mirror of https://gitee.com/bigwinds/arangodb
145 lines
3.4 KiB
C++
145 lines
3.4 KiB
C++
|
|
// Copyright Oliver Kowalke 2014.
|
|
// Distributed under the Boost Software License, Version 1.0.
|
|
// (See accompanying file LICENSE_1_0.txt or copy at
|
|
// http://www.boost.org/LICENSE_1_0.txt)
|
|
|
|
#include <cstdlib>
|
|
#include <exception>
|
|
#include <functional>
|
|
#include <iostream>
|
|
#include <memory>
|
|
#include <sstream>
|
|
|
|
#include <boost/context/all.hpp>
|
|
|
|
namespace ctx = boost::context;
|
|
|
|
/*
|
|
* grammar:
|
|
* P ---> E '\0'
|
|
* E ---> T {('+'|'-') T}
|
|
* T ---> S {('*'|'/') S}
|
|
* S ---> digit | '(' E ')'
|
|
*/
|
|
class Parser{
|
|
char next;
|
|
std::istream& is;
|
|
std::function<void(char)> cb;
|
|
|
|
char pull(){
|
|
return std::char_traits<char>::to_char_type(is.get());
|
|
}
|
|
|
|
void scan(){
|
|
do{
|
|
next=pull();
|
|
}
|
|
while(isspace(next));
|
|
}
|
|
|
|
public:
|
|
Parser(std::istream& is_,std::function<void(char)> cb_) :
|
|
next(), is(is_), cb(cb_)
|
|
{}
|
|
|
|
void run() {
|
|
scan();
|
|
E();
|
|
}
|
|
|
|
private:
|
|
void E(){
|
|
T();
|
|
while (next=='+'||next=='-'){
|
|
cb(next);
|
|
scan();
|
|
T();
|
|
}
|
|
}
|
|
|
|
void T(){
|
|
S();
|
|
while (next=='*'||next=='/'){
|
|
cb(next);
|
|
scan();
|
|
S();
|
|
}
|
|
}
|
|
|
|
void S(){
|
|
if (isdigit(next)){
|
|
cb(next);
|
|
scan();
|
|
}
|
|
else if(next=='('){
|
|
cb(next);
|
|
scan();
|
|
E();
|
|
if (next==')'){
|
|
cb(next);
|
|
scan();
|
|
}else{
|
|
throw std::runtime_error("parsing failed");
|
|
}
|
|
}
|
|
else{
|
|
throw std::runtime_error("parsing failed");
|
|
}
|
|
}
|
|
};
|
|
|
|
int main() {
|
|
try {
|
|
std::istringstream is("1+1");
|
|
bool done=false;
|
|
std::exception_ptr except;
|
|
|
|
// execute parser in new execution context
|
|
boost::context::execution_context<char> source(
|
|
[&is,&done,&except](ctx::execution_context<char> sink,char){
|
|
// create parser with callback function
|
|
Parser p( is,
|
|
[&sink](char ch){
|
|
// resume main execution context
|
|
auto result = sink(ch);
|
|
sink = std::move(std::get<0>(result));
|
|
});
|
|
try {
|
|
// start recursive parsing
|
|
p.run();
|
|
} catch (...) {
|
|
// store other exceptions in exception-pointer
|
|
except = std::current_exception();
|
|
}
|
|
// set termination flag
|
|
done=true;
|
|
// resume main execution context
|
|
return sink;
|
|
});
|
|
|
|
// user-code pulls parsed data from parser
|
|
// invert control flow
|
|
auto result = source('\0');
|
|
source = std::move(std::get<0>(result));
|
|
char c = std::get<1>(result);
|
|
if ( except) {
|
|
std::rethrow_exception(except);
|
|
}
|
|
while( ! done) {
|
|
printf("Parsed: %c\n",c);
|
|
std::tie(source,c) = source('\0');
|
|
if (except) {
|
|
std::rethrow_exception(except);
|
|
}
|
|
}
|
|
|
|
std::cout << "main: done" << std::endl;
|
|
|
|
return EXIT_SUCCESS;
|
|
} catch ( std::exception const& e) {
|
|
std::cerr << "exception: " << e.what() << std::endl;
|
|
}
|
|
return EXIT_FAILURE;
|
|
}
|