[gravypod]

I'd not say this is a feature of functional programming. This is a feature of Object Oriented elements being included in fp languages.

These are the same things we were going to happen when using Java and C++ years ago.

You can even see similar graphics here: https://docs.oracle.com/javase/tutorial/java/concepts/object...

I remember there was another in this tutorial that shared more with the image in this post. Although this is the same idea. You're just hiding Objects in Objects.

[lmm]

The difference is that a "layer interpreter" in functional style is just a pure function that transforms values to values, so it's very easy to test in a very direct way. And we have laws that guarantee that composition works correctly (i.e. the interpretation of a composition is the composition of the interpretations). Whereas it's a lot fiddlier to confirm that an object that uses other objects behaves correctly (you have to mock the inner objects), and virtually impossible to determine whether composition behaves correctly since the object's internal state is opaque.

[mickronome]

Thank you for writing 'functional style' and not 'functional language'. While the latter is usually, and quite naturally, better at expressing the former, there is usually a lot to gain simply by adapting the style to the issue at hand, which not _necessarily_ implies changing languages.

What follows is not necessarily of high value, I'm simply a working programmer since 20 odd years that's bit weary and sad that the craft appears to be stuck in a rut by getting stuck between an unnecessarily theory-less reality and a nirvana of unrealistic purity. It's - maybe - a backdrop to explain why I felt a need to thank you for your choice of words with so many words.

If we consider every problem has a shape (loose analogue for the set of constraints thet uniquely identifies a problem) , then for every shape, or class of shapes a problem embodies, there exists an in some sense - ideal - language to solve that problem. Few are however the times when you only need to solve one discrete class of problem in the same system, but in case of mismatc between language and shape, it's quite common the only solution brought forth is to change languages. Unfortunately that solution is rarely feasible for a multitude of reasons. In the fallout after having to keep working with the same non-ideal language, the entire idea that there are multiple ways - styles - to express a solution is sadly often lost. This would not necessarily happen if the idea that style matters enough that when we can't change language, we could, and would still change how we express the solution within our constraintd. Be it in any language or paradigm under the sun, we need the words from them all to be able to talk about our problems, as they are either unique or already solved.

[lmm]

The functional mindset views programming languages almost as families or toolkits: solutions should be written in the language of the domain, and successively interpreted to the language of the machine. Thus you don't change language to adapt to a different domain; rather you write a new domain sublanguage. The challenge is if anything to avoid going too far in the other direction; lisp in particular is notorious for being so flexible that no two people's lisp styles end up compatible.

I think there's a happy medium to be found. As my programming career has progressed I've become more and more in favour of Scala for everything - I think it gets pretty close to striking the right balance between the flexibility to express any given domain and the consistency to allow programmers to collaborate.

[barrkel]

The architectural pattern of implementing a program in a language close to the domain and iteratively transforming it into something that can be consumed in an execution environment long predates OO, and is in fact the principle behind compilers.

It came out in a different guise under Model Driven Architecture and executable specifications a few years back.

It'll pop up again in the future under some other name. The principle is as old as computing itself, though.

[eternalban]

> At the center of the application, semantics are encoded using the language of the domain model.

Say pg/psql.

> Beginning at the center, each layer is translated into one or more languages with lower-level semantics.

ORM mapping into Java?

> At the outermost layer of the application, the final language is that of the application’s environment — for example, the programming language’s standard library or foreign function interface, or possibly even machine instructions.

Or maybe even html+javascript.

Congratulations, you have (re-)invented the layered architecture.

[ubertaco]

>> At the center of the application, semantics are encoded using the language of the domain model.

> Say pg/psql.

Minor nitpick: "pg/psql" is not the language of the domain model. The language of the domain model is stuff like "A car is considered 'All-Wheel Drive' if the drivetrain delivers power to any/all of the axles, not just a single axle."

pg/psql requires translating that domain-model language into something (roughly) like

    set @awdCars := (select * from cars where drivetrainAxles >= allAxles)

[asciihacker]

    > Beginning at the center, each layer is translated into one or more languages with lower-level semantics.
    ORM mapping into Java?

