Having worked with large Clojure codebases I found the Malli/Spec duct-taping of types to be a poor man's statically typed language, especially with the developer experience being quite poor. While it will runtime validate, I still have no idea what shape anything is by just hovering it - having to constantly navigate between the definitions file, and they are also more cumbersome to use and maintain.
I've come to the conclusion that it is just a better experience using a language that already has static types for large projects, than trying to make a dynamic language have similar things. Having to wrap every function in a error boundary to get somewhat of a meaningful debug experience is just .. awful.
> duct-taping of types to be a poor man's statically typed language
On the other hand, they allow you to do some very interesting things like using specs for complex validation. Once written specs can be then used for generating data for both - UI testing and property-based unit-tests. We once have build set of specs to validate an entire ledger - imagine having to be able to generate a bunch of transactions where numbers intelligently build based on previous entries.
Other languages even though have similar capabilities, like type providers in F#/OCaml, zod in Typescript, quckcheck/scalacheck in Haskell & Scala - Clojure is quite unique here in combining runtime validation, generative testing, and data definition in such a cohesive way. The ability to compose specs and use them across different contexts (validation, generation, documentation) is particularly powerful.
Another impressive thing is that you can easily share the logic between different runtimes - same specs can used in both - JVM and Javascript, which surprisingly difficult to achieve even when writing in Node with TS/JS - you cannot easily share the same validation logic between backend and the browser, even for the same javascript runtime, using its native language. Clojure lets you do that with ease.
For everything, there's a trade-off. Some just accept those trade-offs, build their vision, and launch it into the world; Some waste time, lamenting that reality doesn't align with their ideals.
I've come to the conclusion that it is just a better experience using a language that already has static types for large projects, than trying to make a dynamic language have similar things. Having to wrap every function in a error boundary to get somewhat of a meaningful debug experience is just .. awful.