129 lines
2.8 KiB
C++
129 lines
2.8 KiB
C++
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// Copyright Oliver Kowalke 2016.
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#include <cstdio>
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#include <cstdlib>
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#include <exception>
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#include <functional>
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#include <iostream>
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#include <memory>
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#include <sstream>
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#include <boost/context/continuation.hpp>
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namespace ctx = boost::context;
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/*
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* grammar:
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* P ---> E '\0'
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* E ---> T {('+'|'-') T}
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* T ---> S {('*'|'/') S}
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* S ---> digit | '(' E ')'
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*/
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class Parser{
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char next;
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std::istream& is;
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std::function<void(char)> cb;
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char pull(){
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return std::char_traits<char>::to_char_type(is.get());
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}
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void scan(){
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do{
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next=pull();
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}
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while(isspace(next));
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}
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public:
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Parser(std::istream& is_,std::function<void(char)> cb_) :
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next(), is(is_), cb(cb_)
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{}
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void run() {
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scan();
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E();
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}
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private:
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void E(){
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T();
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while (next=='+'||next=='-'){
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cb(next);
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scan();
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T();
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}
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}
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void T(){
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S();
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while (next=='*'||next=='/'){
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cb(next);
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scan();
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S();
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}
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}
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void S(){
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if (isdigit(next)){
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cb(next);
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scan();
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}
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else if(next=='('){
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cb(next);
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scan();
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E();
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if (next==')'){
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cb(next);
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scan();
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}else{
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throw std::runtime_error("parsing failed");
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}
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}
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else{
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throw std::runtime_error("parsing failed");
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}
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}
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};
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int main() {
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try {
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std::istringstream is("1+1");
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// execute parser in new execution context
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ctx::continuation source;
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// user-code pulls parsed data from parser
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// invert control flow
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char c;
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bool done = false;
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source=ctx::callcc(
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[&is,&c,&done](ctx::continuation && sink){
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// create parser with callback function
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Parser p( is,
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[&sink,&c](char c_){
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// resume main execution context
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c = c_;
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sink=sink.resume();
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});
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// start recursive parsing
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p.run();
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// signal termination
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done = true;
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// resume main execution context
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return std::move(sink);
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});
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while(!done){
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printf("Parsed: %c\n",c);
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source=source.resume();
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}
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std::cout << "main: done" << std::endl;
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return EXIT_SUCCESS;
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} catch (std::exception const& e) {
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std::cerr << "exception: " << e.what() << std::endl;
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}
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return EXIT_FAILURE;
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}
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