A vector may also be constructed using the concatenation operator ``::''. As an example,
(0 :: 1 :: 1 :: 0)
is a vector of length 4. That is, the 4 boolean values in this
expression are treated as vectors of length 1, and concatenated to
produce a vector of length 4.
The concatenation operator is associative. Thus, for example,
((0 :: 1) :: (1 :: 0)) = (0 :: 1 :: 1 :: 0)