Add string rules

src/rules/string.cpp

@@ -0,0 +1,31 @@
+#include "string.h"
+#include "transition_map.h"
+#include "char.h"
+#include "seq.h"
+
+namespace tree_sitter  {
+    namespace rules {
+        String::String(std::string value) : value(value) {};
+        
+        TransitionMap<Rule> String::transitions() const {
+            rule_ptr result = rule_ptr(new Char(value[0]));
+            for (int i = 1; i < value.length(); i++) {
+                result = rule_ptr(new Seq(result, rule_ptr(new Char(value[i]))));
+            }
+            return result->transitions();
+        }
+        
+        bool String::operator==(const Rule &rule) const {
+            const String *other = dynamic_cast<const String *>(&rule);
+            return (other != NULL) && (other->value == value);
+        }
+        
+        String * String::copy() const {
+            return new String(value);
+        }
+        
+        std::string String::to_string() const {
+            return value;
+        }        
+    }
+}