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I understand what you are saying. I'm not sure how your points are at odds with the OOP counterpart I describe though. The essence of your response seems to be

I understand what you are saying. I'm not sure how your points are at odds with the OOP counterpart I describe though. The essence of your response seems to be "because we want to use a pure FP paradigm" to which _I_ would add "despite a clear downside to which F# has the capacity to avoid". If the framework only expects every `Model` to contain 2 methods (`view`, `update`) and never any more (which is the case), I see no reason at all to adopt the Elm architecture. The interface for `update/view/model` is well-defined and un-changing. It's clearly sitting on the wrong side of the expression problem. The program loop could work exactly the same no? Just re-organize: let (model',cmd') = program.update msg state to: let (model', cmd') = state.update msg // I'm not sure where/how program fits in My question is truly as simple as trying to figure out the advantage of the chosen semantics (in F# - I don't know Elm). It can't possibly just be "because we want to stay on the Functional programming realm" can it? Immutability can be achieved in any paradigm. Forgive me if I am coming off overly controversial - I don't mean to be. https://guide.elm-lang.org/webapps/structure.html https://guide.elm-lang.org/webapps/structure.html - Even here in the "MVC" section the documentation _recommends_ you organize your project according to type (containing the `view` and `update` functions). This is very-much akin to my critique. If you reach the point in your project above you have essentially regressed back to OOP (in FP clothes).

reverseblade2 6y ago
let (model', cmd') = state.update msg In order to write that you have to pin a reference to the state. But state is something that has to flow. Sure you can pin it to a ref, make it mutable and change the state but then nothing prevents you to change the state arbitrarily e.g. from a command. I believe yes the answer is because we want to stay on the FP realm. FP imposes some restrictions to keep our sanity. So not having a reference to the state and making it immutable is one of those restrictions.
- kingdomcome50 6y ago
  > In order to write that you have to pin a reference to the state Forgive my ignorance, but why is that the case? Isn't `state` being passed into the loop? Mutability is orthogonal to the question of where one defines a unit of behavior. Maybe an immutable object is not possible to achieve in F#, but one could certainly imagine the concept of an immutable type with methods. My question is more about the modes of organization: Large unions vs discrete modules and how they affect how one's ability to change a program over time. If you say that the architecture was chosen out of a purest sense of FP, then fair enough. I can understand why someone would go that route. Just had to know.

reverseblade2 6y ago

let (model', cmd') = state.update msg In order to write that you have to pin a reference to the state. But state is something that has to flow. Sure you can pin it to a ref, make it mutable and change the state but then nothing prevents you to change the state arbitrarily e.g. from a command. I believe yes the answer is because we want to stay on the FP realm. FP imposes some restrictions to keep our sanity. So not having a reference to the state and making it immutable is one of those restrictions.

kingdomcome50 6y ago
> In order to write that you have to pin a reference to the state Forgive my ignorance, but why is that the case? Isn't `state` being passed into the loop? Mutability is orthogonal to the question of where one defines a unit of behavior. Maybe an immutable object is not possible to achieve in F#, but one could certainly imagine the concept of an immutable type with methods. My question is more about the modes of organization: Large unions vs discrete modules and how they affect how one's ability to change a program over time. If you say that the architecture was chosen out of a purest sense of FP, then fair enough. I can understand why someone would go that route. Just had to know.