May 2011 - Haskell-Cafe

Haskell Weekly News: Issue 183
by Daniel Santa Cruz 25 May '11

25 May '11

Welcome to issue 180 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of May 15 to 21, 2011. Announcements Janis Veigtlander announced that the 20th edition of the Haskell Communities and Activities reports is hot off the press! http://goo.gl/GRi7V Simon Marlow announced that he has put together a tutorial on Parallel and Concurrent programming in Haskell. http://goo.gl/LPst8 Quotes of the Week * Sergey Mironov:I looked further and found that 'Oleg already did it'. * monochrom: just say "yes" Top Reddit Stories * Wolfgang - A Wolfram Alpha clone in Haskell (under heavy load?) Domain: jabberwock.xs4all.nl, Score: 75, Comments: 10 On Reddit: http://goo.gl/okNC7 Original: http://goo.gl/7pSXA * Numeric Haskell: a tutorial about the multi-dimensional, parallel arrays package, Repa Domain: haskell.org, Score: 54, Comments: 7 On Reddit: http://goo.gl/ZRSn3 Original: http://goo.gl/InWB9 * Space leak zoo: a catalog of common space leaks in Haskell programs Domain: blog.ezyang.com, Score: 41, Comments: 7 On Reddit: http://goo.gl/npVLv Original: http://goo.gl/aMbo5 * Exercises in Optimization: A (soon to be) three-part series detailing an adventure in optimizing Haskell code. Domain: csks.wordpress.com, Score: 34, Comments: 0 On Reddit: http://goo.gl/cjWBX Original: http://goo.gl/wPqbl * Tutorial: Parallel and Concurrent Programming in Haskell :: PDF Domain: community.haskell.org, Score: 33, Comments: 7 On Reddit: http://goo.gl/CB1wt Original: http://goo.gl/yzTOU * Anatomy of a thunk leak: How to debug Haskell’s most famous space leak Domain: blog.ezyang.com, Score: 32, Comments: 3 On Reddit: http://goo.gl/f18jX Original: http://goo.gl/PiQ98 * Preview release of diagrams EDSL for declarative drawing Domain: haskell.org, Score: 31, Comments: 9 On Reddit: http://goo.gl/6sykO Original: http://goo.gl/uhbV1 * I/O is not a monad Domain: r6.ca, Score: 31, Comments: 23 On Reddit: http://goo.gl/zAra5 Original: http://goo.gl/mn49r * Eliza in 70 lines of Haskell Domain: github.com, Score: 28, Comments: 7 On Reddit: http://goo.gl/hjgNf Original: http://goo.gl/S7t9m * The "Whole Program" Fallacy Domain: lukepalmer.wordpress.com, Score: 26, Comments: 10 On Reddit: http://goo.gl/Efja3 Original: http://goo.gl/vzXVK Top StackOverflow Questions * What Haskell representation is recommended for 2D, unboxed pixel arrays with millions of pixels? votes: 48, answers: 3 Read on SO: http://goo.gl/gVpwB * Good introductory text about GHC implementation? votes: 24, answers: 2 Read on SO: http://goo.gl/6MZoh * Questions on a Haskell -> C# conversion votes: 13, answers: 3 Read on SO: http://goo.gl/0t3Gu * Can't perform I/O in foldr? votes: 12, answers: 4 Read on SO: http://goo.gl/d9Jg0 * What does "this function will fuse" mean? votes: 11, answers: 3 Read on SO: http://goo.gl/tMdlR * Haskell function type question votes: 10, answers: 3 Read on SO: http://goo.gl/gyTns * Is this always true: fmap (foldr f z) . sequenceA = foldr (liftA2 f) (pure z) votes: 10, answers: 1 Read on SO: http://goo.gl/emKmg * Difference between hsc2hs and c2hs? votes: 8, answers: 2 Read on SO: http://goo.gl/1wnhC * Is it possible to create PHP extensions in Haskell? votes: 8, answers: 2 Read on SO: http://goo.gl/QwkpK * How can configuration tools like sdl-config be used with a cabalized project? votes: 8, answers: 2 Read on SO: http://goo.gl/vHCOu About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz

1 0

[ANN] Released HSnippets, Emacs YASnippets for Haskell
by Christophe McKeon 25 May '11

25 May '11

Just released HSnippets, Emacs YASnippet snippets for Haskell https://github.com/polypus74/HSnippets cheers, _c

1 0

lambdabot hoogle
by Jacek Generowicz 25 May '11

25 May '11

I have recenly installed lambdabot. Its response to *each* *and* *every* hoogle command is *always* A Hoogle error occurred. I'm hoping that someone on Cafe might be able to offer a more helpful diagnosis than this ... erm ... terse ... error message.

6 13

lambdabot check
by Jacek Generowicz 25 May '11

25 May '11

I've installed lambdabot, but check within it seems to be broken: the only answer it ever gives is "Terminated". For example: lambdabot> check True Terminated lambdabot> quickCheck works just fine in a GHCi session: Prelude> :m + Test.QuickCheck [...] Prelude> quickCheck True [...] +++ OK, passed 100 tests. (GHC 7.0.3 on Ubuntu Natty, everything freshly installed with cabal install as far as possible.) Any advice?

