new ForeignPtr without finalizers

[Ashley Yakeley]

In article <200306091001.51091.alastair at reid-consulting-uk.ltd.uk>,
 Alastair Reid <alastair at reid-consulting-uk.ltd.uk> wrote:

> It looks like you're using an idiom we didn't think of when designing the 
> library.  Can you explain what you're trying to do and whether you think we 
> shoud provide direct support for newSimpleForeignPtr (which I'd be tempted to 
> call newForeignPtr_).

Specifically I want a ForeignPtr of a null Ptr that has no finalizers. I 
want a value of type ForeignPtr such that withForeignPtr will extract a 
null Ptr.

My basic JNI ref type is newtype of a ForeignPtr. JNI gives me "global 
references" as Ptrs, and I wrap them in ForeignPtrs with a finalizer 
that tells the Java VM I'm finished with it. When I want to pass such a 
ref back to JNI, I simply call withForeignPtr to extract the underlying 
Ptr.

But sometimes I want to create my own null references. Before GHC 6.0, I 
used to call (newForeignPtr nullPtr (return ())), and that would give me 
a ForeignPtr that would work with withForeignPtr to give a null Ptr. But 
now I can't.

-- 
Ashley Yakeley, Seattle WA