| 1 | |
|---|---|
| 2 | // Copyright Oliver Kowalke 2014. |
| 3 | // Distributed under the Boost Software License, Version 1.0. |
| 4 | // (See accompanying file LICENSE_1_0.txt or copy at |
| 5 | // http://www.boost.org/LICENSE_1_0.txt) |
| 6 | |
| 7 | #include <cctype> |
| 8 | #include <cstdio> |
| 9 | #include <exception> |
| 10 | #include <functional> |
| 11 | #include <iostream> |
| 12 | #include <sstream> |
| 13 | |
| 14 | #include <boost/coroutine2/all.hpp> |
| 15 | |
| 16 | class parser_error : public std::runtime_error { |
| 17 | public: |
| 18 | parser_error() : |
| 19 | std::runtime_error("parsing failed") { |
| 20 | } |
| 21 | }; |
| 22 | |
| 23 | /* |
| 24 | * grammar: |
| 25 | * P ---> E '\0' |
| 26 | * E ---> T {('+'|'-') T} |
| 27 | * T ---> S {('*'|'/') S} |
| 28 | * S ---> digit | '(' E ')' |
| 29 | */ |
| 30 | class Parser{ |
| 31 | char next; |
| 32 | std::istream& is; |
| 33 | std::function<void(char)> cb; |
| 34 | |
| 35 | char pull(){ |
| 36 | return std::char_traits<char>::to_char_type(c: is.get()); |
| 37 | } |
| 38 | |
| 39 | void scan(){ |
| 40 | do{ |
| 41 | next=pull(); |
| 42 | } |
| 43 | while(isspace(next)); |
| 44 | } |
| 45 | |
| 46 | public: |
| 47 | Parser(std::istream& is_,std::function<void(char)> cb_) : |
| 48 | next(), is(is_), cb(cb_) |
| 49 | {} |
| 50 | |
| 51 | void run() { |
| 52 | scan(); |
| 53 | E(); |
| 54 | } |
| 55 | |
| 56 | private: |
| 57 | void E(){ |
| 58 | T(); |
| 59 | while (next=='+'||next=='-'){ |
| 60 | cb(next); |
| 61 | scan(); |
| 62 | T(); |
| 63 | } |
| 64 | } |
| 65 | |
| 66 | void T(){ |
| 67 | S(); |
| 68 | while (next=='*'||next=='/'){ |
| 69 | cb(next); |
| 70 | scan(); |
| 71 | S(); |
| 72 | } |
| 73 | } |
| 74 | |
| 75 | void S(){ |
| 76 | if (std::isdigit(next)){ |
| 77 | cb(next); |
| 78 | scan(); |
| 79 | } |
| 80 | else if(next=='('){ |
| 81 | cb(next); |
| 82 | scan(); |
| 83 | E(); |
| 84 | if (next==')'){ |
| 85 | cb(next); |
| 86 | scan(); |
| 87 | }else{ |
| 88 | throw parser_error(); |
| 89 | } |
| 90 | } |
| 91 | else{ |
| 92 | throw parser_error(); |
| 93 | } |
| 94 | } |
| 95 | }; |
| 96 | |
| 97 | typedef boost::coroutines2::coroutine< char > coro_t; |
| 98 | |
| 99 | int main() { |
| 100 | try { |
| 101 | std::istringstream is("1+1"); |
| 102 | // invert control flow |
| 103 | coro_t::pull_type seq( |
| 104 | [&is]( coro_t::push_type & yield) { |
| 105 | Parser p( is, |
| 106 | [&yield](char ch){ |
| 107 | yield(ch); |
| 108 | }); |
| 109 | p.run(); |
| 110 | }); |
| 111 | // user-code pulls parsed data from parser |
| 112 | for(char c:seq){ |
| 113 | printf(format: "Parsed: %c\n",c); |
| 114 | } |
| 115 | std::cout << "\nDone"<< std::endl; |
| 116 | return EXIT_SUCCESS; |
| 117 | } catch ( std::exception const& ex) { |
| 118 | std::cerr << "exception: "<< ex.what() << std::endl; |
| 119 | } |
| 120 | return EXIT_FAILURE; |
| 121 | } |
| 122 | |
| 123 |