3 6

Calling a C function that returns a struct by value
by Matthew Steele 25 May '11

25 May '11

From Haskell, I want to call a C function that returns a struct by value (rather than, say, returning a pointer). For example: typedef struct { double x; double y; } point_t; point_t polar(double theta); I can create a Haskell type Point and make it an instance of Storable easily enough: data Point = Point CDouble CDouble instance Storable Point where -- insert obvious code here And now I want to do something like this: foreign import ccall unsafe polar :: CDouble -> IO Point ...but that doesn't appear to be legal (at least in GHC 6.12). Is there any way to import this C function into Haskell _without_ having any additional wrapper C code? I mean, I suppose I could write something like: // C: void polar_wrapper(double theta, point_t* output) { *output = polar(theta); } -- Haskell: foreign import ccall unsafe polar_wrapper :: CDouble -> Ptr Point - > IO () polar :: CDouble -> IO Point polar theta = do -- insert obvious code here ...but that's a lot of extra boilerplate if I have many such functions to wrap, and it seems like GHC should be able to do that sort of thing for me. P-: Cheers, -Matt

2 1

code review?
by Chris Bolton 25 May '11

25 May '11

Hey guys. Pretty new to haskell here. I've started off by writing a small command-line interface to plurk.. I was just wondering if anyone would be willing to give everything a look-over and lemme know what kinds of things I should be looking to improve upon, style-wise. Not sure I'm currently doing things in the 'haskell-way' so to speak . Thanks a bunch! https://github.com/saiko-chriskun/hermes (note: the JSON and Plurkell submodules are also mine.)

7 10

uniplate and haskell-src-exts (was: Re: code review?)
by Evan Laforge 25 May '11

25 May '11

> +1 on that, I use uniplate for pretty much all my haskell-src-exts tasks > these days, works like a charm! > I'd love to include some standard traversal functionality in > haskell-src-exts that depends on uniplate, but hesitate to do so because of > HP aspirations for haskell-src-exts. Neil, what do you reckon the chances of > getting uniplate in the HP are? :-) Or, you could just put a note in the documentation suggesting that uniplate is a good way to traverse parsed output, along with an example or two. And maybe mention a separate package haskell-src-exts-uniplate with utility functions, if there are any. Keeping deps under control by splitting packages this way has some precedent, and makes some logical sense too, since it's not like the parsed data types are trying to be abstract by hiding constructors.

1 0

Status of Haskell + Mac + GUIs & graphics
by Conal Elliott 25 May '11

25 May '11

I still haven't found any way to do GUIs or interactive graphics in Haskell on a Mac that isn't plagued one or more of the following serious problems: * Incompatible with ghci, e.g., fails to make a window frame or kills the process the second time one opens a top-level window, * Goes through the X server, and so doesn't look or act like a Mac app, * Doesn't support OpenGL. A year or two ago, I put my Haskell GUI & graphics work on hold while waiting & hoping for a functioning pathway to open. So far I haven't heard of one. If anyone has found a solution, I'd love to hear! - Conal

22 42

Re: [Haskell-cafe] Policy for taking over a package on Hackage
by Ivan Lazar Miljenovic 25 May '11

25 May '11

On 25 May 2011 23:23, Otakar Smrz <otakar.smrz(a)cmu.edu> wrote: > > I took over the maintenance of wl-pprint since Stefan suggested it > himself. I needed to include OverlappingInstances, because that was > required to make better use of the library (there is a difference having > this flag there, which is consistent with the GHC documentation on > OverlappingInstances). > > I was not aware that I have to announce this. I thought people would > know from checking Hackage that there is this maintainer change and a > new version of the package. Sorry. The whole email wasn't aimed at you specifically: it's just that with Hackage's current infrastructure it's quite easy for someone to "take over" a package and possibly do something malicious with it (so the next time they do a "cabal update" they could inadvertently get a package with said malicious code). Especially if there's no announcement of the change, it's difficult to know that someone has indeed taken over maintaining a library, and thus they could keep addressing queries (or throwing blame) at someone "known" to be the maintainer of a package even if they didn't upload the latest version. > Since I do not have any plans to develop wl-pprint further, I have no > problem giving the maintainer's role to you or anyone interested. OK; if no-one has any objections I'll do so and make it class-based as I've discussed in the threads on -cafe (after considering name clashes with Applicative, etc.). > PS: For the point 4 of your suggested rules, I think uploading a new > version of a package if only the maintainer changes, rather than when > there is some actual change to the library, is inappropriate. You could > easily get package versions increasing without any code/documentation > being actually improved or extended. By "point release" I meant incrementing the fourth digit, which is usually used to refer to bug-fixes. My aim with this was that the new maintainer could immediately "make their mark" so that people looking for a project's maintainer on the hackage page knew who to contact (rather than waiting for them to finish of their new & improved version). -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

1 0

Cabal upload failure
by Emil Axelsson 25 May '11

25 May '11

Hello! I'm trying to upload a new version of syntactic, but Hackage gives the error: 500 Internal Server Error <stdin>: hWaitForInput: invalid argument (Invalid or incomplete multibyte or wide character) In fact, I get the same error if I use the "Check" functionality on the earlier version that is already on Hackage. Any idea what causes this? / Emil

4 5