fileVal

`fileVal` Tradeoffs

There are two variations on fileVal.

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. Mischief such as (set! car 0) or (define cdr car) impacts only the module that performs the misdeed.

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 will 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.

So far the second version has worked on each of the Schemes that I have tried it in on.

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

should yield 3 if scheme-report-environment makes namespaces that can be expanded to include new names. If this fails then the first version of fileVal will fail.

(eval 3) ; => 3

fails then the second version will fail.

Just now after (use numbers) the two expressions:

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

both fail in Chicken Scheme after the numbers package has been added and this makes both versions of fileVal fail.

fileVal Tradeoffs

`fileVal` Tradeoffs