3 (define (make-unbound! var val env)
4 (let ((frame (first-frame env)))
5 (define (scan vars vals)
7 (error "variable not bound" var))
10 (set-car! vals (cdr vals))
11 (set-cdr! vars (cdr vars))))
12 (else (scan (cdr vars) (cdr vals)))))
13 (scan (frame-variables frame)
14 (frame-values frame))))
18 Remove binding from the first frame, as removing it from elsewhere
19 would mean also removing all bindings built from it.