[Haskell-cafe] Trouble with [in,string]char* with hdirect

[Vincenzo aka Nick Name]

Hi all,

I am experimenting with hdirect for the first time, and I can't figure 
out how to call an haskell function of type String -> IO Int from C. I 
already can compile and use a function of type Char -> IO Int, so I 
assume to be using the right command line arguments.

I have, in Math.idl

----
module Math {
  int munlink([in,string]char *s);
};
----

in Math.hs

----
module Math where

munlink :: String -> IO Int
munlink s = putStr ("Hey!" ++ s ++ "\n") >> return (-1)
----

This is the generated .hs file:

module MathProxy where

import Prelude (fromEnum, toEnum)
import qualified Prelude
import qualified Foreign.Ptr (Ptr)
import qualified HDirect (unmarshallString)
import qualified Math (munlink)

munlink_proxy :: Prelude.String
              -> Prelude.IO Prelude.Int
munlink_proxy = wrap_munlink Math.munlink

foreign export ccall "munlink" munlink_proxy :: Foreign.Ptr.Ptr 
Prelude.String -> Prelude.IO Prelude.Int
wrap_munlink :: (Prelude.String -> Prelude.IO Prelude.Int)
             -> Foreign.Ptr.Ptr Prelude.String
             -> Prelude.IO Prelude.Int
wrap_munlink munlink_meth s =
  do
    s <- HDirect.unmarshallString s
    munlink_meth s

I get a type error when compiling MathProxy.hs, and the strange thing is 
that commenting out the type declaration for "munlink_proxy" makes my 
program work like a charm.

Errors from the compiler follow, any help will be highly appreciated.

Vincenzo Ciancia

ghc -O2 -fglasgow-exts Math.hs -c
ihc -fshow-idl-in-comments -s -fhs-to-c --gen-headers 
-fuse-ints-everywhere -c Math.idl
ghc -O2 -c main.c -o main.o
ghc -O2 -fglasgow-exts -package hdirect MathProxy.hs -c

MathProxy.hs:15:
    Couldn't match
        `GHC.Ptr.Ptr GHC.Base.String' against `GHC.Base.String'
        Expected type: GHC.Base.String -> GHC.IOBase.IO GHC.Base.Int
        Inferred type: GHC.Ptr.Ptr GHC.Base.String
                       -> GHC.IOBase.IO GHC.Base.Int
    In the application `wrap_munlink Math.munlink'
    In the definition of `munlink_proxy':
        munlink_proxy = wrap_munlink Math.munlink

MathProxy.hs:17:
    Couldn't match
        `GHC.Base.String' against `GHC.Ptr.Ptr GHC.Base.String'
        Expected type: GHC.Ptr.Ptr GHC.Base.String
                       -> GHC.IOBase.IO GHC.Base.Int
        Inferred type: GHC.Base.String -> GHC.IOBase.IO GHC.Base.Int
    When checking declaration:
        foreign export ccall "munlink" munlink_proxy :: GHC.Ptr.Ptr 
GHC.Base.String
                                                        -> GHC.IOBase.IO 
GHC.Base.Int