April 2010 - Haskell-Cafe

Control.Exception try and catch
by Mads Lindstrøm 28 Apr '10

28 Apr '10

Hi From http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Control-Exce… "... The difference between using try and catch for recovery is that in catch the handler is inside an implicit block (see "Asynchronous Exceptions") which is important when catching asynchronous exceptions ..." However, 'try' is implemented by calling catch http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/Control-…: try :: Exception e => IO a -> IO (Either e a) try a = catch (a >>= \ v -> return (Right v)) (\e -> return (Left e)) Thus, I wonder, why do 'try' not "inherit" the implicit block mentioned above? Looking at catch: catch :: Exception e => IO a -- ^ The computation to run -> (e -> IO a) -- ^ Handler to invoke if an exception is raised -> IO a catch io h = H'98.catch io (h . fromJust . fromException . toException) I see no call to 'block'. But maybe it is hidden in H'98.catch? And is H'98.catch == Prelude.catch ? /Mads

2 1

Broken ghc documentation links
by haskell＠kudling.de 28 Apr '10

28 Apr '10

To reproduce: 1) Look for "data IO" on Hoogle, e.g. http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude.html… 2) Click "source", which redirects to http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/GHC-Type… 3) Observe a "Not Found" page Is there anyone interested in fixing this? Bye, Lenny

4 5

Seeking the correct quote
by Jacques Carette 28 Apr '10

28 Apr '10

I have heard generic programming described tongue-in-cheek as "the kind of polymorphism that a language does not (yet) have". I find this description rather apt, and it matches fairly what I see called 'generic' in various communities. But who said this, where and when? Jacques

3 5

Is XHT a good tool for parsing web pages?
by John Creighton 28 Apr '10

28 Apr '10

> Subject: Is XHT a good tool for parsing web pages? > I looked a little bit at XHT and it seems very elegant for writing > concise definitions of parsers by forms but I read that it fails if > the XML isn't strict and I know a lot of web pages don't use strict > XHTML. Therefore I wonder if it is an appropriate tool for web pages. > >

5 5

Getting used and available memory
by Mads Lindstrøm 28 Apr '10

28 Apr '10

Hi I have tried haskell.org, Google and Hoolge, but I cannot find any function to give me the available and/or used memory of a Haskell program. Is it just not there? Or am I missing it somehow? /Mads

4 5

happstack/SOAP
by Johannes Waldmann 28 Apr '10

28 Apr '10

Hi - I'm looking for an example/demo happstack server that handles SOAP requests. - Thanks, J.W.

2 1

A newbie question ?
by zaxis 27 Apr '10

27 Apr '10

newtype TypeMap = TypeMap (Map.Map TypeRep Dynamic) lookup :: Typeable a => TypeMap -> Maybe a lookup (TypeMap mp) = res where res = liftM (fromJust . fromDynamic) $ Map.lookup (typeOf $ fromJust res) mp It seems that the `res` in `fromJust res` has not been defined ? Sincerely! ----- fac n = let { f = foldr (*) 1 [1..n] } in f -- View this message in context: http://old.nabble.com/A-newbie-question---tp28383563p28383563.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

3 3

mtl design (was ``What do _you_ want to see in FGL?'')
by Bradford Larsen 27 Apr '10

27 Apr '10

On Mon, Apr 26, 2010 at 7:35 AM, Ivan Lazar Miljenovic <ivan.miljenovic(a)gmail.com> wrote: > Whilst freezing it is an option, I feel that this will lead to the same > problems that we already face with mtl: most people agree/know that the > approach/design is bad, but we keep using it because there's no (one) > viable alternative to be used (and thus mtl stays in the Platform, which > means more people use it, and thus we have this vicious cycle). Ivan, Could you elaborate on what you mean regarding the mtl approach & design? What makes them bad? Sincerely, Brad

2 1

Number of CPUs/cores?
by Dimitry Golubovsky 27 Apr '10

27 Apr '10

Hi, Does there exist a Haskell library function that returns the number of CPUs/cores (in portable way) on a computer where the program calling it runs? Thanks. -- Dimitry Golubovsky Anywhere on the Web

3 4

Run haskell program in emacs without typing "main" in the ghci buffer.
by Zura_ 27 Apr '10

27 Apr '10

Hello, Is it possible to run haskell program in emacs without typing "main" in the ghci buffer? Assuming "main" function exists of course. Or, maybe automate sending "main\n" string to ghci buffer input. In other words, I want edit/run/see result style session. Thanks in advance, Zura -- View this message in context: http://old.nabble.com/Run-haskell-program-in-emacs-without-typing-%22main%2… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

4 4