Added AstOptimizer.

example/calc3.cc

@@ -49,11 +49,12 @@ int main(int argc, const char** argv)
         "  ~_               <-  [ \t\r\n]*                        "
         );
 
-    parser.enable_ast(true);
+    parser.enable_ast();
 
     auto expr = argv[1];
     shared_ptr<Ast> ast;
     if (parser.parse(expr, ast)) {
+        ast = AstOptimizer(true).optimize(ast);
         ast->print();
         cout << expr << " = " << eval(*ast) << endl;
         return 0;

example/pl0.cc

@@ -8,6 +8,7 @@
 #include <peglib.h>
 #include <fstream>
 #include <iostream>
+#include <sstream>
 
 using namespace peglib;
 using namespace std;
@@ -49,52 +50,71 @@ auto grammar = R"(
     ~_         <- [ \t\r\n]*
 )";
 
+string format_error_message(const string& path, size_t ln, size_t col, const string& msg) {
+    stringstream ss;
+    ss << path << ":" << ln << ":" << col << ": " << msg << endl;
+    return ss.str();
+}
+
 struct Environment
 {
-    Environment(shared_ptr<Environment> outer = nullptr) : outer(outer) {}
+    Environment(shared_ptr<Environment> outer = nullptr)
+        : outer_(outer) {}
+
+    bool has_value(const string& ident) const {
+        return has_constant(ident) || has_variable(ident);
+    }
+
+    bool has_variable(const string& ident) const {
+        if (variables.find(ident) != variables.end()) {
+            return true;
+        } else if (!outer_) {
+            return false;
+        }
+        return outer_->has_variable(ident);
+    }
 
     int get_value(const string& ident) const {
-        try {
+        return has_constant(ident) ? get_constant(ident) : get_variable(ident);
-            return get_constant(ident);
-        } catch (...) {
-            return get_variable(ident);
-        }
     }
 
     void set_variable(const string& ident, int val) {
         if (variables.find(ident) != variables.end()) {
             variables[ident] = val;
-        } else if (outer) {
+            return;
-            return outer->set_variable(ident, val);
-        } else {
-            throw runtime_error("undefined variable");
-        }
-    }
-
-    int get_constant(const string& ident) const {
-        if (constants.find(ident) != constants.end()) {
-            return constants.at(ident);
-        } else if (outer) {
-            return outer->get_constant(ident);
-        } else {
-            throw runtime_error("undefined constants");
-        }
-    }
-
-    int get_variable(const string& ident) const {
-        if (variables.find(ident) != variables.end()) {
-            return variables.at(ident);
-        } else if (outer) {
-            return outer->get_variable(ident);
-        } else {
-            throw runtime_error("undefined variable");
         }
+        outer_->set_variable(ident, val);
     }
 
     map<string, int>             constants;
     map<string, int>             variables;
     map<string, shared_ptr<Ast>> procedures;
-    shared_ptr<Environment>      outer;
+
+private:
+    bool has_constant(const string& ident) const {
+        if (constants.find(ident) != constants.end()) {
+            return true;
+        } else if (!outer_) {
+            return false;
+        }
+        return outer_->has_constant(ident);
+    }
+
+    int get_constant(const string& ident) const {
+        if (constants.find(ident) != constants.end()) {
+            return constants.at(ident);
+        }
+        return outer_->get_constant(ident);
+    }
+
+    int get_variable(const string& ident) const {
+        if (variables.find(ident) != variables.end()) {
+            return variables.at(ident);
+        }
+        return outer_->get_variable(ident);
+    }
+
+    shared_ptr<Environment> outer_;
 };
 
 struct Interpreter
@@ -164,7 +184,13 @@ private:
     void exec_assignment(const shared_ptr<Ast> ast, shared_ptr<Environment> env) {
         // assignment <- ident ':=' _ expression
         const auto& ident = ast->nodes[0]->token;
-        auto val = eval(ast->nodes[1], env);
+        if (!env->has_variable(ident)) {
+            string msg = "undefined variable '" + ident + "'...";
+            string s = format_error_message(ast->path, ast->line, ast->column, msg);
+            throw runtime_error(s);
+        }
+        auto expr = ast->nodes[1];
+        auto val = eval(expr, env);
         env->set_variable(ident, val);
     }
 
@@ -185,8 +211,8 @@ private:
     void exec_if(const shared_ptr<Ast> ast, shared_ptr<Environment> env) {
         // if <- 'IF' _ condition 'THEN' _ statement
         auto cond = eval_condition(ast->nodes[0], env);
-        auto stmt = ast->nodes[1];
         if (cond) {
+            auto stmt = ast->nodes[1];
             exec(stmt, env);
         }
     }
@@ -288,7 +314,9 @@ private:
                     break;
                 case '/':
                     if (rval == 0) {
-                        throw runtime_error("divide by 0 error");
+                        string msg = "divide by 0 error";
+                        string s = format_error_message(ast->path, ast->line, ast->column, msg);
+                        throw runtime_error(s);
                     }
                     val = val / rval;
                     break;
@@ -298,7 +326,13 @@ private:
     }
 
     int eval_ident(const shared_ptr<Ast> ast, shared_ptr<Environment> env) {
-        return env->get_value(ast->token);
+        const auto& ident = ast->token;
+        if (!env->has_value(ident)) {
+            string msg = "undefined variable '" + ident + "'...";
+            string s = format_error_message(ast->path, ast->line, ast->column, msg);
+            throw runtime_error(s);
+        }
+        return env->get_value(ident);
     }
 
     int eval_number(const shared_ptr<Ast> ast, shared_ptr<Environment> env) {
@@ -326,6 +360,7 @@ int main(int argc, const char** argv)
         return 1;
     }
 
