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Choosing color of the track
by Manish Trivedi 18 Sep '12

18 Sep '12

Hi Folks, I am trying to plot two tracks with different colors. Following is my input file, ------ 2012-09-18 00:10:48,166 @CurrentPerHour13057 Red 2012-09-18 00:10:48,166 =CurrentPerHour13057 0.0 2012-09-18 00:10:58,155 =CurrentPerHour13057 0.0 2012-09-18 00:11:08,203 =CurrentPerHour13057 0.0 2012-09-18 00:11:18,166 =CurrentPerHour13057 0.0 2012-09-18 00:11:28,159 =CurrentPerHour13057 0.0 2012-09-18 00:11:38,170 =CurrentPerHour13057 0.0 2012-09-18 00:11:48,175 =CurrentPerHour13057 0.0 2012-09-18 00:11:58,174 =CurrentPerHour13057 0.0 2012-09-18 00:12:08,216 =CurrentPerHour13057 0.0 2012-09-18 00:12:18,218 =CurrentPerHour13057 0.0 2012-09-18 03:58:28,159 @PacingReqPerHr13057 Blue 2012-09-18 03:58:28,159 =PacingReqPerHr13057 2375.0534412521242 2012-09-18 03:58:38,161 =PacingReqPerHr13057 2375.383005739316 2012-09-18 03:58:48,175 =PacingReqPerHr13057 2375.713057258422 2012-09-18 03:58:58,160 =PacingReqPerHr13057 2376.0422443063935 2012-09-18 03:59:08,192 =PacingReqPerHr13057 2376.3730727321126 2012-09-18 03:59:18,207 =PacingReqPerHr13057 2375.9038854561304 2012-09-18 03:59:28,168 =PacingReqPerHr13057 2376.2324444615497 2012-09-18 03:59:38,156 =PacingReqPerHr13057 2376.5619853019184 2012-09-18 03:59:48,160 =PacingReqPerHr13057 2376.892145685344 2012-09-18 03:59:58,160 =PacingReqPerHr13057 2377.222265743067 ----- tplot -o /root/color.png -or 1024x768 -k 'CurrentPerHour' 'lines' -k 'PacingReqPerHr' 'lines' -if /root/color.input -tf 'date %Y-%m-%d %H:%M:%OS' I cant get to print plots in different color. Could anyone point out what am I doing wrong? Thanks, Manish

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ANNOUNCE: MFlow-0.1.5
by Alberto G. Corona 18 Sep '12

18 Sep '12

Hi haskellers and specially the web developers. http://hackage.haskell.org/package/MFlow-0.1.5.3 MFlow is a is a Web framework with some unique, and I mean unique, characteristics that I find exciting: - It is a Web application server that start and restart on-demand stateful web server processes (not request.-response) This means that all the page navigation can be coded in a single procedure. This increases readability of the programmer code. I woul call it a anti-node.js. Buit usual request-response (stateless) server processes are also allowed - When the process is invoqued as result of an URL request, the Web app server not only restart the process but also recover its execution state. The enclosing Workflow monad provides the thread state persistence. There are state timeouts and process timeouts defined by the programmer. Processes with no persistent state (transient) are possible. -The user interface is made of widgets. They are formlets with added formatting, attributes, validations, modifiers and callbacks, that are composable, so the pieces are reusable and return type safe responses to the calling process. Even the links are part of widgets and return back type safe inputs at compile time to the calling server process. Tho glue these components, ordinary applicative combinators and other extra combinators are used. - The widgets and the communication don´t make assumptions about the architecture, so it can be adapted to non-web environments. This versions has interface for WAI-warp, Hack, Text.XHtml (xhtml) , and Haskell Server Pages. -The widget rendering can be converted to ByteStrings automatically with special combinators. A mix of widgets with different formats can be combined in the same source file. For example Text.Html and HSP (Haskell server pages) -These widgets can be cached, to avoid widget rendering on every interaction. -To handle the back button, and because the processes are stateful, they can run backwards until the response match. This is transparent for the programmer, thanks to the embedded FlowM monad. -All the code is in pure Haskell. No deployment, special scripts, formats etc are necessary. -Besides automatic state persistence, TCache provides transactions and user data persistence, that can be configured for SQL databases. Default persistence in files permit very rapid prototyping. Just code and run it with runghc. -Has AJAX support All of this sounds very complicated, but really it is simple!. Most of these things are transparent. The resulting code is quite readable and has very little plumbing! There is a non trivial example that some of these functionalities embedded here that you can run: http://hackage.haskell.org/packages/archive/MFlow/0.1.5.3/doc/html/MFlow-Fo… Take a look and tell me your opinion. I hope that you find it as exciting as me. I´m looking for people to collaborate in the development of MFlow. Although still it is experimental, it is being used in at least one future commercial project. So I have te commitment to continue its development. There are many examples in the documentation and in the package. Alberto

