January 2010 - Haskell-Cafe

cabal install glfw
by Ozgur Akgun 20 Jan '10

20 Jan '10

Dear Cafe and Paul, I am constantly having problems with cabal install in Snow Leopard. Some I solve, some I cannot unfortunately. When I run sudo cabal install glfw -v2 in Snow Leopard, I get the following. glfw/lib/macosx/macosx_enable.c:1:0: error: bad value (apple) for -march= switch glfw/lib/macosx/macosx_enable.c:1:0: error: bad value (apple) for -mtune= switch cabal: Error: some packages failed to install: GLFW-0.4.1 failed during the building phase. The exception was: exit: ExitFailure 1 Regards, -- Ozgur Akgun

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ANNOUNCE: Cardinality-0.1
by Andrey Sisoyev 20 Jan '10

20 Jan '10

Hi everybody! I developed a new package that you may find handy, when transforming containers. With this package we now have unified ways to make safe transforms "from a -> Maybe (to a)" and "from -> Maybe to" between simple containers like [], Maybe, Identity, Map. Test set that returns all True: ((sContTransT []) :: Maybe (Maybe Int)) == Just Nothing ((sContTrans ()) :: Maybe (Maybe Int)) == Just Nothing ((sContTransT [1]) :: (Maybe (Maybe Int))) == Just (Just 1) ((sContTransT [1, 2]) :: (Maybe (Maybe Int))) == Nothing ((sContTransT $ Just "Hello") :: (Maybe (Identity String))) == Just (Identity "Hello") ((sContTransT ["Hello"]) :: Maybe (Identity String)) == Just (Identity "Hello") ((sContTransT (EmptySet :: EmptySet String)) :: (Maybe [String])) == Just [] ((sContTransT "Hello") :: Maybe (EmptySet Char)) == Nothing ((sContTransT ("key", "elem")) :: Maybe (Map String String)) == Just (singleton "key" "elem") ((sContTrans [("key1", "elem1"), ("key2", "elem2")]) :: Maybe (Map String String)) == Just (fromList [("key1", "elem1"), ("key2", "elem2")]) ((sContTrans (EmptySet :: EmptySet (String, String))) :: Maybe (Map String String)) == Just empty ((sContTrans []) :: Maybe ()) == Just () ((sContTrans (NEL 'H' "i!")) :: Maybe String) == Just "Hi!" -- Data.NeverEmptyList ((sContTrans ()) :: Maybe String) == Just "" ((sContTrans "") :: Maybe (Identity Char)) == Nothing ((sContTrans "Hi!") :: Maybe ()) == Nothing Package is to be found here: http://hackage.haskell.org/package/Cardinality It dances around cardinality - a measure of of the number of elements of the set (container); and cardinality constraint of the container. Cardinality constraints: ** (): 0 elements ** Identity a: 1 element ** (Maybe a): 0..1 elements ** [a]: 0..Infinity elements ** Map k e: 0..Infinity elements ** (a,a,a): 3 elements I also introduced 2 containers (which I found strange not to be in the Prelude): ** data EmptySet a = EmptySet -- (0 elements) ** data NeverEmptyList a = NEL a [a] -- (1..Infinity elements) The package provides all sorts of transformation instances between this types (except for tuples, 3ples, 4ples... I didn't make all transforms fo them - only "list -> (N)ple" and opposites) I tried also to deal with transforms like "container a -> a", "a -> container a" using OverlappingInstances. But failed to approve them - probably due to the lack of experience with this extension. I found them introducing too much unwanted complexity into the reasoning about types. It was the last straw to me, when GHC started to proving me, that unity is not less general then any type variable "a", and demanding tribute of IncoherentInstances. ----------------------------------- Any feedback is appreciated. Best regards, Andrey. -- View this message in context: http://old.nabble.com/ANNOUNCE%3A-Cardinality-0.1-tp27239964p27239964.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Fwd: [BostonHaskell] Next meeting: January 21st at MIT (**NEW ROOM** 32G-449)
by Ravi Nanavati 20 Jan '10

