Re: Green Card and Exceptions
On Friday 13 June 2003 3:37 am, Matthew Donadio wrote:
Hi all,
I have a couple of questions about Green Card and exceptions.
[...]
This definition works, but it ignores the return code from the library
function. The various return codes are from an enum defined in a header
file. I would like to throw a Haskell exception (one of the
ArithExceptions defined in Control.Exception) depending on the value of
rc.
The %fail statements (described in the last few paragraphs of
http://www.haskell.org/greencard/downloads/greencard-latest/type-sig.html)
consist of two C expressions. For example:
%fail {f == NULL} {errstring(errno)}
The first is a test for failure.
The second is an expression which returns a C string.
If the test expression fails, the string expression is evaluated and used to
generate a UserError.
If I have to create a
DIS, can this be shared across several modules that all need the same
functionality?
It would be nice to be able to write something like:
%fail POSIX_FD(fd)
where POSIX_FD is something you defined elsewhere (e.g., it might test if its
file-descriptor argument is -1). GreenCard can't do this.
It would also be nice to be able to generate a different error instead of
UserError. We'd need to specify the type and the exception constructor so a
plausible syntax would be:
%fail {f == NULL} (UserError (string {errstring(errno)}))
[Detail: should it be a Haskell98 IOError constructor or a non-standard but
widely implemented exception constructor? Should it be a function or a
constuctor?]
Again, GreenCard can't do that.
As GreenCard maintainer, I've got to ask:
- How many users of GreenCard are still out there?
- Are you developing new libraries or just maintaining the ones you've got?
- Is there a demand for new features?
--
Alastair Reid
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chance to help out on the wiki
Greetings. We added a page Fundamental Concepts to the wiki so that we might have a very specific reference to pass along to people with questions, and to add links to definitions throughout the wiki. http://www.haskell.org/hawiki/FundamentalConcepts A lot of concepts need to be filled in, and if you haven't participated in the Wiki yet, now is a good time :) If you've never used a wiki, you can read about it here: http://www.haskell.org/hawiki/HelpForBeginners You might model your explanations after a page I wrote for PatternMatching which has: - a reference to a tutorial - a reference to the haskell report - an explanation - some examples Feel free to extend and / or correct anything already there. The front page of the wiki is here: http://www.haskell.org/hawiki/FrontPage peace, isaac ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Green Card and Exceptions
Alastair Reid wrote:
The %fail statements (described in the last few paragraphs of
http://www.haskell.org/greencard/downloads/greencard-latest/type-sig.html)
consist of two C expressions. For example:
%fail {f == NULL} {errstring(errno)}
The first is a test for failure.
The second is an expression which returns a C string.
If the test expression fails, the string expression is evaluated and used to
generate a UserError.
OK, I think I misread the manual. Sect 7.6 talks about functions with
side effects, so I assumed that the function had to have type (IO a) to
use %fail.
It would also be nice to be able to generate a different error instead of
UserError. We'd need to specify the type and the exception constructor so a
plausible syntax would be:
%fail {f == NULL} (UserError (string {errstring(errno)}))
[Detail: should it be a Haskell98 IOError constructor or a non-standard but
widely implemented exception constructor? Should it be a function or a
constuctor?]
In the case of what I am doing, I'm not sure if IOError really make
sense philosophically. The failures I need are underflow, overflow,
loss of precision, etc. Since IOError is a type synonym for
IOException, then perhaps accepting an Exception constructor is
appropriate.
To keep compatibility with old libraries it may be wise to keep %fail as
is, and have a new directive %throw that accepts an Exception
constructor, and uses either throw or throwIO.
On the other hand, now that I know that I can use %fail with pure
functions, I can make that work.
As GreenCard maintainer, I've got to ask:
- How many users of GreenCard are still out there?
New GreenCard user. In my case, I need access to C land for typedefs
and macros. I could write my own stubs, but GreenCard saves me this
step.
- Are you developing new libraries or just maintaining the ones you've got?
New library.
- Is there a demand for new features?
A more generic %fail mechanism?
Thanks for the response.
--
Matthew Donadio ([EMAIL PROTECTED])
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please help
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Testing was Re: main modules in GHC, deriving differences between GHC and Hugs
(redirected to haskell-cafe) Hal Daume III wrote: Yes, but there's a problem with this solution. Namely, if Foo.hs takes a long time to compile, then you can't leverage having already created Foo.o and Foo.hi when making the Main. Yeah, it's not perfect, but I think we just have different methodologies for testing. Typically, I do most of my development with ghci or hugs. Each module will have a single variable that represents the tests tests :: [Bool] tests = [ test1, test2, test3 ... ] and then I define a variable called test :: Bool test = and tests so I can just load a module and either evaluate tests or test to check things out. This generalizes to importing and testing several modules at once (as long as I take care of name conflists). This only works for simple modules, though. For more complicated ones, I have a pretty tester. For example, my Haskell FFT library is collection of mutually recursive modules. I have a specialzed test function for this that tests a range of lengths. It looks someone like main = testfft n1 n2 testfft n1 n2 = sequence $ map test1fft [n1..n2] test1fft n = do putStr $ show n ++ :\t putStr $ if ok then OK\n else ERROR\n where ok = and [ test1 n, test2 n, test3 n ] This way I can compile the code, and run the executable as ffttest 2 2048 | grep ERROR and I am confident that I get full coverage of the algorithm. I am always to hear about other methods of automated testing. -- Matthew Donadio ([EMAIL PROTECTED]) ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
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gtk2hs
Hi! I tried to implement a simple counter with gtk2hs. To increase my counter I defined following event: onClicked btn $ do si - textBufferGetStartIter tb ei - textBufferGetEndIter tb val - textBufferGetText tb si ei False textBufferSetText tb $ show $ (+1) $ read val But now I don't want always read the textfield to get my counter-value, I would like to save the state of my increased value and would like to pass it to the next call of the function. How can I do this? thanks Christian This is the complete code: import Gtk quitDialog :: IO Bool quitDialog = . main :: IO () main = do initGUI --main window win - windowNew onDelete win (\_-(quitDialog= (return . not ))) onDestroy win mainQuit vb - vBoxNew True 5 hb - hBoxNew True 5 btn - buttonNewFromStock stockExecute btn2 - buttonNewFromStock stockQuit tv - textViewNew tb - textBufferNew Nothing textBufferSetText tb 0 textViewSetEditable tv False textViewSetCursorVisible tv False textViewSetBuffer tv tb boxPackStartDefaults vb tv boxPackStartDefaults vb hb boxPackStartDefaults hb btn boxPackStartDefaults hb btn2 hgf - onClicked btn $ do si - textBufferGetStartIter tb ei - textBufferGetEndIter tb val - textBufferGetText tb si ei False textBufferSetText tb $ show $ (+1) $ read val disconnect hgf onClicked btn2 $ do quit - quitDialog if quit then widgetDestroy win else return () containerAdd win vb widgetShowAll win mainGUI ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
