Evaluate terms recursively on application

1 files changed, 14 insertions, 1 deletions

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));
+    }
+
 }