Anaphoric lambda macro doesn't work anymore?

Anaphoric lambda macro doesn't work anymore?

[Constantin Kulikov]

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https://github.com/rolandwalker/anaphora/blob/master/anaphora.el#L337

```
(defmacro anaphoric-lambda (args &rest body)
  "Like `lambda', but the function may refer to itself as `self'.
ARGS and BODY are otherwise as documented for `lambda'."
  (declare (debug lambda)
           (indent defun))
  `(labels ((self ,args ,@body))
     #'self))
```

Some versions ago it was working(it seems to me that for 24.4 it works).
(With cl-labels and lexical-binding I can do it, but it is not compatible
with older emacses.)

My current emacs-version is 25.0.50.1.

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Re: Anaphoric lambda macro doesn't work anymore?

[John Wiegley]

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>>>>> Constantin Kulikov <zxnotdead@gmail.com> writes:

> https://github.com/rolandwalker/anaphora/blob/master/anaphora.el#L337

I think your question should go to Roland Walker at GitHub, Constantin, until
you discover a bug in Emacs that we can address.

-- 
John Wiegley                  GPG fingerprint = 4710 CF98 AF9B 327B B80F
http://newartisans.com                          60E1 46C4 BD1A 7AC1 4BA2

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Re: Anaphoric lambda macro doesn't work anymore?

[Constantin Kulikov]

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> your question should go to Roland Walker at GitHub

I don't think so, I used that link to show that this(anaphoric lambda with
labels) pattern is used by someone other than me(actually it came from
common lisp of course https://en.wikipedia.org/wiki/Anaphoric_macro).
And it was working. Now it's broken. It happened because of changes in
emacs, so Roland Walker unlikely will be able to do something about it.
It's breaking change in emacs.

If someone interested -- here is the more/less working version that I use
now:

(when (version< emacs-version "24.4")
  (unless (fboundp 'self)
    (fset 'self nil)))
(defmacro alambda (args &rest body)
  "Anaphoric lambda."
  (declare (indent defun))
  `(lexical-let ((self))
     (setq self #'(lambda ,args
                    (cl-letf (((symbol-function 'self) self))
                      ,@body)))
     self))

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Re: Anaphoric lambda macro doesn't work anymore?

[Alexis]

Constantin Kulikov <zxnotdead@gmail.com> writes:

>> your question should go to Roland Walker at GitHub
>
> I don't think so, I used that link to show that this(anaphoric 
> lambda with labels) pattern is used by someone other than 
> me(actually it came from common lisp of course 
> https://en.wikipedia.org/wiki/Anaphoric_macro).  And it was 
> working. Now it's broken. It happened because of changes in 
> emacs,

What do you mean by "it's broken"? Can you please provide a 
recipe, starting from 'emacs -Q', that demonstrates the problem 
you're encountering?


Alexis.

Re: Anaphoric lambda macro doesn't work anymore?

[Constantin Kulikov]

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emacs -version
GNU Emacs 25.0.50.1

emacs -Q

M-: (require 'cl) RET
M-: (defmacro alambda (args &rest body) `(labels ((self ,args ,@body))
#'self)) RET
M-: (funcall (alambda (a b) (if (a > b) (message "%s %s" a b) (self b a)))
1 2) RET

Debugger entered--Lisp error: (void-function self)

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Re: Anaphoric lambda macro doesn't work anymore?

[Alexis]

Constantin Kulikov <zxnotdead@gmail.com> writes:

> emacs -version GNU Emacs 25.0.50.1
>
> emacs -Q
>
> M-: (require 'cl) RET M-: (defmacro alambda (args &rest body) 
> `(labels ((self ,args ,@body)) #'self)) RET M-: (funcall 
> (alambda (a b) (if (a > b) (message "%s %s" a b) (self b a))) 1 
> 2) RET
>
> Debugger entered--Lisp error: (void-function self)

Try using:

    (require 'cl-lib)

instead.

(Your if-condition should be:

    (> a b)

.)


Alexis.

Re: Anaphoric lambda macro doesn't work anymore?

[Constantin Kulikov]

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> Try using: (require 'cl-lib)
Hmm... I think it has issues and inconsistency with old behavior, however I
can not clearly remember why I don't like cl-labels.
One reason is that it will not work in old emacses and if I remember
correctly in files without -*- lexical-binding: t -*- header.

M-: (require 'cl-lib)
M-: (defmacro alambda (args &rest body) `(cl-labels ((self ,args ,@body))
#'self))
M-: (setq lexical-binding t)
M-: (funcall (alambda (a b) (cl-flet ((a (b c) (> b c))) (let ((> a)) (if
(a > b) (message "%s %s %s" a b (symbol-function 'self)) (self b a))))) 1 2)

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Re: Anaphoric lambda macro doesn't work anymore?

[Stefan Monnier]

> emacs -version
> GNU Emacs 25.0.50.1

> emacs -Q

> M-: (require 'cl) RET
> M-: (defmacro alambda (args &rest body) `(labels ((self ,args ,@body))
> #'self)) RET
> M-: (funcall (alambda (a b) (if (a > b) (message "%s %s" a b) (self b a)))
> 1 2) RET

> Debugger entered--Lisp error: (void-function self)

Indeed, looks like a plain bug: the #'self is not being replaced with
a reference to the `labels' defined function for some reason.
Can you make a proper bug report for it (i.e. send the above recipe
with M-x report-emacs-bug), so we get a tracking number?


        Stefan