6.7 Bool-vectors

A bool-vector is much like a vector, except that it stores only the values t and nil. If you try to store any non-nil value into an element of the bool-vector, the effect is to store t there. As with all arrays, bool-vector indices start from 0, and the length cannot be changed once the bool-vector is created. Bool-vectors are constants when evaluated.

There are two special functions for working with bool-vectors; aside from that, you manipulate them with same functions used for other kinds of arrays.

Function: make-bool-vector length initial

Return a new bool-vector of length elements, each one initialized to initial.

Function: bool-vector-p object

This returns t if object is a bool-vector, and nil otherwise.

There are also some bool-vector set operation functions, described below:

Function: bool-vector-exclusive-or a b &optional c

Return bitwise exclusive or of bool vectors a and b. If optional argument c is given, the result of this operation is stored into c. All arguments should be bool vectors of the same length.

Function: bool-vector-union a b &optional c

Return bitwise or of bool vectors a and b. If optional argument c is given, the result of this operation is stored into c. All arguments should be bool vectors of the same length.

Function: bool-vector-intersection a b &optional c

Return bitwise and of bool vectors a and b. If optional argument c is given, the result of this operation is stored into c. All arguments should be bool vectors of the same length.

Function: bool-vector-set-difference a b &optional c

Return set difference of bool vectors a and b. If optional argument c is given, the result of this operation is stored into c. All arguments should be bool vectors of the same length.

Function: bool-vector-not a &optional b

Return set complement of bool vector a. If optional argument b is given, the result of this operation is stored into b. All arguments should be bool vectors of the same length.

Function: bool-vector-subsetp a b

Return t if every t value in a is also t in b, nil otherwise. All arguments should be bool vectors of the same length.

Function: bool-vector-count-consecutive a b i

Return the number of consecutive elements in a equal b starting at i. a is a bool vector, b is t or nil, and i is an index into a.

Function: bool-vector-count-population a

Return the number of elements that are t in bool vector a.

Here is an example of creating, examining, and updating a bool-vector. Note that the printed form represents up to 8 boolean values as a single character.

(setq bv (make-bool-vector 5 t))
     ⇒ #&5"^_"
(aref bv 1)
     ⇒ t
(aset bv 3 nil)
     ⇒ nil
bv
     ⇒ #&5"^W"

These results make sense because the binary codes for control-_ and control-W are 11111 and 10111, respectively.