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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 <cstdlib> | |
8 | #include <exception> | |
9 | #include <functional> | |
10 | #include <iostream> | |
11 | #include <memory> | |
12 | #include <sstream> | |
13 | ||
14 | #include <boost/context/all.hpp> | |
15 | ||
16 | namespace ctx = boost::context; | |
17 | ||
18 | /* | |
19 | * grammar: | |
20 | * P ---> E '\0' | |
21 | * E ---> T {('+'|'-') T} | |
22 | * T ---> S {('*'|'/') S} | |
23 | * S ---> digit | '(' E ')' | |
24 | */ | |
25 | class Parser{ | |
26 | char next; | |
27 | std::istream& is; | |
28 | std::function<void(char)> cb; | |
29 | ||
30 | char pull(){ | |
31 | return std::char_traits<char>::to_char_type(is.get()); | |
32 | } | |
33 | ||
34 | void scan(){ | |
35 | do{ | |
36 | next=pull(); | |
37 | } | |
38 | while(isspace(next)); | |
39 | } | |
40 | ||
41 | public: | |
42 | Parser(std::istream& is_,std::function<void(char)> cb_) : | |
43 | next(), is(is_), cb(cb_) | |
44 | {} | |
45 | ||
46 | void run() { | |
47 | scan(); | |
48 | E(); | |
49 | } | |
50 | ||
51 | private: | |
52 | void E(){ | |
53 | T(); | |
54 | while (next=='+'||next=='-'){ | |
55 | cb(next); | |
56 | scan(); | |
57 | T(); | |
58 | } | |
59 | } | |
60 | ||
61 | void T(){ | |
62 | S(); | |
63 | while (next=='*'||next=='/'){ | |
64 | cb(next); | |
65 | scan(); | |
66 | S(); | |
67 | } | |
68 | } | |
69 | ||
70 | void S(){ | |
71 | if (isdigit(next)){ | |
72 | cb(next); | |
73 | scan(); | |
74 | } | |
75 | else if(next=='('){ | |
76 | cb(next); | |
77 | scan(); | |
78 | E(); | |
79 | if (next==')'){ | |
80 | cb(next); | |
81 | scan(); | |
82 | }else{ | |
83 | throw std::runtime_error("parsing failed"); | |
84 | } | |
85 | } | |
86 | else{ | |
87 | throw std::runtime_error("parsing failed"); | |
88 | } | |
89 | } | |
90 | }; | |
91 | ||
92 | int main() { | |
93 | try { | |
94 | std::istringstream is("1+1"); | |
95 | bool done=false; | |
96 | std::exception_ptr except; | |
97 | ||
98 | // execute parser in new execution context | |
99 | boost::context::execution_context<char> source( | |
100 | [&is,&done,&except](ctx::execution_context<char> sink,char){ | |
101 | // create parser with callback function | |
102 | Parser p( is, | |
103 | [&sink](char ch){ | |
104 | // resume main execution context | |
105 | auto result = sink(ch); | |
106 | sink = std::move(std::get<0>(result)); | |
107 | }); | |
108 | try { | |
109 | // start recursive parsing | |
110 | p.run(); | |
111 | } catch (...) { | |
112 | // store other exceptions in exception-pointer | |
113 | except = std::current_exception(); | |
114 | } | |
115 | // set termination flag | |
116 | done=true; | |
117 | // resume main execution context | |
118 | return sink; | |
119 | }); | |
120 | ||
121 | // user-code pulls parsed data from parser | |
122 | // invert control flow | |
123 | auto result = source('\0'); | |
124 | source = std::move(std::get<0>(result)); | |
125 | char c = std::get<1>(result); | |
126 | if ( except) { | |
127 | std::rethrow_exception(except); | |
128 | } | |
129 | while( ! done) { | |
130 | printf("Parsed: %c\n",c); | |
131 | std::tie(source,c) = source('\0'); | |
132 | if (except) { | |
133 | std::rethrow_exception(except); | |
134 | } | |
135 | } | |
136 | ||
137 | std::cout << "main: done" << std::endl; | |
138 | ||
139 | return EXIT_SUCCESS; | |
140 | } catch ( std::exception const& e) { | |
141 | std::cerr << "exception: " << e.what() << std::endl; | |
142 | } | |
143 | return EXIT_FAILURE; | |
144 | } |