Re: summary: lilypond, lambda, and local-eval

[David Kastrup <dak@gnu.org>]

Hans Aberg <haberg-1@telia.com> writes:

> On 16 Dec 2011, at 11:33, Mark H Weaver wrote:
>
>> Here's what I currently see:
>> 
>> scheme@(guile-user)> (local-eval #'t (primitive-eval '(let ((t 42))
>> (or #f (the-environment)))))
>> ERROR: In procedure memoize-variable-access!:
>> ERROR: Unbound variable: t
>> 
>> This is the correct behavior, no?
>
> This is what I get when I play around with the following variation of David's code in Guile 2.0.3:
> (define (xxx)
>   (let* ((x 2))
>     (set! x (+ x 3))
>     (interaction-environment)))
>
> (eval '(begin (set! x (+ x 5)) x) (xxx))
>
> My guess (correct?) is that one wants some variation of
> (interaction-environment) that can cause x in the eval expression to
> bind to the environment returned by (xxx).
>
> Might eval be changed to accommodate for that (without introducing the
> name local-eval)?

It would likely help with unasking the question of what to do when
(current-module) is different at the time of local-eval.  I don't know,
however, what the _lexical_ effects of switching the current module are
supposed to be.  If it is supposed to be a noop, then lexical
environments and modules are presumably orthogonal, and eval should
likely be allowed to take both (currently, local-eval is like taking a
lexical environment and using primitive-eval in it).

-- 
David Kastrup