Comment by jimbokun
4 months ago
Some Common Lisp implementations like SBCL have supported this style of development for many years. Everything is dynamically typed by default but as you specify more and more types the compiler uses them to make the generated code more efficient.
I quite like common lisp but I don't believe any existing implementation gets you anywhere near the same level of compile time safety. Maybe something like typed racket but that's still only doing a fraction of what rust does.