[Haskell-cafe] Re: FFI question

[Simon Marlow]

Frederico Franzosi wrote:
> I'll try to make it short.
> 
> I'm developping a package wich imports C functions.
> 
> the fact is that when I try to compile if I call the compiler in the
> usual way, using -package and -llib it gives an undefined reference
> error...
> 
> For example if I use:
> $ghc -package PKGname-PKGversion -fffi -o main Main.hs -llib
> 
> it gives an error message (undefined references of objects from PKG to
> functions in lib)
> 
> 
> but if I use:
> 
> $ghc -fffi -o main Main.hs -llib /path/to/PKGlib.a
> 
> it compiles correctly.

It looks like -llib is appearing earlier on the linker's command line 
than the library from your package, when you use -package.  You haven't 
specified a dependency between the two, so GHC is making an arbitrary 
choice.

The right way to fix this, if your package depends on a library, is to 
include that library in the "extra-libraries" field of the package.

Cheers,
	SImon