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Type error with Type families
by Marco Túlio Pimenta Gontijo 18 Sep '12

18 Sep '12

Hi. I cannot make this program type check: {-# LANGUAGE TypeFamilies, FlexibleContexts #-} import qualified Data.ListLike as LL class LL.ListLike full (Item full) => ReplaceOneOf full where type Item full :: * replaceOneOf :: [Item full] -> full -> full -> full replaceOneOf from to list | LL.null list = list | x `element` from = LL.concat [to, replaceOneOf from to $ LL.dropWhile (`element` from) xs] | otherwise = LL.cons x $ replaceOneOf from to xs where x = LL.head list xs = LL.tail list element :: Item full -> [Item full] -> Bool The error message is: Line 9: 1 error(s), 0 warning(s) Could not deduce (Item full0 ~ Item full) from the context (ReplaceOneOf full) bound by the class declaration for `ReplaceOneOf' at /home/marcot/tmp/test_flymake.hs:(4,1)-(15,45) NB: `Item' is a type function, and may not be injective Expected type: [Item full0] Actual type: [Item full] In the second argument of `element', namely `from' In the expression: x `element` from I have tried using asTypeOf, but it did not work: {-# LANGUAGE TypeFamilies, FlexibleContexts, ScopedTypeVariables #-} import qualified Data.ListLike as LL class LL.ListLike full (Item full) => ReplaceOneOf full where type Item full :: * replaceOneOf :: Item full -> [Item full] -> full -> full -> full replaceOneOf xt from to list | LL.null list = list | (x `asTypeOf` xt) `element` from = LL.concat [to, replaceOneOf xt from to $ LL.dropWhile (`element` from) xs] | otherwise = LL.cons x $ replaceOneOf xt from to xs where x = LL.head list xs = LL.tail list element :: Item full -> [Item full] -> Bool Can someone point me to a solution? Greetings. -- marcot http://marcot.eti.br/

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cost-centre names
by Marco Túlio Pimenta Gontijo 18 Sep '12

18 Sep '12

Hi. I have a question about cost-centre names, as shown on .hp files produced by +RTS -hc. They have the form A/B/C/D/E/F/G/... Usually, it seems that it means A, called by B, called by C, etc, but that's not the case sometimes. I have a case here (called with -L200): replaceOneOf’/clean/tagsText/anyTag/dropTagClose/parseObservations/specificTagText/tagText/parseOab/dropTagText/dropTill/tag/tagOpen... tagsText calls clean which calls replaceOneOf', but anyTag does not call tagsText. parseObservations calls dropTagClose which calss anyTag, but specificTagText does not call parseObservations. They seem to be grouped by three. Is this correct? How should I interpret it? Greetings. -- marcot http://marcot.eti.br/

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Either Monad and Laziness
by oleg＠okmij.org 18 Sep '12

18 Sep '12

> I am currently trying to rewrite the Graphics.Pgm library from hackage > to parse the PGM to a lazy array. Laziness and IO really do not mix. > The problem is that even using a lazy array structure, because the > parser returns an Either structure it is only possible to know if the > parser was successful or not after the whole file is read, That is one of the problems. Unexpected memory blowups could be another problem. The drawbacks of lazy IO are well documented by now. > The behaviour I want to achieve is like this: I want the program when > compiled to read from a file, parsing the PGM and at the same time > apply transformations to the entries as they are read and write them > back to another PGM file. Such problems are the main motivation for iteratees, conduits, pipes, etc. Every such library contains procedures for doing exactly what you want. Please check Hackage. John Lato's iteratee library, for example, has procedure for handling sound (AIFF) files -- which may be very big. IterateeM has the TIFF decoder -- which is incremental and strict. TIFF is much harder to parse than PGM.

