Function Intersperse
(
intersperse < list > < delimeter > &key (last
delimeter) )
Intersperses a list with a delimeter.
If 'last' is specified, it will be used for the last delimeter,
instead of 'delimeter'.
(intersperse '(1 2 3 4 5) 0)
=> (1 0 2 0 3 0 4 0 5)