Allow to evaluate expressions in parent scopes

[toivoh]

Should there be commands to step between the current trap point and different containing scopes for interactive evaluation? Or should the intended scope be specified at each evaluation?

Should the entire call stack be kept, or should it just be possible to evaluate in the lexical parents of the current scope? If the call stack is kept, it should probably be possible to step both lexically and along the call stack. But keeping track of the call stack might be hard if coroutines are involved?