Ada's dependent types, and its types as a whole

Very interesting. As a Zig enthusiast I've long suspected that Ada has the ability to express more invariants and types that we will want in Zig (some, like ranges, are planned, last I heard). I'm definitely interested to learn more about Ada.

Ada is a criminally underrated tool that is unfortunately probably doomed to perpetually take the backseat to Rust despite Rust not solving all the problems Ada does. It's really sad that so many people's idea of safe programming is pretty strictly limited to memory safety, and that because Ada's baseline memory safety (SPARK is a different story) isn't as robust as Rust's borrow checker (in the sense that it doesn't have a borrow checker in favor of just avoiding dynamic allocations whenever possible), that it's a relic of the past.

Ada's type system, SPARK, general clarity on behavior, etc. allows you to structure programs in a manner that makes it hard to Hold It Wrong, especially when dealing with embedded firmware that has all sorts of hardware gotchas. I haven't gotten the chance to use the Tasking primitives in anger yet, but I have a strong suspicion that they're going to bail my ass out of a lot of problems just like the rest of the language has.

My team started at a new employer and made the jump from C to Ada for MCU firmware. We control things that spin real fast and our previous experiences with C definitely resulted in some screwups that left you weak in the knees for a bit. There was some initial hesitation but nobody has any interest in going back now. Rust was floated but we're all glad we didn't opt for it -- memory safety on a system that never allocates memory doesn't hold a candle to Ada's bitfield mapping/representation clauses, ranged types, decimal types, reference manual, formal verification options, concern from the powers that be about providing a stable and trustworthy environment for doing shit that you really don't want to get wrong, etc.

Steve Klabnik (of Rust fame) wrote a (very generous IMO) article about Ada, interesting comparison: https://steveklabnik.com/writing/learning-ada/

Forth is another language with separate control flow and data stacks, for similar reasons, although at a much lower level - the stacks are a part of the language spec that is fully exposed to you, not just an implementation detail.