Eliot,

It turns out that I had already done the #fromInteger: game, but your reply/confirmation gave me a brief second wind.  I added #asExternalAddress (doing the obvious thing given your reply) to both callback thunks and to GSL memory objects (handle bodies that have subclasses for vectors, wavelet entrails, etc.). I took one FFI call parameter from long to struct*.  That was interesting, because getHandle asInteger was giving me a *huge* number; the struct* argument worked where long failed me (it's usually the other way around).

I am now at the point of getting an error in a method being called from a callback!!!  That's a nice problem to have :)  Somehow, I have to figure out how to get one of my handle bodies wrapped around an Alien argument.  Whatever I do will also want to work with non-aliens because I call (with some trickery) the same method myself to generate sample data.

As Sig said, the debugger is available inside of callbacks - that's going to be a huge help.  It's time to shut down for the day or I will hate myself in the morning.

More to come.  Thanks!!!!

Bill