What you are looking for is not available directly in IronScheme. I have been looking for solution for this for a couple of years now, but due to the issue never really coming up, I have not made any progress on this.
The alternative way, is to create a 'stub' class in say C#.
class MyBehavior : MonoBehavior
static Callable foo;
public override int Foo(string bar)
return (int) foo.Call(this, bar);
Depending on your needs, you may not want to make the implementation static of the Callable field.
Now in Scheme you set it up:
(define (my-foo this bar)
(clr-static-field-set! MyBehavior foo my-foo)
(define behave (clr-new MyBehavior))
; do what you need to do with Unity to make behave ie
will now be called.
Hope this helps.