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Dynamic Programming with Data.Vector
by Myles C. Maxfield 18 Sep '12

18 Sep '12

Hello, I've been writing dynamic programming (dp) algorithms in imperative languages for years, and I was thinking recently about how to use it in a Haskell context. In particular, I want to write a function that takes an ordered collection of items and produces a new item to insert into the ordered collection. The most straightforward way to do this would be to use a list, something like the following: recurse :: [Integer] -> [Integer] recurse l = newValue : recurse (take (length l + 1) infiniteList) where newValue = ... infiniteList :: [Integer] infiniteList = initialList ++ recurse initialList where initialList = ... solution :: Integer solution = infiniteList !! 5 I'm assuming that this can run fast because I'm assuming the 'take' function won't actually duplicate the list ([1] doesn't actually list the running time of 'take') Is this a correct assumption to make? Secondarily, and most importantly for me, I'm curious about how to make this fast when the computation of 'newValue' requires random access to the inputted list. I'm assuming that I would use Vectors instead of lists for this kind of computation, and [2] describes how I can use the O(1) 'slice' instead of 'take' above. However, both of Vector's cons and snoc functions are O(n) which defeats the purpose of using this kind of algorithm. Obviously, I can solve this problem with mutable vectors, but that's quite inelegant. Overall, I'm looking for a function, similar to Data.Vector's 'generate' function, but instead of the generation function taking the destination index, I'd like it to take the elements that have previously been constructed. Is there such a function? If there isn't one, is this kind of function feasible to write? If such a function doesn't exist and is feasible to write, I'd be happy to try to write and contribute it. [1] http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html#g… [2] http://hackage.haskell.org/packages/archive/vector/0.9.1/doc/html/Data-Vect…

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Re: [Haskell-cafe] What is the good way to work with list comprehension and UTCTime?
by Chris Heller 17 Sep '12

