The example I gave was contrived. I frequently find myself modeling much of my logic as a series of data transformations. The more I can model logic like this,

The example I gave was contrived. I frequently find myself modeling much of my logic as a series of data transformations. The more I can model logic like this, the easier it is to test. For what it's worth, your example doesn't map 1-to-1 to the intention of what I wrote. Doing it in a more imperative style, I'd have to write emails = list() for user in users: emails.push(user.email) res = sendEmail emails if res.IsError: Error("Error sending emails") else: res (excuse my pseudo Python)