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Test.QuickCheck: generate
by Michael Mossey 08 Oct '09

08 Oct '09

In Test.QuickCheck, the type of 'generate' is generate :: Int -> StdGen -> Gen a -> a I can't find docs that explain what the Int does. Some docs are here: <http://www.haskell.org/ghc/docs/latest/html/libraries/QuickCheck/Test-Quick…>

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On DSLs - one last time
by Günther Schmidt 08 Oct '09

08 Oct '09

Hi all, I'd like to summarize my impressions on the DSL issue, gathered from the responses to my posts. It is absolutely amazing, various people have shown here that it is possible to design languages within haskell that are almost or just as powerful and safe as haskell itself. It is probably even possible to create an EDSL within an EDSL within haskell. Amazing! Uhm... ... but in that case I really wonder why I should not use Haskell directly then. Because out of the EDSL I can clearly see the "E" and I can see the "L" but having slight problems figuring out where the "D" and the "S" come in. In short, yes it's great that you can create a language within Haskell so powerful that it's gone full circle and is general purpose again, but what good is that? The efforts I've seen here where efforts to create a rich and powerful syntax, but aren't we supposed to focus on expressing semantics specific to a problem in a DSL rather? I'm not trying to put the efforts and achievements of the people who have done such amazing work down, but what exactly is it that I missed? Günther

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random question
by Michael Mossey 08 Oct '09

08 Oct '09

My thread about randomness got hijacked so I need to restate my remaining question here. Is it acceptable to write pure routines that use but do not return generators, and then call several of them from an IO monad with a generator obtained by several calls to newStdGen? shuffle :: RandomGen g => g -> [a] -> [a] shuffle = ... foo :: [a] -> [a] -> IO () foo xs ys = do g1 <- newStdGen print $ shuffle g1 xs g2 <- newStdGen print $ shuffle g2 ys Does this kind of thing exhibit good pseudorandomness? Thanks, Mike

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#include path
by Sean McLaughlin 08 Oct '09

08 Oct '09

Hi, I'm trying to compile some code using Cabal. One of the files has a CPP directive #include "undefined.h" The file undefined.h is in the same directory as the file with the directive. If I use the full path name, cabal can compile it. However, if I use the relative path, it complains about not being able to find the file. I tried adding it to extra-source-files, but that didn't help. I see that Hackage packages like Agda use this trick, so I know it's possible. How can I get these paths worked out correctly? There isn't much comment in the Cabal docs. Thanks, Sean

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Cabal, sdist and flags
by Magnus Therning 08 Oct '09

08 Oct '09

A while ago I moved a project away from using a mix of Cabal and make to build (Cabal to build the library and make to build the tests) to using only Cabal. I added a flag and then made a construct like this: flag BuildTests Description: Build unit and quickcheck tests. Default: False ... executable tests if flag(BuildTests) main-is: Test.hs build-depends: test-framework, test-framework-hunit, HUnit, test-framework-quickcheck2, QuickCheck >= 2.1.0.0 hs-source-dirs: test-src src else main-is: Test.hs buildable: False Interestingly that does work for things like 'configure' and 'build', but it doesn't work for 'sdist': % ./Setup.hs sdist Distribution quality errors: Building source dist for dataenc-0.13.0.1... Setup.hs: Test.hsTest.hs doesn't exist To make this work I had to move the 'main-is' outside of the if-else: executable tests main-is: Test.hs hs-source-dirs: test-src src if flag(BuildTests) build-depends: test-framework, test-framework-hunit, HUnit, test-framework-quickcheck2, QuickCheck >= 2.1.0.0 else buildable: False I found this surprising, so I'm tempted to call it a bug. A quick search didn't tell me whether this is well-known already, hence the email. Would you consider it a bug? Has it been raised already? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe

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What *is* a DSL?
by oleg＠okmij.org 08 Oct '09

08 Oct '09

Perhaps it would be appropriate to point out the IFIP conference on exactly that topic, DSL. The conference took place in July, here is the permanent record: http://dsl09.blogspot.com/ with pointers to the slides and the discussions. The panel discussion has debated that very question, what exactly is DSL. http://dsl09.blogspot.com/2009/07/panel.html As you can see, the agreement could not be reached on what is Domain. There will be another DSL conference, in Australia. Perhaps all the Haskell-Cafe debaters may want to participate.

