[antlr-interest] Changes don't affect AST but require code regenration of tree parser?

Raphael Reitzig r_reitzi at cs.uni-kl.de
Fri Aug 1 12:35:14 PDT 2008


Hi all!

Yesterday, I realized that I could spare a parser rule and needed one  
extra possibility in another rule in a rather simple gramar. After the  
changes, however, no other ASTs can be created than before. No more,  
no less.

However, after I generated parser code, even the simplest examples  
won't be accepted anymore. Tree gramar won't read a token it always  
had, stating "No rule viable". I swore and searched and swore and  
despaired - until I reminded myself of the "Clean and rebuild all if  
anything is strange" mantra. I generated all code again, including the  
tree walker. Note that tree gramar never changed! Though, now  
everything works perfectly again.

What happened there? Why did an internal change in parser rules (even  
lexer rules should not have been affected) render the genereated tree  
walker code useless?
I suspect token definitions to have a hand in this, but why should  
they have changed?

Regards

Raphael

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