Put rule transitions in LR namespace

src/compiler/grammar/grammar.cpp

@@ -0,0 +1,24 @@
+#include "grammar.h"
+
+using namespace std;
+
+namespace tree_sitter {
+    Grammar::Grammar(const std::initializer_list<std::pair<const std::string, rules::rule_ptr>> &rules) :
+        rules(rules),
+        start_rule_name(rules.begin()->first) {}
+
+    const rules::rule_ptr Grammar::rule(const std::string &name) const {
+        auto iter = rules.find(name);
+        return (iter == rules.end()) ?
+            rules::rule_ptr(nullptr) :
+            iter->second;
+    }
+    
+    vector<string> Grammar::rule_names() const {
+        vector<string> result;
+        for (auto pair : rules) {
+            result.push_back(pair.first);
+        }
+        return result;
+    }
+}