[Haskell-cafe] Haskell Weekly News: Issue 170

Daniel Santa Cruz dstcruz at gmail.com
Thu Feb 24 06:29:33 CET 2011

   Welcome to issue 170 of the HWN, a newsletter covering developments in
   the [1]Haskell community. This release covers the week of February 13 -
   19, 2011.


   Simon Michael [2]informed us of reviving of FunGEn as a community
   project. "FunGEn (Functional Game Engine) is a platform-independent,
   BSD-licensed, easy-to-install 2D game engine currently based on OpenGL
   and GLUT."

   Alexander McPhail [3]announced the release of vector-buffer. "It
   provides a buffer that can be turned into a Data.Vector.Storable. The
   mapM* functions map from the oldest element, not the first."

   Mark P. Jones [4]announce the availability of 2 openings for
   post-doctoral researches "to help design, develop, and apply a new
   strongly typed, pure functional language for systems programming."

   Trystan Spangler [5]made a second release of his Behavior Driven
   Development for Haskell, and the tool can now be found in Hackage!

   Jeremy Shaw [6]announce the release of Happstack 6. "We fully recomend
   that all Happstack users migrate to the new release."

   Gregory D. Weber [7]published a new release of Sifflet and sifflet-lib.
   "Sifflet is a visual, functional programming language and support
   system for students learning about recursion."

   Johan Tibell [8]announced the release of two new packages:
   unordered-containers (Efficient hashing-based container types), and
   hashable (Efficient hashing of common types).

Quotes of the Week

     * kmc: i started to read the "tutorial" and it was incomprehensible.
       makes the Gentle Introduction to Haskell look like Teach Yourself
       PHP in 24 Hours
     * ConorMcBride: Sometimes it's easier to search for good programs in
       the space of well typed programs, rather than in the space of ascii
     * monochrom: best practice haskell is "go with your heart"
     * accel: one day, it was raining -- I was walking home -- I saw Knuth
       biking home, wearing a helmet, in the rain -- and I freaked out --
       rain was hitting him like any other mortal ... it wasn't bounching
       off his aura of awesomeness

Top Reddit Stories

     * Type level natural numbers ... ready to merge into GHC mainline:
       From (hackage.haskell.org), scored 62 with 44 comments. Read on
       [9]reddit or the [10]original post.

     * Haskell Web Framework Happstack 6 Released: From
       (groups.google.com), scored 45 with 3 comments. Read on [11]reddit
       or the [12]original post.

     * Well-Typed is hiring: From (well-typed.com), scored 41 with 13
       comments. Read on [13]reddit or the [14]original post.

     * Haskell is Better: slides from Mark Lentczner's talk at Ignite
       Silicon Valley: From (scribd.com), scored 40 with 43 comments. Read
       on [15]reddit or the [16]original post.

     * New, faster hashing-based containers library released: From
       (blog.johantibell.com), scored 40 with 6 comments. Read on
       [17]reddit or the [18]original post.

     * Disciple haskell dialect : strict evaluation as default ,
       destructive update of data structures.: From
       (disciple.ouroborus.net), scored 35 with 25 comments. Read on
       [19]reddit or the [20]original post.

     * Yesod: Warp Speed Ahead: From (docs.yesodweb.com), scored 34 with 8
       comments. Read on [21]reddit or the [22]original post.

     * Faster persistent data structures through hashing: From
       (blog.johantibell.com), scored 28 with 15 comments. Read on
       [23]reddit or the [24]original post.

     * Developing iPhone applications in Haskell â a tutorial: From
       (gergo.erdi.hu), scored 25 with 6 comments. Read on [25]reddit or
       the [26]original post.

     * An Introduction to Agda :: PDF: From (dl.dropbox.com), scored 24
       with 4 comments. Read on [27]reddit or the [28]original post.

Top StackOverflow Answers

     * [29]How to tell whether Haskell will cache a result or recompute
       it? votes: 17

       primes, in your code, is not a function, but a constant, in
       haskellspeak known as a CAF. If it would take a parameter
       (say, ()), you would get two different versions of the same
       list back if calling it twice, but as it is a CAF, you get the
       exact same list back both times;

       As a top-level definition, primes never gets out of scope,
       thus the head of the list ...

     * [30]Specific type inference using uncurry function votes: 17

       This has nothing to do with ghci.  This is the monomorphism
       restriction being irritating.  If you try to compile the following file:

       add = uncurry (+)
       main = do
       print $ add (1,2 :: Int)
       print $ add (1,2 :: Double)

       You will get an error.  If you expand:

       main = do
       print $ uncurry (+) (1,2 :: Int)
       print $ uncurry (+) (1,2 :: Double)

     * [31]Haskell: Unexpected output for expression [0, 0.1 .. 1]
       votes: 15

       This is a result of the imprecision of floating point values,
       it isn't particular to Haskell.  If you can't deal with the
       approximation inherent in floating point then you can use
       Rational at a high performance cost:

       > import Data.Ratio
       Data.Ratio> [0,1%10.. 1%1]
       [0 % 1,1 % 10,1 % 5,3 % 10,2 % 5,1 % 2,3 % 5,7 % 10,4 % 5,9 % 10,1 % 1]

       Just to hammer ...

