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7c673cae | 1 | |
b32b8144 | 2 | // Copyright Oliver Kowalke 2016. |
7c673cae FG |
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 | ||
b32b8144 | 7 | #include <cstdio> |
7c673cae FG |
8 | #include <cstdlib> |
9 | #include <exception> | |
10 | #include <functional> | |
11 | #include <iostream> | |
12 | #include <memory> | |
13 | #include <sstream> | |
14 | ||
b32b8144 FG |
15 | #include <boost/context/continuation.hpp> |
16 | ||
17 | namespace ctx = boost::context; | |
7c673cae FG |
18 | |
19 | /* | |
20 | * grammar: | |
21 | * P ---> E '\0' | |
22 | * E ---> T {('+'|'-') T} | |
23 | * T ---> S {('*'|'/') S} | |
24 | * S ---> digit | '(' E ')' | |
25 | */ | |
26 | class Parser{ | |
27 | char next; | |
28 | std::istream& is; | |
29 | std::function<void(char)> cb; | |
30 | ||
31 | char pull(){ | |
32 | return std::char_traits<char>::to_char_type(is.get()); | |
33 | } | |
34 | ||
35 | void scan(){ | |
36 | do{ | |
37 | next=pull(); | |
38 | } | |
39 | while(isspace(next)); | |
40 | } | |
41 | ||
42 | public: | |
43 | Parser(std::istream& is_,std::function<void(char)> cb_) : | |
44 | next(), is(is_), cb(cb_) | |
45 | {} | |
46 | ||
47 | void run() { | |
48 | scan(); | |
49 | E(); | |
50 | } | |
51 | ||
52 | private: | |
53 | void E(){ | |
54 | T(); | |
55 | while (next=='+'||next=='-'){ | |
56 | cb(next); | |
57 | scan(); | |
58 | T(); | |
59 | } | |
60 | } | |
61 | ||
62 | void T(){ | |
63 | S(); | |
64 | while (next=='*'||next=='/'){ | |
65 | cb(next); | |
66 | scan(); | |
67 | S(); | |
68 | } | |
69 | } | |
70 | ||
71 | void S(){ | |
72 | if (isdigit(next)){ | |
73 | cb(next); | |
74 | scan(); | |
75 | } | |
76 | else if(next=='('){ | |
77 | cb(next); | |
78 | scan(); | |
79 | E(); | |
80 | if (next==')'){ | |
81 | cb(next); | |
82 | scan(); | |
83 | }else{ | |
84 | throw std::runtime_error("parsing failed"); | |
85 | } | |
86 | } | |
87 | else{ | |
88 | throw std::runtime_error("parsing failed"); | |
89 | } | |
90 | } | |
91 | }; | |
92 | ||
93 | int main() { | |
94 | try { | |
95 | std::istringstream is("1+1"); | |
7c673cae | 96 | // execute parser in new execution context |
b32b8144 | 97 | ctx::continuation source; |
7c673cae FG |
98 | // user-code pulls parsed data from parser |
99 | // invert control flow | |
b32b8144 FG |
100 | char c; |
101 | bool done = false; | |
102 | source=ctx::callcc( | |
103 | [&is,&c,&done](ctx::continuation && sink){ | |
104 | // create parser with callback function | |
105 | Parser p( is, | |
106 | [&sink,&c](char c_){ | |
107 | // resume main execution context | |
108 | c = c_; | |
109 | sink=sink.resume(); | |
110 | }); | |
111 | // start recursive parsing | |
112 | p.run(); | |
113 | // signal termination | |
114 | done = true; | |
115 | // resume main execution context | |
116 | return std::move(sink); | |
117 | }); | |
118 | while(!done){ | |
119 | printf("Parsed: %c\n",c); | |
120 | source=source.resume(); | |
7c673cae FG |
121 | } |
122 | std::cout << "main: done" << std::endl; | |
123 | return EXIT_SUCCESS; | |
b32b8144 | 124 | } catch (std::exception const& e) { |
7c673cae FG |
125 | std::cerr << "exception: " << e.what() << std::endl; |
126 | } | |
127 | return EXIT_FAILURE; | |
128 | } |