October 2009 - Haskell-Cafe

C headers in cabal dependencies
by Maurício CA 16 Nov '09

16 Nov '09

Hi, I've been using 'install-includes' in a package. I sometimes make small changes to those include files, and I've seen that cabal doesn't consider then dependencies, i.e., doesn't rebuild .hsc files depending on then. I'm not sure if this is an error, as parsing hsc2hs input may not be cabal task. Anyway, I would like to suggest that files in install-includes be considered dependencies and that files under 'includes' be also included when processing '.hsc' files. Thanks. Best, Maurício

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creating documentation links failed with cabal install --haddock-options=--hyperlink-source. is this a bug?
by Thomas Hartman 16 Nov '09

16 Nov '09

cabal haddock -–hyperlink-source installs documentation with links to source code, which also be on by defualt. cabal install –haddock-options=–hyperlink source does not install hyperlinked source. cabal install –haddock-options=-–hyperlink sourceblehblehbleh doesn’t throw an error, which suggests to me that the first command might also be passing the flags with an error. Whatever the case, seems to me the examples section in cabal --help should really include examples using --with-PROG and --PROG-options. I can't find a good one online. fwiw, cabal install --haddock-option=hyperlink-source DID generate an error in the output: target `hyperlink-source' is not a module name or a source file also, blogged about this here: http://blog.patch-tag.com/2009/10/23/cabal-install-a-package-with-documenta…

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Hoogle is great but ...
by zaxis 11 Nov '09

11 Nov '09

http://www.haskell.org/hoogle/ is VERY great for haskeller. However, i feel hoogle should be improved by providing more examples as : isInfixOf :: Eq a => [a] -> [a] -> Bool The isInfixOf function takes two lists and returns True iff the first list is contained, wholly and intact, anywhere within the second. Example: isInfixOf "Haskell" "I really like Haskell." -> True isInfixOf "Ial" "I really like Haskell." -> False The Example code will be helpful for programmer to understand its definition. Sincerely! -- View this message in context: http://www.nabble.com/Hoogle-is-great-but-...-tp26046410p26046410.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Problems with Language.Haskell.Interpreter and errors
by Martin Hofmann 11 Nov '09

11 Nov '09

Hi, The API of Language.Haskell.Interpreter says, that 'runInterpreter' runInterpreter :: (MonadCatchIO m, Functor m) => InterpreterT m a -> m (Either InterpreterError a) returns 'Left' in case of errors and 'GhcExceptions from the underlying GHC API are caught and rethrown as this'. What kind of errors do a generate here, why are they not caught by runInterpreter and how can I catch them? I assumed to get a 'Left InterpreterError' from the first and an error in MonadCatchIO in the second. > :m +Language.Haskell.Interpreter > let estr1 = "let lst [a] = a; lst _ = error \"foo\" in lst []" > let estr1 = "let lst [a] = a; in lst []" > runInterpreter (setImportsQ [("Prelude", Nothing)] >> eval estr1 ) Right "*** Exception: foo > runInterpreter ( eval estr2) Right "*** Exception: <interactive>:1:101-111: Non-exhaustive patterns in function lst Thanks a lot

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is proof by testing possible?
by muad 10 Nov '09

10 Nov '09

Is it possible to prove correctness of a functions by testing it? I think the tests would have to be constructed by inspecting the shape of the function definition. -- View this message in context: http://www.nabble.com/is-proof-by-testing-possible--tp25860155p25860155.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Nice addition to Foreign: castAny
by Maurício CA 07 Nov '09

07 Nov '09

This could be beside castPtr, castCharToCChar etc. ---- castAny :: (Storable a, Storable b) => a -> b castAny = unsafePerformIO . genericCast where genericCast :: (Storable a, Storable b) => a -> IO b genericCast v = return undefined >>= \r -> allocaBytes (max (sizeOf v) (sizeOf r)) $ \p -> poke p v >> if False then return r else peek (castPtr p) ---- GHCi: > let a = -1000 :: Int16 > castAny a :: Word16 --> 64536 > castAny a :: Ptr () 0xb4c2fc18 > castAny (castAny a :: Ptr ()) :: Int16 -1000 > let b = pi :: CLDouble > b 3.141592653589793 > castAny b :: CInt 1413754136 > castAny b :: Ptr () 0x54442d18 > castAny b :: CFloat 3.3702806e12 > castAny b :: Int8 24 At minimum, this is safer than 'unsafeCoerce'. What do you think? Best, Maurício

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RE: Haskell as a first language?
by Simon Peyton-Jones 07 Nov '09

07 Nov '09

Haskell is a great language! Check out haskell.org. I'm ccing the Haskell Cafe which is read by many people better qualified to answer your question than me. (Since I've been working on Haskell for many years, I am not well qualified to say how it seems to a beginner.) S | -----Original Message----- | From: Charles Turner [mailto:charlie.h.turner@googlemail.com] | Sent: 11 July 2009 22:52 | To: Simon Peyton-Jones | Subject: Haskell as a first language? | | I'll make this short! Do you think Haskell is a good language to start | with? I am brand new to programming and have been using Scheme, some of | my peers suggest I should use Haskell. It seems "professional" to me. | Has features that a beginner should not worry about. What would you | suggest. (I'm not worried about bias) | | Thank you very much for your time. | | Charles Turner.

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Re: [Haskell-cafe] Best Editor In Windows
by Tom.Amundsen 04 Nov '09

04 Nov '09

Nathan P. Campos wrote: > > Hello, > I'm very new at Haskell, i'm reading a book and starting, but i want to > know which is the best editor for development under Windows, because now > i'm using Notepad++(That i use to develop in C++). > > Thanks, > Nathan Paullino Campos > If you use emacs, check out http://www.haskell.org/haskell-mode/ -- View this message in context: http://www.nabble.com/Best-Editor-In-Windows-tp25908187p25917670.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Word128, Word256
by Maurício CA 04 Nov '09

04 Nov '09

Hi, Do you think we could have the range of sizes for Int* and Word* expanded to allow also 128 and 256 bits sizes? My reason is that I have a long standing issue trying to bind to C numerical libraries using complex numbers, as those are usually structs passed by value. See this from GNU GSL: typedef struct { double dat[2]; } gsl_complex; I imagine I could do: type GslComplex = Word128 -- size would depend on architecture and then write foreign declarations to have: get_real :: GslComplex -> CDouble get_imag :: GslComplex -> CDouble gsl_complex_sin :: GslComplex -> GslComplex gsl_complex_cos :: GslComplex -> GslComplex Do you think this is a reasonable request? Thanks for your attention, Maurício

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Hugs Trex for GHC / JHC / UHC / ... ?
by Peter Verswyvelen 03 Nov '09

03 Nov '09

I briefly read about Hugs record system Trex, and at first sight this was really nice! I know this question was asked a long time ago already, but are there any plans to add this extension to GHC? What about the other compilers, like JHC, UHC, etc? Is it possible to emulate Trex (lots of other record systems exist), *and* get the same easy to understand errors? What were the problems with Trex (if any)? Thanks, Peter Verswyvelen

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