From 8434ac98a01346c0f995b011a06a145fdab79192 Mon Sep 17 00:00:00 2001
From: Hyeonung Baek <wiserlix@gmail.com>
Date: Sun, 13 Feb 2022 21:10:25 +0900
Subject: [PATCH] (Re)add recursion support

---
 eval.ml | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/eval.ml b/eval.ml
index 1985479..14b65a3 100644
--- a/eval.ml
+++ b/eval.ml
@@ -285,7 +285,14 @@ let rec eval env ast =
           begin match args with
             | [] -> f
             | a::args ->
-              let env = Env.bind (var, aux a) env in
+              let itself = match v with Var v -> Some v | _ -> None in
+              let env =
+                (* binding itself into env for recursion *)
+                Option.fold
+                  ~none: env ~some: (fun v -> Env.bind (v, f) env)
+                  itself
+                |> Env.bind (var, aux a)
+              in
               eval env @@ Apply (e, args)
           end
         | External f ->