[plt-scheme] Defining constants with c-lambda

 From reading the MZC manual, it wasn't clear to me that I could do
something like this to extract a constant value (defined as a C
macro):

(define FOO
  ((c-lambda () int
	     "___result = FOO;")))

As you can see, c-lambda expression is anonymous and I'm immediately
calling it in order to set the Scheme variable FOO.

It seems to work but I wanted to make sure...

Ed