Railway Oriented Programming

Abstract

Railway Oriented Programming (ROP) is an analogy invented by F#’s premier educator, Scott Wlaschin. It describes a programming philosophy in which we embrace errors as a core part of program flow, rather than exiling them to the separate domain of exception handling. Scott didn’t invent the technique, but he did invent the analogy, which has helped many F# developers understand this initially daunting but powerful technique. Although I’ve titled this chapter according to Scott’s analogy, I’m going to use a slightly different way to describe what is going on. Rest assured, I am still talking about ROP. I just thought it might be interesting to look at it using an alternative mental image. You may want to treat this chapter as a companion piece to Scott’s own description of ROP, which you can find (among a cornucopia of other invaluable material) at https://fsharpforfunandprofit.com.