| 1 | # exceptions.pl |
| 2 | # tchrist@convex.com |
| 3 | # |
| 4 | # This library is no longer being maintained, and is included for backward |
| 5 | # compatibility with Perl 4 programs which may require it. |
| 6 | # |
| 7 | # In particular, this should not be used as an example of modern Perl |
| 8 | # programming techniques. |
| 9 | # |
| 10 | # |
| 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. |
| 18 | # |
| 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. |
| 21 | # |
| 22 | # The EXCEPTION: prefix is so you can tell whether it's a user-raised |
| 23 | # exception or a perl-raised one (eval error). |
| 24 | # |
| 25 | # --tom |
| 26 | # |
| 27 | # examples: |
| 28 | # if (&catch('/$user_input/', 'regexp', 'syntax error') { |
| 29 | # warn "oops try again"; |
| 30 | # redo; |
| 31 | # } |
| 32 | # |
| 33 | # if ($error = &catch('&subroutine()')) { # catches anything |
| 34 | # |
| 35 | # &throw('bad input') if /^$/; |
| 36 | |
| 37 | sub catch { |
| 38 | package exception; |
| 39 | local($__code__, @__exceptions__) = @_; |
| 40 | local($__package__) = caller; |
| 41 | local($__exception__); |
| 42 | |
| 43 | eval "package $__package__; $__code__"; |
| 44 | if ($__exception__ = &'thrown) { |
| 45 | for (@__exceptions__) { |
| 46 | return $__exception__ if /$__exception__/; |
| 47 | } |
| 48 | &'throw($__exception__); |
| 49 | } |
| 50 | } |
| 51 | |
| 52 | sub throw { |
| 53 | local($exception) = @_; |
| 54 | die "EXCEPTION: $exception\n"; |
| 55 | } |
| 56 | |
| 57 | sub thrown { |
| 58 | $@ =~ /^(EXCEPTION: )+(.+)/ && $2; |
| 59 | } |
| 60 | |
| 61 | 1; |