Added expression statement

src/Statement.h

@@ -3,19 +3,28 @@
 
 #include <iostream>
 
+#include "Token.h"
+#include "Expression.h"
+
 using namespace std;
 
 class Statement {
 public:
     enum Kind {
+        EXPRESSION,
         INVALID
     };
 
 private:
     Kind kind;
+    Token token;
+    shared_ptr<Expression> expression;
 
 public:
-    Statement(Kind kind);
+    Statement(Kind kind, Token token, shared_ptr<Expression> expression);
+    Token getToken();
+    shared_ptr<Expression> getExpression();
+    bool isValid();
     string toString();
 };