- Haskell-Cafe - Haskell.org

Iteratee stack-consumption
by Tony Morris 30 May '11

30 May '11

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I have written iteratees on the JVM, which does not include tail-call in its instruction set. They incur a stack frame per iteratee input, which can be expensive and unable to scale beyond a few thousand. Is there some trick to permitting this? Some sort of chunking the enumeratee or something? I was unable to find any good general hints in any of the hackage libraries. Thanks for any pointers. - -- Tony Morris http://tmorris.net/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk3jNHEACgkQmnpgrYe6r63QcACfSeZvvy+iYVisZ3e/dhWQd3D6 790AnRZCjJT6eCY21XlsVqcpTuamfuXY =ADo5 -----END PGP SIGNATURE-----

1 0

Re: [Haskell-cafe] State Machine and the Abstractions
by Chuzzle Guevero 29 May '11

29 May '11

For one, you have a kind error. You use Mission as a Monad when it only has kind *. I don't know much of arrows, but I suggest writing the combinators you want to have with specialized types, and see where that takes you. If it happens to lead to an implementation of Arrow, yay. If it doesn't, then you at least still have something that functions. > Message: 13 > Date: Fri, 27 May 2011 21:06:10 +0200 > From: Yves Par?s<limestrael(a)gmail.com> > Subject: [Haskell-cafe] State Machine and the Abstractions > To: Haskell-Cafe<haskell-cafe(a)haskell.org> > Message-ID:<BANLkTikVb-zhyTVR%3DjT03hFiBAKrERxsLQ(a)mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Hello, > > For the purposes of a simple strategy game, I'd like to build an EDSL that > expresses missions. A mission could be represented as a state machine. > With basic bricks such as actions (MoveTo, ShootAt...) or tests > (EnemiesAround, LowHealth...), I could (ideally dynamically) build some > strategic behaviors for the units. > I will take the example of a patrol. Applied to a unit (or a group of > units), it dictates : go from point 1 to point 2 and then go back and > repeat. But when you detect an enemy near, leave the patrol path, destroy it > and then resume your patrol where you left it. > > So if I consider my mission as a monad: > data Mission = MoveTo Point | ShootAt Unit > > patrol = do > MoveTo point1 > MoveTo point2 > patrol > > So far so good, but there, the only advantage to use a monad instead of a > list of MoveTo's is the do-notation. > And I lack the expression of tests. Using a GADT it could be: > > data Mission a where > MoveTo :: Point -> Mission () > ShootAt :: Unit -> Mission Bool -- If we have destroyed it or not > EnemiesAround :: Mission [Unit] -- The enemies that are maybe in sight > LowHealth :: Mission Bool -- If I should retreat > ... > > -- (Monad Mission could be nicely expressed using Heinrich Apfelmus' * > operational* package) > > patrol = do > MoveTo point1 > MoveTo point2 > enemies<- EnemiesAround > mapM_ ShootAt enemies > patrol > > Aaaaaaaand... here comes the trouble: the actions are done *sequentially*. > My units will move and then look at enemies, they will not monitor their > environment while they move. > So I need a way to say: A is your action of patrolling. B is your action of > surveillance. Do both in parallel, but B is preponderant, as if it successes > (if enemies are there) it takes over A. So, it is as if I was running two > state machines in parallel. > Moreover, the last line (the recursive call to patrol) is wrong, as it will > restart the patrol from the beginning, and not from where it has been left. > But this could be corrected by addind a test like "which point is the > closest". > > So I thought about Arrows, as they can express sequential and parallel > actions, but I don't know if it would be a right way to model the > interruptions/recoveries. > What do you think about it? Do you know of similar situations and of the way > they've been solved?

3 2

Utrecht Summer School in Applied Functional Programming
by João Paulo Pizani Flor 29 May '11

29 May '11

Hi dear Haskellers! I'm a senior undergraduate Computer Science student in Brazil, and have always loved Haskell and wrote most of my lab assignments and course projects in it. Haskellers are a very rare species here in Brazil, but I always tried my best to motivate people around me presenting some seminars, writing some tutorials, etc. My personal Haskell project: http://launchpad.net/presto What joy I had then last Friday, when I found out I've been accepted to participate in the Utrecht Summer School 2011, in the course "Applied Functional Programming in Haskell" (http://www.utrechtsummerschool.nl/index.php?type=courses&code=H9) In fact, I got a scholarship from Utrecht University that covers tuition fees and housing, but not the plane tickets to/from the Netherlands. That's the point where I need your advice: without some sort of financial support I won't be able to buy the tickets and travel to Utrecht. I am already searching from grants here in Brazil, but I think it will be hard to find something, not to say impossible. So, do you know any program/fund/foundation to which I can apply and get the needed financial support? Best regards, João Paulo Pizani Flor joaopizani(a)gmail.com Computer Science Federal University of Santa Catarina - Brazil

