- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Random number example
by michael rice 28 Apr '09

28 Apr '09

How do I define type Random [Int] for rollNDice in Exercise 1, given the code below? Michael ============ Exercises 1. Implement rollNDice :: Int -> Random [Int] from the previous subsection with >>= and return. NOTE: Since >>= and return are already present in the Prelude, you may want to use import Prelude hiding ((>>=),return) to avoid compilation errors. ================= {-# LANGUAGE NoImplicitPrelude #-} import Prelude hiding ((>>), (>>=), return) type Seed = Int type Random a = Seed -> (a, Seed) randomNext :: Seed -> Seed randomNext rand = if newRand > 0 then newRand else newRand + 2147483647 where newRand = 16807 * lo - 2836 * hi (hi,lo) = rand `divMod` 127773 rollDie :: Random Int rollDie seed = ((seed `mod` 6) + 1, randomNext seed) (>>) :: Random a -> Random b -> Random b (>>) m n = \seed0 -> let (result1, seed1) = m seed0 (result2, seed2) = n seed1 in (result2, seed2) (>>=) :: Random a -> (a -> Random b) -> Random b (>>=) m g = \seed0 -> let (result1, seed1) = m seed0 (result2, seed2) = (g result1) seed1 in (result2, seed2) return :: a -> Random a return x = \seed0 -> (x, seed0) sumTwoDice :: Random Int sumTwoDice = rollDie >>= (\die1 -> rollDie >>= (\die2 -> return (die1 + die2))) rollNDice :: Int -> Random [Int] --- On Thu, 4/23/09, michael rice <nowgate(a)yahoo.com> wrote: From: michael rice <nowgate(a)yahoo.com> Subject: Re: [Haskell-cafe] Random number example To: "Ross Mellgren" <rmm-haskell(a)z.odi.ac> Cc: haskell-cafe(a)haskell.org Date: Thursday, April 23, 2009, 5:49 PM Hi Ross, Thanks for going the extra mile. A lot of what you did I haven't seen before, so it's going to take me some time to go through it. But I'll be back. Michael --- On Thu, 4/23/09, Ross Mellgren <rmm-haskell(a)z.odi.ac> wrote: From: Ross Mellgren <rmm-haskell(a)z.odi.ac> Subject: Re: [Haskell-cafe] Random number example To: "michael rice" <nowgate(a)yahoo.com> Cc: haskell-cafe(a)haskell.org Date: Thursday, April 23, 2009, 11:51 AM So there are a couple problems. First is you are trying to rebind prelude functions, when instead you should be creating an instance of Monad. This requires a bit of shuffling because without language extensions you can't instance Monad Random for your type of Random, as it is a type synonym. So, changing the type synonym to a newtype and instancing monad, you get: module Rand9b where import Control.Applicative (Applicative(..), (<$>), (<*>))import Control.Monad (ap, liftM) type Seed = Intnewtype Random a = Rand { unRand :: (Seed -> (a, Seed)) } randomNext :: Seed -> SeedrandomNext rand = if newRand > 0 then newRand else newRand + 2147483647 where newRand = 16807 * lo - 2836 * hi (hi,lo) = rand `divMod` 127773 rollDie :: Random IntrollDie = Rand $ \ seed -> ((seed `mod` 6) + 1, randomNext seed) instance Monad Random where (>>=) = randomBind return = randomReturn instance Functor Random where fmap = liftM instance Applicative Random where pure = return (<*>) = ap randomBind :: Random a -> (a -> Random b) -> Random bm `randomBind` g = Rand $ \seed0 -> let (result1, seed1) = unRand m $ seed0 (result2, seed2) = unRand (g result1) $ seed1 in (result2, seed2) randomReturn :: a -> Random arandomReturn x = Rand $ \ seed0 -> (x, seed0) sumTwoDice :: Random IntsumTwoDice = (+) <$> rollDie <*> rollDie I also threw in instances of Functor and Applicative, so that I could simplify sumTwoDice using applicative form (much nicer, no? Applicative is totally rockin') Now you need one more thing, a way to convert a series of Random actions into a pure function: runRandom :: Seed -> Random a -> arunRandom s f = fst . unRand f $ s which now makes what you want to do in GHCi easy and well wrapped: Prelude> :reload[1 of 1] Compiling Rand9b ( rand9b.hs, interpreted )Ok, modules loaded: Rand9b.*Rand9b> runRandom 0 sumTwoDice3 Hope this helps,-Ross On Apr 23, 2009, at 11:28 AM, michael rice wrote: I pretty much followed the sequence of steps that led to this final code (see below), but will be looking it over for a while to make sure it sinks in. In the meantime, I get this when I try to use it (sumTwoDice) at the command line: [michael@localhost ~]$ ghci rand9 GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( rand9.hs, interpreted ) Ok, modules loaded: Main. *Main> sumTwoDice <interactive>:1:0: No instance for (Show (Seed -> (Int, Seed))) arising from a use of `print' at <interactive>:1:0-9 Possible fix: add an instance declaration for (Show (Seed -> (Int, Seed))) In a stmt of a 'do' expression: print it *Main> Can I employ a 'do' expression from the command line? Also, can I now use functions (>>) (>>=) and 'return' defined in the Prelude and still have this code work? Michael ================== {-# LANGUAGE NoImplicitPrelude #-} import Prelude hiding ((>>), (>>=), return) type Seed = Int type Random a = Seed -> (a, Seed) randomNext :: Seed -> Seed randomNext rand = if newRand > 0 then newRand else newRand + 2147483647 where newRand = 16807 * lo - 2836 * hi (hi,lo) = rand `divMod` 127773 rollDie :: Random Int rollDie seed = ((seed `mod` 6) + 1, randomNext seed) (>>) :: Random a -> Random b -> Random b (>>) m n = \seed0 -> let (result1, seed1) = m seed0 (result2, seed2) = n seed1 in (result2, seed2) (>>=) :: Random a -> (a -> Random b) -> Random b (>>=) m g = \seed0 -> let (result1, seed1) = m seed0 (result2, seed2) = (g result1) seed1 in (result2, seed2) return :: a -> Random a return x = \seed0 -> (x, seed0) sumTwoDice :: Random Int sumTwoDice = rollDie >>= (\die1 -> rollDie >>= (\die2 -> return (die1 + die2))) _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -----Inline Attachment Follows----- _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

2 1

Converting IO [XmlTree] to [XmlTree]
by rodrigo.bonifacio 28 Apr '09

28 Apr '09

20 33

ghci debugger problem with :continue. is it broken, or is it me?
by Thomas Hartman 28 Apr '09

28 Apr '09

In the program below, can someone explain the following debugger output to me? After :continue, shouldn't I hit the f breakpoint two more times? Why do I only hit the f breakpoint once? Is this a problem in the debugger? thartman@ubuntu:~/haskell-learning/debugger>cat debugger.hs -- try this: -- ghci debugger.hs -- > :break f -- > :trace t -- > :history -- should show you that f was called from h t = h . g . f $ "hey!" t2 = h . g . f $ "heh!" t3 = h . g . f $ "wey!" f = ("f -- " ++) g = ("g -- " ++) h = ("h -- " ++) ts = do putStrLn $ t putStrLn $ t2 putStrLn $ t3 {- Problems using :continue in the ghci debugger? Can someone explain the following debugger output to me? After :continue, shouldn't I hit the f breakpoint two more times? Why do I only hit the f breakpoint once? Is this a problem in the debugger? thartman@ubuntu:~/haskell-learning/debugger>ghci debugger.hs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( debugger.hs, interpreted ) Ok, modules loaded: Main. *Main> :break f Breakpoint 0 activated at debugger.hs:12:4-15 *Main> ts h -- g -- Stopped at debugger.hs:12:4-15 _result :: [Char] -> [Char] = _ 11 12 f = ("f -- " ++) ^^^^^^^^^^^^ 13 g = ("g -- " ++) [debugger.hs:12:4-15] *Main> :continue f -- hey! h -- g -- f -- heh! h -- g -- f -- wey! *Main> -}

2 3

LondonHUG talk: Engineering Large Projects in Haskell
by Don Stewart 28 Apr '09

28 Apr '09

Slides from last week's London HUG http://www.londonhug.net/ talk are now online. The talk attempts to document some of the tips and tricks Galois has accumulated using Haskell commercially for the past 10 years. You can now read the slides of the talk here: http://www.galois.com/blog/2009/04/27/engineering-large-projects-in-haskell… Cheers, Don

1 0

Problem with installing phooey
by Daryoush Mehrtash 28 Apr '09

28 Apr '09

When I try to install Phooey I get the following error: cabal install --constraint="Stream == 0.3" phooey Resolving dependencies... [1 of 1] Compiling Main ( /tmp/phooey-2.016943/phooey-2.0/Setup.lhs, /tmp/phooey-2.016943/phooey-2.0/dist/setup/Main.o ) Linking /tmp/phooey-2.016943/phooey-2.0/dist/setup/setup ... Configuring phooey-2.0... Warning: No 'build-type' specified. If you do not need a custom Setup.hs or ./configure script then use 'build-type: Simple'. Preprocessing library phooey-2.0... Building phooey-2.0... src/Graphics/UI/Phooey/WinEvents.hs:66:7: Could not find module `Data.Reactive': Use -v to see a list of the files searched for. It seems that the current version of reactive (0.10.5) no longer has Data.Reactive module (it seem to have been removed since 0.5 version of the reactive). Does Phooey really need 0.5 version of the reactive or is there a problem in my installation? Thanks Daryoush

