From bb16c10c4c851018ee5aa905a719abdfd8fdc861 Mon Sep 17 00:00:00 2001
From: Arnaud Bailly <arnaud.bailly@iohk.io>
Date: Wed, 25 Sep 2024 08:17:09 +0200
Subject: Evaluate terms recursively on application

---
 rust/src/lambda.rs | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/rust/src/lambda.rs b/rust/src/lambda.rs
index b05bd22..9b2a6f2 100644
--- a/rust/src/lambda.rs
+++ b/rust/src/lambda.rs
@@ -17,7 +17,14 @@ pub fn run(arg: &str) -> String {
 
 fn interpret(arg: &Value) -> Value {
     match arg {
-        Value::App(l, r) => apply(&interpret(l), &interpret(r)),
+        Value::App(l, r) => {
+            let result = apply(&interpret(l), &interpret(r));
+            if result == *arg {
+                result
+            } else {
+                interpret(&result)
+            }
+        }
         other => other.clone(),
     }
 }
@@ -94,4 +101,10 @@ mod lambda_test {
         assert_eq!(Value::Num(12), interpret(&value));
     }
 
+    #[test]
+    fn reduction_is_applied_until_normal_form_is_reached() {
+        let value = parse("((((lam y (lam x (lam y (x y)))) 13) (lam x x)) 11)");
+        assert_eq!(Value::Num(11), interpret(&value));
+    }
+
 }
-- 
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