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Re: How to mapcar or across a list?
From: |
Emanuel Berg |
Subject: |
Re: How to mapcar or across a list? |
Date: |
Thu, 16 Jul 2015 00:21:06 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.4 (gnu/linux) |
Marcin Borkowski <mbork@mbork.pl> writes:
> so here's my problem: I have a list of Boolean
> values, and I want to `mapcar' an `or' across it
> (IOW, I want to test whether at least one of them is
> true). Of course, (apply #'or my-list) does not
> work. Of course, I can (cl-reduce (lambda (x y) (or
> x y)) my-list) -- but is there a better method?
"Better" I don't know, but how about using your
new-found skills with the backquote? (`or' itself
should be used, of course.)
(setq boolean-list-1 '(t nil nil nil t nil nil))
(setq boolean-list-2 '(nil nil nil nil nil nil nil))
(eval `(or ,@boolean-list-1)) ; t
(eval `(or ,@boolean-list-2)) ; nil
> BTW, my-list doesn't really exist: it is a result of
> `mapcar'ing a function taking some value and
> yielding a Boolean value, so bonus points if the
> method does not process the whole list.
Check. It is a consequence of using `or', which is
"short circuited" as it is called in other languages,
perhaps in Lisp too - I've read
"conditional evaluation" as well in AI books, but
perhaps that is something else.
Anyway:
(or t undefined) ; t
(or undefined t) ; error: (void-variable undefined) in eval
To verify, append "undefined" to "boolean-list-1"
(no error) - but, there will be an error (the same as
above) if appended to "boolean-list-2"!
... I suppose now would be a good time for you to hand
over them points!
--
underground experts united
http://user.it.uu.se/~embe8573
- How to mapcar or across a list?, Marcin Borkowski, 2015/07/15
- Re: How to mapcar or across a list?, Rasmus, 2015/07/15
- Re: How to mapcar or across a list?, John Mastro, 2015/07/15
- Re: How to mapcar or across a list?,
Emanuel Berg <=
- Message not available
- Re: How to mapcar or across a list?, Pascal J. Bourguignon, 2015/07/15
- Re: How to mapcar or across a list?, Emanuel Berg, 2015/07/15
- never use `eval' (was: Re: How to mapcar or across a list?), Emanuel Berg, 2015/07/15
- Re: never use `eval' (was: Re: How to mapcar or across a list?), John Mastro, 2015/07/15
- Re: never use `eval' (was: Re: How to mapcar or across a list?), Emanuel Berg, 2015/07/15
- Re: never use `eval' (was: Re: How to mapcar or across a list?), John Mastro, 2015/07/15
- Message not available
- Re: never use `eval' (was: Re: How to mapcar or across a list?), Barry Margolin, 2015/07/15
- Message not available
- Re: never use `eval' (was: Re: How to mapcar or across a list?), Barry Margolin, 2015/07/15
- Re: never use `eval' (was: Re: How to mapcar or across a list?), Emanuel Berg, 2015/07/15
- Re: never use `eval' (was: Re: How to mapcar or across a list?), Emanuel Berg, 2015/07/16