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Install qtHaskell 1.1.4 using Visual Studio 2010 and GHC 7.4.2
by leonardo davinci 24 Feb '13

24 Feb '13

I am trying to install qtHaskell in Windows. I have Qt 4.8.4 (the Visual Studio 2010 version). I am following the section <<2.3.2 Windows Manual Installation>> from the userGuide of qtHaskell. I set the path as described I added the line to qt.cabal, I changed dir to qws I gave qmake -recursive and then instead of mingw32-make I gave nmake which is the equivalent for VS2010. After the compilation process finished with success I switched back to root directory of qtHaskell and I gave "runhaskell Setup.hs configure --ghc" and I took the message: "Setup.hs:1:12: Warning: -fglasgow-exts is deprecated: Use individual extensions instead Configuring qt-1.1.4... " After that I gave the command: "runhaskell Setup.hs makefile" and I got the message: "Setup.hs:1:12: Warning: -fglasgow-exts is deprecated: Use individual extensions instead unrecognised command: makefile (try --help)" Any help in order to continue? Thank in advance

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Munich Haskell Meeting
by Heinrich Hördegen 24 Feb '13

24 Feb '13

Dear all, please note that our monthly Haskell get-together is scheduled on Wed, 27th Feb 2013 at 19h30 at Cafe Puck in Munich, Germany. If you plan to join, please go to http://www.haskell-munich.de/dates and click the button. Everyone interested in functional programming is welcome! I wish everyone of you, joining or not, a nice week, Heinrich

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Fixing undeduceable instance ==> overlapping instance
by Michael Orlitzky 24 Feb '13

24 Feb '13

I'm trying to write a determinant function that works on matrices parameterized by their dimensions (Peano naturals). If I declare the following, -- Define a class so that we get a different determinant function -- on the base/recursive cases. class (Eq a, Ring.C a) => Determined m a where determinant :: (m a) -> a -- Base case, 1x1 matrices instance (Eq a, Ring.C a) => Determined (Mat (S Z) (S Z)) a where determinant m = m !!! (0,0) -- Recursive case, (n+2) x (n+2) matrices. instance (Eq a, Ring.C a, Arity n) => Determined (Mat (S (S n)) (S (S n))) a where determinant m = ... -- Recursive algorithm, the i,jth minor has dimension -- (n+1) x (n+1). foo bar (determinant (minor m i j)) I get an error stating that I'm missing an instance: Could not deduce (Determined (Mat (S n) (S n)) a) ... Clearly, I *have* an instance for that case: if n == Z, then it's the base case. If not, it's the recursive case. But GHC can't figure that out. So maybe if I define a dummy instance to make it happy, it won't notice that they overlap? instance (Eq a, Ring.C a) => Determined (Mat m m) a where determinant _ = undefined No such luck: >>> let m = fromList [[1,2],[3,4]] :: Mat2 Int >>> determinant m Overlapping instances for Determined (Mat N2 N2) Int arising from a use of `determinant' Matching instances: instance (Eq a, Ring.C a) => Determined (Mat m m) a -- Defined at Linear/Matrix2.hs:353:10 instance (Eq a, Ring.C a, Arity n) => Determined (Mat (S (S n)) (S (S n))) a ... I even tried generalizing the (Mat m m) instance definition so that OverlappingInstances would pick the one I want, but I can't get that to work either. Is there some way to massage this?

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Need urgent help with Network.tls
by C K Kashyap 24 Feb '13

24 Feb '13

Hi, I am trying to use Haskell to download email/attachments from gmail. For which I am exploring Network.TLS. I got this sample from the net that connects to gmail smtp and works just fine - http://hpaste.org/82890 However, when I modify it a bit to try to connect to imap, it simply does not work. To debug, I tried to connect to a webserver, even that seems to not work. I modified the function as follows. emailGmail2 = do let host = "localhost" let port = 443 let params = defaultParamsClient{pCiphers = ciphers} g <- RNG.makeSystem h <- connectTo host (PortNumber (fromIntegral port)) hSetBuffering h LineBuffering cWrite h "GET / HTTP/1.0" cWrite h "" cWaitFor h "ABCD" con <- contextNewOnHandle h params g handshake con bye con And I get a "BAD request" response from the server - Can some please give me a sample code that uses Network.TLS to connect to a imap.google.com (or even a webserver for that matter)? Regards, Kashyap

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Re: [Haskell-cafe] Type checking the content of a string
by Corentin Dupont 23 Feb '13

