Suggestion: Add possibility to write calculate expression inside code block

Currently, when writing a calculation, the third argument is the expression.

For example:

calculate :full_name, :string, expr(first_name <> " " <> last_name)

This looks clean and simple, but when the calculation is a little bit more complex, it starts to get a little bit messy:

    calculate :total_feedbacks_in_class_this_month,
              :integer,
              expr(
                count(feedbacks,
                  query: [
                    filter:
                      expr(
                        class_id == ^arg(:class_id) and
                          inserted_at >= fragment("date_trunc('month', now())") and
                          inserted_at <
                            fragment("date_trunc('month', now()) + interval '1 month'")
                      )
                  ]
                )
              ) do
      argument :class_id, :string, allow_nil?: false
    end

I was wondering if we could add an alternative way to write the calculations where we can not write the third argument and alternatively add it inside the calculate code block.

Something like this:

   calculate :total_feedbacks_in_class_this_month, :integer do
      expression expr(
        count(feedbacks,
          query: [
            filter:
              expr(
                class_id == ^arg(:class_id) and
                  inserted_at >= fragment("date_trunc('month', now())") and
                  inserted_at < fragment("date_trunc('month', now()) + interval '1 month'")
              )
          ]
        )
      )

      argument :class_id, :string, allow_nil?: false
    end

At least for me, this seems easier to read.