February 2008 - Haskell-Cafe

IRC Statistics
by Vlad Dogaru 04 Feb '08

04 Feb '08

Hello, as part of an effort to learn Haskell, me and a few friends want to write an IRC statistcs generator. It would analyse logs and output HTML, text, or whatever other format. However, I have a few questions; we're all pretty new to this and it would be a shame to start off terribly wrong and get bored before we get to the fun parts. 1. Is there a similar effort in Haskell? I've seen a truly awesome IRCStats, but written in C (not that that's a bad thing). 2. I was thinking of the following structure: * a uniform Event format: joins, parts, actions, normal lines, and everything about them: the user, date and time, etc. * functions that parse logs to a list of events. Exotic log format? Just write a different function! (whatever `exotic' may mean) * functions that do various statistics on a list of events. The output will not be uniform. Examples are: who spoke most, what time people speak most, etc. * some way to make these into a common output form, maybe every above module having two functions, one for `internal' format, and one for converting that to proper output. Now, there will probably be a lot of opportunities to ask for feedback on possible statistics and log formats. My (main) question is whether you see anything conceptually wrong in this approach. With a bit of luck, we will be announcing hirst-0.1 in a few weeks or months (we're doing this while having schoool and other engagements). Thank you for your time, Vlad PS: This is my first post here, please point out any inadequacy. -- There is nothing more dangerous than an idea when it is the only one you have.

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ANN: strictify 0.1
by Sterling Clover 04 Feb '08

04 Feb '08

Dear Friend, Have you ever stared at a maze of Haskell code and thought "Gosh, I'm just feeling lazy today. Everything works, and I mainly understand the strictness characteristics of my program. But I just can't decide where to put those last few bangs. Maybe I don't need to micro-optimize anyway." Sure you have. It's ok. You can let it out. You're among friends here. Why, I bet you've even gone and sprinkled some bangs randomly, hoping for the best. We've all been there. Maybe you even got those pesky strictness annotations right, but a new version of GHC with its ever improving strictness analyzer came along and rendered some obsolete. And yet there they still lie, consuming whole tens of picoseconds worth of your hard-earned processor cycles and troubling your dreams. Well, friend, your dreams need be troubled no more. The time has come for a new era! The era of strictifiericization version 0.1. An era where you can kiss those micro-optimization troubles over silly shootout entries goodbye! Instead of brute-forcing your way through permutations of strictness entries let your computer do the work for you. That's why we invented them after all! Rather than putting "!" in just the right places, put "{- ! -}" in every place you _might_ want a strictness annotation. Then sit back, pop open a cool refreshing brew, and wait (and wait and wait) as strictify does the rest!* Available now now now at hackage: http://hackage.haskell.org/cgi-bin/ hackage-scripts/package/strictify-0.1 Darcs repository at: http://code.haskell.org/~sclv/strictify/ *To prevent exponential running time, strictify only produces a local rather than global optimum of strictness patterns, which should be sufficient in 99% of all cases. Strictify only works on POSIX- compliant systems. Strictify is currently only suitable for "shootout"-style executables which are contained in a single main file, accepting input from argv, stdin, or both. Strictify will not fully execute until it recieves an EOF in stdin. If you cannot produce an EOF through ctrl-D and are not streaming an input file in, you may be forced to run "echo "" | strictify". No guarantee is made, express or implied, as to strictify improving the speed of your program or your mental acuity regarding strictness. Offer void where prohibited. As strictify contains small parts, it is not suitable for children under the age of five. Do not ingest strictify more than seventy five times in a one hour period. If symptoms persist, consult your physician. --S

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more haskeem: it's just scheme in haskell now, no more "almost"
by Uwe Hollerbach 04 Feb '08

04 Feb '08

Hello, haskellers, my mud pies are getting bigger: I have added an exception-handling mechanism to haskeem (ie, for handling exceptions at the scheme level, not the haskell level; that was already working), and also hooked up the REPL to gnu readline: the example code for the readline command was practically tailor-made for me! :-) Also, I must apologize: I screwed up the URL earlier: I had said http://www.korgwal.com/software/haskeem/ and then promptly went and stuck it into http://www.korgwal.com/haskeem/ ... you may attribute that to rapidly-advancing senility, if you like, I won't contradict you. Anyway, I've fixed it by simply putting copies into both places. regards, Uwe Hollerbach

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hdbc, Oracle, and Solaris
by Daniil Elovkov 04 Feb '08

04 Feb '08

Hello folks. I don't understand whether hdbc has a specific Oracle backend or not (not via odbc). It is listed in the description of hdbc, but not really found elsewhere, it seems. I'd like to have a non-odbc support because it is very desirable to have it working on Solaris, and I'm not sure if it will be easy to set it up with odbc there. So, the question might go: has somebody had success with native Oracle support on Solaris with hdbc? Well, or hsql?

