- Haskell-Cafe - Haskell.org

Standard 'decorator' class?
by Jacques Carette 23 Sep '11

23 Sep '11

Has a class like class Decoration t where type Datum t :: * value :: t -> Datum t been defined in any of the haskell packages on hackage? [There are so many variants on naming, it is rather difficult to search for this] Jacques

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Re: [Haskell-cafe] Fwd: problem with cabal install MissingH-1.1.1.0
by Tom Murphy 23 Sep '11

23 Sep '11

I used to have a lot of cabal problems when running a version of the GHC installed with MacPorts. I notice you're using homebrew. Maybe that's part of the problem? Tom On Sep 22, 2011 8:11 PM, "Mariano Cortesi" <mcortesi(a)gmail.com> wrote:

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[ANNOUNCE] skein-0.1: Skein, a family of cryptographic hash functions. Includes Skein-MAC as well.
by Felipe Almeida Lessa 23 Sep '11

23 Sep '11

Hello! I'm pleased to announce the first version of the skein package [1]! Skein is a family of fast secure cryptographic hash functions [2]. The skein package provides high-level bindings (using crypto-api [3]) to the optimized Skein C library. Currently we support Skein as a hash function and also Skein as a message authentication code (MAC). The code is well-documented with examples and has many known answer tests (KATs). It currently lives on patch-tag [4]. Hackage will be build the docs soon enough. Meanwhile, here's a short example: Prelude> :s -XOverloadedStrings Prelude> :m Crypto.Skein Crypto.Classes Data.ByteString.Char8 Data.Serialize Prelude Crypto.Skein Crypto.Classes Data.ByteString.Char8 Data.Serialize> encode (hash' "Haskell" :: Skein_512_512) "b\227\213t\170\GS\131w\151\240\160\183\205\US\169\138\&6\239\215\156\227\SI\234\142P\132\182\SOH\180t\203b\147\190\DLE{\168\214\DC1\238\232y\168\161s\207\172\216\a\202\130c$\SYN\asD<\151\201D\138A\SUB" Prelude Crypto.Skein Crypto.Classes Data.ByteString.Char8 Data.Serialize> encode (skeinMAC' "secretkey" "Haskell" :: Skein_512_512) "_i>.Z\129\ENQ\217L\t9BZ\220\163c&9#\135\234A{\181\&2*\149\STX\216_\DC43\bF\189\196D\r ;\208\EOT}\ENQY\147\232\244e/;4\212!\224\US\138\138\234q=1\129\244" Enjoy! =D [1] http://hackage.haskell.org/package/skein [2] http://swww.skein-hash.info/ [3] http://hackage.haskell.org/package/crypto-api [4] https://patch-tag.com/r/felipe/skein/ -- Felipe.

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Package versioning policy - Harmless type changes?
by Heinrich Apfelmus 23 Sep '11

23 Sep '11

Dear all, the package versioning policy specifies that changing the type of any entity makes a change of the B number in A.B.C necessary. However, it seems to me that a small selection of type changes don't break dependent code. In particular, consider the following example, where I drop a Typeable class constraint: - foo :: Typeable a => AddHandler a -> NetworkDescription (Event a) + foo :: AddHandler a -> NetworkDescription (Event a) Can removing a type class constraint on a function break dependent code? Should I change the B number or just the C in version A.B.C when introducing this change? Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com

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regex-applicative library needs your help! (algorithmic challenge)
by Roman Cheplyaka 23 Sep '11

23 Sep '11

Please help make the regex-based parsing library efficient! https://github.com/feuerbach/regex-applicative/wiki/Call-For-Help -- Roman I. Cheplyaka :: http://ro-che.info/

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Quick check finite data generation
by mukesh tiwari 23 Sep '11

23 Sep '11

Hello all I have a data type data Index = Index {indexSize::Float, indexIds::[Int], indexDown::(IntMap.IntMap Index)} | IndexLeaf {indexSize::Float, indexIds::[Int]} | IndexEmpty {indexSize::Float} deriving ( Show , Eq ) I derived some thing like this for QuickCheck testing instance Arbitrary a => Arbitrary ( IntMap a ) where arbitrary = liftM IntMap.fromList arbitrary instance Arbitrary Index where arbitrary = oneof [ liftM3 Index arbitrary arbitrary arbitrary , liftM2 IndexLeaf arbitrary arbitrary , liftM IndexEmpty arbitrary ] but its generating infinite list of data. After reading the paper QuickCheck: A Lightweight Tool for Random Testing of Haskell Programs<http://www.eecs.northwestern.edu/%7Erobby/courses/395-495-2009-fall/quick.p…> <http://www.eecs.northwestern.edu/%7Erobby/courses/395-495-2009-fall/quick.p…> i tried to write above one using sized but i am not sure how to write this . instance Arbitrary a => Arbitrary ( IntMap a ) where arbitrary = liftM IntMap.fromList arbitrary instance Arbitrary Index where arbitrary = sized arbIndex arbIndex 0 = liftM IndexEmpty arbitrary arbIndex 1 = liftM2 IndexLeaf arbitrary arbitrary arbIndex n = frequency [ ( 1 , liftM IndexEmpty arbitrary ) , ( 1 , liftM2 IndexLeaf arbitrary arbitrary ) , ( 2 , liftM2 Index arbitrary arbitrary ( arbIndex $ div n 2 ) ) ] but from this type i can see arbIndex $ div n 2 will return Gen Index not Gen ( IntMap Index ) and i am getting compiler error . Could some one please tell me , how to write arbIndex n in terms of smaller n like in the paper arbTree 0 = liftM Leaf arbitrary arbTree n = frequency[ ( 1 , liftM Leaf arbitrary ) , ( 4 , liftM2 Branch ( arbTree $ div n 2 ) ( arbTree $ div n 2 ) ) ] Thank You Mukesh Tiwari

