[Haskell-cafe] Haskell Weekly News: Issue 169

Daniel Santa Cruz dstcruz at gmail.com
Thu Feb 17 06:35:28 CET 2011

   Welcome to issue 169 of the HWN, a newsletter covering developments in
   the [1]Haskell community. This release covers the week of February 6 -
   12, 2011.

   Congrats to Bryan O'Sullivan and Mark Lentczner for pulling off a
   successfull [2]BayHac 2011!


   Joao Fernandes [3]sent out a call for papers for the 4th International
   Conference on Software Language Engineering to be held in Braga,
   Portugal, 3-6 July 2011.

   Bas van Dijk annouced [4]version 0.1 and [5]version 0.2 of his
   monad-control library. "monad-control is a rewrite of monad-peel than
   uses CPS style operations and exploits RankNTypes language extensions
   to simplify and speed up most functions."

   Gregory Collins and the Snap team [6]proudly announced the release of
   Snap 0.4 "containing a whole bunch of nifty new features."

   Peter Scott [7]announced pwstore, a library that aims to "handle all
   the details of password storage for you, in a way that should be so
   easy to use that there's no reason not to use it."

   Bas van Dijk [8]released case-insensitive 0.1. "The package provides
   the module Data.CaseInsensitive which exports the CI type constructor
   which can be parameterised by a string-like type... Comparisons of
   values of the resulting type are then insensitive to cases."

   Ryan Newton [9]released a package to do accelerated AES and RNG.

   Brent Yorgey [10]sent in a second call for submissions to the
   Monad.Reader -- special poetry and fiction edition.

   John Lato [11]released version 3.0.1 of ListLike, which "provides
   polymorphic functions with Data.List-style api for many different data
   types, including list, arrays, and bytestrings.

   John also [12]released version and of iteratee, after
   discovering a memory leak which affects all current versions of
   iteratee. He states that he would "strongly encourage all users of
   earlier versions to upgrade to one of these releases."

   Ganesh Sittampalam and the darcs team are [13]pleased to announce
   version 2.5.1, a minor upgrade for the 2.5 release. "The main focus of
   this release is support for the GHC 7.0 series and the upcoming
   February 2011 Haskell Platform, but the release also includes bug fixes
   and minor usability improvements."

   Trystan Spangler [14]announced the release of hspec: Behavior Driven
   Development for Haskell. "hspec ties together requirements and code
   that verifies the requirements are met. The verifying code can be a
   boolean expression, a QuickCheck property, or an explination of why
   it's pending. The requirements can then be turned into documentation of
   what the code does and what remains to be implemented."

   Wren Ng Thornton [15]announce bytestring-trie 0.2.3, a "long awaited
   release for efficient finite maps from (byte)strings to values."

   Brent Yorgey would like to invite you to [16]save the date for the
   Haskell hackathon in Philadelphia, July 29-31.

Quotes of the Week

     * smerdyakov: Some might argue that you can derive False from a
       sentence containing both "dependent types" and "contract
     * Einstein: Make everything as simple as possible, but not simpler.
     * Einskell: Make everything as monad as possible, but not monadder.
     * kmc: it's important to show that Haskell is usable not just for
       useless maths, but also for real-world tasks such as rendering
     * ddarius: Attempting to join #not-not-math sent me to #math.
       Freakin' Boole.
     * gwern: [quoting a hypothetical edwardk] 'I HAVE CONSUMED YOUR
     * monochrom: @let germanize = concat . words

Top Reddit Stories

   * Announcing: Snap Framework v0.4
     Domain: snapframework.com, Score: 40, Comments: 3
     On Reddit:
     Original: http://snapframework.com/blog/2011/02/05/snap-0.4-released

   * Haskell Summers of Code retrospective (updated for 2010)
     Domain: gwern.net, Score: 31, Comments: 7
     On Reddit:
     Original: http://www.gwern.net/Haskell%20Summer%20of%20Code.html

   * How to write type-level lambda-abstractions at the value level
     Domain: haskell.org, Score: 26, Comments: 7
     On Reddit:
     Original: http://www.haskell.org/pipermail/haskell-cafe/2011-February/089184.html

   * Storing passwords securely: don't roll your own
     Domain: finger-tree.blogspot.com, Score: 25, Comments: 22
     On Reddit:
     Original: http://finger-tree.blogspot.com/2011/02/storing-passwords-securely-in-haskell.html

   * #haskell-game & Haskellers Game Interest Group
     Domain: self.haskell, Score: 25, Comments: 3
     On Reddit:
     Original: /r/haskell/comments/fjzz0/haskellgame_haskellers_game_interest_group/

   * Type class generics to be replaced in GHC 7.2 or 7.4
     Domain: haskell.org, Score: 24, Comments: 2
     On Reddit:
     Original: http://www.haskell.org/pipermail/glasgow-haskell-users/2011-February/020006.html

   * What can I do with Haskell?
     Domain: self.haskell, Score: 22, Comments: 33
     On Reddit:
     Original: /r/haskell/comments/fgfh9/what_can_i_do_with_haskell/

