elisp: Bool-Vector Type
2.3.11 Bool-Vector Type
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A “bool-vector” is a one-dimensional array whose elements must be ‘t’ or
‘nil’.
The printed representation of a bool-vector is like a string, except
that it begins with ‘#&’ followed by the length. The string constant
that follows actually specifies the contents of the bool-vector as a
bitmap—each character in the string contains 8 bits, which specify the
next 8 elements of the bool-vector (1 stands for ‘t’, and 0 for ‘nil’).
The least significant bits of the character correspond to the lowest
indices in the bool-vector.
(make-bool-vector 3 t)
⇒ #&3"^G"
(make-bool-vector 3 nil)
⇒ #&3"^@"
These results make sense, because the binary code for ‘C-g’ is 111 and
‘C-@’ is the character with code 0.
If the length is not a multiple of 8, the printed representation
shows extra elements, but these extras really make no difference. For
instance, in the next example, the two bool-vectors are equal, because
only the first 3 bits are used:
(equal #&3"\377" #&3"\007")
⇒ t
Info Catalog
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