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ProductProfunctor folds

Haskell on Reddit - Sun, 01/05/2014 - 2:06pm
Categories: Incoming News

relocation R_X86_64_PC32 against undefined symbol?

haskell-cafe - Sun, 01/05/2014 - 2:00pm
I get the following error when trying to build hsimports: [7 of 7] Compiling HsImport ( src/HsImport.hs, dist/build/HsImport.dyn_o ) /usr/bin/ld: dist/build/HsImport/Args.dyn_o: relocation R_X86_64_PC32 against undefined symbol `hsimportzm0zi2zi6zi3_Pathszuhsimport_version1_closure' can not be used when making a shared object; recompile with -fPIC /usr/bin/ld: final link failed: Bad value collect2: error: ld returned 1 exit status What could be causing this? /M
Categories: Offsite Discussion

Broken documentation on Hackage.

libraries list - Sun, 01/05/2014 - 12:15pm
Hi all, It seems that we are having a rather big issue with Hackage in recent months and I'm sure many of you have noticed: a lot of packages aren't getting their docs built. As far as I can tell, there can be multiple reasonable causes: * Dependencies fail to build so your package does * Your package fails to build directly * Your package requires non-cabal libraries which aren't installed * Your package requires different version of install libraries While all of these are understandable, there also seem to be problems with some packages which are seemingly perfectly fine otherwise. This problem is not new and has been reported[1]. There is even a system in place with Hackage 2 that would grant package owners to manually upload documentation and a system where some people (trustees and package maintainers) have the ability to do things like deleting the broken docs to have the builder try again[3] but it seems that this isn't actually used[4]. Over night I hacked up a quick program to parse some Hackag
Categories: Offsite Discussion

Backpack: Retrofitting Haskell with a Module System, at last

Lambda the Ultimate - Sun, 01/05/2014 - 10:59am

Backpack: Retrofitting Haskell with Interfaces
Scott Kilpatrick, Derek Dreyer, Simon Peyton Jones, Simon Marlow

Module systems like that of Haskell permit only a weak form of modularity in which module implementations directly depend on other implementations and must be processed in dependency order. Module systems like that of ML, on the other hand, permit a stronger form of modularity in which explicit interfaces express assumptions about dependencies, and each module can be typechecked and reasoned about independently.

In this paper, we present Backpack, a new language for building separately-typecheckable packages on top of a weak module system like Haskell's. The design of Backpack is inspired by the MixML module calculus of Rossberg and Dreyer, but differs significantly in detail. Like MixML, Backpack supports explicit interfaces and recursive linking. Unlike MixML, Backpack supports a more flexible applicative semantics of instantiation. Moreover, its design is motivated less by foundational concerns and more by the practical concern of integration into Haskell, which has led us to advocate simplicity—in both the syntax and semantics of Backpack—over raw expressive power. The semantics of Backpack packages is defined by elaboration to sets of Haskell modules and binary interface files, thus showing how Backpack maintains interoperability with Haskell while extending it with separate typechecking. Lastly, although Backpack is geared toward integration into Haskell, its design and semantics are largely agnostic with respect to the details of the underlying core language.

Categories: Offsite Discussion

Daniil Frumin: ANN: scotty-hastache 0.2

Planet Haskell - Sun, 01/05/2014 - 7:57am

The scotty-hastache library has been updating, following the introduction of the custom exception types in Scotty. Custom exception types (as opposed to plain-text exception mechanism that was previously employed in Scotty) is a more powerful way of handling exceptional situation; an example usage can be found here. Below are the appropriate release notes for scotty-hastache


Keeping up with the Scotty 0.6 updating. The introduction of the custom exception types is reflected in the scotty-hastache package as well. The main types are now polymorphic over an exception type

type ScottyH e = ScottyT e HState type ActionH e = ActionT e HState

In addition, the specialized (to Text) types and runners are introduced

type ScottyH' = ScottyH Text type ActionH' = ActionH Text scottyH' :: Port -> ScottyH' () -> IO () scottyHOpts' :: Options -> ScottyH' () -> IO ()

Thanks to Kirill Zaborsky for pointing out the incompatibility with 0.6.

