sleep seconds → nil

seconds — a non-negative real.

Causes execution to cease and become dormant for approximately the seconds of real time indicated by seconds, whereupon execution is resumed.

 (sleep 1) → NIL 

;; Actually, since SLEEP is permitted to use approximate timing, 
;; this might not always yield true, but it will often enough that 
;; we felt it to be a productive example of the intent. 
 (let ((then (get-universal-time)) 
       (now  (progn (sleep 10) (get-universal-time)))) 
   (>= (- now then) 10)) 
→ true

Causes processing to pause.

The granularity of the scheduler.

Should signal an error of type type-error if seconds is not a non-negative real.