Re: Closures - do you understand them well?

[Michael Heerdegen]

<tomas@tuxteam.de> writes:

> > > (let ((i 0)
> > >       funs)
> > >   (while (< i 100)
> > >     (push `(lambda () ,i) funs)
> > >     (cl-incf i))
> > >   (mapcar #'funcall funs))
> >
> > Yes, but here there is no "new binding" exactly, rather the
> > value is hard-coded onto the lambda ...
>
> Look closely. There is one. Just at macro expansion (aka compile)
> time.

?!?

The expansion of (push `(lambda () ,i) funs) is

#+begin_src emacs-lisp
(setq funs
      (cons
       (list 'lambda nil i)
       funs))
#+end_src

No binding is created here, neither at compile time (where the symbol i
is not touched), nor at run-time (where the value of `i` is just passed
as an argument to `list').

Stefan would say that this accumulates a list of function expressions in
FUNS, not a list of functions, strictly speaking.  Works only because
the Lisp interpreter is made to be nice to everyone.

Michael.