Definitely Rust, and a bit Haskell.

Rust has made me much more conscious of data ownership through a program, to the point that any C/C++ function I wrote that takes a pointer nowadays gets a comment on ownership.

I wish it was a bit less pedantic about generics sometimes, which is why I've started working on a "less pedantic rust", where generics are done through multiple dispatch à la Julia, but still monomorphising everything I can. I've only started this week, but I already have a tokenizer and most of the type inference system (an SLD tree) ready. Next up is the borrow checker and parsing the tokenized input to whatever the type inference and borrow checker need to work with, and of course actual code generation...

Haskell is my first FP language, and introduced me to some FP patterns which, turns out, are super useful even with less FP languages.