Backtracking through the source

[Dan Sugalski]

Okay, here's a question for those of you with more experience at parsers 
than I have. (Which would be about everyone)

Is there any reasonable case where we would need to backtrack over 
successfully parsed source and redo the parsing? I'm not talking about the 
case where regular expressions run over text and ultimately fail, but 
rather cases where we need to chuck out part of what we have and restart?

                                        Dan

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Dan Sugalski                          even samurai
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                                      teddy bears get drunk