November 2010 - Haskell-Cafe

What's happening at the next Ed Lambda
by Ollie Saunders 04 Nov '10

04 Nov '10

Hello everyone, I know the last meetup was a bit light on content so we've been working hard to make this month different. We've got, not one, but two talks for you: First up: Paul Richards will be talking about functional data structures. In particular, finger trees, which were only discovered in 2006 and offer incredible versatility and performance. Then: I'll be talking about my experiences writing Snake in Haskell using HCurses and property-based testing with QuickCheck. With a bit of luck this talk will assume very little prior knowledge of Haskell. Details: http://www.meetup.com/ed-lambda/calendar/15219997/ Looking forward to seeing you, Ollie

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Re: [Haskell-cafe] Unexpected results from ExitCode
by Peter Schmitz 04 Nov '10

04 Nov '10

Dean, Thanks very much, that indeed worked. -- Peter On Wed, Nov 3, 2010 at 9:16 PM, Dean Herington <heringtonlacey(a)mindspring.com> wrote: > At 8:45 PM -0700 11/3/10, Peter Schmitz wrote: >> >> I have a program (test.hs): >> >>> module Main (main) where >>> import System.Exit >>> main :: IO ExitCode >>> main = do >>> return (ExitFailure 1) >> >> >> In another program, I invoke it via 'system': >> >>> exitCode <- system ".\\test.exe" >>> case (exitCode) of >>> ExitFailure failCnt -> do >>> putStrLn $ "-- Fail count is: " ++ show failCnt >>> exitFailure >>> ExitSuccess -> do >>> putStrLn $ "-- OK." >>> exitSuccess >> >> >> but it always gets ExitSuccess (not ExitFailure failCnt as I expected). >> (I am running under Windows.) >> >> My other use of system (such as with ghc commands) works okay, >> sometimes getting success, sometimes failure, as expected. >> >> Any suggestions much appreciated. >> Thanks, >> -- Peter > > The value returned by `main` is always discarded. You need to use > `exitWith`: > > main = exitWith (ExitFailure 1) >

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Re: [Haskell-cafe] Re: HDBC/ODBC using mysql appears broken...
by John Goerzen 04 Nov '10

04 Nov '10

On 11/04/2010 04:03 PM, Neil Davies wrote: > John > > simple queries seem to work fine. > > main = do > db<- connectODBC connect'string > quickQuery db "select serial from CPE_DEVICE" []>>= print . take 3 > describeTable db "CPE_DEVICE" I'm going to guess that the MySQL ODBC driver isn't implementing the metadata stuff, which is kind of weak in ODBC in general. Can I interest you in PostgreSQL or Sqlite3? ;-) - John > > returns > > [[SqlByteString "1MD16BBV00F74"],[SqlByteString "1MD16BB700D03"],[SqlByteString "1MD16BBH02DCD"]] > *** Exception: Prelude.(!!): index too large > > if that helps.. > > Neil > > On 4 Nov 2010, at 19:41, John Goerzen wrote: > >> On 11/04/2010 01:39 PM, Neil Davies wrote: >>> Hi >>> >>> I've been trying to get the "hello world" example below to work: >>> >>> main = do >>> db<- connectODBC connect'string >>> get Tables db>>= print >> >> I wonder if you might try something other than getTables, which requires some metadata support on the backend? Some simple inserts orselects, perhaps? >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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Re: HDBC/ODBC using mysql appears broken...
by John Goerzen 04 Nov '10

04 Nov '10

On 11/04/2010 01:39 PM, Neil Davies wrote: > Hi > > I've been trying to get the "hello world" example below to work: > > main = do > db<- connectODBC connect'string > get Tables db>>= print I wonder if you might try something other than getTables, which requires some metadata support on the backend? Some simple inserts orselects, perhaps?

