Also, cargo doc --open for offline version of docs.rs :-)

True; but also, "strong typing" on its own isn't a panacea for guidance; unless you're writing Coq or Agda, the API functions you're calling are still going to have preconditions that are not encoded in the type signature, so you're still (partially) reliant on having either good docs or a REPL [or clumsy REPL-equivalent, like exploratory unit tests] to inform you of those preconditions.

And if you are writing Coq or Agda—well, you certainly don't need a REPL at that point. The code writes itself. ;)

Yeah, like I said, doesn't fit all use cases, but it does fit the primary one.