23 Feb '13

Finally, I solved the problem using typeOf instead of interpret: cr :: QuasiQuoter cr = QuasiQuoter { quoteExp = quoteRuleFunc} quoteRuleFunc :: String -> Q TH.Exp quoteRuleFunc s = do res <- runIO $ runInterpreter $ do setImports ["Prelude", "Language.Nomyx.Expression"] typeOf s case res of Right "RuleFunc" -> [| s |] Right _ -> fail $ "Rule doesn't typecheck" Left e -> fail $ show e I don't know really why, but now it's working very well! On Sat, Feb 23, 2013 at 7:56 PM, Daniel Gorín <jcpetruzza(a)gmail.com> wrote: > Hi Corentin, > > I've never used TH, but from what I understand, trying to combine hint and > TH would be redundant (even if it worked): whatever String you can evaluate > using hint, you can evaluate it directly in TH. Is this not the case? > > Cheers, > Daniel > > On Feb 23, 2013, at 6:53 PM, Corentin Dupont wrote: > > > Hi Daniel, > > Did you already tried to use Hint in a QuasiQuote? This would come handy > to check at compile time the validity of some strings... > > However I have the error hereunder. > > The duplicate symbol found in the object file is in fact the first > symbol in this file. So I guess GHCi tries to load it twice... > > Best, > > Corentin > > > > > > On Sat, Feb 23, 2013 at 12:03 AM, Corentin Dupont < > corentin.dupont(a)gmail.com> wrote: > > I'm trying to load my interpreter in the Q monad: > > > > cr :: QuasiQuoter > > cr = QuasiQuoter { quoteExp = quoteRuleFunc} > > > > quoteRuleFunc :: String -> Q TH.Exp > > quoteRuleFunc s = do > > res <- runIO $ runInterpreter $ do > > setImports ["Prelude", "Language.Nomyx.Rule", > "Language.Nomyx.Expression", "Language.Nomyx.Test", > > "Language.Nomyx.Examples", "GHC.Base", "Data.Maybe"] > > interpret s (as :: RuleFunc) > > case res of > > Right _ -> [| s |] > > Left e -> fail $ show e > > > > > > However, I always obtain an error during compilation: > > > > ... > > Loading package XXX ... linking ... done. > > > > > > GHCi runtime linker: fatal error: I found a duplicate definition for > symbol > > __stginit_ghczm7zi4zi1_DsMeta > > whilst processing object file > > /usr/lib/ghc/ghc-7.4.1/libHSghc-7.4.1.a > > This could be caused by: > > * Loading two different object files which export the same symbol > > * Specifying the same object file twice on the GHCi command line > > * An incorrect `package.conf' entry, causing some object to be > > loaded twice. > > GHCi cannot safely continue in this situation. Exiting now. Sorry. > > > > > > I vaguely understand that the interpreted modules are conflicting with > the compiled ones... > > > > > > > > On Fri, Feb 22, 2013 at 11:51 PM, Corentin Dupont < > corentin.dupont(a)gmail.com> wrote: > > Great! That seems very powerful. So you can do what you want during > compilation, readin files, send data over the network? > > Other question, in my example how can I halt the compilation if a test > program is wrong? > > > > > > On Fri, Feb 22, 2013 at 8:30 PM, Francesco Mazzoli <f(a)mazzo.li> wrote: > > At Fri, 22 Feb 2013 19:43:51 +0100, > > Corentin Dupont wrote: > > > Hi Adam, > > > that looks interresting. I'm totally new to TH and QuasiQuotes, though. > > > Can I run IO in a QuasiQuoter? I can run my own interpreter. > > > > Yes, you can: > > < > http://hackage.haskell.org/packages/archive/template-haskell/2.8.0.0/doc/ht… > >. > > > > Francesco > > > > > > > >

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Type checking the content of a string
by Corentin Dupont 23 Feb '13

23 Feb '13

Hi all, I have a program able to read another program as a string, and interpret it (using Hint). I'd like to make unit tests, so I have a file "Test.hs" containing a serie of test programs as strings. However, how could I be sure that these test program are syntactically valid, at compile time? Those programs should have the type "RuleFunc". I tried some TH: printProg :: Q Exp -> String printProg p = unsafePerformIO $ do expr <- runQ p return $ pprint expr myTest = printProg [| <my test program> :: RuleFunc |] But it's not very satisfatory yet. When pretty printing TH changes the program quite a bit and my interpreter cannot compile it due to scoping problems. I'd like to have my test program copied back as is. Is it possible? Any other solutions? Thanks a lot! Corentin

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ANN: data-fix-cse -- Common subexpression elimination for EDSLs
by Anton Kholomiov 23 Feb '13

