fileVal Tradeoffs

The first presumes that the environments (namespaces) returned by scheme-report-environment are mutable, which is not required by the R5RS standard. An advantage of this fileVal is that the user and the resulting modules can not interfere with each other via a shared top level namespace. Vandalism such as (set! car 0) or (define cdr car) impacts only the guilty module.

The second creates no new environments and evaluates the text of the modules in the caller’s environment. This means that:

• If the user has modified names of standard values, or redefined those names, the module may fail.
• If the module modifies or redefines names, the user may fail.
• This fileVal relies on the deprecated one argument form of eval which has security problems.

It is easy to create another fileVal that provides an environment that lacks the file primitives so as to keep untrusted modules from writing your file system. In that case you could pass as a parameter to the yielded function what-ever weakened primitives you wished.

(let ((ns (scheme-report-environment 5)))
   (eval '(define v 3) ns) (eval 'v ns))

If

(eval 3) ; => 3

Just now after (use numbers) the two expressions:

(eval '(- 3 1) (scheme-report-environment 5)) ; => 2
((eval '- (scheme-report-environment 5)) 4 2) ; => 2