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i couldn't find any usage of one of lisp primitives, functionp
the results are either 'nil' or errors.
how i can get a result 't'
undergnd
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In article <·················@hitel.net>, "Kim, Ju Ho"
<········@hitel.net> wrote:
> i couldn't find any usage of one of lisp primitives, functionp
>
> the results are either 'nil' or errors.
> how i can get a result 't'
? (functionp #'functionp)
T
--
Rainer Joswig, Hamburg, Germany
Email: ·············@corporate-world.lisp.de
Web: http://corporate-world.lisp.de/
Rainer Joswig <······@corporate-world.lisp.de> writes:
> In article <·················@hitel.net>, "Kim, Ju Ho"
> <········@hitel.net> wrote:
>
> > i couldn't find any usage of one of lisp primitives, functionp
> >
> > the results are either 'nil' or errors.
> > how i can get a result 't'
>
> ? (functionp #'functionp)
> T
A more typical "use" might be:
(when (functionp *end-of-frobbing-hook*)
(funcall *end-of-frobbing-hook*))
Though often such applications will want to tolerate symbols, as well,
since FUNCALL will tolerate them. As such, one might instead write:
(defun funcallable-p (x)
(or (functionp x)
(and (symbolp x) (fboundp x))))
... (when (funcallable-p *end-of-frobbing-hook*)
(funcall *end-of-frobbing-hook*)) ...
Hi
Functionp is true if its argument is suitable for applying to arguments,
using for example the funcall or apply function. otherwise functionp is
false.
is that any help?
"Kim, Ju Ho" wrote:
> i couldn't find any usage of one of lisp primitives, functionp
>
> the results are either 'nil' or errors.
> how i can get a result 't'
>
> undergnd
Michael J Short <·········@tothemoon.freeserve.co.uk> writes:
> Functionp is true if its argument is suitable for applying to arguments,
> using for example the funcall or apply function. otherwise functionp is
> false.
This isn't actually quite right. FUNCTIONP tests for things of type
function. The CLTL1 definition of FUNCTIONP was, effectively, to test
for things that were "applicable", but the ANSI CL definition is to
test for things of a specific representation type.
The difference is seen in this case:
(functionp 'car) => false
even though
(funcall 'car '(a b c)) => A
(apply 'car '((a b c))) => A
It is true that
(functionp #'car) => true
and that
(funcall #'car '(a b c)) => A
(apply #'car '((a b c))) => A
In CLTL1, it was also true that
(functionp '(lambda (x) x)) => true ;CLTL1 only - NOT in ANSI CL
(funcall '(lambda (x) x) 3) => 3 ;CLTL1 only - NOT in ANSI CL
This kind of thing was repaired in ANSI CL. Neither does FUNCTIONP return
true for a quoted list whose car is LAMBDA, nor does FUNCALL work to call
such a thing. The reason for this has to do with space-efficient
compilation, but a side-benefit of this is that the following weirdness
of the CLTL1 "semantics" has been repaired:
(functionp '(lambda is a greek letter)) => true ;CLTL1 only - NOT in ANSI CL