+    // Read a source file into memory
     auto path = argv[1];
     vector<char> source;
     if (!read_file(path, source)) {
@@ -333,21 +368,34 @@ int main(int argc, const char** argv)
         return -1;
     }
 
+    // Setup a PEG parser
     peg parser(grammar);
-    parser.enable_ast(false, { "program", "statement", "statements", "term", "factor" });
+    parser.enable_ast();
+    parser.log = [&](size_t ln, size_t col, const string& err_msg) {
+        cerr << format_error_message(path, ln, col, err_msg) << endl;
+    };
 
+    // Parse the source and make an AST
     shared_ptr<Ast> ast;
     if (parser.parse_n(source.data(), source.size(), ast, path)) {
+        vector<string> filters = { "program", "statement", "statements", "term", "factor" };
+        ast = AstOptimizer(false, filters).optimize(ast);
+
         if (argc > 2 && string("--ast") == argv[2]) {
             ast->print();
         }
+
+        // Run the AST
+        try {
             Interpreter interp;
             auto env = make_shared<Environment>();
             interp.exec(ast, env);
+        } catch (const runtime_error& e) {
+            cerr << e.what() << endl;
+        }
         return 0;
     }
 
-    cout << "syntax error..." << endl;
     return -1;
 }
 

language/culebra.h

@@ -90,7 +90,7 @@ inline peglib::peg& get_parser()
             throw std::logic_error("invalid peg grammar");
         }
 
-        parser.enable_ast(true, { "PARAMETERS", "ARGUMENTS", "OBJECT", "ARRAY" });
+        parser.enable_ast();
     }
 
     return parser;
@@ -924,6 +924,7 @@ inline bool run(
         };
 
         if (parser.parse_n(expr, len, ast, path.c_str())) {
+            ast = peglib::AstOptimizer(true, { "PARAMETERS", "ARGUMENTS", "OBJECT", "ARRAY" }).optimize(ast);
             val = Eval(debugger).eval(*ast, env);
             return true;
         }

peglib.h

@@ -1990,7 +1990,7 @@ struct Ast
     const std::string                 original_name;
     const bool                        is_token;
     const std::string                 token;
-    const std::vector<std::shared_ptr<Ast>> nodes;
+    std::vector<std::shared_ptr<Ast>> nodes;
     std::shared_ptr<Ast>              parent_node;
 #ifndef PEGLIB_NO_CONSTEXPR_SUPPORT
     const unsigned int                tag;
@@ -2028,11 +2028,9 @@ private:
 
 inline const Ast& Ast::get_smallest_ancestor() const {
     assert(nodes.size() <= 1);
-
     if (nodes.empty()) {
         return *this;
     }
-
     return nodes[0]->get_smallest_ancestor();
 }
 
@@ -2040,6 +2038,37 @@ inline void Ast::print() const {
     AstPrint().print(*this);
 }
 
+struct AstOptimizer
+{
+    AstOptimizer(bool optimize_nodes, const std::vector<std::string>& filters = {})
+        : optimize_nodes_(optimize_nodes)
+        , filters_(filters) {}
+
+    std::shared_ptr<Ast> optimize(std::shared_ptr<Ast> original, std::shared_ptr<Ast> parent = nullptr) {
+
+        auto found = std::find(filters_.begin(), filters_.end(), original->name) != filters_.end();
+        bool opt = optimize_nodes_ ? !found : found;
+
+        if (opt && original->nodes.size() == 1) {
+            auto child = optimize(original->nodes[0], parent);
+            return std::make_shared<Ast>(*child, original->name.c_str());
+        }
+
+        auto ast = std::make_shared<Ast>(*original);
+        ast->parent_node = parent;
+        ast->nodes.clear();
+        for (auto node : original->nodes) {
+            auto child = optimize(node, ast);
+            ast->nodes.push_back(child);
+        }
+        return ast;
+    }
+
+private:
+    const bool                     optimize_nodes_;
+    const std::vector<std::string> filters_;
+};
+
 /*-----------------------------------------------------------------------------
  *  peg
  *---------------------------------------------------------------------------*/
@@ -2193,14 +2222,11 @@ public:
         }
     }
 
-    peg& enable_ast(bool optimize_nodes, const std::initializer_list<std::string>& filters = {}) {
+    peg& enable_ast() {
         for (auto& x: *grammar_) {
             const auto& name = x.first;
             auto& rule = x.second;
 
-            auto found = std::find(filters.begin(), filters.end(), name) != filters.end();
-            bool opt = optimize_nodes ? !found : found;
-
             if (!rule.action) {
                 auto is_token = rule.is_token;
                 rule.action = [=](const SemanticValues& sv) {
@@ -2209,13 +2235,9 @@ public:
                         return std::make_shared<Ast>(sv.path, line.first, line.second, name.c_str(), std::string(sv.s, sv.n));
                     }
 
-                    std::shared_ptr<Ast> ast;
-                    if (opt && sv.size() == 1) {
-                        ast = std::make_shared<Ast>(*sv[0].get<std::shared_ptr<Ast>>(), name.c_str());
-                    } else {
                     auto line = line_info(sv.ss, sv.s);
-                        ast = std::make_shared<Ast>(sv.path, line.first, line.second, name.c_str(), sv.transform<std::shared_ptr<Ast>>());
+                    auto ast = std::make_shared<Ast>(sv.path, line.first, line.second, name.c_str(), sv.transform<std::shared_ptr<Ast>>());
-                    }
+
                     for (auto node: ast->nodes) {
                         node->parent_node = ast;
                     }