15.25.7.3 loop-finish Macro

The macro loop-finish terminates iteration normally and returns any accumulated result. If specified, a ‘finally’ clause is evaluated.

In most cases it is not necessary to use loop-finish because other loop control clauses terminate the loop. Use loop-finish to provide a normal exit from a nested condition inside a loop.

You can use loop-finish inside nested Lisp code to provide a normal exit from a loop. Since loop-finish transfers control to the loop ‘epilogue’, using loop-finish within a ‘finally’ expression can cause infinite looping.

Implementations are allowed to provide this construct as a local macro by using macrolet.

;;; Print a date in February, but exclude leap day.
;;; LOOP-FINISH exits from the nested condition.
(loop for date in date-list
      do (case date
           (29 (when (eq month 'february)
                     (loop-finish))
             (format t "~:@(~A~) ~A" month date))))

;;; Terminate the loop, but return the accumulated count.
(loop for i in '(1 2 3 stop-here 4 5 6)
      when (symbolp i) do (loop-finish)
      count i)

;;; This loop works just as well as the previous example.
(loop for i in '(1 2 3 stop-here 4 5 6)
      until (symbolp i)
      count i)