CL-USER> (let ((foo (lambda () "With docstring" 100500)))
(princ (funcall foo))
(terpri)
(princ (documentation foo t)))
100500
NIL
NIL
CL-USER> (let ((foo (lambda () "With docstring" 100500)))
(princ (funcall foo))
(terpri)
(princ (documentation foo t)))
100500
With docstring
"With docstring"