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5.3.25 return-from [Special Operator]

return-from name [result] ⇒ #<NoValue>

Arguments and Values::

name—a block tag; not evaluated.

result—a form; evaluated. The default is nil.

Description::

Returns control and multiple values_2 from a lexically enclosing block.

A 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 Transfer of Control to an Exit Point.

Examples::

 (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 block form exits normally before the return-from form is attempted.

 (funcall (block nil #'(lambda () (return-from nil)))) is an error.

See Also::

block , return , Evaluation


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