1 0

createProcess problem
by Vasili I. Galchin 28 Apr '09

28 Apr '09

Hello, I am trying to use createProcess. Following is a small fragment. I am trying to run a program called blastall (a bio-informatics program). It is kind of like mv/cp/ln on Unix platforms (where the executable examines the program, i.e. arg[0], and then provides appropriate behavior/semantics). In the case of blastall, it alters its behavior based on the -p(program) CLI argument.WSo in the following it should provide nucleotide behavior ... that is what the 'n' on the end of blastn means. import System.Process main = do handle <- runProcess "blastall" -- executable ["-p blastn"] -- CLI args Nothing -- optional cwd Nothing -- optional env Nothing -- optional stdin Nothing -- optional stdout Nothing -- optional stderr return () When I run this program with ghci, blastall is not a happy camper. It is complaining about "-p blastn": [NULL_Caption] ERROR: Program name undefined: " blastn" <<< the space between the double quote and 'b' is really there!!! [NULL_Caption] ERROR: Program name undefined: " blastn" Yet if I run 'blastall -p blastn' from the DOS prompt no errors(I will try tonight on my Linux machine). If I try 'blastall -p bozo" from the DOS prompt I get the same two errors as when I run my test program using ghci. I feel that it has something to do with double quotes in Haskell ... probably something obviously silly that I am doing. Any ideas? Kind regards, Vasili

2 1

createProcess problem
by Vasili I. Galchin 28 Apr '09

28 Apr '09

Hello, I am trying to use createProcess. Following is a small fragment. I am trying to run a program called blastall (a bio-informatics program). It is kind of like mv/cp/ln on Unix platforms (where the executable examines the program, i.e. arg[0], and then provides appropriate behavior/semantics). In the case of blastall, it alters its behavior based on the -p(program) CLI argument.WSo in the following it should provide nucleotide behavior ... that is what the 'n' on the end of blastn means. import System.Process main = do handle <- runProcess "blastall" -- executable ["-p blastn"] -- CLI args Nothing -- optional cwd Nothing -- optional env Nothing -- optional stdin Nothing -- optional stdout Nothing -- optional stderr return () When I run this program with ghci, blastall is not a happy camper. It is complaining about "-p blastn": [NULL_Caption] ERROR: Program name undefined: " blastn" <<< the space between the double quote and 'b' is really there!!! [NULL_Caption] ERROR: Program name undefined: " blastn" Yet if I run 'blastall -p blastn' from the DOS prompt no errors(I will try tonight on my Linux machine). If I try 'blastall -p bozo" from the DOS prompt I get the same two errors as when I run my test program using ghci. I feel that it has something to do with double quotes in Haskell ... probably something obviously silly that I am doing. Any ideas? Kind regards, Vasili

3 2

Announce: GraphViz: Change of Maintainer
by Matthew Sackman 28 Apr '09

28 Apr '09

I no longer have the time to continue development of the (apparently, judging from the number of emails I'm getting, rather popular) graphviz package. Fortunately, Ivan Lazar Miljenovic who has extended it himself and sent me patches (some of which I did get round to folding in) has agreed to take on the package. Please direct all further queries to him! Many thanks Ivan! Matthew

1 0

LAST CALL: Haskell Communities and Activities Report
by voigt＠tcs.inf.tu-dresden.de 28 Apr '09

28 Apr '09

Dear Haskellers, It is not yet too late to contribute to the May 2009 edition of the Haskell Communities and Activities Report. If you haven't already, please write an entry for your new project, or update your old entry. Please mail your entries to hcar(a)haskell.org in LaTeX format. More information can be found in the original Call for Contributions at http://www.haskell.org/pipermail/haskell/2009-April/021180.html I look forward to receiving your contributions. Thanks a lot, Janis. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

1 0

how can one load Prelude into ghci?
by Thomas Hartman 28 Apr '09

28 Apr '09

One reason it would be nice to be able to do this, is you could then get lambdabot :src style listings of prelude function definitions by using the ghci debugger and :list for prelude functions. is this possible? so far I have tried thartman@ubuntu:~/haskellInstalls/ghcInstalls/source/ghc-6.10.1/libraries/base>head Prelude.hs {-# OPTIONS_GHC -XNoImplicitPrelude #-} ----------------------------------------------------------------------------- thartman@ubuntu:~/haskellInstalls/ghcInstalls/source/ghc-6.10.1/libraries/base>ghci -i. Prelude.hs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. <command line>: module `Prelude' is not loaded thartman@ubuntu:~/haskellInstalls/ghcInstalls/source/ghc-6.10.1/libraries/base>ghci Prelude.hs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. <command line>: module `Prelude' is not loaded

2 1

Memory usage of cabal install
by Krzysztof Kościuszkiewicz 28 Apr '09

28 Apr '09

Hello Haskell-Café, I have a problem with high memory usage of cabal-install. Whenever I try to install or upgrade a package, cabal manages to consume 1,3G of memory before I killed it (on a 32-bit machine with 1 GB of memory). Increasing verbosity does not help, memory consumption goes up after the message "Resolving dependencies..." shows up. I use ghc 6.8.2 and cabal-install version 0.5.1 using version 1.4.0.1 of the Cabal library. Is there a workaround? I would like to avoid fetching & building packages manually. -- Krzysztof Kościuszkiewicz "Simplicity is the ultimate sophistication" -- Leonardo da Vinci

3 4

"subscribing" to the comments, online Real World Haskell
by Michael P Mossey 28 Apr '09

28 Apr '09

I love that Real World Haskell is online, here: <http://book.realworldhaskell.org/read/> I love that it has a comment section embedded with every paragraph. However, I would like some ability to subscribe to specific comments. I want to see if people have replied to me or what the latest discussion is. Anyone know if this is possible by a method other than manually copying down every URL? (In fact, I'm not sure that I can create a URL that goes directly to a part of a chapter.) Thanks, Mike

3 3

old-time conflict when installing phooey
by Daryoush Mehrtash 27 Apr '09

27 Apr '09

When I try to install phooey I get conflict with old-time that I am not sure how to resolve. Any ideas? > cabal install phooey Resolving dependencies... cabal: dependencies conflict: ghc-6.10.1 requires old-time ==1.0.0.2 however old-time-1.0.0.2 was excluded because ghc-6.10.1 requires old-time ==1.0.0.1 Thanks Daryoush

3 2

RE: [Haskell] ANN control-monad-exception-0.1: Explicitly typed exceptions
by Simon Peyton-Jones 27 Apr '09

27 Apr '09

Is there a Haskell Wiki page on extensible exceptions? The paper is a fine reference, it'd be cool to have a wiki page giving programmer-oriented guidance, saying what comes with GHC what other packages are available and some simple examples of how to use them. Simon | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of | Pepe Iborra | Sent: 25 April 2009 19:52 | To: haskell(a)haskell.org | Subject: [Haskell] ANN control-monad-exception-0.1: Explicitly typed exceptions | | The control-monad-exception package [1] provides explicitly typed | exceptions for Haskell. | In other words, this is a perfect example of bundling in a Haskell | library what for other | programming languages is a native feature. | | The type of a computation in the EM monad carries a list of the exceptions that | the computation may throw. A exception is raised with 'throw', which | in addition adds it | to the type, and captured with 'catch', which correspondingly removes | it from the type. | Only safe computations (all exceptions handled) can escape from the monad. | | The encoding used for the exception list is based on a phantom type | variable carrying a | @Throws@ constraint for every exception type. Catching an exception | @e@ satifies the constraint | @Throws e@ thus removing it from the type. It is possible to teach | Throws about exception subtyping | by manually inserting new instances declaring the subtyping relations | between exceptions. I don't | believe there is a better way to handle this, as the existential | wrapper encoding used | for Control.Exception.SomeException does not reveal the subtyping | relations, but ideas are | welcome. | | Example | -------- | GHCi infers the following types | | eval :: (Throws DivideByZero l, Throws SumOverflow l) => Expr -> EM l Double | eval `catch` \ (e::DivideByZero) -> return (-1) :: Throws | SumOverflow l => Expr -> EM l Double | runEM (eval `catch` \ (e::SomeException) -> return (-1)) :: Expr -> Double | | for the code below. | | | > import Control.Monad.Exception | > import Data.Typeable | | > data Expr = Add Expr Expr | Div Expr Expr | Val Double | > eval (Val x) = return x | > eval (Add a1 a2) = do | > v1 <- eval a1 | > v2 <- eval a2 | > let sum = v1 + v2 | > if sum < v1 || sum < v2 then throw SumOverflow else return sum | > eval (Div a1 a2) = do | > v1 <- eval a1 | > v2 <- eval a2 | > if v2 == 0 then throw DivideByZero else return (v1 / v2) | | > data DivideByZero = DivideByZero deriving (Show, Typeable) | > data SumOverflow = SumOverflow deriving (Show, Typeable) | | > instance Exception DivideByZero | > instance Exception SumOverflow | | | Comments and patches are welcome. | Cheers, | Pepe Iborra | | [1] - http://hackage.haskell.org/cgi-bin/hackage-scripts/package/control-monad- | exception | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

