From c2d00aa762cd08dcc4f71ab52fe41d1ef5df6a9e Mon Sep 17 00:00:00 2001
From: pca006132 <john.lck40@gmail.com>
Date: Thu, 15 Jul 2021 16:51:55 +0800
Subject: [PATCH] occur check

---
 nac3core/src/typecheck/test_typedef.rs | 7 +++++++
 nac3core/src/typecheck/typedef.rs      | 4 ++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/nac3core/src/typecheck/test_typedef.rs b/nac3core/src/typecheck/test_typedef.rs
index 4eeb1cd8..f411f689 100644
--- a/nac3core/src/typecheck/test_typedef.rs
+++ b/nac3core/src/typecheck/test_typedef.rs
@@ -242,6 +242,13 @@ mod test {
         (("v1", "v2"), "No such attribute b")
         ; "record obj merge"
     )]
+    #[test_case(2,
+        &[
+            ("v1", "List[v2]"),
+        ],
+        (("v1", "v2"), "Recursive type is prohibited.")
+        ; "recursive type for lists"
+    )]
     fn test_invalid_unification(
         variable_count: u32,
         unify_pairs: &[(&'static str, &'static str)],
diff --git a/nac3core/src/typecheck/typedef.rs b/nac3core/src/typecheck/typedef.rs
index 03b3ae28..645a96bc 100644
--- a/nac3core/src/typecheck/typedef.rs
+++ b/nac3core/src/typecheck/typedef.rs
@@ -216,7 +216,7 @@ impl Unifier {
                         drop(ty_b);
                         if let TypeEnum::TSeq { map: map2 } = &mut *ty_b_cell.as_ref().borrow_mut()
                         {
-                            // unify them to map1
+                            // unify them to map2
                             for (key, value) in map1.iter() {
                                 if let Some(ty) = map2.get(key) {
                                     self.unify(*ty, *value)?;
@@ -377,7 +377,7 @@ impl Unifier {
     fn occur_check(&self, a: TypeIndex, b: Type) -> Result<(), String> {
         let i_b = self.unification_table.borrow_mut().probe_value(b);
         if a == i_b {
-            return Err("Recursive type detected!".to_owned());
+            return Err("Recursive type is prohibited.".to_owned());
         }
         let ty = self.type_arena.borrow().get(i_b.0).unwrap().clone();
         let ty = ty.borrow();