GNU bug report logs - #23550
25.0.93; cl.texi (for var on list by func): Fix documentation

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Tino Calancha <f92capac <at> gmail.com>
Subject: bug#23550: closed (Re: bug#23550: 25.0.93; cl.texi (for var on
 list by func): Fix documentation)
Date: Fri, 31 Mar 2017 08:21:02 +0000

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Your bug report

#23550: 25.0.93; cl.texi (for var on list by func): Fix documentation

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 23550 <at> debbugs.gnu.org.

-- 
23550: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23550
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Tino Calancha <tino.calancha <at> gmail.com>
To: 23550-done <at> debbugs.gnu.org
Subject: Re: bug#23550: 25.0.93;
 cl.texi (for var on list by func): Fix documentation
Date: Fri, 31 Mar 2017 17:20:31 +0900

npostavs <at> users.sourceforge.net writes:

> Tino Calancha <tino.calancha <at> gmail.com> writes:
>
>> It might be useful rewrite that part to make it more clear, but i don't
>> have a clear proposal.
>
> Actually, looking at this some more, I think you should just apply your
> patch that removes this stuff completely.  It's much clearer to write
> that sort of example as
>
>     (cl-loop for y = "lion" then (next-prey y)
>              while y collect y)
>
> And looking down the page, `for VAR = EXPR1 then EXPR2' is already
> explained well enough (as well as the equivalence to the `for VAR on
> LIST by FUNCTION' form).
Thank you.
Pushed fix into emacs-25 branch with commit:
3f0d047d2eb1fb59be2ff962c01392d8c808a654

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From: Tino Calancha <f92capac <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.0.93; cl.texi (for var on list by func): Fix documentation
Date: Tue, 17 May 2016 00:49:02 +0900 (JST)

* doc/misc/cl.texi (for var on list by func): Fix documentation

'cl-loop for var on list by func' behaves as in CL: 'on' expression
need to be a list.

The following tests run in the *scratch* buffer return
same values as in SBCL: 
;; CL cl-loop -> loop

emacs -Q:

(require 'cl-lib)
(setq preys '("grass" "lion" "rabbit"))

(defun next-prey (x)
  "Return the name of the prey of animal X."
  (cl-loop while (not (atom x))
           do (setq x (car x)))
  (cond ((member x preys) ; elisp
  ;; (cond ((member x preys :test #'string=) ; CL
         (cond ((string= x "lion") "rabbit")
               ((string= x "rabbit") "grass")
               (t nil)))
        (t
         nil)))
(defun next-prey-list (x)
  "Return a list with the name of the prey of animal X."
  (let ((res (next-prey x)))
    (if res
        (list res)
      nil)))

[A] (mapcar 'next-prey '("grass" "lion" "rabbit"))
[B] (mapcar 'next-prey-list '("grass" "lion" "rabbit"))

[A] (nil "rabbit" "grass")
[B] (nil ("rabbit") ("grass"))

[I]   (cl-loop for y on preys collect y)
[II]  (cl-loop for y on preys by #'next-prey collect y)
[III] (cl-loop for y on (car preys) by #'next-prey collect y)
[IV]  (cl-loop for y on (car preys) by #'next-prey-list collect y)
[V]   (cl-loop for y on preys by #'next-prey-list collect y)

[I]   (("grass" "lion" "rabbit") ("lion" "rabbit") ("rabbit"))
[II]  (("grass" "lion" "rabbit"))
[III] nil
[IV]  nil
[V]   (("grass" "lion" "rabbit"))


In GNU Emacs 25.0.93.3 (x86_64-pc-linux-gnu, GTK+ Version 2.24.30)
Repository revision: 6de0715f5467d4b925e2dfe082174529ace3b174


From 3e1756fb4d76e34b74b96782d4509582e9ce0cd3 Mon Sep 17 00:00:00 2001
From: Tino Calancha <f92capac <at> gmail.com>
Date: Tue, 17 May 2016 00:04:56 +0900
Subject: [PATCH] ; * cl.texi (clause 'for' with 'on'): Fix documentation

---
 doc/misc/cl.texi | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/doc/misc/cl.texi b/doc/misc/cl.texi
index 4137a95..319592c 100644
--- a/doc/misc/cl.texi
+++ b/doc/misc/cl.texi
@@ -1956,18 +1956,6 @@ For Clauses
         @result{} ((1 2 3 4) (2 3 4) (3 4) (4))
 @end example

-With @code{by}, there is no real reason that the @code{on} expression
-must be a list.  For example:
-
-@example
-(cl-loop for x on first-animal by 'next-animal collect x)
-@end example
-
-@noindent
-where @code{(next-animal x)} takes an ``animal'' @var{x} and returns
-the next in the (assumed) sequence of animals, or @code{nil} if
-@var{x} was the last animal in the sequence.
-
 @item for @var{var} in-ref @var{list} by @var{function}
 This is like a regular @code{in} clause, but @var{var} becomes
 a @code{setf}-able ``reference'' onto the elements of the list
-- 
2.8.1

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