23 Feb '13

I'm glad to announce the package for Common subexpression elimination [1]. It's an implementation of the hashconsig algorithm as described in the paper 'Implementing Explicit and Finding Implicit Sharing in EDSLs' by Oleg Kiselyov. Main point of the library is to define this algorithm in the most generic way. You can define the AST for your DSL as fixpoint type[2]. And then all you need to use the library is to define the instance for type class `Traversable`. This idea is inspired by `data-reify` [3] package which you can use to transform your ASTs to DAGs too. But it relies on inspection of the references for values when `data-fix-cse` doesn't sacrifices the purity. A short example: Let's define a tiny DSL for signals import Data.Fix type Name = String type E = Fix Exp data Exp a = Const Double | ReadPort Name | Tfm Name [a] | Mix a a deriving (Show, Eq, Ord) We can make constant signals, read them from some ports and transform them (apply some named function to the list of signals) and mix two signals. Let's define an instance of the Traversable (hence for the Functor and Foldable) import Control.Applicative import Data.Monoid import Data.Traversable import Data.Foldable instance Functor Exp where fmap f x = case x of Const d -> Const d ReadPort n -> ReadPort n Mix a b -> Mix (f a) (f b) Tfm n as -> Tfm n $ fmap f as instance Foldable Exp where foldMap f x = case x of Mix a b -> f a <> f b Tfm n as -> mconcat $ fmap f as _ -> mempty instance Traversable Exp where traverse f x = case x of Mix a b -> Mix <$> f a <*> f b Tfm n as -> Tfm n <$> traverse f as a -> pure a Now we can use the functio `cse` cse :: (Eq<http://hackage.haskell.org/packages/archive/base/4.6.0.1/doc/html/Data-Eq.h…>(f Int<http://hackage.haskell.org/packages/archive/base/4.6.0.1/doc/html/Data-Int.…>), Ord<http://hackage.haskell.org/packages/archive/base/4.6.0.1/doc/html/Data-Ord.…>(f Int<http://hackage.haskell.org/packages/archive/base/4.6.0.1/doc/html/Data-Int.…>), Traversable<http://hackage.haskell.org/packages/archive/base/4.6.0.1/doc/html/Data-Trav…>f) => Fix<http://hackage.haskell.org/packages/archive/data-fix/0.0.1/doc/html/Data-Fi…>f -> Dag<http://hackage.haskell.org/packages/archive/data-fix-cse/0.0.1/doc/html/Dat…>f to transform our AST to DAG. DAG is already sorted. Later we can define a handy wrapper to hide the details from the client newtype Sig = Sig { unSig :: E } You can find examples in the package archive Extra-Source-Files: test/Exp.hs test/Impl.hs test/Expl.hs If you want to see a real world example of usage you can find it in the csound-expression[4]. An edsl for the Csound language. One side-note form my experience: Fixpoint types can be very flexible. It's easy to compose them. If suddenly we need to add some extra data to all cases from the example above we can easily do it with just another Functor: Imagine that we want to use a SampleRate value with all signals. Then we can do it like this: type E = Fix SampledExp data SampledExp a = SampledExp SampleRate (Exp a) then we should define an instance of the type class Traversable for our new type SampleRate. The Exp doesn't change. [1] http://hackage.haskell.org/package/data-fix-cse-0.0.1 [2] http://hackage.haskell.org/package/data-fix-0.0.1 [3] http://hackage.haskell.org/package/data-reify [4] http://hackage.haskell.org/package/csound-expression Anton

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Parsec without data declarations/AST
by Sean Cormican 22 Feb '13

22 Feb '13

I have been trying to create a parser for a functional programming language, but there is no need to create an AST but merely check that the code is valid according to the grammar. In the following tutorial I have been trying to take some pointers from, data declarations are used to create an AST for the language, There is, as I understand a way to parse the language without an AST. http://www.haskell.org/haskellwiki/Parsing_a_simple_imperative_language My question is what should the type signatures for example parseFile function instead of "Stmt" accept as input if the parser is to accept Strings and numerical expressions alike ? Thanks for any help, Seán

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question about: --hyperlink-source
by Doaitse Swierstra 22 Feb '13

22 Feb '13

I ran into the problem that for the packages which I install using cabal install The generated html does not contain links to the sources. This issue was raised before in: http://stackoverflow.com/questions/1587635/haddock-for-cabal-installed-modu… I have been looking into the documentation available, but could not find a way to set this e.g. as a default in some .haddock file. Am I overlooking something? Doaitse

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How to input Unicode string in Haskell program?
by Semyon Kholodnov 22 Feb '13

22 Feb '13

Imagine we have this simple program: module Main(main) where main = do x <- getLine putStrLn x Now I want to run it somehow, enter "résumé 履歴書 резюме" and see this string printed back as "résumé 履歴書 резюме". Now, the first problem is that my computer runs Windows, which means that I can't use ghci ":main" or result of "ghc main.hs" to enter such an outrageous string — Windows console is locked to one specific local code page, and no codepage contains Latin-1, Cyrillic and Kanji symbols at the same time. But there is also WinGHCi. So I do ":main", copy-paste this string into the window (It works! Because Windows has Unicode for 20 years now), but the output is all messed up. In a rather curious way, actually: the input string is converted to UTF-8 byte string, and its bytes are treated as being characters from my local code page. So, it appears that I have no way to enter Unicode strings into my Haskell programs by hands, I should read them from files. That's sad, and I refuse to think I am the first one with such a problem, so I assume there is a solution/workaround. Now would someone please tell me this solution? Except from "Just stick to 127 letters of ASCII", of course.

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