Implemented constant identifier functionality

* SimpleParser optionally acceps a pointer to an ConstantMap containing string keys mapping to values
* Constants are handled in their own ConstantNode class derived from the standard Node class
* Operator precedence is now determined separated from the TokenType using a new PrecedenceLevel enum
** Conversion between tokens and their PrecedenceLevel is possible using the new utility function getPrecedence
* Added additional test cases for constant identifier resolutions

1 files changed, 8 insertions, 4 deletions

diff --git a/src/tree.h b/src/tree.h
index 68a31c1..0db1404 100644
--- a/src/tree.h
+++ b/src/tree.h
@@ -1,17 +1,20 @@
 #ifndef PARSER_SRC_NODE_H_
 #define PARSER_SRC_NODE_H_
 
-#include <vector>
-#include <string>
 #include <memory>
+#include <string>
+#include <vector>
 
 #include "nodes.h"
 
 namespace SimpleParser {
 
+typedef std::vector<std::unique_ptr<Node>> NodeCollection;
+
 class Tree {
 	public:
 		Tree(std::string);
+		Tree(std::string, const ConstantMap*);
 
 		double solve();
 		std::string print();
@@ -21,9 +24,10 @@ class Tree {
 		Node* addNode(Node**, Args&&... args);
 		Node* buildTree(std::string);
 
-		std::vector<std::unique_ptr<Node>> node_collection_;
-		Node* root_node_;
 		std::string term_;
+		Node* root_node_;
+		NodeCollection node_collection_;
+		const ConstantMap* constants_;
 };
 
 }