Re: [Haskell-cafe] FFI question - FunPtrs to top-level functions
On 8/18/2011 6:49 AM, Antoine Latter wrote: Hi Haskell, I have a question about the Haskell FFI and creating FunPtrs to Haskell functions. Does anyone have any recommendations for when I have a top-level function that I would like to pass to a C function as a function pointer (that is called via a foreign import)? I know that the FFI provides the wrapper foreign import I can use to wrap Haskell functions, but then I would need to jump through hoops to manage the liefetime of of the FunPtr wrapper. If I were closing over interesting state I would want this - but the function (side-effectfully) operates only on its arguments (and the Haskell RTS, of course). Is it okay to place an unsafePerformIO $ mkWrapper myFunc as a top-level declaration, or am I journeying into uncharted lands? Is there something clever I can do with foreign exports and foreign imports, or is this just making things too complex? Thanks, Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe You can export and reimport the same function with no wrapper needed. For example: foreign export ccall foo :: ... foreign import ccall foo fooptr :: FunPtr (...) Cheers, Kyra ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ghc panic when compiling blaze-builder
On 11/21/2010 3:20 AM, JosИ Romildo Malaquias wrote: When compiling blaze-builder-0.2.0.1 with ghc-7.0.1 on my ~amd64 gentoo system, I am getting the shown below. Any clues? Romildo [...] Building blaze-builder-0.2.0.1... [1 of 8] Compiling Blaze.ByteString.Builder.Internal ( Blaze/ByteString/Builder/Internal.hs, dist/build/Blaze/ByteString/Builder/Internal.o ) ghc: panic! (the 'impossible' happened) (GHC version 7.0.1 for x86_64-unknown-linux): dsLet: unlifted Look here: http://hackage.haskell.org/trac/ghc/ticket/4498 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Will GHC 6.14 with LLVM use LLVM C compiler to compile external C Libraries
I wonder if llvm-gcc supports it's own (gcc) extensions. If it supports then there is no need to stuck in clang right now. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to derive instance for type without exported constructor?
Miguel Mitrofanov wrote:
Well, normally - you can't (unless there is some equivalent to the
constructor exported).
But there is a trick. You can use generic classes:
{-# OPTIONS_GHC -fglasgow-exts -XGenerics -package lang #-}
import Generics
class Binary' a where
put' :: a - Put
get' :: Get a
put' {| Unit |} Unit = return ()
get' {| Unit |} = return Unit
put' {| a :+: b |} (Inl x) = putWord8 0 put' x
put' {| a :+: b |} (Inr y) = putWord8 1 put' y
get' {| a :+: b |} =
do w - getWord8
case w of
0 - liftM Left get'
_ - liftM Right get'
put' {| a :*: b |} (x :*: y) = put' x put' y
get' {| a :*: b |} =
do x - get'
y - get'
return $ x :*: y
instance Binary' Int32 where
put' = put
get' = get
instance Binary' StdGen
instance Binary StdGen where
put = put'
get = get'
Isn't it to define an isomorphic type and unsafeCoerce to it pretty much
equivalent?
At least the following simplest example works just fine:
module Main where
import Unsafe.Coerce
class Test a where
test :: a - Int
data Foo = Foo Int Int
data Bar = Bar Int Int
instance Test Bar where test (Bar a b) = a + b
instance Test Foo where test foo = test (unsafeCoerce foo :: Bar)
main :: IO ()
main = print $ test (Foo 123 345)
Cheers,
Kyra
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Looking for Haskellers on Windows
John Goerzen wrote:
GЭnther Schmidt wrote:
Kyra I've tried any sort of values to any sort of columns. I tried insert
into somesinglecolumntable (someNumbercolumn) values (?) [toSql 5] ...
and so on.
So I'm not certain at all the error message does actually give the right
clue.
It just blows no matter what.
It seems, I've managed to track down the issue.
Access ODBC driver doesn't support sqlDescribeParam.
bindCol (Database/HDBC/ODBC/Statement.hsc) contains the following stub
for this:
do poke pdtype #{const SQL_CHAR}
poke pcolsize 0
poke pdecdigits 0
This does not work.
I've made an experiment replacing 'poke pcolsize 0' with 'poke pcolsize
255'. Now all integer or varchar bindings work!
It seems simpleSqlColumns or something similar must be used.
Cheers,
Kyra
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Trouble with FFI on Windows2000...
