2011/4/7 Littlefield, Tyler
Hello all: Sorry for all the questions; I am kind of easing into boost and finding cool things i can do with it, as well as uses for a couple of projects. Eventually I would like to write a small scripting language using boost::spirit, just to do it and get the practice using it. As a starting point, I wrote a quick calculator (that just does small single operations like x+x, x*x, etc).
You can find the calculator examples in your BOOST_ROOT/libs/spirit/example/qi Now i have two questions. 1) My rule seems to be off. the first number comes
through clearly, but no matter what I put in, I always get the first number and then a 42.
Obvoiusly, it's because you messed up the order of members of 'calculation' struct and how the attributes are propogated to it. Let's take a look: BOOST_FUSION_ADAPT_STRUCT( calculation, (int, a) (int, b) (char, op) ) // operandA, operandB, operator crule %= (int_ >> (char_('+')|char_('-')|char_('*')|char_('/')) >> int_); // operandA, operator, operandB Noticed the order? So just change it into: BOOST_FUSION_ADAPT_STRUCT(calculation, (int, a)(char, op)(int, b)) then it'll work as expected. BTW, you used "cin >> str;" to get the line, it can extract the string before any space, you may want to use "getline(cin, str)" here. 2) How would I go about extending this to implement order of operations,
parenthases, and longer operations (like 3+3*3)?
Take a look at those examples.
I'm going to try to implement a small function table so I can do tan(3), so I assume I will need nultiple rules, how might that be accomplished?
You may want to use nabialek-trick: http://boost-spirit.com/home/articles/qi-example/nabialek-trick/ Besides, there's a dedicated Spirit mailing-list, and a good website (above). HTH