Io (http://iolanguage.org) can work this way, as the message tree (maybe including comments - I don't recall) is what the interpreter used to evaluate the code and is accessible at runtime. However, it didn't store the choice of terminator (newline vs return) or indentation info (though it would be easy to add), so the pretty print of the message tree might look different depending on the source conventions.
Coroutines (unlike async/await) would allow one to wait on an async result without losing the stack which is waiting. This would avoid the need for (often) inscrutable callback state machines (Javascript's version of GOTOS).