diff --git a/compiler/erg_common/lib.rs b/compiler/erg_common/lib.rs
index 08db9016..ed50f82f 100644
--- a/compiler/erg_common/lib.rs
+++ b/compiler/erg_common/lib.rs
@@ -118,3 +118,8 @@ where
     }
     Ok(v)
 }
+
+pub fn unique_in_place<T: Eq + std::hash::Hash + Clone>(v: &mut Vec<T>) {
+    let mut uniques = Set::new();
+    v.retain(|e| uniques.insert(e.clone()));
+}
diff --git a/compiler/erg_common/set.rs b/compiler/erg_common/set.rs
index 64272882..08a132f0 100644
--- a/compiler/erg_common/set.rs
+++ b/compiler/erg_common/set.rs
@@ -141,8 +141,8 @@ impl<T: Hash + Eq> Set<T> {
     }
 
     #[inline]
-    pub fn insert(&mut self, value: T) {
-        self.elems.insert(value);
+    pub fn insert(&mut self, value: T) -> bool {
+        self.elems.insert(value)
     }
 
     #[inline]