Picat is a really interesting language in the Prolog family, which adds imperative and convenience features like list comprehensions and mutable maps and arrays. It also includes a built-in constraint solver and SAT solver module, as well as support for calling out to external MIP and SMT solvers like Cbc and z3.

This language crossed my radar a few years ago with people describing it as "Python-like" but with static, inferred types, and much faster. Upon playing with it, I decided it wasn’t very Python-like (check out Acton if you’re really into that though), but it certainly was much faster and had static type inference. My brain seemed to put it into a similar hash slot as Crystal even though they are different in many ways. Crystal is a little more terse and less syntactically noisy, but Nim is really elegant and incredibly memory efficient. The slightly higher level of syntactic/type noise (e.g. needing to declare types in function headers) provides extremely fast compile times in return, and the standard library is fantastic, at least for my needs so far. The default package manager Nimble is also excellent.

At the moment I’d say Nim is my favourite general-purpose language to work with, presenting an excellent balance between conciseness, expressivity, reliability, performance and usability.

I’ve been interested in Haskell for many, many years, and made several attempts to get into it. The first few ended in confusing failure where my brain just didn’t feel big enough to really grok it, but eventually some of the concepts made sense.

This multitier, aka tierless programming language builds on Standard ML (an influential language that isn’t popular nowadays but its ideas directly influenced Ocaml and probably Haskell too). The key idea is that it would be nice not to have to (manually) break up your program into frontend, backend and database layers, since that separation necessitates significant duplication of effort and tends to introduce errors, like:

Ur/web tries to solve this by allowing you to mix frontend and backend code in the same file (or even the same function), using the advanced type system to "slice" it apart automatically and transpile frontend-related code to Javascript. It also prevents many kinds of robustness and security errors like SQL injections and CSRF attacks.

It’s extremely frugal and compiles your web programs into small binaries that can be proxied behind a server like Nginx. Unfortunately, it’s very hard for beginners to get started. The best source of documentation is the official demos which are very helpful, but it still feels hard to understand any of the documentation without being an expert in the ML language family, and especially SML since it relies on notions of modules and functors that seem to originate there. The language manual is written in a very mathematical, academic style. As a result, participation seems to be minimal due to those accessibility barriers. I would love to see more activity around Ur/web but the community appears to have dried up, and the project isn’t welcoming for people who don’t have a heavy ML/FP background.