diff --git a/app/Lexer.hs b/app/Lexer.hs
new file mode 100644
index 0000000..cdf1d19
--- /dev/null
+++ b/app/Lexer.hs
@@ -0,0 +1,10 @@
+module Lexer where
+
+data Token = Plus
+           | Minus
+           | Multiply
+           | Divide
+           | Integer Int
+           | LBrace
+           | RBrace
+           deriving Show
diff --git a/simple-arithmetic-compiler.cabal b/simple-arithmetic-compiler.cabal
index f2f4b2a..7ba5860 100644
--- a/simple-arithmetic-compiler.cabal
+++ b/simple-arithmetic-compiler.cabal
@@ -52,7 +52,7 @@ executable simple-arithmetic-compiler
     main-is:          Main.hs
 
     -- Modules included in this executable, other than Main.
-    -- other-modules:
+    other-modules:    Lexer
 
     -- LANGUAGE extensions used by modules in this package.
     -- other-extensions: