Fauna: Add serial num id to collection

script.fql

Reduce(
  Lambda((acc, value) =>
    Let(
      {
        count: Add(Select("count", acc), 1),
        update: Update(value, { data: { id: Var("count") } })
      },
      {
        count: Var("count")
      }
    )
  ),
  { count: 0 },
  Documents(Collection("applications")) //Target Collection
)