diff --git a/app/Constant.hs b/app/Constant.hs
new file mode 100644
index 0000000..dd48338
--- /dev/null
+++ b/app/Constant.hs
@@ -0,0 +1,7 @@
+module Constant where
+
+data Constant
+  = Atom Int
+  | Number Int
+  | Str String
+  deriving (Show, Eq, Ord)