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Re: [Haskell-cafe] What is simplest extension language to implement?
by Permjacov Evgeniy 04 Nov '10

04 Nov '10

ehm. I missed something and ghc api is well documented and stable ? The problem is that haskell is overkill here and it requires esoteric extensions for some tasks (Rank2Types for reflection, for example). It is inacceptable for scripting language, faced to no-programmers. Such languages must be as plain and regular, as possible. So, statically typed languages are out of consideration: they either have poor expressive power, or have expressive, but complex type system (as haskell), or relies on hacks within language for some tasks(typecasts and duck typing in c++). Scheme may be acceptable, and possibly EcmaScript. I do not know any other acceptable standartized language. Yet, Scheme has really ugly synthax and Ecma-262 standard is 250 pages long (Of course, it is not C++ with about 1000 pages in standart, but it still hurts to read 250 pages of techdocs in foreign language). On 11/02/2010 12:21 PM, Lennart Augustsson wrote: > I don't understand. Why don't you use Haskell as the scripting language? > > On Tue, Nov 2, 2010 at 7:04 AM, Permjacov Evgeniy <permeakra(a)gmail.com> wrote: >> Let us think, that we need some scripting language for our pure haskell >> project and configure-compile-run is not a way. In such a case a >> reasonably simple, yet standartized and wide known language should be >> implemented. What such language may be? >> R(4/5/6)RS ? >> EcmaScript ? >> Some other ? >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >>

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call for a better timing method
by Jiansen He 04 Nov '10

04 Nov '10

Hello, I want to write a timing method to test sub steps in my program. I tested my timing method as follows: ===== time.hs ===== import Data.Time time :: String -> IO a -> IO a time str a = do start <- getCurrentTime v <- a end <- getCurrentTime let diff = diffUTCTime end start putStrLn $ str ++ showNominalDiffTime (diff) return v showNominalDiffTime :: NominalDiffTime -> String showNominalDiffTime nTime = let timeString = show nTime in take (length timeString - 1) timeString ++ " sec" fun :: IO (Int, [Int]) fun = do i <- time "product: " $ return $! product [1..10000] -- testing strictness : evaluated j <- time "product list: " $ return $! map (\_ -> product [1..10000]) [1..3] -- testing strictness : not evaluated List is in hnf return (i, j) main = fun ===== In the shell ===== $ time ./time product: 0.001813 sec product list: 0.000001 sec real 0m0.006s user 0m0.000s sys 0m0.005s Notice that the ($!) operation will reduce a term to head normal form (hnf), not normal form. In the "product list" testing, the "complicated" map evaluation is reduced to a list of redex. Therefore, the result does not reflect the time needed to get the final value. How could I improve my timing method so that it will give the time to reduce a general expression to normal form? Jiansen

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Re: Splittable random numbers
by Bryan O'Sullivan 04 Nov '10

04 Nov '10

On Thu, Nov 4, 2010 at 11:39 AM, Thomas DuBuisson <thomas.dubuisson(a)gmail.com> wrote: > Before we bother to do that I think it would be worth deciding what > level of performance we are trying to achieve. On my laptop (Core2 > 2.5Ghz) I generate 4MB of random values in less than 900ms (HashDRBG). > What is StdGen getting, which I know people consider slow? I measured StdGen last year as generating around a million values per second. My mwc-random library is about 100 times faster when running in the ST monad.

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Re: [Haskell-cafe] DSL libraries
by Dupont Corentin 04 Nov '10

