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Mark H Weaver <mhw@xxxxxxxxxx> wrote: > For example, constraining yourself to an LL(1) grammar probably rules > out a more elegant presentation. Hmm, I've always heard complaints about grammars that are NOT LL(1). The obvious way to make sure it's LL(1)... is to specify it as LL(1). > Another big problem is the amount of redundancy in this grammar. We can look for that, at least! > I suspect that the key to simplifying this grammar (apart from moving > away from ANTLR for purposes of the specification) is to choose a > different set of non-terminals. That may be true, but I'm not sure what they would be. I'll have to think about it, and if you have any other specific examples, please post! > One more nit while I'm on this subject: In the BNF conventions section, > you write "a sweet-expression reader MUST act as if it preprocessed its > input as follows", but as far as I can tell it's not actually possible > to implement this as a preprocessor. This "preprocessing" must be > interleaved with parser, because several syntactic elements affect the > preprocessing. For example, the <* and *> markers manipulate the > preprocessor's stack, and yet you need a full parser to recognize those > markers. You don't need a full parser. ANTLR, for example, really does do manipulations of the parsing stack in its *lexer* when it sees <* and *>. In fact, there's no way in ANTLR for the parser to send messages back to the lexer; ANTLR lexes the entire stream before it calls the parser. I appreciate the comments. I'll have to think about this some more. --- David A. Wheeler