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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.

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.