thanks!

1 0

9.3 - (2 * 4.5) => 0.3000000000000007
by ivan dragolov 16 Jan '13

16 Jan '13

9.3 - (2 * 4.5) => 0.3000000000000007 I expected 0.3 ? -- Иван Драголов dragolov.net GSM: 0888 63 19 46 GSM за SMS: 0878 82 83 93 facebook.com/ivan.dragolov twitter.com/dragolov

9 9

Type hierarchy
by Thiago Negri 16 Jan '13

16 Jan '13

Hello. How do I achieve type hierarchy in Haskell? Suppose we have the following code: foo :: A -> C bar :: B -> C I want something that allow me to say that B is a subtype of A, meaning: 1. I can use a value of type A where a value of type A is needed. 2. I can use a value of type B where a value of type B is needed. 3. I can use a value of type B where a value of type A is needed. 4. I can't use a value of type A where a value of type B is needed. What are my options? I've thought in type classes and data types with an attribute representing the extension. Any other way to do this? Thanks, Thiago.

3 3

ANN: Hakyll 4
by Jasper Van der Jeugt 16 Jan '13

16 Jan '13

After a few weeks of beta status [1], I've now released version 4.0 of the Hakyll static site generator library. I'm really glad with this release, as from what I've found and heard, it makes many things a lot easier. # Main changes - The important `Compiler` type has been changed from `Arrow` to `Monad`: this makes it much easier to write custom compilers, as most Haskellers are more familiar with monads. - The template stays superficially the same, but it has grown much more powerful and flexible underneath. - Early and fast access to metadata makes things such as tags and pagination much easier. - All items (images, css...) can now have metadata associated. Metadata can no longer be manipulated, and this immutability should reduce the number of encountered bugs. - A `check` command has been added. This allows you to check that all internal (or external) links are still alive. # Installation, migration In order to install Hakyll 4, grab it from Hackage: cabal update cabal install hakyll Here are some useful links: - Website: <http://jaspervdj.be/hakyll/> - Tutorial index: <http://jaspervdj.be/hakyll/tutorials.html> - Migration guide: <http://jaspervdj.be/hakyll/tutorials/hakyll-3-to-hakyll4-migration-guide.ht…> All feedback is welcome as always. [1]: https://groups.google.com/d/topic/hakyll/eRKWz8bVB0w/discussion Peace, Jasper

1 0

PhD studentships in Nottingham
by Graham Hutton 16 Jan '13

16 Jan '13

Dear all, The School of Computer Science in Nottingham is advertising a number of PhD studentships. Applicants in the area of the Functional Programming Lab (fp.cs.nott.ac.uk) would be very welcome. If you are interested in applying, please contact a potential academic supervisor in the FP lab prior to submitting your application. Note that I'm not available to supervise new students myself this coming academic year. Graham Hutton University of Nottingham +---------------------------------------------------------------+ Fully-Funded PhD Studentships School of Computer Science University of Nottingham, UK Applications are invited for a number of fully-funded PhD studentships in the School of Computer Science at the University of Nottingham, starting on 1st October 2013. The topics for the studentships are open, but will relate to the research interests of existing members of staff within the School. Applicants should have discussed their interest and obtained the support of a named potential supervisor before applying. The studentships are for three years and include a maintenance grant of 13,726 UK pounds per year and tuition fees for UK students. The positions are open to students of any nationality, but non-UK students will require additional funding to cover tuition fees, which is awarded by the University on a competitive basis. Applicants will normally require a first-class Undergraduate or Masters degree in Computer Science or a related discipline. Informal enquiries may be addressed to Christine Fletcher <Christine.Fletcher(a)nottingham.ac.uk>. To apply, please submit the following items by email to the above address: (1) a brief covering letter that describes your reasons for wishing to pursue a PhD, any ideas you have regarding possible areas or topics, and the name of a potential supervisor; (2) a copy of your CV, including your actual or expected degree class(es), and results of all University examinations; (3) an example of your technical writing, such as a project report or dissertation; (4) contact details for two academic referees. *Closing date for applications:* 8th February 2013 +---------------------------------------------------------------+ -- Prof Graham Hutton Functional Programming Lab School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~gmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

1 0

How to disable document in .cabal file?
by Magicloud Magiclouds 16 Jan '13

16 Jan '13

Hi, I have enabled document in .cabal/config, so I could get document every time I installed libraries or so. But when I compile my own applications, it also takes time on generating non-exist documents. How to disable it just for this project? -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

4 9

Makefile for a Haskell Project
by xuan bach 15 Jan '13

15 Jan '13

Hi everyone, I'm a newbie in Haskell. I'm wondering that if there is any tool support creating Makefile for Haskell project like Ocamlbuild for Ocaml project? Thank you, Regards. -- *Le Dinh Xuan Bach* *Tel: 01234711869 or +65 86967149 * *Email: pig28789(a)gmail.com School of Information and Communication, * *Hanoi University of Science and Technology --------------------------------------------------------------------- レ。ディン。スアン。バイック電話番号：01234711869 or +65 86967149 メール： pig28789(a)gmail.com *

5 7

hackage builds stopped?
by Alberto G. Corona 15 Jan '13

15 Jan '13

What is the schedule of the hackage builds?. My package has been uploaded since three days ago, and it has not been compiled yet... -- Alberto.

1 1

Cannot read a large integer on linux
by Arnaud Bailly 14 Jan '13

14 Jan '13

Hello, I am encountering a strange issue while trying to read a string into an integer. On windows 7 64bit, I have: > read "18780189038289e49" :: Integer =187801890382890000000000000000000000000000000000000000000000000 On linux (64bit, libgmp.so.3.5.2) I have: > read "18780189038289e49" :: Integer *** Exception: Prelude.read: no parse That's weird and I really have no clue what's going on. I use ghci 7.4.2 on linux and 7.4.1 on windows. What am I doing wrong ? Arnaud

3 2