How to avoid conflicts in grammar?

Parsers: What are good ways to avoid conflicts in grammar?

• I have a grammar file — https://github.com/itrelease/fubar-script/blob/jsast/src/grammar.js but I get conflicts — https://gist.github.com/2597616 and I don't really know how to solve this. If someone could explain me it would be helpful.

• Answer:

  These conflicts imply that your grammar is ambiguous. That is, for some strings the grammar can be parsed in multiple ways by the parser because at some point more than one rule is applicable during the derivation of the parse tree. This is obviously disastrous because it makes your compiler's behavior dependent on the parser itself, so the parser raises an error instead. A good way to design a grammar is to incrementally add features and resolve any conflicts that turn up. In your case, all the conflicts appear between the FormalParameterList and PrimaryExpressionNoBrace non-terminals whenever there is a THIS or IDENTIFIER token in the string. You should probably be able to resolve this by creating a new non-terminal that parses the conflicting cases and using it in both FormalParameterList and PrimaryExpressionNoBrace.