April 2014 - Haskell-Cafe

How to get access to Haddock HTML for newly cabal installed package?
by David Banas 24 Apr '14

24 Apr '14

Does anyone know how I get the link to the Haddock generated HTML for a newly cabal installed package to show up in: file:///Users/dbanas/Library/Haskell/doc/index.html ? I’ve got documentation=True set, in ~/.cabal/config. Thanks, -db

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Diony Rosa
by Diony Rosa 24 Apr '14

24 Apr '14

http://kagankoc.av.tr/wpjbk/fowmsjjzqavbptwpdmgezeghq.wiodhkueoruzhok

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ANN: Monad.Reader Issue 23
by Edward Z. Yang 24 Apr '14

24 Apr '14

I am pleased to announce that Issue 23 of the Monad Reader is now available. http://themonadreader.files.wordpress.com/2014/04/issue23.pdf http://themonadreader.wordpress.com/2014/04/23/issue-23/ Issue 23 consists of the following five articles: * FizzBuzz in Haskell by Embedding a Domain-Specific Language by Maciej Pírog http://themonadreader.files.wordpress.com/2014/04/fizzbuzz.pdf * Supercompilation: Ideas and Methods (+appendix) by Ilya Klyuchnikov and Dimitur Krustev http://themonadreader.files.wordpress.com/2014/04/super-final.pdf * A Haskell sound specification DSL: Ludic support and deep immersion in Nordic technology-supported LARP by Henrik Bäärnhielm, Daniel Sundström and Mikael Vejdemo-Johansson http://themonadreader.files.wordpress.com/2014/04/celestria_main.pdf * MFlow, a continuation-based web framework without continuations by Alberto Gomez Corona http://themonadreader.files.wordpress.com/2014/04/mflow.pdf * Practical Type System Benefits by Neil Brown http://themonadreader.files.wordpress.com/2014/04/nccb.pdf This time around, I have individual article files for each (and the supercompilation article has an extra appendix not included in the full issue PDF). Feel free to browse the source files. You can check out the entire repository using Git: git clone https://github.com/ezyang/tmr-issue23.git If you’d like to write something for Issue 24, please get in touch! Cheers, Edward

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Haskell Weekly News: Issue 292
by Daniel Santa Cruz 24 Apr '14

