Re: [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:

[...@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 \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
[...@monire asdf]$

Matt

On Fri, May 29, 2009 at 11:41 AM, Khudyakov Alexey <
alexey.sklad...@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
> ___
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Re: [Haskell-cafe] Haskell and symbolic references

[Khudyakov Alexey]

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
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Re: [Haskell-cafe] Haskell and symbolic references

[Jake McArthur]

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]


You could use Data.Map:

call_func = (funcMap !)
where funcMap = fromList [ ("add", add)
 , ("sub", sub)
 , ("mul", mul)
 , ("div", div)]

Or a version using lookup instead of (!) if you aren't sure that the 
string will be a valid function name.


- Jake
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RE: [Haskell-cafe] Haskell and symbolic references

[Bayley, Alistair]

> From: haskell-cafe-boun...@haskell.org 
> [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of 
> 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?


Dynamic loading via plugins will do this. It was broken on Windows for
some time; not sure if it works there now.
  http://hackage.haskell.org/cgi-bin/hackage-scripts/package/plugins

Alistair
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