Is there a way to extract all elements of a list i

问题:

Im looking for a way to extract all the elements of a list in common lisp. Like this

[194]> (break-out-of-list '(a b c d))
A
B
C
D

Edit: The usage example I gave was not thought out very well, however I'm still curious if it is possible to break out of a list like in the example above.

回答1:

What you demonstrate seems to be the question how to get the elements of a list as multiple values:

CL-USER> (values 1 2 3)
1
2
3
CL-USER> (apply #'values '(1 2 3))
1
2
3

See also multiple-value-bind and nth-value in the hyperspec.

回答2:

Sure, just use apply:

(defun wraptest (&rest arguments)
  (apply #'test arguments))

This technically doesn't "break out of list"; it simply uses a list's elements as arguments to a function call.

(Disclaimer: I'm a Schemer, not a Common Lisper, and there may be a more-idiomatic way to achieve the same result in CL.)

回答3:

While (apply #'values '(1 2 3)) works there is also a function to this called values-list which is used like this:

(values-list '(1 2 3))

And it has the same result.

回答4:

I think you might be looking for this:

http://cl-cookbook.sourceforge.net/macros.html#LtohTOCentry-2

That's mostly all there is to backquote. There are just two extra items to point out. First, if you write ",@e" instead of ",e" then the value of e is spliced into the result. So if v=(oh boy), then `(zap ,@v ,v) evaluates to (zap oh boy (oh boy)). The second occurrence of v is replaced by its value. The first is replaced by the elements of its value. If v had had value (), it would have disappeared entirely: the value of (zap ,@v ,v) would have been (zap ()), which is the same as (zap nil).

Reading your comments:

(some-macro (break-list '(a b c d))) is equivalent to (some-macro 'a 'b 'c 'd)

With this, you could do:

`(some-macro ,@'(a b c d))

and you'd get:

(some-macro a b c d)