Arithmetic evaluation: Difference between revisions
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m (Moved to Arith cat) |
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{{libheader|Boost.Spirit}}1.8.4
<cpp>
////////////////////////////////////////////////////////////////////////////
using namespace std;
using namespace boost::spirit;
{
member1 val;
};
struct calculator : public grammar<calculator, calc_closure::context_t>
{
template <typename ScannerT>
struct definition
{
definition(calculator const& self)
top = expression[self.val = arg1];
expression
= term[expression.val =
>>
)
= factor[term.val = arg1]
>> *( ('*' >> factor[term.val *= arg1])
| ('/' >> factor[term.val /= arg1])
)
;
factor
= ureal_p[factor.val = arg1]
| '(' >> expression[factor.val = arg1] >> ')'
| ('-' >> factor[factor.val = -arg1])
| ('+' >> factor[factor.val = arg1])
;
typedef rule<ScannerT, calc_closure::context_t> rule_t;
rule_t expression, term, factor;
rule<ScannerT> const&
start() const { return top; }
};
////////////////////////////////////////////////////////////////////////////
// Main program
////////////////////////////////////////////////////////////////////////////
int
main()
{
cout << "/////////////////////////////////////////////////////////\n\n";
cout << "\t\tExpression parser using Phoenix...\n\n";
cout << "/////////////////////////////////////////////////////////\n\n";
cout << "Type an expression...or [q or Q] to quit\n\n";
calculator calc; // Our parser
string str;
while (getline(cin, str))
{
if (str.empty() || str[0] == 'q' || str[0] == 'Q')
break;
double n = 0;
parse_info<> info = parse(str.c_str(), calc[var(n) = arg1], space_p);
// calc[var(n) = arg1] invokes the calculator and extracts
// the result of the computation. See calculator grammar
cout << "-------------------------\n";
cout << "Parsing succeeded\n";
cout << "-------------------------\n";
cout << "-------------------------\n";
cout << "Parsing failed\n";
cout << "stopped at: \": " << info.stop << "\"\n";
cout << "-------------------------\n";
}
}
}
</cpp>
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