As always, the scotty-hastache library is available on Hackage and on GitHub

Tagged: haskell, scotty, web
Categories: Offsite Blogs

My first non-trivial Haskell project - any help appreciated.

Haskell on Reddit - Sun, 01/05/2014 - 6:56am

I've written the back-end for a simple Bridge (card game) bidding helper in Haskell as my first non-trivial project.


The idea is to expand this into a more useful general Bridge playing system. Before I go further, I'd really appreciate any feedback on the code: idiomatic use of Haskell; libraries I could have used; code formatting; anything!

submitted by derek-mcloughlin
[link] [27 comments]
Categories: Incoming News

gist:8255552 - Sun, 01/05/2014 - 4:35am
Categories: Offsite Blogs

Ken T Takusagawa: [qupqknlc] Greedy leap years

Planet Haskell - Sun, 01/05/2014 - 4:12am

Leap day every 4 years.
Omit leap day every 33*4=132 years.
Keep leap day every 100*33*4=13200 years.

This sequence of multipliers [4,33,100] were found by the greedy method. The entire cycle has the same average year length as the Gregorian calendar = 365 + 97/400 days, which uses multipliers [4,25,4]. We alternate between keeping and omitting leap days at each larger multiplier.

countDays accum (h:t) offset = countDays (accum*h+offset) t (negate offset);
countDays accum [] _ = accum;
averageYear :: [Integer] -> Rational;
averageYear leapPattern = (countDays 365 leapPattern 1) % (product leapPattern)

What is going on such that averageYear [4,33,100] == averageYear [4,25,4]? Find a set of multipliers which minimizes the product, i.e., cycle length. I suspect this is related to Egyptian fractions or continued fractions. I suspect that the greedy method yields a sequence which monotonically increases.

Update: these are Pierce expansions, a variant of Engel expansions.

Applying the greedy algorithm to 365 + 71/293 days (as proposed by the Symmetry454 calendar) yields multipliers [4,32,58,97,146,293] for a cycle of 11251521835008 days in 30805635584 years. (This is far less efficient than the 293 year cycle.)

When applied to adding "leap weeks" to the Gregorian calendar, we find the sequence [5,8,10] as reported in calendar based on 7. If we apply leap weeks to the 365+71/293 year-length, we get the sequence [5,8,10,97,146,293].

Some disorganized Haskell code for these calculations.

Categories: Offsite Blogs - Sun, 01/05/2014 - 1:35am
Categories: Offsite Blogs - Sun, 01/05/2014 - 1:35am
Categories: Offsite Blogs

Emacs and our API | FP Complete - Sun, 01/05/2014 - 12:17am
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365 Tidal Patterns - Sun, 01/05/2014 - 12:07am
Categories: Offsite Blogs

Who remembers HP 2013.4.0.0...?

libraries list - Sat, 01/04/2014 - 11:35pm
I do - I'm just a lame-o this cycle! Please review the status below - I'll have the 'prerelease' branch in github updated this weekend, and packages out (src tarball and Mac installers) out this coming week. - Mark *Resolved Issues* - fgl - haven't heard from Ivan, so we'll stay with the status quo. - aeson / dlist - log round'a'bout discussion resulted in decision to omit aeson this cycle. - alex / happy - I haven't heard from the maintainers on the major version bump, but they are both active here and so I'm assuming it is a go. *Current Proposed Versions* *GHC 7.6.3* -- same as last time (erroneously listed as a version bump last time) *Packages with no changes:* fgl, haskell-src, html, HUnit, mtl, parsec, QuickCheck, random, regex-base, regex-compat, regex-posix, split, stm, text, transformers, xhtml, zlib *Packages held back:* cgi: 3001.1.7.5 (3001.1.8.4* requires MonadCatchIO-mtl)* *Packages with minor version bumps:* HTTP:
Categories: Offsite Discussion

Haskell Repa库使用心得 - Sat, 01/04/2014 - 9:39pm
Categories: Offsite Blogs

Haskell Repa库使用心得 - Sat, 01/04/2014 - 9:39pm
Categories: Offsite Blogs

Haskell + Cairo - Sat, 01/04/2014 - 9:37pm
Categories: Offsite Blogs

Haskell + Cairo - Sat, 01/04/2014 - 9:37pm
Categories: Offsite Blogs