20 Jan '10

---------- Forwarded message ---------- From: Ravi Nanavati <ravi_n(a)alum.mit.edu> Date: Wed, Jan 20, 2010 at 12:13 AM Subject: Next meeting: January 21st at MIT (**NEW ROOM** 32G-449) To: bostonhaskell(a)googlegroups.com I'm pleased to announce the January meeting of the Boston Area Haskell Users' Group. The meeting has been scheduled for Thursday, January 21st from 7pm to 9pm. Like recent meetings, it will be at MIT. However, it will be in the Patil/Kiva conference room, NOT the CSAIL reading room. That room is 32G-449 (i.e. a room on the 4th floor of the Gates Tower of MIT's Stata Center at 32 Vassar St in Cambridge, MA). My apologies for the late notice - I've been busy recently. This month, Paul Chiusano and Runar Bjarnason will be presenting "Scala for Haskell Programmers". Scala is a statically-typed functional language that targets the JVM and it has a type system that, in its own way, is as unique as Haskell's. This presentation will take up the bulk of the meeting, but if anyone wants to give a Lightning Talk, there is room for that. The January attendance poll is at: http://doodle.com/xnwcec4w4hbh6y65 As always, responding to this poll will help with two things: 1. Getting an idea of what fraction of the Boston-area Haskell community can and can't attend this meeting (to help with future scheduling). 2. Giving me an estimated count of attendees, since I have talked my wife into baking some more goodies and bringing drinks again. By the way, if someone is willing to edit the HaskellWiki page, post to reddit or otherwise publicize the meeting please just go ahead and do that (especially as I'm sending this out on the later side). If you have any questions about the meeting please send them to them BostonHaskell mailing list: bostonhaskell(a)googlegroups.com or contact me directly. I look forward to seeing many Boston-area Haskellers at the January meeting! Thank you, - Ravi Nanavati

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Re: Atom bug(?)
by Tom Hawkins 19 Jan '10

19 Jan '10

On Tue, Jan 19, 2010 at 10:42 PM, Lee Pike <leepike(a)gmail.com> wrote: > Tom, > > Is this a bug? The following program compiles, but the rule is scheduled at > period 1 (rather than 0). I wouldn't have thought to have an assignment > outside of an atom until another engineer here wrote it. In any event, I > would have expected that the rule should have period 3. > > Lee > > example :: Atom () > example = period 3 $ do > > a <- word32 "a" 0 > > a <== 21 The top-most rule is implied with the compile command. This makes it appear as if the assignment doesn't belong to a rule, when if fact it belongs to the implicit top level rule. The top level rule always has a period of 1. Period constraints are only applied to sub-rules, not the current rule. This prevents ambiguous situations, such as: atom "something" $ do period 1 (a <== 1) -- Does 'something' execute every 1 or ... period 2 (b <== 2) -- 2 cycles? So in your example, 'period 3' has no sub rules that it applies to. -Tom

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Parsers for Text Adventures
by Mark Spezzano 19 Jan '10

19 Jan '10

Hi, I am writing a Text Adventure game in Haskell (like Zork) I have all of the basic parser stuff written as described in Hutton's Programming in Haskell and his associated papers. (I'm trying to avoid using 3rd party libraries, so that I can learn this myself) Everything that I have works (so far...) except for the following problem: I want to define a grammar using a series of Verbs like this: data Verb = Go | Get | Jump | Climb | Give etc, etc deriving (Show, Read) and then have my parser "get" one of these Verb tokens if possible; otherwise it should do something (?) else like give an error message stating "I don't know that command" Now, Hutton gives examples of parsing strings into string whereas I want to parse Strings into my Verbs So, if the user types "get sword" then it will tokenise "get" as type Verb's data constructor Get and perhaps "sword" into a Noun called Sword My parser is defined like this: newtype Parser a = Parser (String -> [(a, String)]) So I CAN give it a Verb type but this is where I run into a problem.... I've written a Parser called keyword keyword :: Parser Verb keyword = do x <- many1 letter return (read x) (read this as "take-at-least-one-alphabetic-letter-and-convert-to-a-Verb-type") which DOES work provided that the user types in one of my Verbs. If they don't, well, the whole thing fails with an Exception and halts processing, returning to GHCi prompt. Question: Am I going about this the right way? I want to put together lots of "data" types like Verb and Noun etc so that I can build a kind of "BNF grammar". Question: If I am going about this the right way then what do I about the "read x" bit failing when the user stops typing in a recognised keyword. I could catch the exception, but typing an incorrect sentence is just a typo, not really appropriate for an exception, I shouldn't think. If it IS appropriate to do this in Haskell, then how do I catch this exception and continue processing. I thought that exceptions should be for exceptional circumstances, and it would seem that I might be misusing them in this context. Thanks Mark Spezzano

