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Re: [Haskell-beginners] Signature of monadic functions
by Lorenzo Tabacchini 22 Oct '13

22 Oct '13

I think I am looking at the problem in a wrong way... What I want to do is using higher-order functions with IO (or an IO-based transformer). For example, let's say I want to apply a function to all the keys in a Map. With pure functions, I would do: Map.mapKeys doSomething myMap But let's suppose the function has a signature: doSomething :: a -> IO b Is there an easy way to apply it?

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Re: [Haskell-beginners] -with-rtsopts ignored at compile time
by Brandon Allbery 22 Oct '13

22 Oct '13

On Mon, Oct 21, 2013 at 1:51 PM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > I understand the problem. I’ve set the GHCRTS environment variable and > when I run the program I get : <unknown>: Most RTS options are disabled. > Link with –rtsopts to enable them. **** > > Then I added rtsopts to the command line: ghc -shared -rtsopts -O2 -o > TBGlas.dll TBGlasDll.hs**** > > and I get the same errormessage again: Most RTS options are…… What is > the problem? > Exact same issue. Those cannot be per DLL, they apply to the final program (what would it mean for only some DLLs to allow RTS options? There's only one runtime!); and you'd probably have to use the same mechanism I pointed at before if you're invoking hs_main() from C instead of using a Haskell main function. -- brandon s allbery kf8nh sine nomine associates allbery.b(a)gmail.com ballbery(a)sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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Re: [Haskell-beginners] -with-rtsopts ignored at compile time
by Brandon Allbery 22 Oct '13

22 Oct '13

On Mon, Oct 21, 2013 at 8:01 AM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > When I run my program, I get a stack overflow message (current stacksize > is 8388608 bytes) and the advice to use +RTS –Ksize -RTS**** > > The Haskell code creates a Windows dll, so no command line. That’s why I > want to change the stack size at compile time. > I think the default RTS options are only settable in a compile that produces an executable; otherwise there would have to be a chunk of code that retrieved all the rtsopts from every Haskell-compiled DLL and somehow reconciled any conflicts between them. Also note that if the main program is in C, you don't get -with-rtsopts processing at all; see http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi-ghc.html#using-… how you set RTS options in this case. (See at "To use +RTS flags with hs_init()".) In this particular case you may be better off just using the %GHCRTS% environment variable. -- brandon s allbery kf8nh sine nomine associates allbery.b(a)gmail.com ballbery(a)sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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-with-rtsopts ignored at compile time
by Kees Bleijenberg 21 Oct '13

21 Oct '13

When I run my program, I get a stack overflow message (current stacksize is 8388608 bytes) and the advice to use +RTS -Ksize -RTS The Haskell code creates a Windows dll, so no command line. That's why I want to change the stack size at compile time. I tried ghc -shared -O2 -o -with-rtsopts="-H128m -K64m" TBGlas.dll TBGlasDll.hs Ghc tells that it links with "-H128m -K64m". When I run the program I still get a message overflow with again the same (?) 8388608 stack size. I also changed the stacksize of the calling program, but no luck (same message). I wonder whether ghc ignores the -with-rtsopts parameter? Probably the problem is caused by not enough strictness, but still I want te make sure that it is not the stacksize (it is a big program). Kees

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storage leak in NetSNMP?
by Lieven Marchand 21 Oct '13

21 Oct '13

Hi, I have a small script that computes a list of network devices, directs an SNMP query at each of them, computes a report from the result of that query and prints that. I would expect that to run in constant space but instead memory usage keeps going up until the script is killed by the OOM killer. Is it possible that the NetSNMP library is keeping hold of all the results of its session? Here's part of my code: analyzeSNMP :: Line -> IO() analyzeSNMP x = do snmp <- getSNMP x putStrLn $ getNetworks (x, snmp) getSNMP :: Line -> IO (Either String [SnmpResult]) getSNMP line = snmpWalk snmp_version_2c (encodeUtf8 (primaryRouterLoopback line)) (DBC.pack "XXX") mib2 getNetworks :: (Line, Either String [SnmpResult]) -> String main = do initialize args <- arguments wans <- case wanInventoryFileName args of Just s -> parseWANInventory s Nothing -> return DefaultWAN.wans let lines = makeLines (tail wans) mapM_ analyzeSNMP lines

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Re: [Haskell-beginners] Actions v. Functions
by MJ Williams 20 Oct '13

