You can use backquote:
(let ((sing_under "new_post"))
`(create new ,(format nil "~a" sing_under)))
=> (CREATE NEW "new_post")
Alberto
--
Give a man a fish and he will eat for one day. Teach him programming,
and he will develop a multi tasking intelligent planning algorithm to
optimize the route of a fleet of deep sea fishing boats, with
real-time GPS tracking, weather satellite link, automatic analysis of
fish market prices, the whole thing controlled by an AJAX-enabled web
interface. In the meantime, he will die of hunger.