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ANN: New releases in the lightweight monadic regions family
by Bas van Dijk 22 Sep '11

22 Sep '11

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problem with cabal install MissingH-1.1.1.0
by Mariano Cortesi 22 Sep '11

22 Sep '11

Hi, My name is mariano and I'm quite new to haskell. I trying to setup up my environment and use the eclipse plugin for haskell. But is not working property because, it tries to compile the scion browser and this depends on MissingH which fails on build. I'm with mac OS X lion, ghc version 7.2.1 and when a i try to install MissingH version 1.1.1.0 it fails with [24 of 47] Compiling Data.BinPacking ( src/Data/BinPacking.hs, dist/build/Data/BinPacking.o ) src/Data/BinPacking.hs:45:6: Illegal datatype context (use -XDatatypeContexts): (Num size, Ord size, Show size, Show obj) => cabal: Error: some packages failed to install: MissingH-1.1.1.0 failed during the building phase. The exception was: ExitFailure 1 Any ideas? I don't know what to do :S best, Mariano

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Re: [Haskell-cafe] Quickcheck, Arbitrary and Overlapping instances
by Valentin Robert 22 Sep '11

22 Sep '11

I think it is one case where you should use newtype instead of type, so that it is not just a simple type synonym, but an actual "other" type. With type, you're just making an alias, but Haskell sees the same type. A newtype wrapper will hide this, at the price of having to define a (unique) constructor... So yes, you'll have to change some code.

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Proposal: Subcomputations in arrow notation
by Ertugrul Soeylemez 22 Sep '11

22 Sep '11

Hello fellow Haskellers, this is a proposal to extend the arrow notation (-XArrows). I find myself writing the following very often: system :: Wire IO () String system = proc _ -> do botAddPeriod <- succ ^<< noise -< () botAddSpeed <- noise1 -< () botAddStart <- noise1 -< () botMsg <- event addBot -< (botAddPeriod, botAddSpeed, botAddStart) bots <- manager -< ((), maybe MgrNop id botMsg) let botStr = concatMap (printf "%8.2") . M.elems $ bots :: String identity -< printf "Bot positions: %s" botStr where addBot :: Wire IO (Double, Double, Double) (MgrMsg Int IO () Double) addBot = proc (addPeriod, addSpeed, addStart) -> do periodically -< addPeriod botId <- identifier -< () identity -< MgrAdd botId (constant addSpeed >>> integral addStart) The relevant part is the first paragraph of the first arrow computation: botAddPeriod <- succ ^<< noise -< () botAddSpeed <- noise1 -< () botAddStart <- noise1 -< () botMsg <- event addBot -< (botAddPeriod, botAddSpeed, botAddStart) This line should generate a message for the bot manager at random intervals. The actual event generator is in the second arrow computation 'addBot'. I would like to be able to write this more in line with the rest of the code. The following is possible: system :: Wire IO () String system = proc _ -> do botAddPeriod <- succ ^<< noise -< () botAddSpeed <- noise1 -< () botAddStart <- noise1 -< () botMsg <- event (proc (addPeriod, addSpeed, addStart) -> do periodically -< addPeriod botId <- identifier -< () identity -< MgrAdd botId (constant addSpeed >>> integral addStart)) -< (botAddPeriod, botAddSpeed, botAddStart) bots <- manager -< ((), maybe MgrNop id botMsg) let botStr = concatMap (printf "%8.2") . M.elems $ bots :: String identity -< printf "Bot positions: %s" botStr This is probably not a big improvement. It's more concise, but also harder to understand. My proposal is to add syntax to allow the following notation: system :: Wire IO () String system = proc _ -> do botAddPeriod <- succ ^<< noise -< () botAddSpeed <- noise1 -< () botAddStart <- noise1 -< () botMsg <- event $ do periodically -< addPeriod botId <- identifier -< () identity -< MgrAdd botId (constant addSpeed >>> integral addStart) bots <- manager -< ((), maybe MgrNop id botMsg) let botStr = concatMap (printf "%8.2") . M.elems $ bots :: String identity -< printf "Bot positions: %s" botStr Again the relevant part is the event generator in the middle. In this hypothetical syntax, the compiler would figure out from the inner computation, which variables from the outer scope are used and pass them automatically in an appropriate tuple. You wouldn't need any explicit passing anymore. If others like the idea, too, and there is nobody to implement it, then I would be willing to get in touch with the GHC code and implement this as a patch myself. What do you think? Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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