[CM] something like let-set! for undefined vars?

[bil at ccrma.Stanford.EDU]

Another possibility:

    (let init-loop ((args init-args))
       (unless (null? args)
         ((if (defined? (car args) env) let-set! varlet) env (car args) 
(cadr args))
         (init-loop (cddr args)))))

varlet adds a new binding to the let even if one already
exists for the symbol (shadowing the old one).