Serge LE HUITOUZE wrote: I do the following: dlltool -d cproj1.def -l libcproj1.a ghc --make testFFI_2.hs -optl-lcproj1 -optl-L. This seems fine, since it produces a testFFI_2.exe. However, executing it, I get a MSWindows error box with a message that looks like (approximate translation): DLL (null) not found on specified path At first, I didn't have the LIBRARY directive in the .def file, so I thought that was the reason for the (null) appearing in the message. But adding said directive didn't change anything... dlltool -d cproj1.def -l libcproj1.a -D cproj1.dll ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FFI and struct arguments
Felipe Lessa wrote:
Hi,
I tried googling and searching the haskellwiki about this but wasn't
lucky enough. My question is: is there a way to send struct arguments
to C functions via the FFI or do I need to create a C wrapper? I guess
there isn't, and while I can live without it, I'd like to leave no
doubt.
Sometimes there is such a way. See below.
Details:
I have something like
typedef struct vect {
float x,y;
} vect;
void func(vect v);
For most architectures stack layout of
void func(vect v);
and
void func(float x, float y);
is exactly the same, so for FFI purposes this 'func' can be declared as
something like:
foreign import ccall unsafe :: Float - Float - IO ()
Cheers,
Kyra
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FFI and struct arguments
If the struct is passed by reference of course then you're fine, but if it's by value then you need a C wrapper. The reason is because it's beyond the scope of the FFI to know the structure layout and how to map that to haskell types. That's the domain of FFI pre-processors. However I don't know of any FFI pre-processors that help in this case. Passing C structs by value seems to be pretty rare in exported C APIs. Yes, but programmer *knows* the structure layout, so she usually can emulate it with a sequence of primary ffi type arguments. It's pretty trivial for the original example (see my previous post on this subj) and can be extended further. For example, in my homebrew COM library I pretty successfully marshall 16-byte Variants *by value* by means of two consecutive legal Word64 arguments. Cheers, Kyra ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell DLL crashes Excel
Andreas Marth wrote: type BSTR8 = Ptr Word8 createBSTR8 :: String - IO BSTR8 createBSTR8 s = do let len :: Word32 = fromIntegral (length s) low_l :: Word8 = fromIntegral (len .. 0x) low_h :: Word8 = fromIntegral (shiftR len 8 .. 0x) high_l :: Word8 = fromIntegral (shiftR len 16 .. 0x) high_h :: Word8 = fromIntegral (shiftR len 24 .. 0x) arr - newArray ([low_l,low_h,high_l,high_h] ++ map (fromIntegral . fromEnum) s ++ [0]) return $! plusPtr arr 4 Use SysAllocString... family. Also, remember they (by convention) have to be released from the client side. Cheers, Kyra ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell DLL crashes Excel
Kyra wrote: Use SysAllocString... family. Also, remember they (by convention) have to be released from the client side. Oops, they = such allocated BSTRs. Cheers, Kyra ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] using of data types as kinds
Bulat Ziganshin wrote: Hello Simon, Tuesday, November 22, 2005, 8:17:38 PM, you wrote: SPJ I have not written anything about what I plan to do in GHC, but SPJ basically it amounts to allowing you to use a data type as a SPJ kind. Busy doing GADTs and impredicativity at the moment though Simon, i can't download file http://research.microsoft.com/~simonpj/papers/boxy/boxy-pldi.ps.gz reffered at http://research.microsoft.com/~simonpj/papers/boxy/ Google gives http://www.cis.upenn.edu/~dimitriv/boxy/boxy.ps ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Oracle + Haskell advice?
Keean Schupke wrote: Well, I'll put my hand up, I use Haskell with databases and web stuff... Unfortunately when I started the common tools were not available. I have a home-grown Haskell-Servlet server, with monadic continuation based HTML composition and a HaskellDB like database layer. It all works very well, but being written for internal use (and me being lazy) it has only those features that I need. It is however designed as an integrated Web-Application platform... I was considering releasing it - but since I started other projects like HaskellDB restarted, WASH was written, HSQL started to support unix, and somebody added plugins to the Haskell Web-Server - So I didn't bother, although I am still using it myself... Still I now know that HaskellDB has significant limitations, and the relational algebra approach I took is far more robust and flexable... I don't have time to take this from a usable but incomplete project to a fully implemented API - what I mean here is that not all ODBC calls are implemented, some SQL features might be missing, some tags are not defined... not all HTTP requests and errors are generated, oh and there's no documentation. If anyone were interested in using/contributing I could give CVS access to the code. Keean. Yes, I'm definitely interested in evaluating/using/contributing your framework. Regards, Kyra ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