20 Oct '13

For example, `main = do input <- getLine ...', where `getLine' is an action as distinguished from a function such as `main'. Other examples of actions in Haskell include `print', `putStrLn' and any process that reads from or writes to a file. Of course, the list of actions doesn't end there, though the examples here should answer your question. Sincerely, Matt At 21:44 19/10/2013, you wrote: >What do you mean by "action"? > >Antoine > > >On Fri, Oct 18, 2013 at 9:26 PM, MJ Williams ><<mailto:matthewjwilliams101@gmail.com>matthewjwilliams101(a)gmail.com> wrote: >Hello >What are the formal properties of an action? >How does an action differ from a function? >Sincerely, >Matthew > >_______________________________________________ >Beginners mailing list ><mailto:Beginners@haskell.org>Beginners(a)haskell.org >http://www.haskell.org/mailman/listinfo/beginners > > >_______________________________________________ >Beginners mailing list >Beginners(a)haskell.org >http://www.haskell.org/mailman/listinfo/beginners

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Actions v. Functions
by MJ Williams 20 Oct '13

20 Oct '13

Hello What are the formal properties of an action? How does an action differ from a function? Sincerely, Matthew

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Re: [Haskell-beginners] How do I give a type for this code?
by Todd Wilson 18 Oct '13

18 Oct '13

Thanks, Daniel, for your suggestion, but I think it misses a key aspect of my situation (unless I've misunderstood). Every model is supposed to be a quadruple (m, q, f, p), with m a list, q an element of m, f a list of ordered pairs of elements of m, and p a sublist of m. By contrast, it looks like your definition makes a model either a single element, or a single pair, or a single list, etc. --Todd On Thu, Oct 17, 2013 at 4:12 AM, Daniel Trstenjak < daniel.trstenjak(a)gmail.com> wrote: > > Hi Todd, > > the problem is, that 'model_of' tries to return different types: Model a, > Model (a,a) and Model [a]. > > I think you have to use some kind of ADT also for the Model, like you > already did for ModName. > > Something like: > > data Model a = Model a > | ProductModel (a,a) > | PowerModel [a] > ... > > > Greetings, > Daniel > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners >

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How do I give a type for this code?
by Todd Wilson 17 Oct '13

17 Oct '13

Haskell community, I'm in one of those situations where I have the code I want to write, but need to find the right types to get it to typecheck. What follows is a generic version of my situation. Suppose I want to represent the finite models of a language (in the sense of mathematical logic) with a single constant c, unary function symbol f, and predicate P. I can represent the carrier as a list m, the constant as an element of m, the function as a list of ordered pairs of elements of m, and the predicate as the list of the elements in the model that satisfy it: -- a model is (m, c, f, p) type Model a = ([a], a, [(a,a)], [a]) -- a is the "base type" I can then construct particular models and operations on models. The details aren't important for my question, just the types: unitModel :: Model () unitModel = ([()], (), [((),())], []) cycleModel :: Int -> Model Int cycleModel n = ([0..n-1], 0, [(i, (i+1)`mod`n) | i<-[0..n-1]], [0]) -- function application, assuming function is total ap :: Eq a => [(a,b)] -> a -> b ap ((x',y'):ps) x = if x == x' then y' else ap ps x -- cartesian product of models productModel :: (Eq a, Eq b) => Model a -> Model b -> Model (a,b) productModel (m1, c1, f1, p1) (m2, c2, f2, p2) = (m12, c12, f12, p12) where m12 = [(x1,x2) | x1 <- m1, x2 <- m2] c12 = (c1, c2) f12 = [(x12, (ap f1 (fst x12), ap f2 (snd x12))) | x12 <- m12] p12 = [x12 | x12 <- m12, elem (fst x12) p1 && elem (snd x12) p2] -- powerset of model powerModel :: (Eq a, Ord a) => Model a -> Model [a] powerModel (m, c, f, p) = (ms, cs, fs, ps) where ms = subsequences m cs = [c] fs = [(xs, nub (sort (map (ap f) xs))) | xs <- ms] ps = [xs | xs <- ms, elem c xs] Now, I want to give a name to all of these models: data ModName = UnitModel | CycleModel Int | Product ModName ModName | Power ModName deriving (Show, Eq) And finally, I want to associate each name with its associated model: model_of UnitModel = unitModel model_of (CycleModel n) = cycleModel n model_of (Product m1 m2) = productModel (model_of m1) (model_of m2) model_of (Power m1) = powerModel (model_of m1) I've tried a number of ways of getting this to work, in the sense of defining types so that I can use exactly this definition of model_of (some involving GADTs and type families) but haven't found a best way. How should I do it? Todd Wilson

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Signature of monadic functions
by Lorenzo Tabacchini 17 Oct '13

17 Oct '13

Hi, is there an easy way to transform a function from: Monad m => a -> m b to: Monad m => m (a -> b) ?

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