I am merely suggesting that it would be more efficient if JavaCC produced 'switch' statements for these rather than the nested 'if' statements.
So far, I haven't been able to determine how to modify the sqlgrammar.jj file to achieve this.
It's time for me to out myself. I wrote most of sqlgrammar.jj, along with a lot of the other Cloudscape/Derby language code. I no longer work on Cloudscape or Derby, but I'm still interested in it.
The code in SQLParser.java consists mostly of rules from sqlgrammar.jj and lookahead code. I suspect the massive nested if statements are for lookahead.
sqlgrammar.jj uses a single token of lookahead by default. The first implementation of sqlgrammar.jj used numeric lookahead to disambiguate the grammar. That is, where javacc would report that more tokens of lookahead were needed, I would put in LOOKAHEAD(2) (or 3 or 4, or whatever javacc suggested). This led to a very large parser.
The javacc development team told me that the size of the parser would be reduced significantly if, in those places where more than one token of lookahead is needed, we used semantic lookahead rather than numeric lookahead. What that means is that, where the grammar is ambiguous with a single token of lookahead, we use a hand-written method for lookahead rather than tell javacc to look ahead two or more tokens. When I made this change, the number of generated methods starting with "jj_" shrank significantly.
I suspect the ugly massive nested if statements in SQLParser.java have to do with lookahead. I thought that maybe someone had put in some numeric lookahead, but I didn't find any such thing when I looked through sqlgrammar.jj. It's possible that I missed something, though.
In any case, it would help to have the complete call stack for the methods in question. I am particularly interested in which grammar rules are calling these methods. Given that, I might be able to figure out what's going on by looking at sqlgrammar.jj
- Jeff Lichtman
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