;; call/cc 的型別: (forall (A B C) in Any) (-> (-> (-> A C) B) (U A B))


;; 異常處理 call/cc
https://csl.name/post/lambda-macros-continuations/
(define-library (try-catch)
  (import (scheme base)
          (print))

  (export
    try)

  (begin
    (define-syntax try
      (syntax-rules (catch)
        ((try 
           (exception-handler handler)
           body ...
           (catch exception-catcher))
         (begin
           (define handler (lambda (error) #f)) ; default: do nothing
           (call/cc
             (lambda (exit)
               (set! handler
                 (lambda (error)
                   (exception-catcher error)
                   (exit)))
               body ...))))))))

Example usage:

(import (scheme base)
        (print)
        (try-catch))

(println  "--start--")

(try
  (exception-handler oops)

  (define (divide a b)
    (if (zero? b)
      (oops "Division by zero")
      (println a "/" b " = " (inexact (/ a b)))))

  (divide 10 2)
  (divide 1 3)
  (divide 3 0)
  (println "This should not execute")

  (catch
    (lambda (error)
      (println "Hey, we caught an error: " error))))

(println "--end--")