For those reading this thread, I could solve my problme by using ragel (http://www.cs.queensu.ca/~thurston/ragel/). You can define leaving actions but also 'any change' actions. It was also easier to include in a C++ project then lemon/flex. If my grammar becomes more complicated, I heard it is possible to make a good collaboration between ragel and lemon (ragel is then used as a tokenizer).
2007/10/25, Gaspard Bucher <[EMAIL PROTECTED]>: > > >>>> I do not understand why lemon waits for one more token when it has > > >>>> enough information to reduce > ... > > >>>> > > >>> I don't think you can. Why do you want to? Why not just go > > >>> ahead and send it the next token? > > >>> > > >> Most people find a way around this problem using white-space. This > > >> could be a solution but then my grammar will be filled with > > >> "white-space | nothing" rules and I thought Lemon could reduce when > > >> there is no other way out of the current stack as it is more elegant. > > >> > > >> > > LA(LR) is the answer - just drop Your's tokens as their arrive and give > > a chance for the parser to be LALR, not LR or SLR :) > > > > mak > > > Lookahead improves what we can do with a grammar, but when there is no > ambiguity, it should resolve without waiting for the next token. If > your grammar is so simple it's an SLR, why not treat it so and ease > the creation of grammars without needing to add "separator" tokens > just so there is a lookahead (most languages use ";" or white space > for that purpose). > > My grammar works with all "whitespace or nothing" rules, but I have to > be careful to avoid conflicts. When I write it without the whitespace > stuff (eaten in the tokenizer), I have no conflict. Simple example: > main ::= commands. > commands ::= . > commands ::= commands ws command. > command ::= variable EQUAL value. > variable ::= ws IDENTIFIER ws. > value ::= ws NUMBER ws. > ws ::= . > ws ::= WHITE. > > 2 parsing conflicts. > > Whithout whitespace stuff: > main ::= commands. > commands ::= . > commands ::= commands command. > command ::= variable EQUAL value. > variable ::= IDENTIFIER. > value ::= NUMBER. > > no conflicts, easier and cleaner. > > I know how to fix the first grammar, but you have to think of the > actual succession to avoid two "ws" from coming next to the other, > this thinking is not really related to the grammar from my point of > view. > > Gaspard > ----------------------------------------------------------------------------- To unsubscribe, send email to [EMAIL PROTECTED] -----------------------------------------------------------------------------
