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1 # exceptions.pl
2 # tchrist@convex.com
4 # This library is no longer being maintained, and is included for backward
5 # compatibility with Perl 4 programs which may require it.
7 # In particular, this should not be used as an example of modern Perl
8 # programming techniques.
11 # Here's a little code I use for exception handling. It's really just
12 # glorfied eval/die. The way to use use it is when you might otherwise
13 # exit, use &throw to raise an exception. The first enclosing &catch
14 # handler looks at the exception and decides whether it can catch this kind
15 # (catch takes a list of regexps to catch), and if so, it returns the one it
16 # caught. If it *can't* catch it, then it will reraise the exception
17 # for someone else to possibly see, or to die otherwise.
19 # I use oddly named variables in order to make darn sure I don't conflict
20 # with my caller. I also hide in my own package, and eval the code in his.
22 # The EXCEPTION: prefix is so you can tell whether it's a user-raised
23 # exception or a perl-raised one (eval error).
25 # --tom
27 # examples:
28 # if (&catch('/$user_input/', 'regexp', 'syntax error') {
29 # warn "oops try again";
30 # redo;
31 # }
33 # if ($error = &catch('&subroutine()')) { # catches anything
35 # &throw('bad input') if /^$/;
37 sub catch {
38 package exception;
39 local($__code__, @__exceptions__) = @_;
40 local($__package__) = caller;
41 local($__exception__);
43 eval "package $__package__; $__code__";
44 if ($__exception__ = &'thrown) {
45 for (@__exceptions__) {
46 return $__exception__ if /$__exception__/;
48 &'throw($__exception__);
52 sub throw {
53 local($exception) = @_;
54 die "EXCEPTION: $exception\n";
57 sub thrown {
58 $@ =~ /^(EXCEPTION: )+(.+)/ && $2;