24 Apr '14

Welcome to issue 292 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from April 13 to 19, 2014 Edward Kemett wrote in to remind us of the Call For Proposals for CUFP 2014, which is going to be held in Gothenburg, Sweden between September 4-6. See more details here [1] http://goo.gl/X62cBO Quotes of the Week * pdxleif: see s.p. jones & h.p. lovecraft's paper on the subject: "generic programming with lenses, barbed wire, and the fibres of sanity" Top Reddit Stories * A time traveling debugger for Elm - pause, rewind, replay, and change history Domain: debug.elm-lang.org, Score: 87, Comments: 6 On Reddit: [2] http://goo.gl/GJahIU Original: [3] http://goo.gl/V2kcCP * OC: Haskell programming font with ligatures Domain: github.com, Score: 78, Comments: 59 On Reddit: [4] http://goo.gl/ZaFRJ4 Original: [5] http://goo.gl/m17EUj * Porting GHC: A Tale of Two Architectures Domain: chiark.greenend.org.uk, Score: 77, Comments: 12 On Reddit: [6] http://goo.gl/MJ196R Original: [7] http://goo.gl/PVVHZo * Try Idris Domain: tryidris.org, Score: 70, Comments: 22 On Reddit: [8] http://goo.gl/7hn84J Original: [9] http://goo.gl/6iPW8S * Why are examples completely absent from hackage? Am I missing something? Domain: self.haskell, Score: 67, Comments: 68 On Reddit: [10] http://goo.gl/QmZjZs Original: [11] http://goo.gl/QmZjZs * Implementing Python in Haskell - Melbourne Haskell Users Group, April 24 Domain: meetup.com, Score: 53, Comments: 6 On Reddit: [12] http://goo.gl/tYRtG9 Original: [13] http://goo.gl/oClHGb * Blog post - Haskell Gets Static Typing Right - Andres Löh Domain: skillsmatterblog.wordpress.com, Score: 51, Comments: 25 On Reddit: [14] http://goo.gl/5AQO4h Original: [15] http://goo.gl/WddMUA * Haskell for all: Scalable program architectures Domain: haskellforall.com, Score: 45, Comments: 19 On Reddit: [16] http://goo.gl/JDYSQl Original: [17] http://goo.gl/MUrRRg * GHC 7.8′s -staticlib flag makes compiling Mac libs easy Domain: maxs.io, Score: 42, Comments: 5 On Reddit: [18] http://goo.gl/SVICOm Original: [19] http://goo.gl/FwVdOv * Autocomplete command line options with GHC 7.8 Domain: self.haskell, Score: 39, Comments: 10 On Reddit: [20] http://goo.gl/bXNI20 Original: [21] http://goo.gl/bXNI20 * How to learn Haskell Domain: acm3.wustl.edu, Score: 39, Comments: 16 On Reddit: [22] http://goo.gl/oaQsAL Original: [23] http://goo.gl/TLbCEL * Calling Python from Haskell Domain: lunaryorn.com, Score: 36, Comments: 14 On Reddit: [24] http://goo.gl/9n8O4m Original: [25] http://goo.gl/j8YqgK * "latest API" link in Hackage Domain: self.haskell, Score: 30, Comments: 15 On Reddit: [26] http://goo.gl/RJnphF Original: [27] http://goo.gl/RJnphF * Functional Pearl: F for Functor Domain: cs.ox.ac.uk, Score: 27, Comments: 14 On Reddit: [28] http://goo.gl/i7TPuf Original: [29] http://goo.gl/7c33Xn Top StackOverflow Questions * Idris eager evaluation votes: 14, answers: 1 Read on SO: [30] http://goo.gl/LDpNtI * Why use such a peculiar function type in monads? votes: 11, answers: 4 Read on SO: [31] http://goo.gl/XX8KSX * How does mapA work with a Stream Function Arrow in Haskell? votes: 8, answers: 1 Read on SO: [32] http://goo.gl/vECKBa * Lenses and Monomorphism Restriction votes: 8, answers: 2 Read on SO: [33] http://goo.gl/hG44KA * Is this a GHC bug? votes: 7, answers: 1 Read on SO: [34] http://goo.gl/sqByI2 * Why do some of threepenny-gui FRP combinators operate on a MonadIO monad instead of being pure? votes: 6, answers: 2 Read on SO: [35] http://goo.gl/ySVqya * S combinator in Haskell votes: 6, answers: 2 Read on SO: [36] http://goo.gl/vnb64N * Graphing criterion benchmarks taking different orders of magnitude of time votes: 6, answers: 1 Read on SO: [37] http://goo.gl/J3jgWf * Fun with fixity votes: 6, answers: 1 Read on SO: [38] http://goo.gl/molyi9 Until next time, [39]+Daniel Santa Cruz References 1. http://cufp.org/2014cfp 2. http://debug.elm-lang.org/ 3. http://www.reddit.com/r/haskell/comments/233ff9/a_time_traveling_debugger_f… 4. https://github.com/i-tu/source-code-pro-L/ 5. http://www.reddit.com/r/haskell/comments/23g9dv/oc_haskell_programming_font… 6. http://www.chiark.greenend.org.uk/ucgi/~cjwatson/blosxom/2014-04-15-porting… 7. http://www.reddit.com/r/haskell/comments/232erb/porting_ghc_a_tale_of_two_a… 8. http://www.tryidris.org/console 9. http://www.reddit.com/r/haskell/comments/22yww7/try_idris/ 10. http://www.reddit.com/r/haskell/comments/23dxli/why_are_examples_completely… 11. http://www.reddit.com/r/haskell/comments/23dxli/why_are_examples_completely… 12. http://www.meetup.com/Melbourne-Haskell-Users-Group/events/174401572/ 13. http://www.reddit.com/r/haskell/comments/238akv/implementing_python_in_hask… 14. http://skillsmatterblog.wordpress.com/2014/04/15/guest-post-haskell-gets-st… 15. http://www.reddit.com/r/haskell/comments/233njg/blog_post_haskell_gets_stat… 16. http://www.haskellforall.com/2014/04/scalable-program-architectures.html 17. http://www.reddit.com/r/haskell/comments/2300zb/haskell_for_all_scalable_pr… 18. http://maxs.io/ghc-78-static-lib-flag/ 19. http://www.reddit.com/r/haskell/comments/23fyok/ghc_78s_staticlib_flag_make… 20. http://www.reddit.com/r/haskell/comments/236qkb/autocomplete_command_line_o… 21. http://www.reddit.com/r/haskell/comments/236qkb/autocomplete_command_line_o… 22. http://acm3.wustl.edu/functional/haskell.php 23. http://www.reddit.com/r/haskell/comments/239f2m/how_to_learn_haskell/ 24. http://www.lunaryorn.com/2014/04/15/calling-python-from-haskell.html 25. http://www.reddit.com/r/haskell/comments/2330aj/calling_python_from_haskell/ 26. http://www.reddit.com/r/haskell/comments/22xz96/latest_api_link_in_hackage/ 27. http://www.reddit.com/r/haskell/comments/22xz96/latest_api_link_in_hackage/ 28. http://www.cs.ox.ac.uk/people/daniel.james/functor/functor.pdf 29. http://www.reddit.com/r/haskell/comments/2327e7/functional_pearl_f_for_func… 30. http://stackoverflow.com/questions/23149532/idris-eager-evaluation 31. http://stackoverflow.com/questions/23051800/why-use-such-a-peculiar-functio… 32. http://stackoverflow.com/questions/23048100/how-does-mapa-work-with-a-strea… 33. http://stackoverflow.com/questions/23066099/lenses-and-monomorphism-restric… 34. http://stackoverflow.com/questions/23091080/is-this-a-ghc-bug 35. http://stackoverflow.com/questions/23044464/why-do-some-of-threepenny-gui-f… 36. http://stackoverflow.com/questions/23095224/s-combinator-in-haskell 37. http://stackoverflow.com/questions/23129649/graphing-criterion-benchmarks-t… 38. http://stackoverflow.com/questions/23142075/fun-with-fixity 39. https://plus.google.com/105107667630152149014/about

