bit, sbit

bit-array — for bit, a bit array; for sbit, a simple bit array.

subscripts — a list of valid array indices for the bit-array.

bit — a bit.

bit and sbit access the bit-array element specified by subscripts.

These functions ignore the fill pointer when accessing elements.

(bit (setq ba (make-array 8 
                           :element-type 'bit 
                           :initial-element 1)) 
      3) → 1 
(setf (bit ba 3) 0) → 0 
(bit ba 3) → 0 
(sbit ba 5) → 1 
(setf (sbit ba 5) 1) → 1 
(sbit ba 5) → 1

aref, Section 3.2.1 (Compiler Terminology)

bit and sbit are like aref except that they require arrays to be a bit array and a simple bit array, respectively.

bit and sbit, unlike char and schar, allow the first argument to be an array of any rank.