An ORM would not have lower-level semantics would it?

[eternalban]

Lower in this context does not mean 'weaker'. An ORM maps between the lower level relational semantics and higher level object semantics.

[nickpsecurity]

Nah, if it's this topic, more like how AllegroCache object-database maps high-level commands on database manipulation in LISP that look similar to regular manipulation of objects to lower-level LISP that's more efficient which compiles to machine code that efficiently implements those structures on target CPU. Typical ORM's take two things that are very different from one another and never intended to match up then try to force them to match up. Not a great example.

Here's another for you: Lilith. Assembly is messy. So, they create a stack machine (M-code - P-code variant) that idealizes it plus easily compiles to it or implementable at CPU level. Then, they create a 3GL called Modula-2 that's closer to how they express programs but has underlying model of M-code and outputs M-code. In theory, they could go further like 4GL's did to build domain-specific languages that abstract away boiler plate with code generation but still consistent with Modula-2 style. And so on. Easier in functional languages but I'm sure you can see the pattern.

That's what you usually get out of the DSL or interpreter approaches if using a LISP, Haskell, or imperative language designed to make it easy. Languages designed to do them well. A series of transforms with a certain amount of consistency from start to finish. These days, there's even safety techniques for the transforms that they didn't have way back in the day. :)

[lmm]

Only if you can express your domain well in SQL. For most domains you can't, you need a... domain specific language.

[wtetzner]

Well, he says this pretty early on:

> The onion architecture can be implemented in object-oriented programming or in functional programming.

[nickpsecurity]

It started in CompSci sort of in parallel with Bob Barton's B5000 designed for ALGOL, the work of Dijkstra, McCarthy's LISP, Hamilton's USL, and so on. They each came up with abstract ways to specify or implement programs for greater correctness, readability, safety, and composition. Using provers, compilers, or manual work, these would be converted into specific code at lower levels or final, machine level in ways intended to preserve high-level properties. Dijkstra went furthest in THE where the did hierarchical layers that were loop free. In parallel, there was a group trying to figure out how to compile Monte Carlo simulations on their computers in a way that was easy to specify. Their Simula was first, OOP language. SimScript, a RAND language, was a discrete, event simulation tool that came out with many similarities to emerging Simula and OOP. The main programmer had already been exposed to ALGOL, loved the heck out of it, and took some inspiration from SimScript.

Hierarchical layering, careful interfaces, dynamic programming, functional composition, refinement, event-based simulation... all showing up before Simula was published in 1967. So, it anywhere from depended on to came after many things with properties key to OOP's effectiveness. It certainly got a powerful technique for structuring programs started but didn't happen in isolation or even necessarily ahead in many ways. It surprised me that needs of Monte Carlo apps is what led to OOP but not that ALGOL60 was involved.

http://phobos.ramapo.edu/~ldant/oop/simula_history.pdf

https://www.rand.org/content/dam/rand/pubs/research_memorand...

[munro]

The graphics are both indeed circular which makes them look alike, but the meaning is completely different.

In the OO graphic, it's representing a single cell organism, hence the circle. This is not the complete application. It's encapsulating the state of a single process, and only through externally interacting with the organism can the state be inspected & changed, all based on time.

The circles in the FP represent domain logic, the inner most circle represents your high level business logic. This is the complete application. Then translating your logic to the next lower level domain, until the physical hardware layer is reached and your program becomes something concrete and runnable. This layering resembles an onion, which is also a circle.

[gravypod]

Them being circular has nothing to do with what are they representing. They are showing off the idea of hiding implementation through abstracting it. This is the exact same concept that both of these photos are showing.

[munro]

> Them being circular has nothing to do with what are they representing.

Please read my comment, that's what it says right after the first comma.

> They are showing off the idea of hiding implementation through abstracting it. This is the exact same concept that both of these photos are showing.

My comment breaks down how the hiding of implementation is completely different between the two, can you point what you think is incorrect so we're not talking past each other? Or is there anything you need clarification on?

[gclaramunt]

As far I understand, the difference is that in OO you normally transform data as you jump from layer to layer, here what do you have assembled is a simple program that will be interpreted by the lower layer