Using ruby-1.9, I just got the helpful exception "bin/pp-pretty:60: undefined (?...) sequence: / (RegexpError)". I don't know what it's complaining about since it's not telling me where inside the 70 line regexp it started failing.
When I write Perl, I get useful context like:
Reference to nonexistent named group in regex; marked by <-- HERE in m/
: [ \t\n]*
0x[0-9a-f]+ [ \t\n]* (?=\@) (?&object_data <-- HERE )