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Re: About `funcall'
From: |
Pascal J. Bourguignon |
Subject: |
Re: About `funcall' |
Date: |
Tue, 05 Mar 2013 00:23:08 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux) |
Xue Fuqiao <xfq.free@gmail.com> writes:
>> Xue Fuqiao <xfq.free@gmail.com> writes:
>>
>>> In `yank-pop', there is an sexp about `funcall':
>>>
>>> (funcall (or yank-undo-function 'delete-region) (point) (mark t))
>>>
>>> IIRC the first argument for `funcall' should be a function, so I'm
>>> confused with this usage. Can somebody explain it to me? Thanks.
>>
>> `or' returns the first argument that is not nil, or nil when all the
>> arguments are nil.
>
> I see, thanks.
>
>> (defmacro .or (&rest args)
>> (if (null args)
>> 'nil
>> (let ((var (gensym)))
>> `(let ((,var ,(first args)))
>> (if ,var
>> ,var
>> (.or ,@(rest args)))))))
>>
>> (macroexpand '(.or a b))
>> --> (let ((#1=#:G90861 a)) (if #1# #1# (\.or b)))--
>
> What does "(first args)" mean here? Does it mean "(car args)"?
Yes. And (rest args) is the same as (cdr args).
But since I consider here args to be a list, and not a cons cell, then I
use first and rest. I use car and cdr only when I consider cons cells.
--
__Pascal Bourguignon__ http://www.informatimago.com/
A bad day in () is better than a good day in {}.