Arithmetic evaluation: Difference between revisions
Added C++ version using Boost.Spirit
m (→{{header|D}}: removed bug code and set incorrect tag, for no AST build) |
(Added C++ version using Boost.Spirit) |
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end Arithmetic_Evaluator;
=={{header|C++}}==
{{Works with|g++|4.1.2 20061115 (prerelease) (SUSE Linux)}}
'''Libraries:''' Boost.Spirit 1.8.4
#include <boost/spirit.hpp>
#include <boost/spirit/tree/ast.hpp>
#include <string>
#include <cassert>
#include <iostream>
#include <istream>
#include <ostream>
using boost::spirit::rule;
using boost::spirit::parser_tag;
using boost::spirit::ch_p;
using boost::spirit::real_p;
using boost::spirit::tree_node;
using boost::spirit::node_val_data;
// The grammar
struct parser: public boost::spirit::grammar<parser>
{
enum rule_ids { addsub_id, multdiv_id, value_id, real_id };
struct set_value
{
set_value(parser const& p): self(p) {}
void operator()(tree_node<node_val_data<std::string::iterator,
double> >& node,
std::string::iterator begin,
std::string::iterator end) const
{
node.value.value(self.tmp);
}
parser const& self;
};
mutable double tmp;
template<typename Scanner> struct definition
{
rule<Scanner, parser_tag<addsub_id> > addsub;
rule<Scanner, parser_tag<multdiv_id> > multdiv;
rule<Scanner, parser_tag<value_id> > value;
rule<Scanner, parser_tag<real_id> > real;
definition(parser const& self)
{
using namespace boost::spirit;
addsub = multdiv
>> *((root_node_d[ch_p('+')] | root_node_d[ch_p('-')]) >> multdiv);
multdiv = value
>> *((root_node_d[ch_p('*')] | root_node_d[ch_p('/')]) >> value);
value = real | inner_node_d[('(' >> addsub >> ')')];
real = leaf_node_d[access_node_d[real_p[assign_a(self.tmp)]][set_value(self)]];
}
rule<Scanner, parser_tag<addsub_id> > const& start() const
{
return addsub;
}
};
};
template<typename TreeIter>
double evaluate(TreeIter const& i)
{
double op1, op2;
switch (i->value.id().to_long())
{
case parser::real_id:
return i->value.value();
case parser::value_id:
case parser::addsub_id:
case parser::multdiv_id:
op1 = evaluate(i->children.begin());
op2 = evaluate(i->children.begin()+1);
switch(*i->value.begin())
{
case '+':
return op1 + op2;
case '-':
return op1 - op2;
case '*':
return op1 * op2;
case '/':
return op1 / op2;
default:
assert(!"Should not happen");
}
default:
assert(!"Should not happen");
}
return 0;
}
// the read/eval/write loop
int main()
{
parser eval;
std::string line;
while (std::cout << "Expression: "
&& std::getline(std::cin, line)
&& !line.empty())
{
typedef boost::spirit::node_val_data_factory<double> factory_t;
boost::spirit::tree_parse_info<std::string::iterator, factory_t> info =
boost::spirit::ast_parse<factory_t>(line.begin(), line.end(),
eval, boost::spirit::space_p);
if (info.full)
{
std::cout << "Result: " << evaluate(info.trees.begin()) << std::endl;
}
else
{
std::cout << "Error in expression." << std::endl;
}
}
};
=={{header|D}}==
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