diff --git a/parser.cpp b/parser.cpp
index dc4f98a..937388b 100644
--- a/parser.cpp
+++ b/parser.cpp
@@ -1 +1,31 @@
 #include "global.h"
+
+// base class
+class ExprAST {
+	public:
+		virtual ~ExprAST() {}
+};
+
+// class for double
+class DoubleExprAST : public ExprAST {
+	double Val;
+
+	public:
+		DoubleExprAST(double Val) : Val(Val) {}
+};
+
+// class for integer
+class IntegerExprAST : public ExprAST {
+	long Val;
+
+	public:
+		IntegerExprAST(long Val) : Val(Val) {}
+};
+
+// class for variable 
+class VariableExprAST : public ExprAST {
+	std::string Name;
+
+	public:
+		VariableExprAST(const std::string &Name) : Name(Name) {}
+};
\ No newline at end of file