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 /^$/; 36 37sub catch { 38 package exception; 39 local($__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($__exception__); 49 } 50} 51 52sub throw { 53 local($exception) = @_; 54 die "EXCEPTION: $exception\n"; 55} 56 57sub thrown { 58 $@ =~ /^(EXCEPTION: )+(.+)/ && $2; 59} 60 611; 62