My process in these languages (Haskell I know pretty well, now in the process of learning Rust) is to sprinkle in `undefined`s and `unimplemented!()`s and whatnot so I can continuously use the compiler to check my work without actually running the code.

It's a good way to test assumptions and refine a mental model, and it's also just plain useful for catching boneheaded mistakes as you go. I'm not sure if I'd say I use it as a crutch, but I certainly miss it when I have to use languages like ruby and Python.