1 0

Escaping of string literals
by Michael Snoyman 29 May '11

29 May '11

Hi all, I'm working on a program right now that will involve embedding some static files inside my Haskell program as bytestrings. I've done this in the past with file-embed[1]. In this case, I have a strange requirement: I need to be able to modify the embedded data after the compiler has run. In general, I've gotten the code to work (and will soon be following up with a blog post explaining). But in this process, I ran into something I found interesting. If I run this program: {-# LANGUAGE TemplateHaskell #-} import Data.ByteString.Unsafe (unsafePackAddressLen) import Language.Haskell.TH.Syntax import qualified Data.ByteString as S main = do fromAddr <- unsafePackAddressLen 7 $(return $ LitE $ StringPrimL "123\0\&456") print fromAddr let fromStr = S.pack $ map (toEnum . fromEnum) $(return $ LitE $ StringL "123\0\&456") print fromStr I get the result: "123\192\128\&45" "123\NUL456" My understanding is that GHC is automatically escaping the non-ASCII characters in the strings. When I use StringL, GHC also automatically unescapes the bytes, so everything works as expected. In the case of StringPrimL, there is no point at which the unescaping occurs. I haven't been able to find the rules on how this escaping functions. Can anyone point it out to me? Also, for my case, it would be very useful to be able to bypass the escaping. I can easily do so with a post-process on the executable to embed raw bytes, but I'm wondering if there's some way to convince StringPrimL not to do any escaping. Thanks, Michael [1] http://hackage.haskell.org/package/file-embed

2 2

No fish, please
by Andrew Coppin 28 May '11

28 May '11

Both Hackage and Cabal seem to assume as a matter of course that I want to use Haddock to generate all my documentation. Suppose I decide to violate this assumption. Then what? 1. Is there some way I can include my own HTML documentation in the package tarball and have Hackage/Cabal use it? 2. Is there a way to tell Hackage/Cabal to use some tool besides Haddock?

8 13

representing spreadsheets
by Eric Rasmussen 28 May '11

28 May '11

Hi everyone, I'm hoping someone can point me in the right direction for a project I'm working on. Essentially I would like to represent a grid of data (much like a spreadsheet) in pure code. In this sense, one would need functions to operate on the concepts of "rows" and "columns". A simple "cell" might be represented like this: data Cell = CellStr Text | CellInt Integer | CellDbl Double | CellEmpty The spreadsheet analogy isn't too literal as I'll be using this for data with a more regular structure. For instance, one grid might have 3 columns where every item in column one is a CellStr, every item in column two a CellStr, and every item in column 3 a CellDbl, but within a given grid there won't be surprise rows with extra columns or columns that contain some cell strings, some cell ints, etc. Representing cells in a matrix makes the most sense to me, in order to facilitate access by columns or rows or both, and I'd like to know if there's a particular matrix library that would work well with this idea. However, I'm certainly open to any other data structures that may be better suited to the task. Thanks! Eric

4 6

Enterprise Haskell -- help
by Srinivasan Balram 27 May '11

27 May '11

folks: I was advised to post this request here. This is about needs of daily-grind enterprise development. Enterprise developers need 3 categories of books in Haskell urgently: (i) Haskell (CookBooks / Recipes) (ii) Haskell Enterprise Development i.e. how to connect commercial RDBMS and use Haskell along with SQL effectively (iii) Haskell Web/Network Development Books by Don Stewart & Miran Lipovaca are excellent for beginner/intermediaries. Erik Meijer's tutorial videos were very useful as well. But they are not enough. This may sound boring, but such books are badly needed "today". It's hard to convince clients/devs to start projects "without such resources". I am trying to push for Enterprise Haskell projects. Would appreciate pointers to resources for doing large scale Haskell development Thank you -ram

8 12

Re: [Haskell-cafe] Policy for taking over a package on Hackage
by Mario Blažević 27 May '11

