Fixed backtrack problem.

lint/cmdline/peglint.vcxproj

@@ -58,7 +58,7 @@
       <WarningLevel>Level3</WarningLevel>
       <Optimization>Disabled</Optimization>
       <PreprocessorDefinitions>WIN32;_DEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
-      <AdditionalIncludeDirectories>..</AdditionalIncludeDirectories>
+      <AdditionalIncludeDirectories>../..</AdditionalIncludeDirectories>
     </ClCompile>
     <Link>
       <SubSystem>Console</SubSystem>
@@ -75,7 +75,7 @@
       <FunctionLevelLinking>true</FunctionLevelLinking>
       <IntrinsicFunctions>true</IntrinsicFunctions>
       <PreprocessorDefinitions>WIN32;NDEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
-      <AdditionalIncludeDirectories>..</AdditionalIncludeDirectories>
+      <AdditionalIncludeDirectories>../..</AdditionalIncludeDirectories>
     </ClCompile>
     <Link>
       <SubSystem>Console</SubSystem>
@@ -88,4 +88,4 @@
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>
-</Project>
+</Project>

peglib.h

@@ -221,6 +221,16 @@ struct SemanticValues : protected std::vector<SemanticValue>
         return this->transform(beg, end, [](const SemanticValue& v) { return v.get<T>(); });
     }
 
+    void rewind(const char* s) {
+        auto it = rbegin();
+        while (it != rend() && it->s >= s) {
+            ++it;
+        }
+        if (it != rbegin()) {
+            erase(it.base());
+        }
+    }
+
 private:
     template <typename F>
     auto transform(F f) const -> vector<typename std::remove_const<decltype(f(SemanticValue()))>::type> {
@@ -410,13 +420,14 @@ struct Context
 {
     const char*                                  path;
     const char*                                  s;
-    size_t                                       l;
+    const size_t                                 l;
 
     const char*                                  error_pos;
     const char*                                  message_pos;
     std::string                                  message; // TODO: should be `int`.
 
-    size_t                                       def_count;
+    const size_t                                 def_count;
+    const bool                                   enablePackratParsing;
     std::vector<bool>                            cache_register;
     std::vector<bool>                            cache_success;
 
@@ -432,6 +443,7 @@ struct Context
         , error_pos(nullptr)
         , message_pos(nullptr)
         , def_count(def_count)
+        , enablePackratParsing(enablePackratParsing)
         , cache_register(enablePackratParsing ? def_count * (l + 1) : 0)
         , cache_success(enablePackratParsing ? def_count * (l + 1) : 0)
         , stack_size(0)
@@ -440,7 +452,7 @@ struct Context
 
     template <typename T>
     void packrat(const char* s, size_t def_id, size_t& len, any& val, T fn) {
-        if (cache_register.empty()) {
+        if (!enablePackratParsing) {
             fn(val);
             return;
         }
@@ -611,6 +623,7 @@ public:
             const auto& rule = *ope_;
             auto len = rule.parse(s + i, n - i, sv, c, dt);
             if (fail(len)) {
+                sv.rewind(s + i);
                 break;
             }
             i += len;

test/test.cc

@@ -251,6 +251,21 @@ TEST_CASE("Backtracking test", "[general]")
     REQUIRE(count == 1); // Skip second time
 }
 
+TEST_CASE("Backtracking with AST", "[general]")
+{
+    peg parser(R"(
+        S <- A? B (A B)* A
+        A <- 'a'
+        B <- 'b'
+    )");
+
+    parser.enable_ast();
+    shared_ptr<Ast> ast;
+    bool ret = parser.parse("ba", ast);
+    REQUIRE(ret == true);
+    REQUIRE(ast->nodes.size() == 2);
+}
+
 TEST_CASE("Octal/Hex value test", "[general]")
 {
     peglib::peg parser(