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# exceptions.pl
# tchrist@convex.com
#
# This library is no longer being maintained, and is included for backward
# compatibility with Perl 4 programs which may require it.
# This legacy library is deprecated and will be removed in a future
# release of perl.
#
# In particular, this should not be used as an example of modern Perl
# programming techniques.
# Here's a little code I use for exception handling. It's really just
# glorfied eval/die. The way to use use it is when you might otherwise
# exit, use &throw to raise an exception. The first enclosing &catch
# handler looks at the exception and decides whether it can catch this kind
# (catch takes a list of regexps to catch), and if so, it returns the one it
# caught. If it *can't* catch it, then it will reraise the exception
# for someone else to possibly see, or to die otherwise.
#
# I use oddly named variables in order to make darn sure I don't conflict
# with my caller. I also hide in my own package, and eval the code in his.
#
# The EXCEPTION: prefix is so you can tell whether it's a user-raised
# exception or a perl-raised one (eval error).
#
# --tom
#
# examples:
# if (&catch('/$user_input/', 'regexp', 'syntax error') {
# warn "oops try again";
# redo;
# }
#
# if ($error = &catch('&subroutine()')) { # catches anything
#
# &throw('bad input') if /^$/;
sub catch {
package exception;
local($__code__, @__exceptions__) = @_;
local($__package__) = caller;
local($__exception__);
eval "package $__package__; $__code__";
if ($__exception__ = &'thrown) {
for (@__exceptions__) {
return $__exception__ if /$__exception__/;
}
&'throw($__exception__);
}
}
sub throw {
local($exception) = @_;
die "EXCEPTION: $exception\n";
}
sub thrown {
$@ =~ /^(EXCEPTION: )+(.+)/ && $2;
}
1;
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