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Syntax proposal for "reverse apply"/"pipeline apply" (flip ($))
by Alexey Muranov 24 Apr '14

24 Apr '14

Hello, i am completely new to Haskell, but i am somewhat fascinated by lambda-calculus and programming. For whatever it is worth, i would like to propose for discussion a syntax for "(flip ($))" operation in Haskell. I think that a good syntax would be "|^", for example: square x = x * x y = 3 |^ square -- y == 9 Explanation: * i would have suggested just ^, but it would conflict with number exponentiation, * it is rather common in mathematics to write function application in exponential notation: x ^ f instead of f(x), especially if f is an automorphism of some structure, * (flip ($)) is exactly the exponentiation of Church numerals, * in "The calculi of lambda-conversion", Alonzo Church uses the "shorthand" notation "[N^M]" for "(MN)", where M and N are lambda-terms. * I am probably not the only person missing the ability to apply functions from the right: http://stackoverflow.com/questions/1457140/haskell-composition-vs-fs-pipe-f… Well, other notations i've thought of are "\^" and "~$". Alexey.

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Info on dependencies among libs distributed with ghc?
by Magnus Therning 23 Apr '14

23 Apr '14

I'm working on the packaging of Ghc for Arch Linux and the packaging of Ghc 7.8 was in place about a week ago. It was delivered with `Cabal` 1.18, and already now there's a 1.20 available, which is required by the latest version of `cabal-install` :( Ghc 7.8 comes with quite a few other basic libraries. Are there any dependencies between these libraries besides the obvious one on `base`? In other words, can I update Cabal without running into the diamond-dependency problem? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus Most software today is very much like an Egyptian pyramid with millions of bricks piled on top of each other, with no structural integrity, but just done by brute force and thousands of slaves. -- Alan Kay

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Re: [Haskell-cafe] imports at bottom
by Doug McIlroy 23 Apr '14

23 Apr '14

> A language pragma could be used to select between top imports or bottom > imports (can't use both). > > What do you think? Warning. This one touches a personal hot button, mostly off topic. To my mind, language pragmas are blemishes. Reasonable, assuredly, to announce that code uses some nonstandard feature of a compiler, but generally unreasonable as an integral part of the language definition. As originally promulgated for ALGOL, pragmas had no effect on the meaning of a program or its conformance to the standard, though they could, for example, affect the efficiency of object code. Language pragmas stray far from this intent. As unstable features, often incompletely described (just what does FlexibleInstances permit, anyway?), language pragmas might well be banned from the Haskell Platform. Doug McIlroy

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Contract opportunity
by Ian Ross 22 Apr '14

