rho

Do you mean type parameters or regular parameters? If it's the former(and Scala is allowed) then I think Rho's Result type is a pretty good bet with it's ~60 type arguments: https://github.com/http4s/rho/blob/989db04e6dd828518770a42fd...

I could never give up higher-kinded types: there are plenty of ad-hoc solutions to various effects, but a single reusable solution[1] means you can build up libraries that not only handle all the common effects, but your own custom ones as well. Even if you don't use them directly, you benefit from the ecosystem they make possible. Few other languages let you use something like treelog[2], fewer still let you fold a custom tree type while managing an effect as nicely as with matryoshka. Typeclass derivation is reflection done right, with compile-time safety and corresponding performance. I've never seen another language that made it so easy to put a database transaction boundary in exactly the right place but in a type-safe way so that you can never forget, or even have transactions implicitly applied to web endpoints that need them in a

A good DSL is just a library - or at least, there's no clear sharp line between them. Likewise, I think good programming looks a lot like creating a DSL (or rather a succession of them, with a tower of interpreters from the business logic at top level down to lower-level DSLs until you get to one that can be interpreted directly by the machine). The difference between a good DSL and a bad DSL is that a good DSL lets you reason about it the way you reason about normal, plain old code: you can factor out repeated function calls, inline constants that are only used in one place, and so on, and it will all just work the way you'd expect. A good DSL should just be plain old code, as should most of the language standard library, and then it doesn't really matter whether a given function is part of the language or a library. I've been very happy

I'd go the other way - rather than generate code from templates, declare the dynamic parts of the page in code, and generate both the implementation and the test accessors from that (I'd use a Wicket-like approach where the HTML fragments only included ids and all the logic was in code). I haven't seen this done for the actual HTML side of things, but https://github.com/http4s/rho gives you a declarative way to, uh, declare your HTTP routes, and then you can generate swagger or a client from the exact same declarative routing construct value that you're using to run your actual routes.