schema VS malli

Plumatic schema (https://github.com/plumatic/schema) , or friends I might be wrong, but I think schema might make more sense to you coming from the F# world (might be wrong)

This one? I didn't. I hear good things about it, and it's reached a point of maturity, being widely used in production.

Uhhh spec has existed for a long time and before that, schema Nowadays we also have the excellent malli. If his codebase is full of functions where the shape of the data isn’t obvious, isn’t documented and isn’t specified in a specific/schema, that’s on him and his bad coding practices and really no different from passing data in other dynamic languages. A class by itself (without additional effort) only gives you field names.

I don't understand this reputation either. There are very large systems built on other Lisps. For example, Emacs has a massive amount of Elisp. Elisp is much more primitive than Clojure, and traditionally libraries don't use e.g. data schemas [1] as runtime contracts for data.

Obviously, once a system built on top of a dynamic language grows beyond certain threshold, you need to be very disciplined as there are no static types to ensure some degree of correctness.

[1] https://github.com/plumatic/schema

Try to learn a schema library early, like Malli or Prismatic Schema. Do not mistook them as "static-typing" things - it's more for data validation and coercion than "security that things will get the right typing information". The idea to learn them early is how you'll shape future code: validating all "output data" first, them using that data inside your program without "defensive programming" like checking every time if a specific value on a map is nil, etc

In Clojure, declarative data specifications for validation and generation are also very mainstream. Schema was first out the door, Clojure Spec is the most popular library, while malli is gaining popularity fast at the moment.

Clojure's lazy sequences by default are wonderful ergonomically, but it provides many ways to use strict evaluation if you want to. They aren't really a hassle either. I've been doing Clojure for the last few years and have a few grievances, but overall it's the most coherent, well thought out language I've used and I can't recommend it enough.

There is the issue of startup time with the JVM, but you can also do AOT compilation now so that really isn't a problem. Here are some other cool projects to look at if you're interested:

Malli: https://github.com/metosin/malli

Babashka: https://github.com/babashka/babashka

Clerk: https://github.com/nextjournal/clerk

BREAKING: walking a :schema passes children instead of [id] to the walker function #884

When you get to larger, more complex validations, I'd recommend checking out Malli or Spec.

for specs, you can try malli - feels pretty well supported and full featured: https://github.com/metosin/malli (i'm not 100% sure how popular it is for others, but I use it on my personal projects)

Have you tried malli: Data-driven Schemas for Clojure/Script?

All that being said, I particularly use malli and I don't find anything to complain about. There is a very nice and sound ecosystem being built around it (malli-ts is one of my contributions to it, but still in early development stages). I highly recommend reading its README, very informative stuff.

Any large codebase can be broken up into small isolated components that can be reasoned about independently. This is how you structure Clojure projects if you want them to be maintainable. Clojure inherently encourages doing this by defaulting to immutability. The contract between components is the data being passed to the component and returned by it. Using Malli schemas at the edges of the components is a typical approach to documenting their APIs https://github.com/metosin/malli

I see the fact that people often end up creating large and tightly coupled monolithic codebases in static languages as a negative aspect of static typing. Such codebases are difficult to reason about even if you have guarantees that the types align. Ultimately, you need to understand the relationships in code, and how they relate to business logic. The more coupling an application has the harder it becomes to reason about it as a whole.

Ideally, I think applications should be structured as a bunch of Lego blocks that can be composed together. Each component should encapsulate some functionality, and then the flow of the business logic should bubble up to the top and expressed in how these components are chained together.

Uhhh spec has existed for a long time and before that, schema Nowadays we also have the excellent malli. If his codebase is full of functions where the shape of the data isn’t obvious, isn’t documented and isn’t specified in a specific/schema, that’s on him and his bad coding practices and really no different from passing data in other dynamic languages. A class by itself (without additional effort) only gives you field names.