while
(while test_expression expression1 ...)
The while construct allows iteration to continue until the specified expression evaluates to nil.
The function returns the result of the last expression evaluated.
: (setq x 0)
0
: (while (< x 5) (princ "X=")(princ x)(terpri) (setq x (+ x 1)))
X=0
X=1
X=2
X=3
X=4
5