diff --git a/ast.ml b/ast.ml
index 8db8724..4b49ed0 100644
--- a/ast.ml
+++ b/ast.ml
@@ -61,6 +61,10 @@ let print ast =
     | Nexternal e -> pr "(extern %s)" e
 
     | Var v -> pr "%s" v
+    | Let (v, Nfunction (args, e)) ->
+      pr "(define (%s" v;
+      List.iter (pr " %s") args;
+      pr ") "; aux e; pr ")"
     | Let (v, e) ->
       pr "(define %s " v; aux e; pr ")"
     | Letin (v, e, f) ->
diff --git a/eval.ml b/eval.ml
index 4e9c8d6..0a5e022 100644
--- a/eval.ml
+++ b/eval.ml
@@ -329,6 +329,7 @@ and apply global env expr args =
     begin match args with
       | [] -> f
       | args ->
+        (* bind arguments to variables *)
         let rec aux e = function
           | [], [] -> [], [], e
           | vars, [] -> vars, [], e
diff --git a/parser.ml b/parser.ml
index 5a7be02..c420626 100644
--- a/parser.ml
+++ b/parser.ml
@@ -177,9 +177,13 @@ and nothing seq =
 and let_global seq =
   let _, seq = ident "let" seq in
   let id, seq = any_ident seq in
+  let args, seq = more any_ident seq in
   let _, seq = token Token.Equal seq in
   let e, seq = expr min_int seq in
-  Let (id, e), seq
+  (if args = []
+   then Let (id, e)
+   else Let (id, Nfunction (args, e))),
+  seq
 
 (* expr := level
  *       | let_value
diff --git a/todo.md b/todo.md
new file mode 100644
index 0000000..85ba1bf
--- /dev/null
+++ b/todo.md
@@ -0,0 +1,5 @@
+# Todo
+
+- macro
+- implementing custom operator
+- abstract stack machine & compiler