1 0

Re: Is 78 characters still a good option? Was: [Haskell-cafe] breaking too long lines
by Jason Dusek 27 Apr '09

27 Apr '09

2009/04/26 Miguel <miguelimo38(a)yandex.ru>: > 2009/04/26 Jason Dusek <jason.dusek(a)gmail.com>: >> If we do not preserve the old ways, it'll be anarchy all the >> way down. > > How exactly are you going to preserve old ways? Whenever are we are presented with the a question of correct conduct, we must re-affirm our commitment to the practices handed down to us. When we revisit this question -- "Should we maintain the 80 column limit?" -- it as an opporunity to affirm this practice. Through this exercize, we perenially renew our faith in this convention, accepting the bonds of convention. This ritual -- the "line-length reminding ritual" -- is played out across all programming communities several times a year. Everyone says the same things. Then they all go away with the 80 column limit re-established in their minds. -- Jason Dusek

1 0

installing Sqlite3 driver for windows
by Michael P Mossey 27 Apr '09

27 Apr '09

I'm working from Real World Haskell, trying to install HDBC and the Sqlite3 driver on Windows XP. It was easy enough to use Cabal to install HDBC. However, for the Sqlite3 driver things get fuzzy. I downloaded hdbc-sqlite3_2.1.0.0.zip, but don't know what I'm supposed to do with it. Also, it wasn't clear what to do with the sqlite3.dll file. On this page <http://software.complete.org/software/wiki/hdbc/FrequentlyAskedQuestions> it seems to imply you need to put it in 'gch --print-libdir'\include and %windir%\system32 but that page is really about building the driver from source. Maybe it only needs to go in the system32 directory. Thanks, Mike

2 1

Haskell/JS -- better through typeclasses?
by Jason Dusek 27 Apr '09

27 Apr '09

I'd like to be able to translate Haskell to JavaScript. Many Haskell/JS bridges provide libraries for writing complete JavaScript programs in Haskell; some of them even include jQuery. However, my goals are more limited -- I'd like to be able to take a Haskell module and turn it into a JavaScript object. For example, I'd like to write a nice parser in Haskell and then reuse it on the client side. No need to handle all the DOM events or implement multi-threading. Of course, the place to start is by reading the commentary. A little bit of browsing suggests some questions of strategy: . Maybe a new backend is not the right thing? All the backends seem to be for real computers with real instruction sets. . Is it better to just work on transforming Core into JS directly? It seems that "External Core" is still in limbo. . Some translations strike me as baffling in principle. For example, a value like `ones`: ones = 1 : ones We'd want to avoid most native JavaScript containers, it seems; however, we are then unable to leverage the speed of native containers. It's entirely possible that translating Haskell to JavaScript may turn out not to be the best idea; maybe it is better to have a type class for types (for example, `Parser Char`) to provide their own translators? The it would be straightforward to prevent translation of programs that use concurrency libs, native ops or `IO`. -- Jason Dusek

7 11

ANN: Bamse-0.9.4, a Windows Installer generator
by Sigbjorn Finne 27 Apr '09

27 Apr '09

Hi, a new version of Bamse has been uploaded to hackage, http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bamse Bamse is a package and application for letting you quickly put together Windows Installers for your software projects/products from within the comforts of Haskell. New in this release is the support for generating MSIs from your Cabal projects, having them either be built from source or just have them be installed and registered at install-time. i.e., one-click installation of Cabal packages. See examples/Cabal.hs for a worked example of how to bundle up Cabal packages. I've found this functionality a bit useful, hope others do too. The new version also adds support for handling .NET assemblies. enjoy --sigbjorn

2 2

Haskell/JS -- better through typeclasses?
by Dimitry Golubovsky 27 Apr '09

27 Apr '09

John wrote: > I can't speak for Jason, but for me, this is not very useful. I don't > want to write in a Haskell DSL, I want to write in Haskell. And not > the whole program, either, just the parts that really lend themselves > to functional programming (parsers, numeric computations, code > generators, various algorithms). What I presented is of course not a complete solution; this is just a tool to construct Javascript expressions in haskellized type-safe form. What I also mentioned: this monadic form may be an end-point for some other conversion, like GRIN. This answers the question how to translate a true Haskell program (like a parser) into Javascript (or a similar language). There are some experimental compilers with GRIN backends, plus I did my own experiments with GRIN that gave me some ideas. So I would just look at it as a starting point of some new family of tools which hopefully will end up opening possibility to translate Haskell things to Javascript. PS For now I am more concerned with the IDL part of it, but any suggestions on GRIN are welcome. -- Dimitry Golubovsky Anywhere on the Web

2 1

Haskell/JS -- better through typeclasses?
by Dimitry Golubovsky 27 Apr '09

27 Apr '09

Jason and everybody interested, Please check out a package I recently (just by coincidence: I haven't seen this topic on the list until after I uploaded it) uploaded to Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/jsmw-0.1 This is a basic monadic interface to Javascript code generator (based on WebBits), providing sort of a macro (like in macro-assembler) facility. HJScript was used as a (sort of) prototype, but I chose slightly different notation for EDSL. >From here, I think two directions may be taken: 1. Some techniques are described in the GRIN thesis [1] how to convert a Haskell core to monadic form. These may be explored for this case. 2. Similarly to how the Web Consortium defined interfaces to its components using IDL *, Haskell modules converted to Javascript may expose their interfaces same way, thus providing a basis for a reusable component-based approach. Any discussions and suggestions are welcome. >From my own impressions, EDSL approach is better for interactive/AJAX parts of a Javascript application, as translation of non-strict evaluation (like it was done in the Yhc/Javascript project) just causes a lot of code generated, and does not improve the user interaction performance at all. For other (internal) components, translation from Haskell may be more appropriate, just to be able to reuse the existing libraries. One of experiments with Yhc involved a user-exposed form, and a parser to validate user's input. With this hybrid approach, the user interface part might be coded using an EDSL, and the parser could be translated from Haskell core. An IDL might be generated for the parser interface, thus making the parser module a reusable component. These are of course just thoughts and ideas for now. ------------------------------------ * See the DOM package: this is an auto-generated Haskel approximation of IDL specs provided for the basic DOM components. [1] http://www.cs.chalmers.se/~boquist/phd/index.html [2] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DOM-2.0.1 -- Dimitry Golubovsky Anywhere on the Web

3 4

Problems with Haskell Program Coverage
by Dominic Steinitz 27 Apr '09

27 Apr '09

I want to use hpc to check that the ASN.1 library tests cover all the code. When I run it with a set of tests that I *know* don't test certain things, it reports that they have been covered i.e. there are not coloured in the markup that hpc produces. I would have expected a lot of yellow. It seems to work ok on small amounts of code so I'm not clear what I'm doing wrong. I'd be happy to provide the .tix file or put the .html files somewhere if that would be helpful. Here's what I use: ghc -o NewTest NewTest.hs -fhpc --make NewTest hpc markup NewTest Dominic.

4 3

Type constraints and classes
by Neil Brown 26 Apr '09

26 Apr '09

Hi, I have a Haskell problem that keeps cropping up and I wondered if there was any solution/work-around/dirty-hack that could help. I keep wanting to define class instances for things like Functor or Monad, but with restrictions on the inner type. I'll explain with an example, because I find explaining this in words a bit difficult. Let's say I want to create a Monad instance for Set akin to that for lists: == import Data.Set import Prelude hiding (map) instance Monad Set where return = singleton m >>= f = fold union empty (map f m) -- Error: Could not deduce (Ord a, Ord b) from the context (Monad Set) == Everything fits (I think) -- except the type-class constraints. Obviously my Monad instance won't work if you have things inside the set that aren't Ord, but I can't work out how to define a restricted instance that only exists for types that have Ord instances. I can't express the constraint on the instance because the a and b types of return and >>= aren't visible in the class header. Shifting the constraint to be present in the type doesn't seem to help either (e.g. newtype Ord a => MySet a = MySet (Set a)...). Is there any way to get such instances as the one for Set working? I cannot carry around a compare function myself in a data type that wraps Set, because return cannot create such functions without the original type-class instance. I don't actually need a Monad for Set, but it neatly demonstrates my problem of wanting constraints on the type inside a Monad (or a Functor, or an Applicative, etc). I worked around a similar problem with Functor by opting for a new Functor-like type-class with the constraints, but doing that with Monad rules out using all the monad helper functions (liftM, mapM, etc), and the do notation, which would be a step too far. All suggestions are welcome, no matter how hacky, or how many GHC extensions are required :-) (provided they don't break all the other monads, e.g. redefining the signature of Monad). Thanks, Neil.