22 Apr '14

Dear all, This is kind of weird, but it might be of interest to someone and I think it's within the remit of this list, so here goes. Sorry to everyone who's not interested! I'm looking for someone to take over a contract I've been working on -- I've been offered something better and I won't have the time to carry on with this thing. I can't say too much about the details, but it's mostly GIS and geoprocessing work for a smallish business consulting firm, probably expanding to some statistical modelling soon. I've been using PostGIS with postgresql-simple to do some quite complicated geoprocessing of OpenStreetMap data for them: much of the Haskell content is really only using Haskell as a fancy scripting language to run lots of SQL, but there are a couple of more interesting bits. Anyone who was going to take this over would need to be a reasonably proficient Haskeller, know SQL well (including having some idea about query optimisation), have some familiarity with GIS work (data formats, something like QGIS or ArcGIS, ideally PostGIS and/or spatial SQL) and be persistent enough to deal with the places where the OpenStreetMap data isn't all you might hope. The client has a large number of sites in different cities that they're interested in, which means that everything has to be automated as much as possible, and that often means iterating again and again to discover geometrical or metadata problems that you need to work around. It can be quite frustrating. What's there now is pretty solid, I think, but it's quite fragile to changes in the OSM data. The rate of pay is good, there's enough work to occupy someone full-time, and the client is OK. There are the usual on-again-off-again rushes associated with this sort of business consulting. The timescale for me moving on is quite short: 2-3 weeks. I'll be organising notes and things for any potential handover, and there's another Haskell person at the client, so you would have someone to talk things over with. If you're interested, either get in touch with me if you have questions, or directly with Chad Scherrer (the Haskeller at the client: cscherrer(a)melinae.com) Cheers, Ian. -- Ian Ross Tel: +43(0)6804451378 ian(a)skybluetrades.net www.skybluetrades.net

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Job offer at Create-Net, Italy
by Corentin Dupont 22 Apr '14

22 Apr '14

Hi guys, I'm surprised I didn't got any reply from the community to this job offer, that I posted some time ago: http://www.create-net.org/work-with-us/postdoctoral-researcher-cloud-comput… While it's not 100% guarantee to work in Haskell, the position is still very interesting with technologies such as Constraint Programming (I'm currently exploring SMT with the SBV library), Cloud computing and energy efficiency. Ciao, Corentin

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Correctly setting up emacs + ghc-mod
by Arnaud Bailly 22 Apr '14

22 Apr '14

Hello, I am struggling to get my emacs settings right for doing significant Haskell development, eg. something more involved than a bunch of source files in a single directory. The issue I am running in currently is that when trying to load files in the interpreter, most source paths are missing which means loading inevitably fails. This is especially annoying with tests: To get things working correctly I need to explicitly add in the console > :set -iwhere/my/src/are Is there any configuration I should be aware of in my cabal files or .emacs file that would correctly set the source roots? Am I missing something? Here is my .emacs configuration. Thanks for any help. ;; haskell coding (require 'auto-complete) (require 'haskell-mode) (require 'haskell-cabal) (autoload 'ghc-init "ghc" nil t) (add-hook 'haskell-mode-hook (lambda () (ghc-init))) (eval-after-load "haskell-mode" '(progn (setq haskell-stylish-on-save t) (setq haskell-process-args-cabal-repl '("--ghc-option=-ferror-spans" "--with-ghc=ghci-ng")) (define-key haskell-mode-map (kbd "C-,") 'haskell-move-nested-left) (define-key haskell-mode-map (kbd "C-.") 'haskell-move-nested-right) (define-key haskell-mode-map (kbd "C-c v c") 'haskell-cabal-visit-file) (define-key haskell-mode-map (kbd "C-c C-c") 'haskell-compile) (define-key haskell-mode-map (kbd "C-x C-d") nil) (setq haskell-font-lock-symbols t) ;; Do this to get a variable in scope (auto-complete-mode) ;; from http://pastebin.com/tJyyEBAS (ac-define-source ghc-mod '((depends ghc) (candidates . (ghc-select-completion-symbol)) (symbol . "s") (cache))) (defun my-ac-haskell-mode () (setq ac-sources '(ac-source-words-in-same-mode-buffers ac-source-dictionary ac-source-ghc-mod))) (add-hook 'haskell-mode-hook 'my-ac-haskell-mode) (defun my-haskell-ac-init () (when (member (file-name-extension buffer-file-name) '("hs" "lhs")) (auto-complete-mode t) (setq ac-sources '(ac-source-words-in-same-mode-buffers ac-source-dictionary ac-source-ghc-mod)))) (add-hook 'find-file-hook 'my-haskell-ac-init))) (add-hook 'haskell-mode-hook 'turn-on-haskell-decl-scan) (add-hook 'haskell-mode-hook 'turn-on-haskell-indentation) (eval-after-load "which-func" '(add-to-list 'which-func-modes 'haskell-mode)) (eval-after-load "haskell-cabal" '(define-key haskell-cabal-mode-map (kbd "C-c C-c") 'haskell-compile))

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