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ANNOUNCE: Functional Programming Bibliography
by James Russell 19 Jan '10

19 Jan '10

I am pleased to announce the Functional Programming Bibliography at http://www.catamorphism.net/ The functional programming bibliography was created in the hope that it will be a useful resource to the functional programming community. The site is still in an early stage of development, and is pretty raw, and incomplete in a number of ways. Keyword categorization, in particular, is still fairly spotty. It currently contains in excess of 1500 references, heavily slanted toward Haskell-related topics, and contains links to publicly available versions of many papers, as well as links to gated versions of some papers. I am eager for suggestions as to how the site could be made more useful. Regards, James Russell

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#haskell stopped being logged on tunes.org
by Eugene Kirpichov 19 Jan '10

19 Jan '10

Hello. The #haskell channel stopped being logged because now it accepts only someone who has IDENTIFY'd. For the last 3 days essentially nothing has been recorded. I am not even sure whether this should be fixed on the tunes.org site or on #haskell's, but something has to be done, and I plea those with sufficient power for that to do it :) -- Eugene Kirpichov Web IR developer, market.yandex.ru

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ZuriHac registration deadline on February 14, 2010
by Johan Tibell 19 Jan '10

19 Jan '10

Hi all, Due to budget and security constraints, we need to know the final number of attendees a bit in advance. We've therefore set a registration deadline on February 14, 2010. To register please follow the instructions on the registration page: http://www.haskell.org/haskellwiki/ZuriHac/Register Cheers, Johan & Christophe

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parallel matrix multiply (dph, par/pseq)
by Johannes Waldmann 19 Jan '10

19 Jan '10

Hello. How can I multiply matrices (of Doubles) with dph (-0.4.0)? (ghc-6.12.1) - I was trying type Vector = [:Double:] type Matrix = [:Vector:] times :: Matrix -> Matrix -> Matrix times a b = mapP ( \ row -> mapP ( \ col -> sumP ( zipWithP (*) row col ) ) ( transposeP b ) ) a but there is no such thing as transposeP. When I try any kind of index manipulations, the compiler invariably tells me that it does not want to build [: :] - lists of indices (e.g., there is no enumFromToP) (I guess because I'm using Data.Array.Parallel.Prelude.Double) Puzzled - J.W. PS: what's the recommended way to multiply matrices (better modelled as Array (Int,Int) Double or [[Double]] ?) with the par/pseq approach (if this is recommended at all)? As I said earlier, I just want to have some nice and easy benchmarks for demonstration in a lecture (to be run on 2, 4, or 8 cores). Of course if they work, I'd use them in real life as well...

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Declarative binary protocols
by Antoine Latter 19 Jan '10

19 Jan '10

Cafe, We have some fantastic tools for binary parsing in packages like binary and cereal (and presumably attoparsec, which I've not used). But they don't quite scratch an itch I have when writing implementations of binary communication protocols. A good example of my problem is in my implementation of the memcached binary wire protocol: http://hackage.haskell.org/package/starling What I've tried to do is divide up the library into a declarative protocol description and an imperative machine to sit on a handle and link together a server response with the source request. In the declarative core all of the types which come off of the wire have an associated Data.Binary.Get action - but this isn't quite good enough. Data.Binary works on ByteStrings, but I have a handle. I don't want to use hGetContents because I have trouble working out when lazy IO is and is not correct. I can't use hGet because I don't know how much to get until I'm in the middle of the Get action. How do other folks solve this issue? What I've done is broken down and included (getResponse :: Handle -> IO Response) in my core protocol description module, which gets a fixed-length header from which we can figure out how much else to get to form the complete response. But it would be nice to have something cleaner. One thing I've thought of is generalizing Data.Binary.Get to operate over either ByteStrings or Handles. But then I would be doing reads from the handle every couple of bytes. To avoid that I could extend the monad to include declarations of how many bytes the parser will require, which may be declared mutliple times throughout the parser. This felt a bit weird to me, though. Thanks, Antoine Declarative core module: http://hackage.haskell.org/packages/archive/starling/0.1.1/doc/html/Network… IO-centric module: http://hackage.haskell.org/packages/archive/starling/0.1.1/doc/html/Network…

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