Re: let-bind a varlist only known at run time

[Michael Heerdegen <michael_heerdegen@web.de>]

"Roland Winkler" <winkler@gnu.org> writes:

> Normally the varlist for the special let form is hardcoded.  Is it
> possible to specify the varlist only at runtime?

`cl-progv'?

> On the other hand, I expect that efficiency is not an issue for the
> body appearing in let.  So if there is nothing else I could construct
> the complete let-form at runtime and pass it on to `eval'.

FWIW that's what `cl-progv' is doing, more or less.  The body is pasted
into a lambda constructed before calling eval so that it can be
compiled.  The resulting semantics can be a bit surprising, though; for
example

(let ((x 0))
  (cl-progv (list 'x) (list 1)
    (funcall (lambda () x))))

yields 0 with lexical-binding on, and

(cl-progv (list 'x) (list 1)
    (funcall (lambda () x)))

yields 1.


Michael.