Test if array is inside a list in lisp

Question

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.

Blamed

Answer 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.

Epiphytotic

In most newer scripting languages, something akin to CL's equal is the ordinary comparison operator. Notably, it works intuitively on strings and vectors. It may be that the possibility of making circular lists in Lisp is the reason why equal was not chosen as the default. equal doesn't need to be slower than eql when comparing different types, as it only needs to traverse the data structure if all its arguments are of the same type. – Aftertime