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ANNOUNCE: vty-ui 0.2
by Jonathan Daugherty 08 Oct '09

08 Oct '09

I'm happy to announce the release of vty-ui 0.2. Get it from Hackage: http://hackage.haskell.org/package/vty-ui Or get the source with darcs: http://repos.codevine.org/vty-ui This version of vty-ui is everything you hoped it would be: fewer bugs, more widget types, cleaner code, better abstractions, and more generality. If you've written any applications to use vty-ui, only a few of your type signatures will need to change. Here's a summary of changes: General * Unify HBorder and VBorder types (now called Border) * Unify HFill and VFill types (now called Fill) * Unify HBox and VBox types (now called Box) * Box layout: layout documentation, edge case bug fixes * Widget class: refactor growthPolicy into growHorizontal and growVertical * Add Graphics.Vty.Widgets.Composed for high-level widget compositions * Add Graphics.Vty.Widgets.All convenience module to export everything in the library Lists * List items may now be of any widget type! * Add resize, pageUp, pageDown, scrollBy functions and expose other list functionality * Generalize scrolling API * Add convenience API for using lists of Text widgets * Support internal identifiers for list items * Always consume scrollWindowSize lines of space even if the list is smaller New widgets * WrappedText: automatically wraps text in available space; try resizing the demo. * Borders module: one-row/one-column ASCII borders between boxed widgets; ASCII art box container * Demo: use crazy boxed list items to show off border boxes and generic widget support in Lists! * Demo: support PageUp/PageDown to demonstrate List paging API Enjoy! -- Jonathan Daugherty

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dsl and gui toolkit
by Andrew U. Frank 07 Oct '09

07 Oct '09

thanks for the connection to the gui runner - it is interesting and worthwile, but a different approach. my approach is strictly declarative and does not describe sequences of process. it describes screens and links operations to buttons. then it takes inputs from the screen and runs the operations and posts the result on the screen. some operations open new screens etc. i started with the idea that ontologies describe the semantics of data in a static way; this should be (nearly) enough to create the user interface - which is all about semantics of the data. of course, you have to include in the ontology the semantics of the operations (as class with functions). the implementation is close to a reactive framework - adding a representation of all what is visible on the screen (the universer of discourse) in a format usable by the operations. then you have only to connect this 'universe of discourse' to the programs which operate on the data and post their reaction in the UoD and map the UoD to the screen the details are messy as i attempted to construct the internal data structures etc. as automatically as possible and with minimal designer input I did not use template haskell, yet, but will need to (i think). i am happy to share it with interested parties and hear the comments and perhaps somebody can help me with using templates to reduce the . it is IMHO not yet ready for posting in a library - but this is certainly the goal.

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New to Haskell - List Comprehension Question
by Steven1990 07 Oct '09

07 Oct '09

Hi, I'm currently learning Haskell, and I've been trying to work out a function for the following problem for a couple of days now. I want to use a list comprehension method to change the first letter of a string to upper case, and the rest of the string to lower case. Eg: "heLLo" -> "Hello" As I'm trying to learn this, I would appreciate hints rather than the explicit solution if possible? I'm sure I'm close to a solution, I must be missing something though. Driving me crazy! My attempts are something similar to this: upperCase :: String -> String upperCase xs = [toUpper(x):toLower(xs) | x <- xs] I think 'toLower' expects a single character rather than the list which is one place I'm going wrong? Thanks in advance, Steven -- View this message in context: http://www.nabble.com/New-to-Haskell---List-Comprehension-Question-tp257941… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Finally tagless - stuck with implementation of "lam"
by Günther Schmidt 07 Oct '09

07 Oct '09

Hi all, I'm playing around with finally tagless. Here is the class for my Syntax: class HOAS repr where lam :: (repr a -> repr b) -> repr (a -> b) app :: repr (a -> b) -> repr a -> repr b fix :: (repr a -> repr a) -> repr a let_ :: repr a -> (repr a -> repr b) -> repr b int :: Int -> repr Int add :: repr Int -> repr Int -> repr Int sub :: repr Int -> repr Int -> repr Int mul :: repr Int -> repr Int -> repr Int and here is one instance of that class for semantics. newtype I a = I { unI :: IO a } instance HOAS I where app e1 e2 = I (do e1' <- unI e1 e2' <- unI e2 return $ e1' e2') int i = I (putStrLn ("setting an integer: " ++ show i) >> return i) add e1 e2 = I (do e1' <- unI e1 e2' <- unI e2 putStrLn (printf "adding %d with %d" e1' e2') return $ e1' + e2') sub e1 e2 = I (do e1' <- unI e1 e2' <- unI e2 putStrLn (printf "subtracting %d from %d" e1' e2') return $ e1' - e2') mul e1 e2 = I (do e1' <- unI e1 e2' <- unI e2 putStrLn (printf "multiplying %d with %d" e1' e2') return $ e1' * e2') I'm stuck with the "lam" method, for 2 days now I've been trying to get it right, but failed. Is there a possibility that it isn't even possible? Günther

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