4 3

Re: [Haskell-cafe] ANNOUNCE: fad 1.0 -- Forward Automatic Differentiation library
by Kalman Noel 26 Apr '09

26 Apr '09

Henning Thielemann schrieb: > with advanced type classes: > http://hackage.haskell.org/packages/archive/numeric-prelude/0.0.5/doc/html/… I'll take this as another opportunity to point out that the Haddock docs of the Numeric Prelude are highly unreadable, due to all qualified class and type names appearing as just C or T. I'm wondering, too, if the Numeric Prelude could be organized more cleanly if we had a fancier module system - does someone have sufficient experience with, say, ML-style module systems to tell? Kalman

3 5

Haskell Weekly News: Issue 115 - April 25, 2009
by Brent Yorgey 26 Apr '09

26 Apr '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090425 Issue 115 - April 25, 2009 --------------------------------------------------------------------------- Welcome to issue 115 of HWN, a newsletter covering developments in the [1]Haskell community. By all reports, the [2]5th Haskell Hackathon was a resounding success, with over 50 hackers present and many interesting Haskell projects worked on! Announcements darcs hacking sprint 2 and hac5 report. Eric Kow [3]sent out a link to a [4]report on the second darcs hacking sprint, held as part of the Haskell Hackathon. HPong-0.1.2: A simple OpenGL Pong game based on GLFW. R.A. Niemeijer [5]announced the release of [6]HPong, a simple Pong game implemented using OpenGL and GLFW. Hac5 roundup. Martijn van Steenbergen [7]reported on the 5th Haskell Hackathon. See the [8]wiki page for details, pictures, and links to blog posts. HTTP-4000.0.6. Sigbjorn Finne [9]announced a new release of the [10]HTTP package, which adds more robust handling of ill-formed cookies, and fixes a bug in normalization of certain proxy-bound requests. dataenc 0.12.1.0. Magnus Therning [11]announced version 0.12.1.0 of the [12]dataenc package. This version adds a bunch of new encodings, including xxencode, hexadecimal, quoted-printable, python escaping, and url encoding; and also fixed some bugs. list-tries-0.0 - first release. Matti Niemenmaa [13]announced the first public release of [14]list-tries, a library providing implementations of finite sets and maps for list keys using tries, both simple and of the Patricia kind. The data types are parametrized over the map type they use internally to store the child nodes: this allows extending them to support different kinds of key types or increasing efficiency. curl-1.3.5. Sigbjorn Finne [15]announced a new release of the [16]curl package, which provides Haskell bindings to libcurl. It works with ghc 6.10.2, taking into account the updated story on how to register Haskell-based finalizers. Runge-Kutta library -- solve ODEs. Uwe Hollerbach [17]announced a [18]Runge-Kutta library for numerically solving ordinary differential equations. funsat-0.6. Denis Bueno [19]announced version 0.6 of [20]funsat, a modern, DPLL-style SAT solver written in Haskell. Funsat solves formulas in conjunctive normal form and produces a total variable assignment for satisfiable problems. Version 0.6 adds a representation for logical circuits (and, or, not, onlyif, iff, if-then-else) supporting efficient conversion to CNF, and now uses the BSD3 license. control-monad-exception-0.1: Explicitly typed exceptions. Pepe Iborra [21]announced the [22]control-monad-exception package, which provides explicitly typed exceptions for Haskell. The type of a computation in the EM monad carries a list of the exceptions that the computation may throw. A exception is raised with 'throw', which in addition adds it to the type, and captured with 'catch', which correspondingly removes it from the type. Only safe computations (all exceptions handled) can escape from the monad. Haskell Implementers' Workshop 2009 (co-located with ICFP). Simon Marlow [23]issued a call for talks to be given at the ACM SIGPLAN [24]Haskell Implementers' Workshop, to be held on September 3 in Edinburgh, Scotland, in conjunction with [25]ICFP 2009. The proposal deadline in 15 June. The Haskell Implementers Workshop is a new workshop to be held alongside ICFP 2009 this year in Edinburgh, Scotland. There will be no proceedings; it is an informal gathering of people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure. persistent-map-0.0.0. Peter Robinson [26]announced the [27]persistent-map package, which provides a thread-safe (STM) frontend for finite map types together with a backend interface for persistent storage. A pragmatic Haskell .NET interop layer, 0.4.0. Sigbjorn Finne [28]announced a new release of [29]hs-dotnet, a Haskell .NET interop layer. It lets you access .NET functionality from Haskell and vice versa. The new version includes development done since the start of the year. Apart from rewriting the internals completely to put it all on a sounder footing, this release includes proper support for .NET generic types (classes and interfaces), mapping them naturally on to Haskell parameterized types. Utrecht Haskell Compiler (UHC) -- first release. atze [30]announced the first public release of the [31]Utrecht Haskell Compiler (UHC). UHC supports almost all Haskell98 features plus many experimental extensions. The compiler runs on MacOSX, Windows (cygwin), and various Unix flavors. Features include multiple backends, including a bytecode interpreter backend and a GRIN based, full program analysing backend; experimental language extensions, some of which have not been implemented before; implementation via attribute grammars and other high-level tools; and ease of experimentation with language variants, thanks to an aspect-oriented internal organisation. 6.10.3 plans. Ian Lynagh [32]announced plans for a 6.10.3 release of GHC, in order to fix the handling of ^C in ghci. 6.10.3 will also use haskeline instead of editline. A HERE Document syntax. Jason Dusek [33]proposed a lightweight syntax for HERE documents in Haskell. Discussion Functor and Haskell. Daryoush Mehrtash [34]asked about the link between functors in category theory and Haskell's Functor class; the resulting thread is a good introduction to the connections between Haskell and category theory for those just learning the latter. breaking too long lines. Christian Maeder [35]asked how to break long lines in Haskell source, leading to an interesting discussion of coding style. Jobs Haskell consultant wanted to develop small, Mac-based utility in Haskell or AppleScript. R J [36]announced an opportunity to develop a short program to annotate lists of words with their definitions. Blog noise [37]Haskell news from the [38]blogosphere. * Twan van Laarhoven: [39]Where do I get my non-regular types?. * Sebastian Fischer: [40]Reinventing Haskell Backtracking. * Darcs: [41]darcs hacking sprint #2 report. * Well-Typed.Com: [42]Platform progress and the Hackathon. * Roman Cheplyaka: [43]Hac5: the rest of the story (almost). * Twan van Laarhoven: [44]A non-regular data type challenge. * Magnus Therning: [45]dataenc 0.12.1.0 released. * Galois, Inc: [46]Portland Next Week: ICFP PC Functional Programming Workshop. * Christophe Poucet (vincenz): [47]Flattening Data.Map. * Roman Cheplyaka: [48]Hac5: second day. * Xmonad: [49]contribs review. * GHC / OpenSPARC Project: [50]Loose ends and register pairing. * Sean Leather: [51]Latest on the incremental fold and attributes. * >>> Matthew Podwysocki: [52]Functional Solution for the Shortest Path Problem . * Chris Smith: [53]Code for Manipulating Graphs in Haskell. * Austin Seipp: [54]A little fun with Haskabelle. Proving things about *existing* Haskell code in Isabelle. * Tupil: [55]Running Happstack applications with FastCGI. * Martijn van Steenbergen: [56]Hac5-Saturday. * beelsebob: [57]Bottoms. * Antoine Latter: [58]Using Haskeline. * Darcs: [59]darcs weekly news #26. * Martijn van Steenbergen: [60]Hacking GHC-What I've learned. * >>> Brandon Simmons: [61]Initial tests of Tries: Follow Up. * >>> Lab 49: [62]The Algebra of Data, and the Calculus of Mutation. * Martijn van Steenbergen: [63]Hac5-Friday. Pictures from the Hackathon. * >>> Matthew Podwysocki: [64]Haskell and Collective Intelligence . Quotes of the Week * Gracenotes: foldr chosen for its magical evil terminating powers * uninverted: Moving from lisp to haskell with respect to functions is like moving from c to perl with respect to strings. * Berengal: [On infinitely fast computers] The OS probably has a failsafe built in: If a program is running it's in an infinite loop and needs to be killed... * nikki93: After a bit more delving, I've come to see the power of haskell at last. You have to treat functions like crap, forget about the C idea that they're 'big things'. They're not. * Berengal: I was squashing a bug, got frustrated, and typed "fix error" in ghci... About the Haskell Weekly News New editions are posted to [65]the Haskell mailing list as well as to [66]the Haskell Sequence and [67]Planet Haskell. [68]RSS is also available, and headlines appear on [69]haskell.org. To help create new editions of this newsletter, please see the information on [70]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [71]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org/haskellwiki/Hac5 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57551 4. http://blog.darcs.net/2009/04/darcs-hacking-sprint-2-report.html 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57493 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HPong 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57470 8. http://www.haskell.org/haskellwiki/Hac5 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57336 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTTP 11. http://article.gmane.org/gmane.comp.lang.haskell.libraries/10945 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dataenc 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57311 14. http://iki.fi/matti.niemenmaa/list-tries/ 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57251 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/curl 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57160 18. http://www.korgwal.com/software/rk-1.0.0.tar.gz 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57101 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/funsat 21. http://article.gmane.org/gmane.comp.lang.haskell.general/17120 22. http://article.gmane.org/gmane.comp.lang.haskell.general/17120 23. http://article.gmane.org/gmane.comp.lang.haskell.general/17113 24. http://haskell.org/haskellwiki/HaskellImplementorsWorkshop 25. http://www.cs.nott.ac.uk/~gmh/icfp09.html 26. http://article.gmane.org/gmane.comp.lang.haskell.general/17106 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/persistent-map 28. http://article.gmane.org/gmane.comp.lang.haskell.general/17105 29. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hs%2Ddotnet 30. http://article.gmane.org/gmane.comp.lang.haskell.general/17103 31. http://www.cs.uu.nl/wiki/UHC 32. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/16792 33. http://article.gmane.org/gmane.comp.lang.haskell.prime/2787 34. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/57324 35. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/57207 36. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57568 37. http://planet.haskell.org/ 38. http://haskell.org/haskellwiki/Blog_articles 39. http://twan.home.fmf.nl/blog/haskell/non-regular2.details 40. http://www-ps.informatik.uni-kiel.de/~sebf/pub/atps09.html 41. http://blog.darcs.net/2009/04/darcs-hacking-sprint-2-report.html 42. http://blog.well-typed.com/2009/04/platform-progress-and-the-hackathon/ 43. http://ro-che.blogspot.com/2009/04/hac5-rest-of-story-almost.html 44. http://twan.home.fmf.nl/blog/haskell/non-regular1.details 45. http://therning.org/magnus/archives/568 46. http://www.galois.com/blog/2009/04/23/portland-next-week-icfp-pc-functional… 47. http://cpoucet.wordpress.com/2009/04/18/flattening-datamap/ 48. http://ro-che.blogspot.com/2009/04/hac5-second-day.html 49. http://xmonad.wordpress.com/2009/04/22/contribs-review/ 50. http://ghcsparc.blogspot.com/2009/04/loose-ends-and-register-pairing.html 51. http://feedproxy.google.com/~r/splonderzoek/~3/KWqNCgsK1ww/latest-on-increm… 52. http://codebetter.com/blogs/matthew.podwysocki/archive/2009/04/21/functiona… 53. http://cdsmith.wordpress.com/2009/04/20/code-for-manipulating-graphs-in-has… 54. http://www.jedi-ninja.net/2009/04/20/A-little-fun.html 55. http://blog.tupil.com/running-happstack-applications-with-fastcgi/ 56. http://martijn.van.steenbergen.nl/journal/2009/04/19/hac5-saturday/ 57. http://noordering.wordpress.com/2009/04/19/bottoms/ 58. http://panicsonic.blogspot.com/2009/04/using-haskeline.html 59. http://blog.darcs.net/2009/04/darcs-weekly-news-26.html 60. http://martijn.van.steenbergen.nl/journal/2009/04/18/hacking-ghc-what-ive-l… 61. http://coder.bsimmons.name/blog/2009/04/initial-tests-of-tries-follow-up/ 62. http://blog.lab49.com/archives/3011 63. http://martijn.van.steenbergen.nl/journal/2009/04/17/hac5-friday/ 64. http://codebetter.com/blogs/matthew.podwysocki/archive/2009/04/17/haskell-a… 65. http://www.haskell.org/mailman/listinfo/haskell 66. http://sequence.complete.org/ 67. http://planet.haskell.org/ 68. http://sequence.complete.org/node/feed 69. http://haskell.org/ 70. http://haskell.org/haskellwiki/HWN 71. http://code.haskell.org/~byorgey/code/hwn/

