Nested matches don't reconstruct the original variable properly

[developedby]

Reproducing the behavior

I was writing a program with nested matches on the same variable and noticed that the interaction count was a bit high

def reverse(xs):
  fold xs with acc=[]:
    case List/Cons:
      return xs.tail(List/Cons(xs.head, acc))
    case List/Nil:
      return acc

def split(list, len):
  switch len:
    case 0:
      return ([], list)
    case _:
      match list:
        case List/Cons:
          (left, right) = split(list.tail, len-1)
          return (List/Cons(list.head, left), right)
        case List/Nil:
          return ([], [])

def range(start, end):
  switch start < end:
    case 0:
      return []
    case _:
      return List/Cons(start, range(start + 1, end))

def merge_sort(list, len):
  match list:
    case List/Cons:
      match list.tail:
        case List/Cons:
          new_len = len / 2
          (left, right) = split(list, new_len)
          return merge(merge_sort(left, new_len), merge_sort(right, len - new_len))
        case List/Nil:
          return [list.head]
    case List/Nil:
      return []

def merge(left, right):
  match left:
    case List/Cons:
      match right:
        case List/Cons:
          if (left.head <= right.head):
            return List/Cons(left.head, merge(left.tail, (right)))
          else:
            return List/Cons(right.head, merge(left, right.tail))
        case List/Nil:
          return left
    case List/Nil:
      return right

def main():
  len = 100
  list = reverse(range(1, len))
  sorted = merge_sort(list, len)
  return *

In merge_sort, changing (left, right) = split(list, new_len) to (left, right) = split(List/Cons(list.head, list.tail), new_len) reduces the number of interactions significantly, so it seems to not be reconstructing the list variable correctly across nested matches.

System Settings

• Bend: commit a0aa467

Additional context

No response