name—a block tag; not evaluated.
result—a form; evaluated.
The default is
Returns control and multiple values2 from a lexically enclosing block.
block form named name must lexically enclose
the occurrence of
return-from; any values yielded
by the evaluation of result are immediately returned from
the innermost such lexically enclosing block.
The transfer of control initiated by
return-from is performed
as described in Section 5.2 (Transfer of Control to an Exit Point).
(block alpha (return-from alpha) 1) → NIL (block alpha (return-from alpha 1) 2) → 1 (block alpha (return-from alpha (values 1 2)) 3) → 1, 2 (let ((a 0)) (dotimes (i 10) (incf a) (when (oddp i) (return))) a) → 2 (defun temp (x) (if x (return-from temp 'dummy)) 44) → TEMP (temp nil) → 44 (temp t) → DUMMY (block out (flet ((exit (n) (return-from out n))) (block out (exit 1))) 2) → 1 (block nil (unwind-protect (return-from nil 1) (return-from nil 2))) → 2 (dolist (flag '(nil t)) (block nil (let ((x 5)) (declare (special x)) (unwind-protect (return-from nil) (print x)))) (print 'here)) ▷ 5 ▷ HERE ▷ 5 ▷ HERE → NIL (dolist (flag '(nil t)) (block nil (let ((x 5)) (declare (special x)) (unwind-protect (if flag (return-from nil)) (print x)))) (print 'here)) ▷ 5 ▷ HERE ▷ 5 ▷ HERE → NIL
The following has undefined consequences because the
exits normally before the
return-from form is attempted.
(funcall (block nil #'(lambda () (return-from nil)))) is an error.
block, return, Section 3.1 (Evaluation)