1 0

Takusen, postgres and boolean fields
by Sasha Shipka 26 Apr '09

26 Apr '09

Let say one has to do something similar to this: execDML $ cmdbind (sql "update some_table set some_boolean_field = ? where ...") [bindP True, ...] When I do it, I have an error: DBError ("42","804") 7 "ERROR: 42804: column \"some_boolean_field\" is of type boolean but expression is of type text ..." I've noticed that when I read boolean fields from postgres it reads them as string "t" or "f". So I also tried bindP "t" and had same error.

3 3

Not in scope
by siso dagbovie 26 Apr '09

26 Apr '09

Hi, I've defined the datatype: data Graph a b = Empty | Context a b :& Graph a b and the function isEmpty :: Graph a b -> Bool isEmpty Empty = True isEmpty _ = False and when I do a test run with the graph, ( [ ],2,'c',[("down",3)]) :& Empty Haskell is bringing the message " Not in scope: data constructor `:&' " Why is that so? Kind regards

2 1

compilation to C, not via-C
by Sam Martin 26 Apr '09

26 Apr '09

Hi Everyone, It appears the GHC compiler (and other) compile Haskell *via-C* but not *to C*. I've never really understood why there isn't a C generation option, or why GDC ships with its own compulsory copy of gcc. I work in Games middleware, and am very interested in looking at how Haskell could help us. We basically sell C++ libraries. I would like to be able to write some areas of our libraries in Haskell, compile the Haskell to C and incorporate that code into a C++ library. As an example, I think Haskell would be great at doing geometry processing. I don't want to write all our geometry processing code in C++. I'd prefer to write a big chunk of it in Haskell and wrap that in C++. The pattern here is using Haskell to generate C code as the end result. It sounds like this end result isn't that far out of reach, so I'm curious as to why it doesn't appear to be possible at present. Have I missed something? Is there some fundamental reason this isn't possible? Has anyone wished for this before? Any thoughts/help much appreciated, Thanks, Sam Martin --- Lead Programmer www.geomerics.com

10 18

parse error on input `&'
by siso dagbovie 26 Apr '09

26 Apr '09

Hi, I've defined the following datatype with haskell data Graph a b = Empty | Context a b & Graph a b But I am having the error message: " parse error on input `&' ". I am wondering what it is wrong with my definition. How can I fix this? Thanks in advance. Kind regards

3 2

Binary I/O options
by David Leimbach 25 Apr '09

25 Apr '09

I see that there are a few approaches to doing Binary I/O with Haskell, and the one I'm currently looking at using is Data.Binary from Hackage. I was just wondering what folks were choosing for building networked applications and doing Binary I/O. The approach I was about to take was to use Data.Binary to create ByteString for Network calls with a standard I/O package. Are there other good options? Dave

5 6

leksah on window - problems with installation.
by Raja Koduru 25 Apr '09

25 Apr '09

Hello, I want to install leksah haskell IDE on my windows(xp) system. I download leksah's source (leksah-0.4.4.1). I also have gtk2hs (0.10.0) in my path. I am having ghc-6.10.2. As suggested on leksah's website.. I used "runhaskell setup configure" command But it is failing with this error "Configuring leksah-0.4.4.1... Setup: At least the following dependencies are missing: glib >=0.10, gtk >=0.10, gtksourceview2 >=0.10.0" I tried to do "cabal install glib" but not able to do so. Can you give me clues on how to go forward. with thanks & regards, raja koduru

1 0

OT: Good Linux distro for netbook + Haskell?
by Magnus Therning 25 Apr '09

25 Apr '09

I've decided to shop around for other options when it comes to a Debian distro to put on my Eee PC 900. Since it has no HDD I want something that isn't too bloated (some is all right) and ideally leaves up to me what to install and what not to. At the same time I'd like to have up-to-date Haskell packages in the native packaging system available (sure, cabal-install is all right for the odd package, but I'd rather use the native packaging system). Debian Sid would be a contender, though (no offence, I know they work hard) it's often slow in providing the latest versions of packages. Arch Linux is very up-to-date, but I'm not convinced it's a distro suitable for an Eee without HDD (I'm prepared to be proven wrong though). Is there something else out there I should be looking at? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe Haskell is an even 'redder' pill than Lisp or Scheme. -- PaulPotts

5 7

ANN: Cute Hack - Hyena handler + Bamboo Blog Engine :)
by Jinjing Wang 25 Apr '09

25 Apr '09

Hia, A few interesting progress on Hack: * many middleware ported from Rack, including a lambda! ( just like a pony for wsgi, and a lobster for rack ) * 2 handlers, one for Kibro on fcgi / lighttpd, one for Hyena web server * apps are portable, Bamboo is a port of Panda that runs on Hack, works fine with both handlers * Hyena handler is still experimental A lambda app looks like this -- Main.hs source module Main where import Hack import Hack.Utils import Hack.Handler.Hyena import Hack.Contrib.Lambda main = run $ lambda dummy_app -- compile ghc --make -O2 Main.hs -- run ./Main now go to http://localhost:3000/lambda Cheers, Links: * [Hack] (http://github.com/nfjinjing/hack/tree/master) * [Bamboo] (http://github.com/nfjinjing/bamboo/tree/master) -- jinjing

2 2

RE: [Haskell-cafe] Thread priority?
by John Van Enk 25 Apr '09

25 Apr '09

+1 Incredibly interested if this goes anywhere. Willing to help! -----Original Message----- From: Christopher Lane Hinson <lane(a)downstairspeople.org> Sent: Friday, April 24, 2009 10:48 PM To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] Thread priority? Is there any interest or movement in developing thread priority or any other realtime support in Haskell? Right now, if I have tasks that need to be responsive in real time, even if the realtime needs are very soft, it seems that the only option is to try to ensure that at least one hardware thread is kept clear of any other activity. To be very useful to me, thread priority would not need to come with very strict guarantees, but there would need to be a way to make sure that `par` sparks and DPH inherit the priority of the sparking thread. In part I ask because I'm working on a small library to support a degree of cooperative task prioritization. Friendly, --Lane _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

Haskell consultant wanted to develop small, Mac-based utility in Haskell or AppleScript
by R J 25 Apr '09