17 Sep '12

You might want to have a look at the time-recurrence package: http://hackage.haskell.org/package/time-recurrence For your simple cases you would do something like: Each second: starting (UTCTime ...) $ recur secondly Each minute: starting (UTCTime ...) $ recur minutely The rules can get quite a bit more complex than that. I am the author of time-recurrence, so if you have questions feel free to ping me. -Chris On Fri, Sep 14, 2012 at 6:00 AM, <haskell-cafe-request(a)haskell.org> wrote: > Send Haskell-Cafe mailing list submissions to > haskell-cafe(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://www.haskell.org/mailman/listinfo/haskell-cafe > or, via email, send a message with subject or body 'help' to > haskell-cafe-request(a)haskell.org > > You can reach the person managing the list at > haskell-cafe-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Haskell-Cafe digest..." > > > Today's Topics: > > 1. Fwd: How Type inference work in presence of Functional > Dependencies (Dan Doel) > 2. Re: [ANN] Cumino 0.2 - Now supports pretty indentation > through stylish-haskell (Brandon Allbery) > 3. Re: [ANN] Cumino 0.2 - Now supports pretty indentation > through stylish-haskell (Alfredo Di Napoli) > 4. ANNOUNCE: Groundhog 0.1.0.1 - high-level database library > (Boris Lykah) > 5. Re: ANNOUNCE: Groundhog 0.1.0.1 - high-level database library > (Tom Murphy) > 6. Re: Either Monad and Laziness (wren ng thornton) > 7. How do I generate random numbers using random-fu, with > platform-agnostic code? (Andrew Pennebaker) > 8. Is Hackage down? (C K Kashyap) > 9. Re: Is Hackage down? (damodar kulkarni) > 10. What is the good way to work with list comprehension and > UTCTime? (Magicloud Magiclouds) > 11. Re: What is the good way to work with list comprehension and > UTCTime? (Karl Voelker) > 12. Re: [ANN] Cumino 0.2 - Now supports pretty indentation > through stylish-haskell (Alfredo Di Napoli) > 13. Re: Is Hackage down? (John Wiegley) > 14. Re: [ANN] Cumino 0.2 - Now supports pretty indentation > through stylish-haskell (Alfredo Di Napoli) > 15. Re: What is the good way to work with list comprehension and > UTCTime? (Roman Cheplyaka) > 16. Re: What is the good way to work with list comprehension and > UTCTime? (Magicloud Magiclouds) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 13 Sep 2012 10:44:17 -0400 > From: Dan Doel <dan.doel(a)gmail.com> > Subject: [Haskell-cafe] Fwd: How Type inference work in presence of > Functional Dependencies > To: Haskell Caf? List <haskell-cafe(a)haskell.org> > Message-ID: > < > CAHEA9tPsGTUX4Ke9eGCpA%2B-f_b_Ky9--y6RZkHPAmN9LW8MxHA(a)mail.gmail.com> > Content-Type: text/plain; charset=ISO-8859-1 > > Copying the mailing list, because I forgot. > > On Thu, Sep 13, 2012 at 5:18 AM, satvik chauhan <mystic.satvik(a)gmail.com> > wrote: > > Consider the code below : > > > > {-# LANGUAGE > > > MultiParamTypeClasses,FlexibleInstances,FunctionalDependencies,UndecidableInstances,FlexibleContexts > > #-} > > class Foo a c | a -> c > > instance Foo Int Float > > f :: (Foo Int a) => Int -> a > > f = undefined > > > > Now when I see the inferred type of f in ghci > > > >> :t f > > > >> f :: Int -> Float > > > > Now If I add the following code > > > > g :: Int -> Float > > g = undefined > > > > h :: (Foo Int a) => Int -> a > > h = g > > > > > > I get the error > > > > Could not deduce (a ~ Float) > > > > > > I am not able to understand what has happened here ? The restriction "Foo > > Int a" should have restricted the type of h to "Int -> Float" as shown in > > the inferred type of f. > > The answer, I believe, is that the difference between the fundep > implementation and type families is local constraint information. > Fundeps do no local propagation. > > So in your first definition, you've locally provided 'Int -> a', which > is acceptable to GHC. Then it figures out externally to the function > that '(Foo Int a) => Int -> a' is actually Int -> Float. > > In the second definition, you're trying to give 'Int -> Float', but > GHC only knows locally that you need to provide 'Int -> a' with a > constraint 'Foo Int a' which it _won't_ use to determine that a ~ > Float. > > This is not inherent to fundeps. One could make a version of fundeps > that has the local constraint rules (easily so by translating to the > new type families stuff). But, the difference is also the reason that > overlapping instances are supported for fundeps and not type families. > But I won't get into that right now. > > -- Dan > > > > ------------------------------ > > Message: 2 > Date: Thu, 13 Sep 2012 11:20:51 -0400 > From: Brandon Allbery <allbery.b(a)gmail.com> > Subject: Re: [Haskell-cafe] [ANN] Cumino 0.2 - Now supports pretty > indentation through stylish-haskell > To: Alfredo Di Napoli <alfredo.dinapoli(a)gmail.com> > Cc: Ray <i(a)maskray.tk>, haskell-cafe <haskell-cafe(a)haskell.org> > Message-ID: > <CAKFCL4WAtx6R0NVtP7nxnj1ZFp= > KHDx1dGeO-s9EsG4H9nMsvQ(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > On Thu, Sep 13, 2012 at 2:22 AM, Alfredo Di Napoli < > alfredo.dinapoli(a)gmail.com> wrote: > > > urxvtc -e sh -c 'echo a' > >> xterm -e echo a > >> > > > > I would like to, and in fact I've already tried, but urxvt is trickier > > than other shells. Using the command you gave me does not create a new > > window, tested both on XMonad and Gnome. This is > > the error you can see using the option "-hold", this way: > > > > urxvt --hold -e "echo a" > > > > This opens a new window with the error: *urxvt: Unable to exec child. > > * > > > > I think you misunderstood; as I read it (and as I would expect it to work > given the above descrtiption) that would be > > urxvt --hold -e sh -c 'echo a' > > -- > brandon s allbery allbery.b(a)gmail.com > wandering unix systems administrator (available) (412) 475-9364 vm/sms >

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Re: [Haskell-cafe] Either Monad and Laziness
by John Lato 17 Sep '12

17 Sep '12

> Subject: Re: [Haskell-cafe] Either Monad and Laziness > > On 9/14/12 5:16 PM, Eric Velten de Melo wrote: >> But now I'm kinda lost. Is there an easy way to explain the difference between: >> -iteratee >> -conduit >> -enumerator I tend to group them into three families. 'iteratee' and 'enumerator' are fairly directly drawn from Oleg's code, with mostly implementation differences (at least when compared to the other families). They've tended to keep Oleg's original names (iteratee, enumerator, enumeratee). The biggest user-visible difference between iteratee and enumerator is the level of datastream abstraction. iteratee abstracts over the stream, and enumerator abstracts over elements of the stream. The stream is explicitly a list of elements. This exposes some of the details of data chunking to the user, which has both advantages and disadvantages (iteratee exposes this also, but it's not necessary as is the case for enumerator). The second family (chronologically) includes conduit and (maybe) iterIO. I've written a little about this group at http://johnlato.blogspot.sg/2012/06/understandings-of-iteratees.html Although they serve the same goals in spirit, the implementation may or may not necessarily be an iteratee/enumerator arrangement (e.g. conduit). This is a technical observation, not a criticism, depending on exactly what you consider to define the style in the first place. This group has usually renamed functions. I discuss some of the other differences on my blog. The third familiy is all the pipes-* stuff. This group tends towards emphasizing the relationship between iteratee/enumerator pairs and coroutines, and also emphasizing (to use Oleg terminology) composition of enumeratees. I've been meaning to write more about this group, but thus far have been unable to do so. I'd rather not hijack by evangelizing, but obviously I think iteratee provides several important advantages over the other options. John L.

