Mark H Weaver <m...@netris.org> writes:
> David Kastrup <d...@gnu.org> writes:
>> within local-eval, what is the return value of calling
>> (current-module)? I would expect that it is the same as outside of
>> local-eval
>
> Actually, this is not true. Within `local-eval', (current-module) is
> temporarily restored (using dynamic-wind) to the module saved in the
> lexical environment.
>
> This is probably not optimal. Among other things, it breaks the nice
> equivalence <expr> == (local-eval '<expr> (the-environment)), but
> `local-eval' and `local-compile' are based on `eval' and `compile', and
> this is what `eval' and `compile' do (for some reason unknown to me).
This is likely going to be a problem. One can probably fudge around it
with something like
(local-eval `(let ((current-environment (lambda ()
,(current-environment))))
...
but that does not look like it would really prettify things.
>> so that (define x 5) inside of local-eval
>
> As Andy pointed out, I deliberately restrict the form passed to
> `local-eval' (or `local-compile') to be an _expression_. (define x 5)
> is not an expression; it is a definition. I explained the reason for
> this restriction a few days ago[1] on this list.
>
>> would _not_ be equivalent to (module-define! (current-module) 'x 5) as
>> the first one would take the current module at the-environment time,
>> and the second one would take it at local-eval time.
Well, use set! amd module-set! then for the example.
> Actually, because `local-eval' restores (current-module) to the one
> saved in the lexical environment, (module-define! (current-module) 'x
> 5) within `local-eval' actually defines the variable within the saved
> module, i.e. the module used for lookup if you replace
> (the-environment) with a top-level variable reference.
Looks awkward. And is not compatible with Guilev1 behavior:
guile> (save-module-excursion (lambda () (let ((env (the-environment)))
(set-current-module (resolve-module '(none))) (local-eval '(current-module)
env))))
#<directory (none) b6f7c360>
guile>
--
David Kastrup
