Strange Binding

[Emmanuel Castro <castro at lirmm dot fr>]

Consider the following program:
(define plus +)
(define glob 5)

(define (p) (display plus) (display (plus glob glob)) (newline))
(define (q) (set! glob 8) (set! plus -))

(p)
(q)
(p)

It prints out:
#<procedure +>10        // ok, 5 + 5 makes 10 , then changing plus to - and glob to 8
#<procedure ->16  // here, plus is both -, and +. In fact it should print #<procedure ->0
                  // Other schemes: DrScheme, ChezScheme... print 0 instead of 16

Comments:
if you change (define plus +) to (define (plus x x) (+ x x)).
The behavior of q becomes normal. It prints out:
#<procedure plus>10
#<procedure ->16

I suppose that it is due to compilation optimisation. Maybe changing the value of
a variable whose the value was a primitive function should show a warning.

Emmanuel Castro
LIRMM