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guards in applicative style
by felipe zapata 17 Sep '12

17 Sep '12

Hi Haskellers, Suppose I have two list and I want to calculate the cartesian product between the two of them, constrained to a predicate. In List comprehension notation is just result = [ (x, y) | x <- list1, y <-list2, somePredicate x y ] or in monadic notation result = do x <- list1 y <- list2 guard (somePredicate x y) return $ (x,y) Then I was wondering if we can do something similar using an applicative style result = (,) <$> list1 <*> list2 (somePredicate ???) The question is then, there is a way for defining a guard in applicative Style? Thanks in advance, Felipe Zapata.

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Transforming a ADT to a GADT
by Florian Lorenzen 17 Sep '12

17 Sep '12

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hello cafe, I have a question wrt. to GADTs and type families in GHC (7.6.1). I'd like to transform a value of an ADT to a GADT. Suppose I have the simple expression language > data Exp = Lit Int > | Succ Exp > | IsZero Exp > | If Exp Exp Exp and the GADT > data Term t where > TLit :: Int -> Term Int > TSucc :: Term Int -> Term Int > TIsZero :: Term Int -> Term Bool > TIf :: Term Bool -> Term ty -> Term ty -> Term ty that encodes the typing rules. Now, I'd like to have a function > typecheck :: Exp -> Maybe (Term t) > typecheck exp = <...> that returns the GADT value corresponding to `exp' if `exp' is type correct. I found a solution at http://okmij.org/ftp/tagless-final/TypecheckedDSLTH.hs but this has as type (slightly adapted) > typecheck :: Exp -> Maybe TypedTerm with > data TypedTerm = forall ty. (Typ ty) (Term ty) > data Typ ty = > TInt Int | TBool Bool That is, the GADT value is hidden inside the existential and cannot be unpacked. Therefore, I cannot write a type preserving transformation function like > transform :: Term t -> Term t that gets the result of the `typecheck' function as input. The solution mentioned above uses Template Haskell to extract the `Term t' type from the existential package and argues that type errors cannot occur during splicing. Is there a possibility to avoid the existential and hence Template Haskell? Of course, the result type of typecheck depends on the type and type correctness of its input. My idea was to express this dependency by parameterizing `Exp' and using a type family `ExpType' like: > typecheck :: Exp e -> Maybe (Term (ExpType e)) > typecheck (ELit > i) = Just (TLit i) > typecheck (ESucc exp1) = case typecheck exp1 of > Nothing -> Nothing > Just t -> Just (TSucc t) > <...> with > data TEXP = L | S TEXP | IZ TEXP | I TEXP TEXP TEXP -- datakind > > > data Exp (e::TEXP) where > ELit :: Int -> Exp L > ESucc :: Exp e1 -> Exp (S e1) > EIsZero :: Exp e1 -> Exp (IZ e1) > EIf :: Exp e1 -> Exp e2 -> Exp e3 -> Exp (I e1 e2 e3) It seems to me that `ExpType' then would be a reification of the type checker for `Exp' at the type level. But I did not know how to define it. Does it make sense at all? Is it possible in GHC? All the examples on the net I looked at either start with the GADT right away or use Template Haskell at some point. So, perhaps this `typecheck' function is not possible to write in GHC Haskell. I very much appreciate any hints and explanations on this. Best regards, Florian - -- Florian Lorenzen Technische Universität Berlin Fakultät IV - Elektrotechnik und Informatik Übersetzerbau und Programmiersprachen Sekr. TEL12-2, Ernst-Reuter-Platz 7, D-10587 Berlin Tel.: +49 (30) 314-24618 E-Mail: florian.lorenzen(a)tu-berlin.de WWW: http://www.user.tu-berlin.de/florenz/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://www.enigmail.net/ iEYEARECAAYFAlBTCr8ACgkQvjzICpVvX7ZfTgCeOPflPtaEW/w1McjYWheaRaqq oUQAnRXSrGP3se+3oiI3nnd+B/rK8yx8 =X1hR -----END PGP SIGNATURE-----

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