[Haskell-cafe] Haskell and symbolic references

[Matt Morrow]

(i always forget to reply-to-all)

If you'd like to reference C functions with Strings, one possible way is to
use System.Posix.DynamicLinker and the wrapper over libffi that's been
uploaded to hackage recently:

[m at monire asdf]$ ghci
GHCi, version 6.10.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.

ghci> :m + Foreign.LibFFI
ghci> :m + Foreign.Ptr Foreign.Storable
ghci> :m + Foreign.C.Types Foreign.C.String
ghci> :m + System.Posix.DynamicLinker

ghci> malloc <- dlsym Default "malloc"
Loading package unix-2.3.1.0 ... linking ... done.
ghci> syscall <- dlsym Default "syscall"

ghci> :! echo -ne "#include <syscall.h>\n__NR_execve\n" | cpp | tac | grep
-E "^[0-9]+$" | head -1 > NOODLES
ghci> nr_execve :: CLong <- (read . head . words) `fmap` readFile "NOODLES"
ghci> :! rm -f NOODLES

ghci> let sizeOfPtrCChar = sizeOf(undefined::Ptr())
ghci> argv <- callFFI malloc (retPtr (retPtr retCChar)) [argCSize
(2*fromIntegral sizeOfPtrCChar)]
Loading package bytestring-0.9.1.4 ... linking ... done.
Loading package libffi-0.1 ... linking ... done.

ghci> sh <- newCString "/bin/sh"
ghci> poke argv sh
ghci> poke (argv`plusPtr`sizeOfPtrCChar) 0

ghci> callFFI syscall retCLong [argCLong nr_execve, argPtr sh, argPtr argv,
argCInt 0] {-never returns-}
sh-3.2$ echo $0
/bin/sh
sh-3.2$ exit
exit
[m at monire asdf]$

Matt

On Fri, May 29, 2009 at 11:41 AM, Khudyakov Alexey <
alexey.skladnoy at gmail.com> wrote:

> On Friday 29 of May 2009 19:34:44 Patrick LeBoutillier wrote:
> > Hi all,
> >
> > Is it possible with Haskell to call a function whose name is contained
> > in a String?
> > Something like:
> >
> > five = call_func "add" [2, 3]
> >
> > If not, perhaps this is acheivable using FFI?
> >
> Or maybe you are asking for template haskell[1]. With it you can actually
> generate function at compile time. It depends on waht you actually need.
>
> > {-# LANGUAGE TemplateHaskell #-}
> > import Language.Haskell.TH
> >
> > five = $( foldl appE (varE $ mkName "+") [ litE $ integerL 2
> >                                          , litE $ integerL 3 ] )
>
>
> [1] http://haskell.org/haskellwiki/Template_Haskell
>
> --
>   Khudyakov Alexey
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
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