lib/perl5/5.6.1/exceptions.pl

   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;