LISP 汽车的最后一个元素？
LISP 再次难倒了我...为什么我无法获取列表中最后一个元素的值？我有一个与此类似的列表设置：
(setq bar '(((1 2) 3 4 5)((6 7) 8 9 10)))
现在我得到 4 的回报：
(caddar bar)
有 (5) 的回报：
(cdddar bar)
但我无法得到 5 的：
(cadddar bar)
这是为什么——以及如何获得5的值？
错误：
; Warning: This function is undefined:
; CADDDAR
Error in KERNEL:%COERCE-TO-FUNCTION: the function CADDDAR is undefined.
[Condition of type UNDEFINED-FUNCTION]
LISP stumps me yet again... Why can't I get the value of the last element in a list? I have a list set up similar to this:
(setq bar '(((1 2) 3 4 5)((6 7) 8 9 10)))
Now I get a return of 4 for:
(caddar bar)
There is a return of (5) for:
(cdddar bar)
But I can't get a 5 for:
(cadddar bar)
Why is this--and how do I get the value of the 5?
Error:
; Warning: This function is undefined:
; CADDDAR
Error in KERNEL:%COERCE-TO-FUNCTION: the function CADDDAR is undefined.
[Condition of type UNDEFINED-FUNCTION]
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具有 5 个或更多 a 和 d 的函数未定义。只有 4 个或更少。这么长的函数可能有太多，不切实际。
你必须把它拼出来：
(car (cdr (cdr (cdr (cdr (car x))))))The functions with 5 or more a's and d's are not defined. Only 4 and fewer. There are too many possible functions of that length for it be be practical.
You have to just spell it out:
(car (cdr (cdr (cdr (cdr (car x))))))嗯，根据错误消息，没有
cadddar函数。请记住，car和cdr是原始列表读取函数。其他诸如caddar是由一个或多个car和cdr组合构建的便利函数。也就是说，如果caddar等不存在，您可以仅使用car和cdr执行列表操作，扩展函数只是使你的生活更轻松一点。因此，解决此问题的方法是使用
car和cdr合成您自己的cadddar。如果不太清楚如何执行此操作，请从更简单的开始（例如，使用cadr或cdar），然后逐步构建到cadddar。Well, per the error message, there is no
cadddarfunction. Keep in mind thatcarandcdrare the primitive list-reading functions. Others likecaddarare convenience functions that are built from a combination of one or morecarandcdr. That is, you could perform list manipulation just fine with onlycarandcdrifcaddaretc. didn't exist, the extended functions just make your life a bit easier.So, the way to approach this is to synthesize your own
cadddarusingcarandcdr. If it isn't immediately apparent how to do this, start simplier (with, say,cadrorcdar) and build up tocadddar.标准没有定义超过 4 个
a和d的函数，可能是因为它们有 32 个 [并且从那时起它变得更加混乱] 。获取列表最后一个元素的可靠方法：
last返回最后一个 cons 单元格，因此为您提供最后一个列表元素。当然，
list也可以是其他内容，如(first list)。The functions with more than 4
as andds aren't defined by the standard, maybe because there are 32 of them [and it gets exponentially messier from then on].A sure-fire way to get the last element of a list:
lastreturns the last cons cell, sogives you the last list element. Of course,
listcould be something else like(first list).