04 Nov '10

Hello, With your version it compiles. Thanks. Corentin On Thu, Nov 4, 2010 at 7:03 PM, Sebastiaan Visser <s(a)fvisser.nl> wrote: > Dupont, > > The `AwesomePrelude' (we apologize for this name) is a very experimental > project that is not a workable library or executable at all. You can better > consider it to be a `bunch of code' with some interesting ideas and some > interesting potential. > > At least my branch[1] runs on my machine and I'm still able to produce > javascript code. > > But don't expect it to solve any of your problems. ;-) We (at least I) > still have some ideas for this project and hope we can someday revive it. > > Cheers, > Sebastiaan > > [1] https://github.com/sebastiaanvisser/AwesomePrelude > > On Nov 4, 2010, at 6:51 PM, Dupont Corentin wrote: > > Nobody had the compilation messages I had? > > > > ---------- Forwarded message ---------- > > From: Dupont Corentin <corentin.dupont(a)gmail.com> > > Date: Tue, Nov 2, 2010 at 2:30 PM > > Subject: [Haskell-cafe] DSL libraries (Was: Map constructor in a DSL) > > To: steffen <steffen.siering(a)googlemail.com>, haskell-cafe(a)haskell.org > > > > > > Hello Steffen, > > can you compile AwesomePrelude? > > I've got error messages (see below). > > > > By the way, I've looked at some DSLs made in Haskell, if I don't mistake > there are lots of similarities between them. > > There similarities could be put in a library to help the implementors of > a DSL, more or less like AwesomePrelude. > > > > Is there already packages on Hackage dealing with that? > > > > Cheers, > > Corentin > > > > AwesomePrelude compilation error: > > I'm using GHC 6.12.1. > > > > > cd tomlokhorst-AwesomePrelude-9819315 > > > cabal install > > (...) > > Warning: Lang.Haskell: Instances of type and data families are not yet > supported. Instances of the following families will be filtered out: H > > > > > > Then, when trying with a very simple GATD in GHCI, I've got: > > > > <interactive>: HSAwesomePrelude-0.1.0.o: unknown symbol > `AwesomePreludezm0zi1zi0_ > > CompilerziLiftDefinitions_inline_closure' > > ghc: unable to load package `AwesomePrelude-0.1.0' > > > > > > > > On Thu, Oct 28, 2010 at 2:02 PM, steffen <steffen.siering(a)googlemail.com> > wrote: > > I think you would love to have a look at AwesomePrelude[1] or a fork > > of AwesomePrelude using associated types[2] > > Some more background information by Tom Lokhorst [3][4]. > > > > [1] http://github.com/tomlokhorst/AwesomePrelude > > [2] http://github.com/urso/AwesomePrelude > > [3] http://tom.lokhorst.eu/2009/09/deeply-embedded-dsls > > [4] http://tom.lokhorst.eu/2010/02/awesomeprelude-presentation-video > > > > On 28 Okt., 12:09, Dupont Corentin <corentin.dup...(a)gmail.com> wrote: > > > Thank you for your rich responses. > > > > > > Indeed I think I miss some thinks in my DSL, that would make things > easier > > > to deal with lists and first class functions. > > > I don't really know what for now. > > > Perhaps a List Constructor? Or a constructor on functions like yours > Ryan? > > > EAp :: Exp ref (a -> b) -> Exp ref a -> Exp ref b > > > It's from which DSL? It is accessible on the net? > > > > > > Chris suggested me that I can only define the Foldr constructor and > deduce > > > Map from it. > > > But maybe I have to add a List constructor for that. > > > > > > But in the suggestions from Ryan and Brandon I don't understand why I > should > > > add an extra type parameter and what it is! > > > > > > Steffen: Wow nice. I'll integrate that ;) > > > > > > I'm also looking at the Atom's DSL to get inspiration. > > > Something I don't understand in it is that it has two languages, on > typed: > > > > > > data E a where > > > VRef :: V a -> E a > > > Const :: a -> E a > > > Cast :: (NumE a, NumE b) => E a -> E b > > > Add :: NumE a => E a -> E a -> E a > > > etc. > > > > > > And, along with it, an untyped counterpart: > > > > > > -- | An untyped term. > > > data UE > > > = UVRef UV > > > | UConst Const > > > | UCast Type UE > > > | UAdd UE UE > > > etc. > > > > > > What that for? What's the use of having beautiful GADT if you have to > > > maintain an untyped ADT aside?? > > > > > > Corentin > > > > > > _______________________________________________ > > > Haskell-Cafe mailing list > > > Haskell-C...@haskell.orghttp:// > www.haskell.org/mailman/listinfo/haskell-cafe > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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Non-hackage cabal source
by Tony Morris 04 Nov '10

04 Nov '10

I am trying to set up an apache server as an additional source to hackage for haskell packages. I have added to my ~/.cabal/config file: remote-repo: myhackage:http://myhackage/packages I am able to successfully make the HTTP requests: http://myhackage/packages/00-index.tar.gz http://myhackage/packages/MyPackage/0.0.1/MyPackage-0.0.1-tar.gz I can execute: $ tar -tvf 00-index.tar.gz -rw-r--r-- root/root 1491 2010-11-03 15:16 ./MyPackage/0.0.1/MyPackage.cabal However, when I try to unpack my package with cabal: $ cabal unpack MyPackage Downloading MyPackage-0.0.1... cabal: Failed to download http://myhackage/packages/package/MyPackage-0.0.1.tar.gz : ErrorMisc "Unsucessful HTTP code: 404" Why is cabal even making this request? Why is it not making the request to http://myhackage/packages/MyPackage/0.0.1/MyPackage-0.0.1.tar.gz Thanks for any tips. -- Tony Morris http://tmorris.net/

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Import proposal from Haskell'?
by John Smith 04 Nov '10

04 Nov '10

Type-directed name resolution was proposed by SPJ for Haskell', but not for GHC. Is there any particular process for importing tickets from Haskell' to GHC? http://hackage.haskell.org/trac/haskell-prime/ticket/129

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