Re: Naming FCRs

[Tomas Hlavaty]

On Thu 30 Dec 2021 at 09:43, <tomas@tuxteam.de> wrote:
> Possibly because it diverges somewhat from the canonical meaning of
> "closure" -- it might confuse people.

I don't think so.  Lisps usually expose a way to see the closed over
variables, so in reality, there is no such thing as "closures that don't
permit access".

You can do that in Emacs right now (maybe not portably across different
compiler backends):

ELISP> (defun foo (a b) (lambda (c) (+ a b c)))
foo
ELISP> (foo 3 5)
(closure
 ((b . 5)
  (a . 3)
  t)
 (c)
 (+ a b c))

ELISP> (defun faz (a b) (lambda (c) (error "a=%d b=%d" a b)))
faz
ELISP> (setq baz (faz 3 5))
(closure
 ((b . 5)
  (a . 3)
  t)
 (c)
 (error "a=%d b=%d" a b))
ELISP> (funcall baz 13)
*** Eval error ***  a=3 b=5
ELISP> (setq debug-on-error t)
t
ELISP> (funcall baz 13)
Debugger entered--Lisp error: (error "a=3 b=5")
  signal(error ("a=3 b=5"))
  error("a=%d b=%d" 3 5)
  (closure ((b . 5) (a . 3) t) (c) (error "a=%d b=%d" a b))(13)
  funcall((closure ((b . 5) (a . 3) t) (c) (error "a=%d b=%d" a b)) 13)
  eval((funcall baz 13) t)
  ielm-eval-input(#("(funcall baz 13)" 0 16 (fontified t)) nil)
  ielm-send-input(nil)
  ielm-return()
  funcall-interactively(ielm-return)
  call-interactively(ielm-return nil nil)
  command-execute(ielm-return)

ELISP> (car baz)
closure
ELISP> (cdr (assoc 'a (cadr baz)))
3 (#o3, #x3, ?\C-c)

ELISP> (rplacd (assoc 'a (cadr baz)) 42)
42 (#o52, #x2a, ?*)
ELISP> baz
(closure
 ((b . 5)
  (a . 42)
  t)
 (c)
 (error "a=%d b=%d" a b))