add call/cc example

docs/docs/scheme-intro/continuations.md

@@ -4,3 +4,18 @@ description: Powerful feature of Scheme that allow to add new control flows
 ---
 
 # Continuations
+
+## Early exit
+
+Scheme doesn't have a return expression, but with continuations you can add one.
+
+```scheme
+(define (find item lst)
+  (call/cc (lambda (return)
+             (let loop ((lst lst))
+                (if (null? lst)
+                    (return #f)
+                    (if (equal? item (car lst))
+                        (return lst)
+                        (loop (cdr lst))))))))
+```