- Haskell-Cafe - Haskell.org

Cabal test interface, what/where is it?
by Magnus Therning 19 Mar '11

19 Mar '11

After upgrading to ghc7 and Cabal 1.10 I get the following message when running 'Setup configure' on one of my packages: Setup.hs:3:1: Warning: In the use of `runTests' (imported from Distribution.Simple, but defined in Distribution.Simple.UserHooks): Deprecated: "Please use the new testing interface instead!" I usually turn to the Cabal docs at [1], but the new testing interface isn't mentioned. Looking through the haddock API reference doesn't offer any obvious pointers. So, where should I turn to get rid of the warning? /M [1] http://www.haskell.org/ghc/docs/latest/html/Cabal/ -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus I invented the term Object-Oriented, and I can tell you I did not have C++ in mind. -- Alan Kay

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Missing e-mail @haskell-cafe
by Mario Blažević 19 Mar '11

19 Mar '11

I've sent an e-mail to Haskell Café this morning about my troubles with Trac confirmation e-mails. The e-mail must have reached the server, because it showed up in the mailing list archive: http://www.haskell.org/pipermail/haskell-cafe/2011-March/090311.html This other archive, however, doesn't list it: http://www.mail-archive.com/haskell-cafe@haskell.org/ I thereby infer that the message was never forwarded to the mailing list. Is that correct, and does anybody have a clue why?

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Wanted: composoable parsers from haskell-src-exts
by J. Waldmann 18 Mar '11

18 Mar '11

Hi. I want to use parsers from haskell-src-exts as sub-parsers, which does not seem to work since they insist on consuming the input completely. I would need them to parse a maximal prefix, and return the (unconsumed) rest of input as well (cf. http://hackage.haskell.org/packages/archive/parsec/3.1.1/doc/html/Text-Pars… ) I figure that happy has the %partial directive for that, but the description http://www.haskell.org/happy/doc/html/sec-directives.html#sec-partial-parse… does not really tell me how to obtain the rest of the input. Any hints (or code samples) appreciated. Thanks - J.W.

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Could not deduce ... using functional dependencies with GHC7
by JP Moresmau 18 Mar '11

18 Mar '11

Hello, when moving to GHC7 a body of code that I'm not immensely familiar with, I got an error compiling with GHC 7.0.2. Can somebody kindly explain to me what it means and how to get around it? This is in the scion code base so is using some GHC types. I have a class with a functional dependency (I think :-p): class Search id a | a -> id where search :: (SrcSpan -> Bool) -> SrcSpan -> a -> SearchResults id And some instances, notably: instance Search Id Id where search _ _ i = only (FoundId i) And the error occurs on another instance: instance (Search id id) => Search id (Sig id) where search p s (IdSig i) = search p s i ... other cases here, that work The error is: Could not deduce (id ~ Id) from the context (Search id id) bound by the instance declaration at lib\Scion\Inspect\Find.hs:477:10-45 `id' is a rigid type variable bound by the instance declaration at lib\Scion\Inspect\Find.hs:477:18 When using functional dependencies to combine Search Id Id, arising from the dependency `a -> id' in the instance declaration at lib\Scion\Inspect\Find.hs:183:10 Search id Id, arising from a use of `search' at lib\Scion\Inspect\Find.hs:479:32-37 In the expression: search p s i In an equation for `search': search p s (IdSig i) = search p s i If I replace the call to search with the actual implementation of search for Id, it compiles, so at some level the code "makes sense". I much prefer when error messages end with "Possible fix:..."! Thanks! -- JP Moresmau http://jpmoresmau.blogspot.com/

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Re: [Haskell-cafe] trac.haskell.org problem
by Mario Blažević 18 Mar '11

18 Mar '11

I've tried to send the verification e-mail from trac.haskell.org to three different e-mail accounts in the last 24 hours. None arrived. Note that I'm not trying to create a new account, I'm trying to verify my e-mail address in order to edit the Wiki pages of my projects. Can anybody else confirm this problem? > Ah, I suppose that's to do with the trac server itself, that's beyond me. > > Moving to café: Does anyone know what's up with trac.haskell.org not > sending > out verification emails? > > Cheers, > > /Niklas > > ________________________________________ > From: Jurriaan Hage [jur at cs.uu.nl] > Sent: Monday, February 28, 2011 8:41 AM > To: Niklas Broberg > Subject: Re: Again a question about haskell-src-exts. > > On Feb 28, 2011, at 8:39 AM, Niklas Broberg wrote: > > > I suppose I do - to the extend I can. What's the issue? :-) > The system does not send out verification e-mails, so I can not really > register completely and submit new issues. > I have tried it with two different e-mail accounts, and somebody else has > tried too. > They also do not show up in spam folders. > > Jur >