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Yi, or Gtk2hs or fedora rpm problem?
by Jon Fairbairn 04 Feb '08

04 Feb '08

This was mentioned on the yi-devel list <http://groups.google.com/group/yi-devel/browse_frm/thread/392c3cd612490b1a/…> but didn't cause much excitement as it's not clear whose problem it is, so I'll ask here as well: I recently downloaded yi-0.3 and tried to build it, but get Loading package base ... linking ... done. Loading package array-0.1.0.0 ... linking ... done. Loading package bytestring-0.9.0.1 ... linking ... done. Loading package regex-base-0.72.0.1 ... linking ... done. Loading package regex-posix-0.72.0.2 ... linking ... done. Loading package regex-compat-0.71.0.1 ... linking ... done. Loading package fingertree-0.0 ... linking ... done. Loading package mtl-1.1.0.0 ... linking ... done. Loading package glib-0.9.12.1 ... linking ... done. Loading package cairo-0.9.12.1 ... linking ... done. yi: /usr/lib/ghc/6.8.2/gtk2hs/HSgtk.o: unknown symbol `containerszm0zi1zi0zi1_DataziSequence_length_info' Loading package gtk-0.9.12.1 ... linking ... yi: exception :: GhcException for any attempted invocation of yi. I don't know whether this problem is specific to yi, to gtk2hs or to the fedora 8 rpm of gtk2hs or something else (ghc 6.8.2). I tried to rpm --rebuild the gtk2hs source rpm, but the build failed, complaining of missing documentation files (the spec file can't be right, or I'd have seen an unsatisfied build-dependency message instead). What's the next step? -- Jón Fairbairn Jon.Fairbairn(a)cl.cam.ac.uk

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SPJ on the radio (at .NET Rocks :)
by Don Stewart 04 Feb '08

04 Feb '08

Simon talks about laziness, purity and other FP concepts to some .NET guys. Simon starts 7minutes 20seconds in. http://www.dotnetrocks.com/default.aspx?ShowNum=310 Good work Simon! -- Don

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ANN: Hlist 0.1 on Hackage
by gwern0＠gmail.com 03 Feb '08

03 Feb '08

Hey everyone: I'd like to make a short announcement that with the permission of its maintainer, I've uploaded HList v0.1 to Hackage. You can find the Hackage page here: <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HList-0.1>. 'cabal install HList' should also work. HList for those who don't know is a sort of OO Haskell package which permits heterogeneous lists; you can find out more at <http://homepages.cwi.nl/~ralf/HList/>. (The Darcs repository is at <http://darcs.haskell.org/HList>.) What changes have been made to the darcs repo? Well, they are mostly updates and cleanups - I've updated build-depends for GHC 6.8.x; largely moved from -fglasgow-exts to LANGUAGE pragmas; put the modules in a proper module namespace; fixed up Haddock generation; removed some unused files, and other things of that nature. -- gwern Covert data bank Armani Larson Missiles Dick CTP SO13 AUTODIN

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Refactoring from State monad to ST monad, for STUArray
by Denis Bueno 03 Feb '08

03 Feb '08

Is it possible to use the ST monad as a (drop-in) replacement for the State monad in the following situation? If not, is there a "best practice" for refactoring? I have a bunch of functions that return state actions: type MyState = ... foo1 :: T1 -> State MyState a foo2 :: T2 -> State MyState a ... foon :: Tn -> State MyState a And I'd like to refactor this to use the ST monad, mechanically, if possible. All uses of the MyState inside State are single-threaded. In my application, MyState is a record with 5 or so fields. One of those fields uses a list to keep track of some information, and I'd like to change that to STUArray, because it changes my bottleneck operations from O(n) to O(1). This, of course, requires having the ST monad around, in order to achieve the proper time complexity. Is there an easy way to do this? In the future, should I *start out* with the ST monad if I suspect I'll need to use an imperative data structure for efficiency reasons? I started out with State because I'm modeling a transition system, so it seemed natural. Any advice is appreciated. -- Denis

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strange GHC assembler failure
by Tim Newsham 03 Feb '08

03 Feb '08

I'm getting a weird build error: [ 9 of 95] Compiling Plugin.Pl.Common ( Plugin/Pl/Common.hs, dist/build/lambdabot/lambdabot-tmp/Plugin/Pl/Common.o ) /tmp/ghc52608_0/ghc52608_0.s: Assembler messages: /tmp/ghc52608_0/ghc52608_0.s:36:0: Error: unassigned file number 1 [... more of these ...] I narrowed this down -- this happens when I add my new library "silc-client" to the "Build-depends:" line in the cabal file even if none of its code is referenced. Removing the dependency makes the error go away. The module I'm referencing is a new one I'm still working on and it makes use of FFI and references external headers and libraries. (I put a copy at http://www.thenewsh.com/~newsham/silc-client.tgz if it helps anyone debug.. this is not release-quality code though). Any idea what is going on here? Tim Newsham http://www.thenewsh.com/~newsham/

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Re: [Haskell-cafe] Circular enums
by Ben Butler-Cole 03 Feb '08

03 Feb '08

On Feb 2, 2008, at 18:41 , I wrote: > No instance for (Bounded a) > arising from use of `maxBound' at Hbot.hs:6:34-41 > (...) > My (clearly flawed) understanding of the signature I've specified > for 'turn' means *exactly* that a is Bounded. Brandon Allbery replied: > The problem is that the scope of a is the type signature; it does > *not* extend to the definition. > > You can try omitting the type on maxBound and minBound, or you > can enable the scoped type variables extension Thank you. This compiles fine with the Glasgow extensions turned on as long as the type in the function signature is universally quantified: turn :: forall a. (Enum a, Bounded a) => Int -> a -> a turn n e = toEnum (add (fromEnum (maxBound::a) + 1) (fromEnum e) n) where add mod x y = (x + y + mod) `rem` mod

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