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bug#23550: 25.0.93; cl.texi (for var on list by func): Fix documentation
From: |
npostavs |
Subject: |
bug#23550: 25.0.93; cl.texi (for var on list by func): Fix documentation |
Date: |
Sat, 25 Mar 2017 23:01:45 -0400 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux) |
Tino Calancha <f92capac@gmail.com> writes:
> * 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.
Well, it only needs to be a cons, because that's what the loop checks
for.
>
> 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)))
I guess the idea behind that statement is that the rest of the list can
be implied by the stepping function, e.g.
(cl-loop for y on (list "lion") by #'next-prey-list collect (car y))
;=> ("lion" "rabbit" "grass")
Works with the "in" clause too:
(cl-loop for y in (list "lion") by #'next-prey-list collect y)
;=> ("lion" "rabbit" "grass")
I guess it could be useful in combination with streams? Not sure if
it's worth having this in the manual.
- bug#23550: 25.0.93; cl.texi (for var on list by func): Fix documentation,
npostavs <=