diff --git a/array/moon.pkg.json b/array/moon.pkg.json
index e45419ab0..ab16d6b1e 100644
--- a/array/moon.pkg.json
+++ b/array/moon.pkg.json
@@ -1,5 +1,3 @@
 {
-    "import": [
-      "moonbitlang/core/assertion"
-    ]
-}
\ No newline at end of file
+  "import": ["moonbitlang/core/assertion", "moonbitlang/core/math"]
+}
diff --git a/array/slice.mbt b/array/slice.mbt
new file mode 100644
index 000000000..4f970d9af
--- /dev/null
+++ b/array/slice.mbt
@@ -0,0 +1,47 @@
+// Copyright 2024 International Digital Economy Academy
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+priv struct ArraySlice[T] {
+  array : Array[T]
+  start : Int
+  end : Int
+}
+
+fn length[T](self : ArraySlice[T]) -> Int {
+  self.end - self.start
+}
+
+fn op_get[T](self : ArraySlice[T], index : Int) -> T {
+  self.array[self.start + index]
+}
+
+fn op_set[T](self : ArraySlice[T], index : Int, value : T) -> Unit {
+  self.array[self.start + index] = value
+}
+
+fn swap[T](self : ArraySlice[T], a : Int, b : Int) -> Unit {
+  self.array.swap(self.start + a, self.start + b)
+}
+
+fn reverse[T](self : ArraySlice[T]) -> Unit {
+  let mid_len = self.length() / 2
+  for i = 0; i < mid_len; i = i + 1 {
+    let j = self.length() - i - 1
+    self.swap(i, j)
+  }
+}
+
+fn slice[T](self : ArraySlice[T], start : Int, end : Int) -> ArraySlice[T] {
+  { array: self.array, start: self.start + start, end: self.start + end }
+}
diff --git a/array/sort.mbt b/array/sort.mbt
index 440d9a11a..351233f08 100644
--- a/array/sort.mbt
+++ b/array/sort.mbt
@@ -12,40 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-struct ArraySlice[T] {
-  array : Array[T]
-  start : Int
-  end : Int
-}
-
-fn length[T](self : ArraySlice[T]) -> Int {
-  self.end - self.start
-}
-
-fn op_get[T](self : ArraySlice[T], index : Int) -> T {
-  self.array[self.start + index]
-}
-
-fn op_set[T](self : ArraySlice[T], index : Int, value : T) -> Unit {
-  self.array[self.start + index] = value
-}
-
-fn swap[T](self : ArraySlice[T], a : Int, b : Int) -> Unit {
-  self.array.swap(self.start + a, self.start + b)
-}
-
-fn reverse[T](self : ArraySlice[T]) -> Unit {
-  let mid_len = self.length() / 2
-  for i = 0; i < mid_len; i = i + 1 {
-    let j = self.length() - i - 1
-    self.swap(i, j)
-  }
-}
-
-fn slice[T](self : ArraySlice[T], start : Int, end : Int) -> ArraySlice[T] {
-  { array: self.array, start: self.start + start, end: self.start + end }
-}
-
 /// Sorts the array
 /// 
 /// It's an in-place, unstable sort(it will reorder equal elements). The time complexity is O(n log n) in the worst case.
@@ -141,7 +107,7 @@ fn quick_sort[T](
     }
     let (pivot, partitioned) = partition(arr, cmp, pivot_index)
     was_partitioned = partitioned
-    balanced = min(pivot, len - pivot) >= len / 8
+    balanced = @math.minimum(pivot, len - pivot) >= len / 8
     if not(balanced) {
       limit -= 1
     }
@@ -183,29 +149,22 @@ fn get_limit(len : Int) -> Int {
   limit
 }
 
