Welcome to MzScheme v371 [3m], Copyright (c) 2004-2007 PLT Scheme Inc.
; One argument eval.
(eval 'a) ; => reference to undefined identifier: a
(let ((a 42)) (eval 'a)) ; => reference to undefined identifier: a
(define a 43)
(let ((a 42)) (eval 'a)) ; => 43
; Curious -- Seems to be current top level environ of REPL.
(eval 'car) ; => #<primitive:car>
(set! car 55)
(eval 'car) ; => 55
 ; relaunch Scheme
(define a 4)
(eval 'a (scheme-report-environment 5)) ; => reference to undefined identifier: a
(eval 'car (null-environment 5)) ; => reference to undefined identifier: car
(let ((n (scheme-report-environment 5))) (eval '(define a 13) n) (eval 'a n)) ; => 13
(define a (scheme-report-environment 5))
(define b (scheme-report-environment 5))
(eq? a b) ; => #f
(eval '(define a 13) a)
(eval '(define a 14) b)
(eval 'a a) ; => 13
(eval 'a b) ; => 14
; It would seem that MzScheme's <namespace>s are mutable and that
; scheme-report-environment returns a new mutable namespace.
; Maybe that is why they don't call it an environment.
; I can't see that the report is clear on whether this is right.
; I have no objections.
(eval '(set! a 42) a)
(eval 'a a) ; => 42
(eq? (null-environment 5) (null-environment 5)) ; => #f
((λ (e) (+ e e)) 6) ; => 12
; Bravo!!
(eval '(define a ()) a)
(define sa (eval '(λ (x) (set! a x)) a)) ; => reference to undefined identifier: λ
; Bizarre!
(define sa (eval '(lambda (x) (set! a x)) a))
(define ga (eval '(lambda () a) a))
(sa 43)
(ga) ; => 43
a ; => #<namespace>
((eval (lambda () 4))) ; => 4
; I think the above is reasonable but I can't find it spelled out in the report.
; MzScheme does not like the peculiar form:
(cond (else r)(else t)) => cond: bad syntax (`else' clause must be last) ...
; A literal reading of the report suggests it is valid, if dumb.