with-exception-handler -- r7rs Definition

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Kind

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procedure;

Implemented by

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• with-exception-handler (from vonuvoli);

Procedure signature

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Procedure variants:

• (((handler exception-handler) (thunk procedure-0)) -> (any))
  • inputs:
    • handler of type exception-handler;
    • thunk of type procedure-0;
  • output: a value of type any;

Exports

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• scheme:base -- (scheme base);

Exports recursive

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• scheme -- (scheme);

Description

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(with-exception-handler handler thunk)

Domain: It is an error if handler does not accept one argument. It is also an error if thunk does not accept zero arguments.

The with-exception-handler procedure returns the results of invoking thunk. Handler is installed as the current exception handler in the dynamic environment used for the invocation of thunk.

(call-with-current-continuation
 (lambda (k)
  (with-exception-handler
   (lambda (x)
    (display "condition: ")
    (write x)
    (newline)
    (k 'exception))
   (lambda ()
    (+ 1 (raise 'an-error))))))
         ===>  exception
; and prints:  condition: an-error

(with-exception-handler
 (lambda (x)
  (display "something went wrong\n"))
 (lambda ()
  (+ 1 (raise 'an-error))))
; prints:      something went wrong

After printing, the second example then raises another exception.

---

The text herein was sourced and adapted as described in the "R7RS attribution of various text snippets" appendix.

Examples

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Examples 1

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1. evaluating:

(call-with-current-continuation
 (lambda (k)
  (with-exception-handler
   (lambda (x)
    (display "condition: ")
    (write x)
    (newline)
    (k 'exception))
   (lambda ()
    (+ 1 (raise 'an-error))))))

2. stdout output:

condition: an-error

3. raises:

exception

Examples 2

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1. evaluating:

(with-exception-handler
 (lambda (x)
  (display "something went wrong\n"))
 (lambda ()
  (+ 1 (raise 'an-error))))

2. stdout output:

something went wrong

Referenced-types

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• exception-handler;
• procedure-0;
• any;