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Data constructor synonyms
by Grigory Sarnitskiy 18 Mar '11

18 Mar '11

Hello! Assume I have a type MyType with the constructor GeneralConstructor: data MyType = GeneralConstructor [Double] but I also want to have a separate name for special case of this constructor: SpecialConstructor Double so SpecialConstructor a = GeneralConstructor (a:[]) that is SpecialConstructor 5 was exactly the same as GeneralConstructor [5]. And for example instead of writing GeneralConstructor [0] I would like to use constructor Zero. It's all just for convenience. How can I achieve this? Well, of course I always can use sed to replace SpecialConstructor 5 with GeneralConstructor [5] in program sources, but it's not convenient.

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tplot and splot - analyst's swiss army knifes for visualizing log files
by Eugene Kirpichov 18 Mar '11

18 Mar '11

Hi cafe, I've published a large presentation about two Haskell-based tools of mine - tplot and splot. Their motto is "visualize system behavior from logs with a shell one-liner". Based on my experience, they usually seem to live up to this motto. http://www.slideshare.net/jkff/two-visualization-tools [attention attractor: the presentation has *really a lot* of pictures] hackage: http://hackage.haskell.org/package/timeplot http://hackage.haskell.org/package/splot other docs: http://www.haskell.org/haskellwiki/Timeplot http://www.haskell.org/haskellwiki/Splot -- Eugene Kirpichov Senior Software Engineer, Grid Dynamics http://www.griddynamics.com/

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order of arguments matters
by Peter Padawitz 18 Mar '11

18 Mar '11

Why does only tr2 work, although the only difference between tr1 and tr2 is the order of arguments? import Data.Tree (Tree(..)) data Type a where Tree :: Type a -> Type (Tree a) Int :: Type Int String :: Type String type Traversal1 = forall a.a -> Type a -> a type Traversal2 = forall a.Type a -> a -> a tr1 :: Traversal1 tr1 (Node _ (t:_)) (Tree Int) = Node 1 [t] tr1 n Int = n+n tr1 s String = s++s tr2 :: Traversal2 tr2 (Tree Int) (Node _ (t:_)) = Node 1 [t] tr2 Int n = n+n tr2 String s = s++s Couldn't match expected type `a' against inferred type `Tree Int' `a' is a rigid type variable bound by the type signature for `tr1' at tratest.hs:9:25 In the pattern: Node _ (t : _) In the definition of `tr1': tr1 (Node _ (t : _)) (Tree Int) = Node 1 [t]

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How to contact OpenGL package maintainer (where is Sven?)
by Jason Dagit 18 Mar '11

18 Mar '11

Hello, It looks like the OpenGL packages on hackage[1,2,3,4] have not been updated in some time. No updates later than Oct 2009. I tried to email Sven directly using the email address listed on hackage but after about a week I still haven't heard from him. I sent some patches to the opengl list yesterday, and then today I noticed that Sven hasn't posted on that list since Oct 2009 when he released the current version of OpenGLRaw. None of the public darcs repos have patches newer than Oct 2009. Also, the homepage url listed in the packages is a 404: http://www.haskell.org/HOpenGL/ My concern is that Sven has disappeared for some reason. I hope he's well. He has always done top notch work in the past maintaining these libraries. Perhaps he's simply busy or lost interest? Does anyone know if he was looking for a new maintainer? Perhaps you've heard from him more recently than Oct 2009? If a new maintainer is needed, I would consider nominating myself :) Thanks, Jason [1] http://hackage.haskell.org/package/OpenGLRaw [2] http://hackage.haskell.org/package/OpenGL [3] http://hackage.haskell.org/package/GLURaw [4] http://hackage.haskell.org/package/GLUT

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ghci Vim completion within Vim - need some advice
by Marc Weber 18 Mar '11

18 Mar '11

Hi, https://github.com/MarcWeber/vim-addon-async implements a hacky way to run external processes asynchronously. An external helper application send stdout of the process to Vim which adds the bytes to the buffer. Its not perfect but quite usable. Now I'd like to show the completion of \t sent to ghci to the user. I've done so for Ruby, Python and Scala: Vim sends input to ghci, and the reply is catched and put into Vim's completion list. issue 1): ghci's tab only works if its connected to a "terminal". This can be fixed easily by using a pseudo terminal issue 2): ghci's prompt sends data to /dev/tty (the controlling terminal) rather than to stdout/err. I don't know how to fix issue 2). Any ideas? The result could look like this python REPL screenshot: http://mawercer.de/~marc/vim-addon-async-python-repl.jpg Marc Weber

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