On Wed, 2008-12-10 at 08:33 -0200, Mauricio wrote: > Hi, > > When I do: > > foreign import "nameOfFunction" nameOfFunction > :: IO MyType > > I can get a function that return MyType only if > it's a pointer or some of the C* type family. Is > it possible to write a new MyType and make it > allowed as a return type from foreign functions? > Is changing the compiler the only way to do that?
Of course you're not really returning a MyType but a pointer to one. So use: foreign import "nameOfFunction" nameOfFunction :: IO (Ptr MyType) Using raw Ptrs is not very nice, so we would usually either wrap that in a ForeignPtr or use a Storable instance to get a MyType directly. Which approach to use depends on if you want MyType to have value or reference semantics. If the C type is abstract and you only access it via a pointer then the ForeignPtr approach is sensible. If you directly access all the fields of the C type then using an equivalent Haskell MyType and converting using Storable is the sensible approach. If do recommend reading the FFI spec. It's quite readable and explains a lot of the issues. Getting familiar with the Foreign libraries will help too. The most important bits are understanding ForeignPtr and the Storable class. Duncan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