25 Apr '09

I need someone to code a short program for use on a Mac OS X (Leopard) that, in essence, takes as input a file containing a list of English words, and produces as output a file containing the words plus definitions, as extracted from any good dictionary. Though Haskell might not be the ideal language for this project, the utility is almost trivial, I'm a fan of Haskell, and would like to support the community. Those interested should email me at rj248842(a)hotmail.com. The specs are: 1. Takes as input a .txt file containing lines delimited by newline characters, with each line containing either no characters, an English word or phrase, or a comment (denoted by, for example, "--"). Thus, the input file might look like: -- Comment 1frustum bon mot -- Comment 2octagon rectangle 2. Produces as output a file (.txt, .rtf, or .docx format) containing the comments, the words or phrases (in bold), and their definitions, using either the dictionary (New Oxford American Dictionary, "NOAD") bundled with OS X or some credible online dictionary (such as merriam-webster.com) for words whose definitions aren't found in the NOAD. For example, given the above input file, the output file would be: -- Comment 1frustum |ˈfrəstəm| noun ( pl. -ta |-tə| or -tums ) Geometry the portion of a cone or pyramid that remains after its upper part has been cut off by a plane parallel to its base, or that is intercepted between two such planes. ORIGIN mid 17th cent.: from Latin, ‘piece cut off.’ bon mot |ˈbän ˈmō; ˌbô n ˈmō| noun ( pl. bons mots pronunc. same or |ˈmōz|) a witty remark. ORIGIN mid 18th cent.: French, literally ‘good word.’ -- Comment 2 octagon |ˈäktəˌgän; -gən| noun a plane figure with eight straight sides and eight angles. • an object or building with a plan or cross section of this shape. DERIVATIVES octagonal |äkˈtagənl| |ɑkˈtøgənl| |-ˈtag(ə)n(ə)l| adjective octagonally |äkˈtagənəlē| |ɑkˈtøgənəli| |ɑkˈtøgənli| |-ˈtag(ə)n(ə)li| adverbORIGIN late 16th cent.: via Latin from Greek octagōnos ‘eight-angled.’ rectangle |ˈrekˌta ng gəl|noun a plane figure with four straight sides and four right angles, esp. one with unequal adjacent sides, in contrast to a square. ORIGIN late 16th cent.: from medieval Latin rectangulum, from late Latin rectiangulum, based on Latin rectus ‘straight’ + angulus ‘an angle.’ I've attached a (zipped) AppleScript--it's just a few lines--and Automator workflow that work ok using Automator's "Get Definition of a Word" action. It took about fifteen minutes to write, but for some reason, that action doesn't extract the entire definition from the dictionary. If it would save time, you could work off of that code and deliver an AppleScript solution, or you could write Haskell code. _________________________________________________________________ Rediscover Hotmail®: Now available on your iPhone or BlackBerry http://windowslive.com/RediscoverHotmail?ocid=TXT_TAGLM_WL_HM_Rediscover_Mo…

1 0

GHC 6.10.2 compatible problem.
by Andy Stewart 25 Apr '09

25 Apr '09

Hi, all! I saw GHC release new version now, and fix some bug. I want to know below pacakges whether works fine with GHC-6.10.2 before i upgrade it: cabal, gtk2hs, xmonad, yi, leksah Thanks! -- Andy

2 1

Being impure within a 'pure' function
by Daniel K. 25 Apr '09

25 Apr '09

Hello, imagine the following situation: You want to implement e.g. Dijkstra's algorithm to find a shortest path between nodes u and v in a graph. This algorithm relies heavily on mutating arrays, so the type signature would look something like getDistance :: Graph -> Node -> Node -> IO Int Not mutating the underlying arrays would probably result in poor performance. BUT: For a constant graph, the distance between two nodes stays the same all the time, so in fact getDistance should be a pure function! So here is my question: Is there a way to write functions in Haskell that do some IO internally, but that are guaranteed to be side-effect free? Of course one would have to make sure that the array that is mutated inside getDistance must not be accessible from outside the function. Is that possible? If not, wouldn't that be desirable? If not, why not? Thanks Daniel

7 7

ANNOUNCE: vacuum-cairo: a cairo frontend to vacuum for live Haskell data visualization
by Don Stewart 25 Apr '09

25 Apr '09

I am pleased to announce the release of vacuum-cairo, a Haskell library for interactive rendering and display of values on the GHC heap using Matt Morrow's vacuum library. This library takes vacuum's output, generates dot graph format from it, renders it to SVG with graphviz, and displays the resulting structure using the gtk2hs Cairo vector graphics bindings ... all at the GHCi command line. This tool is useful for examining Haskell data structures as they are represented directly in the heap. In particular, it makes sharing visible for the first time, as well as unboxed values. It should be useful for teaching Haskell, or for library authors debugging the design of their data structures. You can see pictures of the rendered display here: http://code.haskell.org/~dons/images/vacuum/intmap.png And youtube screencasts of vacuum-cairo in action: http://www.youtube.com/watch?v=oujaqo9GAmA Get it: cabal install vacuum-cairo And on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vacuum-cairo -- Don

16 29

darcs hacking sprint 2 and hac5 report
by Eric Kow 25 Apr '09

25 Apr '09

Dear darcs users and Haskellers, Here's our report from the 2nd darcs hacking sprint, held as part of the Haskell Hackathon. http://blog.darcs.net/2009/04/darcs-hacking-sprint-2-report.html Thanks very much to the Hac5 team, to Hac5 sponsors, darcs donors, and to all participants at the Hackathon. We really enjoyed meeting everybody and hope to see you soon at the next event! -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

1 0

Confusing change causing space leak
by Denis Bueno 25 Apr '09

25 Apr '09

Hi all, I discussed this with a few people in #haskell-in-depth, and we thought I should send this to the list. The following paste shows the only changes required to remove a space leak: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=4185#a4185. Summary: if I reduce a tuple-from-IO to whnf in the "allocate" function passed to "bracket", no leak. For example, this also doesn't leak: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=4185#a4189 That paste page also contains the code for "externalSort". The "externalSort" function used in the example corresponds to the "sort" function provided by the Algorithms.ExternalSort module. Can anyone explain why the leak happens at all, or why it goes away? Denis

1 0

Template Haskell + Profiling
by Krzysztof Skrzętnicki 24 Apr '09

24 Apr '09

Hi I'm trying to build some modules that use TH with profiling enabled. The normal build works: $ ghc -fforce-recomp --make -cpp -O -DXQUERY2_TEST Main [1 of 8] Compiling Text.XML.Expat.FormatCustom ( Text/XML/Expat/FormatCustom.hs, Text/XML/Expat/FormatCustom.o ) [2 of 8] Compiling DataStructures ( DataStructures.hs, DataStructures.o ) Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Loading package syb ... linking ... done. Loading package array-0.2.0.0 ... linking ... done. Loading package packedstring-0.1.0.1 ... linking ... done. Loading package containers-0.2.0.1 ... linking ... done. Loading package pretty-1.0.1.0 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package filepath-1.1.0.2 ... linking ... done. Loading package old-locale-1.0.0.1 ... linking ... done. Loading package old-time-1.0.0.2 ... linking ... done. Loading package unix-2.3.2.0 ... linking ... done. Loading package directory-1.0.0.3 ... linking ... done. Loading package process-1.0.1.1 ... linking ... done. Loading package random-1.0.0.1 ... linking ... done. Loading package derive-0.1.4 ... linking ... done. [3 of 8] Compiling Utils ( Utils.hs, Utils.o ) [4 of 8] Compiling Semantics.Pure ( Semantics/Pure.hs, Semantics/Pure.o ) [5 of 8] Compiling Database ( Database.hs, Database.o ) [6 of 8] Compiling XPathDSL ( XPathDSL.hs, XPathDSL.o ) [7 of 8] Compiling QueryParse ( QueryParse.hs, QueryParse.o ) [8 of 8] Compiling Main ( Main.hs, Main.o ) Linking Main ... But profiling one fails: $ ghc -prof -auto -auto-all -fforce-recomp --make -cpp -O -DXQUERY2_TEST Main [1 of 8] Compiling Text.XML.Expat.FormatCustom ( Text/XML/Expat/FormatCustom.hs, Text/XML/Expat/FormatCustom.o ) [2 of 8] Compiling DataStructures ( DataStructures.hs, DataStructures.o ) Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. DataStructures.hs:1:0: Dynamic linking required, but this is a non-standard build (eg. prof). You need to build the program twice: once the normal way, and then in the desired way using -osuf to set the object file suffix. The error message is somewhat cryptic to me. Does anyone know how to perform profiling build when using TH? Regards Christopher Skrzętnicki

2 2

(integer) linear programming
by Johannes Waldmann 24 Apr '09

24 Apr '09

Hi. I'm looking for linear programming solvers in Haskell (or a Haskell binding for glpk, or similar). - Thanks, J.W.