-fn min[T : Compare](a : T, b : T) -> T {
-  if a < b {
-    a
-  } else {
-    b
-  }
-}
-
 /// Try to sort the array with bubble sort.
 /// 
 /// It will only tolerate at most 8 unsorted elements. The time complexity is O(n).
 /// 
 /// Returns whether the array is sorted.
-fn try_bubble_sort[T](arr : ArraySlice[T], cmp : (T, T) -> Int) -> Bool {
-  let max_tries = 8
+fn try_bubble_sort[T](
+  arr : ArraySlice[T],
+  cmp : (T, T) -> Int,
+  ~max_tries : Int = 8
+) -> Bool {
   let mut tries = 0
   for i = 1; i < arr.length(); i = i + 1 {
-    let mut j = i
     let mut sorted = true
-    while j > 0 && cmp(arr[j - 1], arr[j]) > 0 {
+    for j = i; j > 0 && cmp(arr[j - 1], arr[j]) > 0; j = j - 1 {
       sorted = false
       arr.swap(j, j - 1)
-      j = j - 1
     }
     if not(sorted) {
       tries += 1
@@ -224,12 +183,8 @@ fn try_bubble_sort[T](arr : ArraySlice[T], cmp : (T, T) -> Int) -> Bool {
 /// Returns whether the array is sorted.
 fn bubble_sort[T](arr : ArraySlice[T], cmp : (T, T) -> Int) -> Unit {
   for i = 1; i < arr.length(); i = i + 1 {
-    let mut j = i
-    let mut sorted = true
-    while j > 0 && cmp(arr[j - 1], arr[j]) > 0 {
-      sorted = false
+    for j = i; j > 0 && cmp(arr[j - 1], arr[j]) > 0; j = j - 1 {
       arr.swap(j, j - 1)
-      j = j - 1
     }
   }
 }
diff --git a/priority_queue/priority_queue.mbt b/priority_queue/priority_queue.mbt
index 97ea42f97..e2783e88a 100644
--- a/priority_queue/priority_queue.mbt
+++ b/priority_queue/priority_queue.mbt
@@ -12,22 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-struct Cont[T] {
-  content : T
-  mut sibling : Node[T]
-  mut child : Node[T]
-}
-
-enum Node[T] {
-  Nil
-  Cons(Cont[T])
-}
 
-struct PriorityQueue[T] {
-  min : Bool
-  mut len : Int
-  mut top : Node[T]
-}
 
 /// Creates a new empty priority queue.
 /// 
@@ -66,11 +51,15 @@ pub fn PriorityQueue::from_array[T : Compare](
   arr : Array[T],
   ~min : Bool = false
 ) -> PriorityQueue[T] {
-  for i = 0, acc = (Nil : Node[T]); i < arr.length(); {
-    continue i + 1,
-      meld(acc, Cons({ content: arr[i], sibling: Nil, child: Nil }), min)
-  } else {
-    { min, len: arr.length(), top: acc }
+  // CR: bad formatting  
+  let len = arr.length()
+  for i = 0, acc = Node::Nil {
+    if i < len {
+      continue i + 1,
+        meld(acc, Cons({ content: arr[i], sibling: Nil, child: Nil }), min)
+    } else {
+      break { min, len, top: acc }
+    }
   }
 }
 
@@ -84,11 +73,12 @@ fn meld[T : Compare](x : Node[T], y : Node[T], min : Bool) -> Node[T] {
     (Nil, _) => y
     (_, Nil) => x
     (Cons(x_top), Cons(y_top)) =>
-      if if min {
+      // CR: bad formatting
+      if (if min {
         x_top.content < y_top.content
       } else {
         x_top.content > y_top.content
-      } {
+      }) {
         y_top.sibling = x_top.child
         x_top.child = y
         x
@@ -277,10 +267,7 @@ test "clear" {
 /// let is_empty = queue.is_empty() // true
 /// ```
 pub fn is_empty[T](self : PriorityQueue[T]) -> Bool {
-  match self.top {
-    Nil => true
-    _ => false
-  }
+  self.len == 0
 }
 
 test "is_empty" {
diff --git a/priority_queue/types.mbt b/priority_queue/types.mbt
new file mode 100644
index 000000000..84f1df77b
--- /dev/null
+++ b/priority_queue/types.mbt
@@ -0,0 +1,26 @@
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+priv struct Cont[T] {
+  content : T
+  mut sibling : Node[T]
+  mut child : Node[T]
+}
+
+priv enum Node[T] {
+  Nil
+  Cons(Cont[T])
+}
+
+struct PriorityQueue[T] {
+  min : Bool
+  mut len : Int
+  mut top : Node[T]
+}
diff --git a/vec/vec.mbt b/vec/vec.mbt
index 0f8dc366d..ac5ef1335 100644
--- a/vec/vec.mbt
+++ b/vec/vec.mbt
@@ -35,13 +35,12 @@ pub fn to_string[T : Show](self : Vec[T]) -> String {
     return "Vec::[]"
   }
   let first = self.buf[0]
-  for i = 1, init = "Vec::[\(first)"; ; {
-    if i < self.len {
-      let cur = self.buf[i]
-      continue i + 1, "\(init),\(cur)"
-    } else {
+  for i = 1, init = "Vec::[\(first)" {
+    if i >= self.len {
       break "\(init)]"
     }
+    let cur = self.buf[i]
+    continue i + 1, "\(init),\(cur)"
   }
 }