     * [32]valid haskell function names votes: 14

       From the Haskell report:

       Haskell uses the Unicode character set. However, source programs are
       currently biased toward the ASCII character set used in earlier
       versions of Haskell. Recent versions of GHC seem to be fine with
       unicode (at least in the form of UTF-8):...

     * [33]Haskell range notation to generate list. Unexpected output
       votes: 13

       The notation is meant to mimic the usual way to write simple
       sequences mathematics. The second element is not the step, but
       in fact the actual second element of the list.  The rest is
       linearly extrapolated from there.  Examples:

       [1,2..10] = [1,2,3,4,5,6,7,8,9,10]
       [1,3..10] = [1,3,5,7,9]
       [4,3..0]  = [4,3,2,1,0]
       [0,5..]   = [0,5,10,15,20,25,30,35...

Top StackOverflow Questions

     * How to tell whether Haskell will cache a result or recompute it?
       (votes: 11, answers: 1) [34]read

     * How can one distribute Haskell programs to non-technical end users?
       (votes: 8, answers: 2) [35]read

     * Haskell range notation to generate list. Unexpected output (votes:
       8, answers: 2) [36]read

     * Appropriate uses of Monad `fail` vs. MonadPlus `mzero` (votes: 8,
       answers: 2) [37]read

     * Why does Haskell not have an I Monad (for input only, unlike the IO
       monad)? (votes: 8, answers: 3) [38]read

About the Haskell Weekly News

   To help create new editions of this newsletter, please send stories to
   dstcruz at gmail.com.

   Until next time,
   Daniel Santa Cruz


   1. http://haskell.org/
   2. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/86330
   3. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/86371
   4. http://www.haskell.org/pipermail/haskell/2011-February/022585.html
   5. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18510
   6. http://www.mail-archive.com/haskell-cafe@haskell.org/msg87352.html
   7. http://www.mail-archive.com/haskell@haskell.org/msg23319.html
   8. http://article.gmane.org/gmane.comp.lang.haskell.general/18515
   9. http://www.reddit.com/r/haskell/comments/fnc80/type_level_natural_numbers_ready_to_merge_into/
  10. http://hackage.haskell.org/trac/ghc/ticket/4385
  11. http://www.reddit.com/r/haskell/comments/fnit9/haskell_web_framework_happstack_6_released/
  12. http://groups.google.com/group/happs/browse_thread/thread/f72d7ff313ea9fa0
  13. http://www.reddit.com/r/haskell/comments/flyyg/welltyped_is_hiring/
  14. http://www.well-typed.com/blog/50
  15. http://www.reddit.com/r/haskell/comments/flajs/haskell_is_better_slides_from_mark_lentczners/
  16. http://www.scribd.com/doc/48773692/Ignite-SV-Haskell-is-Better
  17. http://www.reddit.com/r/haskell/comments/fo9gm/new_faster_hashingbased_containers_library/
  18. http://blog.johantibell.com/2011/02/new-faster-containers-library.html
  19. http://www.reddit.com/r/haskell/comments/fojb4/disciple_haskell_dialect_strict_evaluation_as/
  20. http://disciple.ouroborus.net/
  21. http://www.reddit.com/r/haskell/comments/flp87/yesod_warp_speed_ahead/
  22. http://docs.yesodweb.com/blog/warp-speed-ahead
  23. http://www.reddit.com/r/haskell/comments/fm6gg/faster_persistent_data_structures_through_hashing/
  24. http://blog.johantibell.com/2011/02/slides-from-my-hashing-based-containers.html
  25. http://www.reddit.com/r/haskell/comments/fkqe1/developing_iphone_applications_in_haskell_a/
  26. http://gergo.erdi.hu/blog/2011-02-13-developing_iphone_applications_in_haskell___a_tutorial/
  27. http://www.reddit.com/r/haskell/comments/fl0wr/an_introduction_to_agda_pdf/
  28. http://dl.dropbox.com/u/361503/Agda%20and%20dependent%20types.pdf
  29. http://stackoverflow.com/questions/5032750/how-to-tell-whether-haskell-will-cache-a-result-or-recompute-it/5032920#5032920
  30. http://stackoverflow.com/questions/4999020/specific-type-inference-using-uncurry-function/4999860#4999860
  31. http://stackoverflow.com/questions/5048920/haskell-unexpected-output-for-expression-0-0-1-1/5048970#5048970
  32. http://stackoverflow.com/questions/5023485/valid-haskell-function-names/5023519#5023519
  33. http://stackoverflow.com/questions/5012185/haskell-range-notation-to-generate-list-unexpected-output/5012276#5012276
  34. http://stackoverflow.com/questions/5032750/how-to-tell-whether-haskell-will-cache-a-result-or-recompute-it
  35. http://stackoverflow.com/questions/5004902/how-can-one-distribute-haskell-programs-to-non-technical-end-users
  36. http://stackoverflow.com/questions/5012185/haskell-range-notation-to-generate-list-unexpected-output
  37. http://stackoverflow.com/questions/5023969/appropriate-uses-of-monad-fail-vs-monadplus-mzero
  38. http://stackoverflow.com/questions/5032475/why-does-haskell-not-have-an-i-monad-for-input-only-unlike-the-io-monad

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