How can you help someone see the beauty and benefit of Typed FP without asking them to just trust you and spend a few months with it? I used to dismiss this as

How can you help someone see the beauty and benefit of Typed FP without asking them to just trust you and spend a few months with it? I used to dismiss this as academic noodling till I got tired of OO and started going back to my procedural roots with just plain functions organized into namespaces. I was pretty happy with it till the codebase grew to a point I couldn't keep track of the flow of data. Objects help you to some extent here since they group related values into one instance, but I didn't want objects anymore. This was when I started seeing references to OCaml, especially "Why ML/OCaml are good for writing compilers" (http://flint.cs.yale.edu/cs421/case-for-ml.html http://flint.cs.yale.edu/cs421/case-for-ml.html), and also saw a presentation by a programmer I respected where he built a general game playing engine in OCaml. Seeing someone use it for practical, advanced programming was the first catalyst. Then Jordan Walke mentioned somewhere that he first prototyped React in OCaml, and shortly after they released ReasonML. The type system was amazing. All values are typed, even complex nested structures have a type. There are variants which mean I can express different shapes of the same value using types, and the compiler will tell me if I ever forget to handle a particular case of this variant. I've been programming with Reason/OCaml for about six months now, and Typed Immutable Programming still takes me more time than just gluing together a pack of cards with imperative code. But once the code is written, it sits on an iron-clad foundation. Most systems as they grow start to fold under its own weight, but here the accretion of code is an almost unmitigated good thing. It means my system's cognitive wealth is increasing without an exponential increase in maintenance cost. But how can you help someone understand all this in a single conversation? A lot of people come to this because they worked on systems with pain points that Typed FP can address. But for most others who haven't had that sort of clarifying experience, what can you tell them to give it the non-trivial amount of effort it requires?