1 files changed, 125 insertions, 0 deletions
diff --git a/libs/context/example/execution_context/parser.cpp b/libs/context/example/execution_context/parser.cpp
new file mode 100644
index 000000000..da16fee96
--- /dev/null
+++ b/libs/context/example/execution_context/parser.cpp
@@ -0,0 +1,125 @@
+
+//          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 <functional>
+#include <iostream>
+#include <sstream>
+
+#include <boost/context/all.hpp>
+
+/*
+ * 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 (std::isdigit(next)){
+         cb(next);
+         scan();
+      }
+      else if(next=='('){
+         cb(next); 
+         scan();
+         E();
+         if (next==')'){
+             cb(next); 
+             scan();
+         }else{
+             exit(2);
+         }
+      }
+      else{
+         exit(3);
+      }
+   }
+};
+
+int main() {
+    std::istringstream is("1+1");
+    bool done=false;
+    char c;
+
+    // create handle to main execution context
+    boost::context::execution_context main_ctx(
+        boost::context::execution_context::current() );
+
+    // executes parser in new execution context
+    boost::context::execution_context parser_ctx(
+        boost::context::fixedsize_stack(),
+        [&main_ctx,&is,&c,&done](){
+            // create parser with callback function
+            Parser p( is,
+                      [&main_ctx,&c](char ch){
+                          c=ch;
+                          // resume main execution context
+                          main_ctx.resume();
+                      });
+            // start recursive parsing
+            p.run();
+            done=true;
+            main_ctx.resume();
+        });
+
+    // user-code pulls parsed data from parser
+    // invert control flow
+    parser_ctx.resume();
+    do {
+        printf("Parsed: %c\n",c);
+        parser_ctx.resume();
+    } while( ! done);
+
+    std::cout << "main: done" << std::endl;
+
+    return EXIT_SUCCESS;
+}