1 0

ANNOUNCE: Utrecht Haskell Compiler (UHC) -- first release
by atze＠cs.uu.nl 24 Apr '09

24 Apr '09

Utrecht Haskell Compiler -- first release, version 1.0.0 ======================================================== The UHC team is happy to announce the first public release of the Utrecht Haskell Compiler (UHC). UHC supports almost all Haskell98 features plus many experimental extensions. The compiler runs on MacOSX, Windows (cygwin), and various Unix flavors. Features: * Multiple backends, including a bytecode interpreter backend and a GRIN based, full program analysing backend, both via C. * Experimental language extensions, some of which have not been implemented before. * Implementation via attribute grammars and other high-level tools. * Ease of experimentation with language variants, thanks to an aspect-oriented internal organisation. Getting started & Download -------------------------- UHC is available for download as source distribution via the UHC home page: http://www.cs.uu.nl/wiki/UHC Here you will also find instructions to get started. Status of the implementation ---------------------------- Like any university project UHC is very much work in progress. We feel that it is mature and stable enough to offer to the public, but much work still needs to be done; hence we welcome contributions by others. UHC grew out of our Haskell compiler project (called Essential Haskell Compiler, or EHC) over the past 5 years. UHC internally is organised as a combination of separate aspects, which makes UHC very suitable to experiment with; it is relatively easy to build compilers for sublanguages, or to generate related tools such as documentation generators, all from the same code base. Extensions to the language can be described separately, and be switched on or of as need arises. Warning ------- Although we think that the compiler is stable enough to compile subtantial Haskell programs, we do not recommend yet to use it for any serious development work in Haskell. We ourselves use the GHC as a development platform! We think however that it provides a great platform for experimenting with language implementations, language extensions, etc. Mailing lists ------------- For UHC users and developers respectively: http://mail.cs.uu.nl/mailman/listinfo/uhc-users http://mail.cs.uu.nl/mailman/listinfo/uhc-developers Bug reporting ------------- Please report bugs at: http://code.google.com/p/uhc/issues/list The UHC Team -- Atze Dijkstra, Department of Information and Computing Sciences. /|\ Utrecht University, PO Box 80089, 3508 TB Utrecht, Netherlands. / | \ Tel.: +31-30-2534118/1454 | WWW : http://www.cs.uu.nl/~atze . /--| \ Fax : +31-30-2513971 .... | Email: atze(a)cs.uu.nl ............ / |___\

34 111

"Search" vs "search" vs "search"
by haskell＠kudling.de 24 Apr '09

24 Apr '09

Hi, I have some usability issues with the Haskell homepage. What is the best place to discuss them? 1) "Search" vs "search" vs "search" The front page has 3 search boxes: * at the top with the buttons "Go" and "Search" * the third link on the left called "Search" * the next link below "Search haskell.org" What is the difference? Is it really necessary to have 3 search boxes? Most webpages have only one. 2) "Libraries" vs "Packages" The front pages says "Find a library" and links to Hackages which lists "packages". To reduce confusion, i think we should settle to the usage of only "packages". Opinions? 3) Haskell frontpage in general I also would like to discuss a general simplification. The Haskell wiki provides a lot of deep information but the front page is overwhelming. The Haskell front page offers more than 50 links = choices. Compare that with http://rubyonrails.org/ (my favorite) http://www.ruby-lang.org/ http://www.python.org/ (also a bit laden) Regarding the rule of 7 we should reduce the information we present on the front page. Who are our visitors and what do they want? * Beginners. People who have no clue what Haskell is want to find answers to the following questions ** What is Haskell? ** How does Haskell look and "feel"? ** Why should i care? ** Who else i using Haskell? ** How do i get started? * Intermediates. People who are getting an idea what Haskell is but want to find out more about it, want to find answers to the following questions ** Where can i read some tutorials? ** Where can i read the API documentation? ** What is going on in the Haskell comunity? * Experts. People who know a lot about Haskell, but come back here, because they want to find answers to the following questions ** What is going on in the Haskell comunity? ** Where can i read about Haskell's future? I'd propose something like the following grouping: * About Haskell ** What is Haskell? ** How does Haskell feels like? ** Haskell success stories ** Getting Started *** Installation guide *** First steps guides * Download * Documentation ** Tutorials ** How to install packages via Cabal/Hackages ** API documentation *** Static pages *** Hoogle ** Community *** Blogs *** Events *** Projects * News See also http://www.haskell.org/haskellwiki/Talk:Haskell bye, lenny

2 1

Re: [Haskell-cafe] Overriding a Prelude function?
by michael rice 24 Apr '09

24 Apr '09

OK, I changed the operator from (>>) to (~>>). When I try to use it I get this: [michael@localhost ~]$ ghci rand GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( rand.hs, interpreted ) Ok, modules loaded: Main. *Main> rollDie ~>> (rollDie ~>> rollDie) <interactive>:1:0: No instance for (Show (Seed -> (Int, Seed))) arising from a use of `print' at <interactive>:1:0-32 Possible fix: add an instance declaration for (Show (Seed -> (Int, Seed))) In a stmt of a 'do' expression: print it *Main> Michael --- On Wed, 4/22/09, Luke Palmer <lrpalmer(a)gmail.com> wrote: From: Luke Palmer <lrpalmer(a)gmail.com> Subject: Re: [Haskell-cafe] Overriding a Prelude function? To: "michael rice" <nowgate(a)yahoo.com> Cc: "Ross Mellgren" <rmm-haskell(a)z.odi.ac>, "Dan Weston" <westondan(a)imageworks.com>, "haskell-cafe(a)haskell.org" <haskell-cafe(a)haskell.org> Date: Wednesday, April 22, 2009, 5:02 PM On Wed, Apr 22, 2009 at 1:47 PM, michael rice <nowgate(a)yahoo.com> wrote: Here's what I get: [michael@localhost ~]$ ghci GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> import Prelude hiding ((>>)) You know, to avoid this nonsense you could just name the operator something else, like >>~, or ~>>, or $@**!. Operators are just names. Luke <interactive>:1:0: parse error on input `import' Prelude> ===== I was passing seed0 to rollDie and getting back (r1,seed1) passing seed1 to rollDie and getting back (r2,seed2) passing seed2 to rollDie and getting back (r3,seed3) Just based on the problem text, I would guess that passing rollDie and seed0 to (>>) I would get back (r3,seed3), losing the intermediate random numbers r1 and r2 along the way, at least that's what I understood it to say. So, I know that next I'm probably going to have to do something to remedy that, but I haven't gotten to that next step yet. What is unsugar? Thanks in advance for your patience. Michael --- On Wed, 4/22/09, Dan Weston <westondan(a)imageworks.com> wrote: From: Dan Weston <westondan(a)imageworks.com> Subject: Re: [Haskell-cafe] Overriding a Prelude function? To: "Ross Mellgren" <rmm-haskell(a)z.odi.ac> Cc: "michael rice" <nowgate(a)yahoo.com>, "haskell-cafe(a)haskell.org" <haskell-cafe(a)haskell.org> Date: Wednesday, April 22, 2009, 12:37 PM Be aware that the do unsugars to (Prelude.>>), not your (>>), even if you hide (Prelude.>>): import Prelude hiding ((>>)) m >> f = error "Call me!" main = putStrLn . show $ do [3,4] [5] The desugaring of the do { [3,4]; [5] } is (Prelude.>>) [3,4] [5] = [5,5], whereas you might have hoped for [3,4] >> [5] = error "Call me!" Dan Ross Mellgren wrote: > I think > > import Prelude hiding ((>>)) > > does that. > > -Ross > > On Apr 22, 2009, at 11:44 AM, michael rice wrote: > >> I've been working through this example from: http://en.wikibooks.org/wiki/Haskell/Understanding_monads >> >> I understand what they're doing all the way up to the definition of (>>), which duplicates Prelude function (>>). To continue following the example, I need to know how to override the Prelude (>>) with the (>>) definition in my file rand.hs. >> >> Michael >> >> ============== >> >> [michael@localhost ~]$ cat rand.hs >> import System.Random >> >> type Seed = Int >> >> randomNext :: Seed -> Seed >> randomNext rand = if newRand > 0 then newRand else newRand + 2147483647 >> where newRand = 16807 * lo - 2836 * hi >> (hi,lo) = rand `divMod` 127773 >> >> toDieRoll :: Seed -> Int >> toDieRoll seed = (seed `mod` 6) + 1 >> >> rollDie :: Seed -> (Int, Seed) >> rollDie seed = ((seed `mod` 6) + 1, randomNext seed) >> >> sumTwoDice :: Seed -> (Int, Seed) >> sumTwoDice seed0 = >> let (die1, seed1) = rollDie seed0 >> (die2, seed2) = rollDie seed1 >> in (die1 + die2, seed2) >> >> (>>) m n = \seed0 -> >> let (result1, seed1) = m seed0 >> (result2, seed2) = n seed1 >> in (result2, seed2) >> >> [michael@localhost ~]$ >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@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

7 8

Functor and Haskell
by Daryoush Mehrtash 24 Apr '09

24 Apr '09

In category theory functors are defined between two category of C and D where every object and morphism from C is mapped to D. I am trying to make sense of the above definition with functor class in Haskell. Let say I am dealing with List type. When I define List to be a instance of a functor I am saying the source category (C) is Haskell types and the destination category is List (D). In this the "fmap" is implementation of the mapping between every morphism in my Haskell Categroy (C) to morphism in List cataegory (D). With type constructor I also have the mapping of types (objects in Haskell Category, or my source cataegroy C) to List category (D). So my functor in the catarogy sense is actually the fmap and type constructor. Am I remotely correct? If this is correct.... With this example, then can you then help me understand the transformation between functors and natural transformations? Specifically, what does it means to have two different functors between Haskell cateogry and List category? Thanks, Daryoush

