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Improve `with-handlers' an exceptions description.

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This commit is contained in:
Eli Barzilay 2013-07-16 03:32:03 -04:00
parent 8a065aa256
commit c11ec1f137
1 changed files with 11 additions and 6 deletions
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17
racket.html.markdown
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@ -375,12 +375,17 @@ m ; => '#hash((b . 2) (a . 1) (c . 3)) <-- no `d'
;;; Exceptions
;; To catch an exception, use the `with-handlers' form
;; To throw an exception use `raise'
(with-handlers
([(lambda (v) (equal? v "infinity"))
(lambda (exn) +inf.0)])
(raise "infinity"))
;; To catch exceptions, use the `with-handlers' form
(with-handlers ([exn:fail? (lambda (exn) 999)])
(+ 1 "2")) ; => 999
(with-handlers ([exn:break? (lambda (exn) "no time")])
(sleep 3)
"phew") ; => "phew", but if you break it => "no time"
;; Use `raise' to throw exceptions or any other value
(with-handlers ([number? ; catch numeric values raised
identity]) ; return them as plain values
(+ 1 (raise 2))) ; => 2
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 6. Mutation