On 3/26/2012 1:22 AM, Brian Budge wrote:
Hi all -
I'm trying to transition my grammar from something like this:
simple_expr = _int | '(' >> full_expr >> ')' ; sum_expr = simple_expr | (simple_expr >> '+' >> simple_expr)[_ret = _1 + _2] ; ...
to something like
sum_expr = simple_expr >> *(sum_expr >> '+' >> sum_expr) ;
I have full grammars coded up for essentially all integer operations that could be done in C. I extended one of the simple AST examples that Joel de Guzman has written, by adding the bitwise ops and ternary operations. I'm not entirely sure why (not a grammar/parser guru), but the latter grammer is far more efficient to parse using spirit than the former. I remember writing grammars more like the first back when I used bison, but I understand the kind of parser is different (LR vs recursive descent).
Iteration is always faster than recursion in an RD parser like Spirit.
Anyway, on to my question. I am fine using the second type of grammar, but I've timed the parsing and evaluation of my little calculator, and AST creation and desctruction actually dwarfs parsing time. I wonder if using phoenix could speed up evaluation, and also how exactly something like the "plus" operator could be evaluated in this curried context? I've tried many searches in google, but haven't found the magic example.
What do you mean by "speed up evaluation"? Do you mean interpretation of your expressions? FYI, there's a separate Spirit mailing list. I suggest posting Spirit related support requests there: http://boost-spirit.com/home/feedback-and-support/ Also, please post more info. E.g. timing results, test code, etc. Regards, -- Joel de Guzman http://www.boostpro.com http://boost-spirit.com