bug#28725: 26.0.60; Error when using Edebug on a generator

bug#28725: 26.0.60; Error when using Edebug on a generator

[Gemini Lasswell]

Running a generator under Edebug results in an error message when it
gets to iter-yield.

To reproduce, put the code below into *scratch* and:

M-x edebug-all-defs RET
M-x eval-buffer RET
M-: (my-iter-do) RET
g

Result: Symbol’s function definition is void: cps-internal-yield


;;;  -*- lexical-binding: t -*-

(iter-defun mycounter (start)
  (let* ((i start))
    (while t
      (iter-yield i)
      (setq i (1+ i)))))

(defun my-iter-do ()
  (let (results
	(tally (mycounter 10)))
    (dotimes (_ 4)
      (push (iter-next tally) results))
    results))

bug#28725: alternative

[Paul Pogonyshev]

You may want to try `iter2' package, which is a fully compatible
reimplementation of `generator'. Among other advantages, generator
functions it produces are compatible with Edebug. However, it's not
well-established, so be aware of possible misbehaving generators.

bug#28725: alternative

[Gemini Lasswell]

Paul Pogonyshev <pogonyshev@gmail.com> writes:

> You may want to try `iter2' package, which is a fully compatible
> reimplementation of `generator'. Among other advantages, generator
> functions it produces are compatible with Edebug.

Hi Paul,

Thanks for letting me know about iter2 and it's good to hear that it
works with Edebug. My interest in this bug is more about Edebug than
it is about generators, because I've been working on finding and
fixing code that ships with Emacs but doesn't work with Edebug.

Best,
Gemini

bug#28725: 26.0.60; Error when using Edebug on a generator

[Lars Ingebrigtsen]

Gemini Lasswell <gazally@runbox.com> writes:

> Running a generator under Edebug results in an error message when it
> gets to iter-yield.
>
> To reproduce, put the code below into *scratch* and:
>
> M-x edebug-all-defs RET
> M-x eval-buffer RET
> M-: (my-iter-do) RET
> g
>
> Result: Symbol’s function definition is void: cps-internal-yield

I'm able to reproduce this bug in Emacs 27.

Does anybody know what's causing this?  It's bugging out in the
`iter-yield' call.

> ;;;  -*- lexical-binding: t -*-
>
> (iter-defun mycounter (start)
>   (let* ((i start))
>     (while t
>       (iter-yield i)
>       (setq i (1+ i)))))
>
> (defun my-iter-do ()
>   (let (results
> 	(tally (mycounter 10)))
>     (dotimes (_ 4)
>       (push (iter-next tally) results))
>     results))

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#28725: 26.0.60; Error when using Edebug on a generator

[Gemini Lasswell]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> I'm able to reproduce this bug in Emacs 27.
>
> Does anybody know what's causing this?  It's bugging out in the
> `iter-yield' call.

I took a look and I think the problem is that cps--transform-1 doesn't
look inside lambda forms.  When Edebug instruments a function, it wraps
the body of the function in a lambda form.

Here's a code sample to reproduce the bug with just eval-buffer, no
Edebug necessary:

;;;  -*- lexical-binding: t -*-

(require 'generator)

(iter-defun mycounter (start)
  (let ((i 0)
	(offset-yield-func (lambda (x) (iter-yield (+ x start)))))
    (while t
      (funcall offset-yield-func i)
      (setq i (1+ i)))))

(defun my-iter-do ()
  (let (results
	(tally (mycounter 10)))
    (dotimes (_ 4)
      (push (iter-next tally) results))
    results))

(my-iter-do)