27 May '11

On 11-05-25 08:52 AM, Johan Tibell wrote: > On Wed, May 25, 2011 at 2:01 PM, Ivan Lazar Miljenovic > <ivan.miljenovic(a)gmail.com> wrote: >> With my wl-pprint-text package, Jason Dagit suggested to me on >> #haskell that it would make sense to make such a pretty-printer be >> class-based so that the same API could be used for String, ByteString, >> Text, etc. > I'm a bit skeptical of using type classes to abstract over Unicode > string types and byte sequence types. The only API shared by the two > kind of types is that of a sequence. Things like dot , spaces, etc. > don't make much sense on binary data. You must assume that the > ByteString contains text in some encoding to make sense of such > concepts. You don't necessarily need spaces and dot to abstract over bytestrings and Unicode string types. They both implement IsString and Monoid classes, as well as operations null, length, isPrefixOf, take, and drop. That's sufficient to implement a generic parser that works on any input type supporting these operations (see [1] for example), though there is some performance cost. I don't see why a pretty-printer should be any more difficult. [1] http://hackage.haskell.org/package/incremental-parser

1 0

Parallel compilation and execution?
by michael rice 27 May '11

27 May '11

How do I compile and run this parallel program? Michael =========================== import Control.Parallel nfib :: Int -> Intnfib n | n <= 1 = 1 | otherwise = par n1 (seq n2 (n1 + n2 + 1)) where n1 = nfib (n-1) n2 = nfib (n-2) {-nfib :: Int -> Intnfib n | n <= 1 = 1 | otherwise = nfib (n-1) + nfib (n-2)-} main = do putStrLn $ show $ nfib 39 =========================== [michael@hostname ~]$ ghc --make -threaded nfib.hs[michael@hostname ~]$ ./nfib +RTS -N3nfib: the flag -N3 requires the program to be built with -threadednfib: nfib: Usage: <prog> <args> [+RTS <rtsopts> | -RTS <args>] ... --RTS <args>nfib: nfib: +RTS Indicates run time system options follownfib: -RTS Indicates program arguments follownfib: --RTS Indicates that ALL subsequent arguments will be given to thenfib: program (including any of these RTS flags)nfib: nfib: The following run time system options are available:nfib: nfib: -? Prints this message and exits; the program is not executednfib: --info Print information about the RTS used by this programnfib: nfib: -K<size> Sets the maximum stack size (default 8M) Egs: -K32k -K512knfib: -k<size> Sets the initial thread stack size (default 1k) Egs: -k4k -k2mnfib: nfib: -A<size> Sets the minimum allocation area size (default 512k) Egs: -A1m -A10knfib: -M<size> Sets the maximum heap size (default unlimited) Egs: -M256k -M1Gnfib: -H<size> Sets the minimum heap size (default 0M) Egs: -H24m -H1Gnfib: -m<n> Minimum % of heap which must be available (default 3%)nfib: -G<n> Number of generations (default: 2)nfib: -T<n> Number of steps in younger generations (default: 2)nfib: -c<n> Use in-place compaction instead of copying in the oldest generationnfib: when live data is at least <n>% of the maximum heap size set withnfib: -M (default: 30%)nfib: -c Use in-place compaction for all oldest generation collectionsnfib: (the default is to use copying)nfib: -w Use mark-region for the oldest generation (experimental)nfib: nfib: -t[<file>] One-line GC statistics (if <file> omitted, uses stderr)nfib: -s[<file>] Summary GC statistics (if <file> omitted, uses stderr)nfib: -S[<file>] Detailed GC statistics (if <file> omitted, uses stderr)nfib: nfib: nfib: -Z Don't squeeze out update frames on stack overflownfib: -B Sound the bell at the start of each garbage collectionnfib: nfib: -hT Heap residency profile (output file <program>.hp)nfib: -i<sec> Time between heap samples (seconds, default: 0.1)nfib: nfib: -C<secs> Context-switch interval in seconds.nfib: 0 or no argument means switch as often as possible.nfib: Default: 0.02 sec; resolution is set by -V below.nfib: -V<secs> Master tick interval in seconds (0 == disable timer).nfib: This sets the resolution for -C and the profile timer -i.nfib: Default: 0.02 sec.nfib: nfib: --install-signal-handlers=<yes|no>nfib: Install signal handlers (default: yes)nfib: nfib: RTS options may also be specified using the GHCRTS environment variable.nfib: nfib: Other RTS options may be available for programs compiled a different way.nfib: The GHC User's Guide has full details.nfib: [michael@hostname ~]$

6 10

Strange Type Error
by jean-christophe mincke 27 May '11

27 May '11

Hello, Could anyone help me understand what is wrong with the definition of f2 in the code below? class C a b where convert :: a -> b convertToInt :: (C a Int) => a -> Int convertToInt x = convert x f1 x = convertToInt x f2 = \x -> convertToInt x f3 :: (C a Int) => a -> Int f3 = \x -> convertToInt x Thank you Regards J-C

3 4