CLHS: Section 2.4.8.12

2.4.8.12 Sharpsign A

#nA

#nAobject constructs an n-dimensional array, using object as the value of the :initial-contents argument to make-array.

For example, #2A((0 1 5) (foo 2 (hot dog))) represents a 2-by-3 matrix:

 0       1       5
 foo     2       (hot dog)

In contrast, #1A((0 1 5) (foo 2 (hot dog))) represents a vector of length 2 whose elements are lists:

 (0 1 5) (foo 2 (hot dog))

#0A((0 1 5) (foo 2 (hot dog))) represents a zero-dimensional array whose sole element is a list:

 ((0 1 5) (foo 2 (hot dog)))

#0A foo represents a zero-dimensional array whose sole element is the symbol foo. The notation #1A foo is not valid because foo is not a sequence.

If some dimension of the array whose representation is being parsed is found to be 0, all dimensions to the right (i.e., the higher numbered dimensions) are also considered to be 0.

For information on how the Lisp printer prints arrays, see Section 22.1.3.4 (Printing Strings), Section 22.1.3.6 (Printing Bit Vectors), Section 22.1.3.7 (Printing Other Vectors), or Section 22.1.3.8 (Printing Other Arrays).