This reminds me of an irritating problem in CPS based compilers where you can have a transformation that is obvious and legal except that after the transformati

This reminds me of an irritating problem in CPS based compilers where you can have a transformation that is obvious and legal except that after the transformation one of the relevant variables would not be in scope. The solution(s) are to decline to do that transformation, fart around with sinking and hoisting in order to get the scope right, or ditch scope and move to a graph model in which dependence is represented with explicit edges rather than being approximated by the lexical structure of the program. I'm guessing that the lexical borrow problems that Rust are facing are an instance of the same problem. It will be interesting to read the follow up post and see what relation, if any, the suggested solution has to the graph approaches that I am familiar with.