#lang racket

; pattern for
; TRY
; CATCH
; RESUME

(define testit (lambda (x y default)
  
; RESUME                 
(call/cc
 (lambda (RESUME)  ; when everything is finished we invoke RESUME
   
   (let ( (exception 
           
           ; the context around this is the catch, it expects an exception result
           (call/cc 
            (lambda (THROW)  
              ; TRY
              ; here is the body of the try, which computes result
              
              (let ((result
                     ; compute the result in here, or throw
                     (if (not (eq? 0 y)) (/ x y) (THROW "DivBy0"))
                     ))
                
                ; it worked, so return result
                (RESUME result)
                )
              )
            ) ) )

   
   ; CATCH
   ; what happens here is the catch, invoked only if we throw
   ; in this case we return the default value
   (display "Caught ")(display exception)(newline)
   (RESUME default)

   )
 )
                 
)))

(testit 4 2 "Arrgh, do not divide by 0")
(testit 4 0 "Arrgh, do not divide by 0")