问题
I have two items. The first, a-child, is a list which contains an array as its first element and then some strings as the remaining elements. The other, mapped, is a list which contains a number of arrays. By inspection, it\'s easy to see that a-child is in mapped, though I can\'t find a function which will find it for me.
I apologize for the poor lisp style below - I started a few days ago, so I haven\'t picked up all the conventions yet.
(defparameter a-child (list (#2A((1 2 3) (7 4 5) (9 8 6))) \"U\" \"R\" \"R\"))
(defparameter mapped (list (#2A((1 2 3) (7 4 5) (9 8 6))) (#2A((1 2 3) (4 5 6) (7 8 9)))))
(find (car a-child) mapped) ;;returns NIL
(member (car a-child) mapped) ;;returns NIL
(position (car a-child) mapped) ;;returns NIL
(equalp (car a-child) (car mapped)) ;;returns T
What function can I use to look for arrays within a list of arrays?? Thank you.
回答1:
The Answer
Your sequence functions marked "returns NIL" will return T if you pass :test #'equalp to them.
The Reason
The default Two-Argument Test in Common Lisp is eql.
It is the most reasonable choice between the 4(!) general purpose comparison functions provided for by the ANSI CL standard:
eq is too implementation-dependent and does not work as one probably wants on numbers and characters
equal and equalp traverse objects and thus take long time for huge ones and may never terminate for circular ones.
See also the difference between eq, eql, equal, and equalp in Common Lisp.
来源：https://stackoverflow.com/questions/19287777/test-if-array-is-inside-a-list-in-lisp