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(condition-case EXPRESSION CLAUSE ...)syntax

Evaluates EXPRESSION and handles any exceptions that are covered by CLAUSE ..., where CLAUSE should be of the following form:


If provided, VARIABLE will be bound to the signaled exception object. BODY ... is executed when the exception is a property- or composite condition with the kinds given KIND ... (unevaluated). If no clause applies, the exception is re-signaled in the same dynamic context as the condition-case form.

(define (check thunk)
  (condition-case (thunk)
    [(exn file) (print "file error")]
    [(exn) (print "other error")]
    [var () (print "something else")] ) )

(check (lambda () (open-input-file "")))   ; -> "file error"
(check (lambda () some-unbound-variable))  ; -> "othererror"
(check (lambda () (signal 99)))            ; -> "something else"

(condition-case some-unbound-variable
  ((exn file) (print "ignored")) )      ; -> signals error