   * There seems to be lots of interest in SMT solvers in the Haskell
community these days, so I started ##smt on freenode
     Domain: self.haskell, Score: 20, Comments: 6
     On Reddit:
     Original: /r/haskell/comments/fh2zw/there_seems_to_be_lots_of_interest_in_smt_solvers/

   * darcs 2.5.1 released
     Domain: lists.osuosl.org, Score: 16, Comments: 0
     On Reddit:
     Original: http://lists.osuosl.org/pipermail/darcs-users/2011-February/026018.html

   * monad-control
     Domain: mail-archive.com, Score: 11, Comments: 2
     On Reddit: http://www.reddit.com/r/haskell/comments/fgbao/monadcontrol/
     Original: http://www.mail-archive.com/haskell@haskell.org/msg23278.html

Top StackOverflow Answers

   * How does Data.MemoCombinators work?
     votes: 20
     Read on SO:

     This library is a straightforward combinatorization of the well-known
     technique of memoization.  Let's start with the canonical example:

     fib = (map fib' [0..] !!)
	 fib' 0 = 0
    	 fib' 1 = 1
    	 fib' n = fib (n-1) + fib (n-2)

     I interpret what you said to mean that you know how and why this works.
     So I'll focus on the combinatorization.

     We ...

   * What's similar to fmap for monadic values?
     votes: 16
     Read on SO:

     pelotom's answer is the straightforward one. But not the fun one! sequence
     is the Haskell function that one can think of as flipping the order of
     type constructors between a list and a monad.

     sequence :: (Monad m) => [m a] -> m [a]

     Now what you want is, so to speak, to flip the order of type
     constructors between a Maybe and a monad. Data.Traversable ...

   * Does there exist a monad instance for Data.Map / Data.IntMap?
     votes: 15
     Read on SO:

     Is there any particular reason you want to avoid using monad transformers?
     if you get the MaybeT package from Hackage you can achieve what you
     want like this:

     import Control.Monad
     import Control.Monad.Maybe
     import Control.Monad.State
     import qualified Data.Map as Map

     type MapM k v a = MaybeT (State (Map.Map k v)) a
     lookupM k = MaybeT $ Map.lookup k `liftM` ...

   * How to split a string in Haskell?
     votes: 11
     Read on SO:

     There is a package for this called split.

     cabal install split

     Use it like this:

     ghci> splitOn "," "my,comma,separated,list"

     It comes with a lot of other functions for splitting on matching
     delimiters or having several delimiters.

   * Haskell (n+1) in pattern matching
     votes: 10
     Read on SO:

     It's a specific case of what is called "n+k patterns", which is generally
     disliked, and will be has been removed from the language. See here for
     more information.

     Here is a good note on n+k patterns, which quotes the following from the
     Haskell 98 Report (emphasis mine):

     	     Matching an n+k pattern (where n is a
  	     variable and k is a positive integer

   * Setting upper limit to the input set according to the output function
     votes: 10
     Read on SO:

     The check fib x < 1000000 in the list comprehension filters away the
     fib x values that are less than 1000000; but the list comprehension has
     no way of knowing that greater values of x imply greater value of
     fib x and hence must continue until all x have been checked.

     Use takeWhile instead:

     takeWhile (< 1000000) [ fib x | x <- [0..35]]

Top StackOverflow Questions

   * How does Data.MemoCombinators work?
     votes: 13, answers: 4
     Read on SO:

   * How to best synchronize game engine and network server in Haskell?
     votes: 10, answers: 3
     Read on SO:

   * How to choose right Haskell C type?
     votes: 9, answers: 1
     Read on SO:

   * How to split a string in Haskell?
     votes: 9, answers: 5
     Read on SO:

   * Haskell (n+1) in pattern matching
     votes: 7, answers: 1
     Read on SO:

About the Haskell Weekly News

   You can find an html version of this newsletter at:

   To help create new editions of this newsletter, please send stories to
   dstcruz at gmail.com. I'm in dire need of finding good "quotes of the
   week". If you happen to come across any, please don't hesitate to send
   it along.

   Until next time,
   Daniel Santa Cruz


   1. http://haskell.org/
   2. http://mtnviewmark.wordpress.com/2011/02/13/bayhac-2011-wrap-up/
   3. http://article.gmane.org/gmane.comp.lang.haskell.general/18473/match=call+papers
   4. http://article.gmane.org/gmane.comp.lang.haskell.general/18474
   5. http://article.gmane.org/gmane.comp.lang.haskell.general/18485
   6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86087
   7. http://article.gmane.org/gmane.comp.lang.haskell.general/18476
   8. http://article.gmane.org/gmane.comp.lang.haskell.general/18475
   9. http://article.gmane.org/gmane.comp.lang.haskell.general/18481
  10. http://themonadreader.wordpress.com/2011/01/19/call-for-copy-special-poetry-and-fiction-edition/
  11. http://article.gmane.org/gmane.comp.lang.haskell.general/18486
  12. http://article.gmane.org/gmane.comp.lang.haskell.general/18490
  13. http://article.gmane.org/gmane.comp.version-control.darcs.user/25902
  14. http://article.gmane.org/gmane.comp.lang.haskell.general/18493
  15. http://article.gmane.org/gmane.comp.lang.haskell.libraries/15294
  16. http://article.gmane.org/gmane.comp.lang.haskell.general/18501

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