7 13

can I query if package is in Hackage?
by Vasili I. Galchin 24 Apr '09

24 Apr '09

Hello, Hoogle allows me to query about Haskell functionality. But is there a mechanism for querying about a package, e.g. Swish? Kind regards, Vasili

2 1

Re: [Haskell-cafe] HPong-0.1.2 fails to compile in Debian ghc 6.10.1
by trentbuck＠gmail.com 24 Apr '09

24 Apr '09

"Ahn, Ki Yung" <kyagrd(a)gmail.com> writes: >>> I think this is because the filename of the OpenGL shared library is >>> /usr/lib/libGL.so.1 rather than libGL.so. >> >> No. Do not manually create the symlink. It sounds like you don't >> have the -dev packages for OpenGL installed. > > I do already have the dev package libgl1-mesa-dev installed. [...] > It's just seems to the bug of libgl1-mesa-dev 7.4-2 packaging. It > doesn't seem to make the symbolic link which it claims to make. Duh The file exists in that package, so it seems to me the problem is on your workstation, rather than in the package. I suggest you just reinstall the package in question. You may also want to use cruft(8) to find out if any other files have gone missing, and run a fsck over your root partition. $ aptitude download -t unstable libgl1-mesa-dev [...] Get:1 http://mirror.internode.on.net unstable/main libgl1-mesa-dev 7.4-2 $ dpkg -x libgl1-mesa-dev_7.4-2_all.deb . $ find -name \*.so -ls 13003 0 lrwxrwxrwx 1 twb twb 10 Apr 24 10:41 ./usr/lib/libGL.so -> libGL.so.1 $

1 0

Re: [Haskell-cafe] Random number example
by michael rice 24 Apr '09

24 Apr '09

Hi Ross, Thanks for going the extra mile. A lot of what you did I haven't seen before, so it's going to take me some time to go through it. But I'll be back. Michael --- On Thu, 4/23/09, Ross Mellgren <rmm-haskell(a)z.odi.ac> wrote: From: Ross Mellgren <rmm-haskell(a)z.odi.ac> Subject: Re: [Haskell-cafe] Random number example To: "michael rice" <nowgate(a)yahoo.com> Cc: haskell-cafe(a)haskell.org Date: Thursday, April 23, 2009, 11:51 AM So there are a couple problems. First is you are trying to rebind prelude functions, when instead you should be creating an instance of Monad. This requires a bit of shuffling because without language extensions you can't instance Monad Random for your type of Random, as it is a type synonym. So, changing the type synonym to a newtype and instancing monad, you get: module Rand9b where import Control.Applicative (Applicative(..), (<$>), (<*>))import Control.Monad (ap, liftM) type Seed = Intnewtype Random a = Rand { unRand :: (Seed -> (a, Seed)) } randomNext :: Seed -> SeedrandomNext rand = if newRand > 0 then newRand else newRand + 2147483647 where newRand = 16807 * lo - 2836 * hi (hi,lo) = rand `divMod` 127773 rollDie :: Random IntrollDie = Rand $ \ seed -> ((seed `mod` 6) + 1, randomNext seed) instance Monad Random where (>>=) = randomBind return = randomReturn instance Functor Random where fmap = liftM instance Applicative Random where pure = return (<*>) = ap randomBind :: Random a -> (a -> Random b) -> Random bm `randomBind` g = Rand $ \seed0 -> let (result1, seed1) = unRand m $ seed0 (result2, seed2) = unRand (g result1) $ seed1 in (result2, seed2) randomReturn :: a -> Random arandomReturn x = Rand $ \ seed0 -> (x, seed0) sumTwoDice :: Random IntsumTwoDice = (+) <$> rollDie <*> rollDie I also threw in instances of Functor and Applicative, so that I could simplify sumTwoDice using applicative form (much nicer, no? Applicative is totally rockin') Now you need one more thing, a way to convert a series of Random actions into a pure function: runRandom :: Seed -> Random a -> arunRandom s f = fst . unRand f $ s which now makes what you want to do in GHCi easy and well wrapped: Prelude> :reload[1 of 1] Compiling Rand9b ( rand9b.hs, interpreted )Ok, modules loaded: Rand9b.*Rand9b> runRandom 0 sumTwoDice3 Hope this helps,-Ross On Apr 23, 2009, at 11:28 AM, michael rice wrote: I pretty much followed the sequence of steps that led to this final code (see below), but will be looking it over for a while to make sure it sinks in. In the meantime, I get this when I try to use it (sumTwoDice) at the command line: [michael@localhost ~]$ ghci rand9 GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( rand9.hs, interpreted ) Ok, modules loaded: Main. *Main> sumTwoDice <interactive>:1:0: No instance for (Show (Seed -> (Int, Seed))) arising from a use of `print' at <interactive>:1:0-9 Possible fix: add an instance declaration for (Show (Seed -> (Int, Seed))) In a stmt of a 'do' expression: print it *Main> Can I employ a 'do' expression from the command line? Also, can I now use functions (>>) (>>=) and 'return' defined in the Prelude and still have this code work? Michael ================== {-# LANGUAGE NoImplicitPrelude #-} import Prelude hiding ((>>), (>>=), return) type Seed = Int type Random a = Seed -> (a, Seed) randomNext :: Seed -> Seed randomNext rand = if newRand > 0 then newRand else newRand + 2147483647 where newRand = 16807 * lo - 2836 * hi (hi,lo) = rand `divMod` 127773 rollDie :: Random Int rollDie seed = ((seed `mod` 6) + 1, randomNext seed) (>>) :: Random a -> Random b -> Random b (>>) m n = \seed0 -> let (result1, seed1) = m seed0 (result2, seed2) = n seed1 in (result2, seed2) (>>=) :: Random a -> (a -> Random b) -> Random b (>>=) m g = \seed0 -> let (result1, seed1) = m seed0 (result2, seed2) = (g result1) seed1 in (result2, seed2) return :: a -> Random a return x = \seed0 -> (x, seed0) sumTwoDice :: Random Int sumTwoDice = rollDie >>= (\die1 -> rollDie >>= (\die2 -> return (die1 + die2))) _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

ANNOUNCE: HPong-0.1.2: A simple OpenGL Pong game based on GLFW
by Niemeijer, R.A. 24 Apr '09

24 Apr '09

About two days ago the beta version of the Haskell Platform was released. Since it comes with an OpenGL library, it is now trivially easy to start making OpenGL programs with Haskell. To test this, I decided to make a simple Pong clone for two reasons: * To experiment with making an OpenGL game * I chose to use the GLFW instead of the GLUT library because GLUT doesn’t respond to closing a window with the close button very well. However, I could only find one piece of sample code for GLFW. Because of that, I decided to make a small game that others can use as a starting point for their own games. The controls are very simple: The up and down arrow keys move your paddle and Esc quits the game. This is my first upload to Hackage, so any comments or suggestions are welcome.

3 2

a question about *** Exception: stack overflow ..
by Luke Palmer 24 Apr '09

24 Apr '09

On Thu, Apr 23, 2009 at 7:02 AM, Mozhgan Kabiri <mozhgan_kch(a)hotmail.com>wrote: > Hi Luck , > > I got you email from the Haskell Cafe list. Hope you don't mind. > Recently I was running a simple program in Haskell and keep getting *** > Exception: stack overflow error ! > > I don't know how to solve it or handle it ! I tried to find the same > problem on the web in order to get some guide but it wasn't successful.Hope > you can give me some clue. > In the future, why don't you ask this kind of question on haskell-cafe or haskell-beginners? > > > Here is the code : > > import Control.Monad > import Text.Printf > > sumit :: Int -> Int > sumit n = sumCal 0 n 0 where > sumCal i n sum | i < n = sumCal (i+1) n (sum+i) > | otherwise = sum > This is probably your problem. If you do tail recursion, it needs to be strict. If you don't strictly tail recurse, you end up returning a massive thunk (i.e. a lazy expression like 0+1+2+3+4+5+6+7+8+9+10+11+12+...) which needs to be evaluated all in one go, which will overflow your stack. It is a little tricky, I know... sumCal i n sum | i < n = sumCal (i+1) n $! sum+i | otherwise = sum However, there is a function "sum" in the prelude, so you can do this much more simply: sumit :: Int -> Int sumit n = sum [1..n] :-) Luke > > loopOut :: Int -> IO() > loopOut n | n <= 1000000 > = do > loopIn 0 (1000000000*n) n 0 > loopOut (n*10) > | otherwise = printf "Done!" > > > loopIn :: Int -> Int -> Int -> Int -> IO() > loopIn i ub n sum | i < ub > = do > loopIn (i+1) ub n (sumit n) > printf "n=%10d sum=%15d" n sum > | otherwise = printf "\n" > > main :: IO () > main > =do > printf "Started .." > loopOut 1000 > > Actually the next step it to parallelize the code with STM.But even at this > stage it doesn't work ! So, if you can help me with this,I'd be grateful. > > Thanks, > Mozhgan > > ------------------------------ > " Upgrade to Internet Explorer 8 Optimised for MSN. " Download Now<http://extras.uk.msn.com/internet-explorer-8/?ocid=T010MSN07A0716U> >

2 1