About the "whatever is d[k]" in five minutes comment: If I created an explict closure like: `thunk = lambda: d[k]` and then mutated `d` before evaluating the closure you would have the same issue. I don't think it is that confusing. If you need to know what `d[k]` evaluates to right now then the order of evaluation is part of the correctness of your program and you need to sequence execution such that `d` is evaluated before creating that closure.
On Fri, Feb 17, 2017 at 4:17 PM, Joseph Jevnik <joe...@gmail.com> wrote: > There is no existing code that uses delayed execution so we don't need to > worry about breaking it. I think it would be much easier to reason about if > forcing an expression was always explicit. I am not sure what you mean with > the second case; why are you delaying a function if you care about the > observable side-effect? > > On Fri, Feb 17, 2017 at 4:14 PM, Ed Kellett <edk...@gmail.com> wrote: > >> On Fri, 17 Feb 2017 at 19:38 Joseph Jevnik <joe...@gmail.com> wrote: >> >>> Delayed execution and respecting mutable semantics seems like a >>> nightmare. For most indexers we assume hashability which implies >>> immutability, why can't we also do that here? Also, why do we need to >>> evaluate callables eagerly? >>> >> >> Respecting mutability: we just have to always, we don't know if a delayed >> thing is hashable until we evaluate it. This thing has implications for >> existing code (since delayed objects can get anywhere) so it should be >> careful not to do anything too unpredictable, and I think d[k] meaning >> "whatever is in d[k] in five minutes' time" is unpredictable. One can >> always delay: d[k] if it's wanted. >> >> Evaluate calls: because if you don't, there's no way to say "strictly >> evaluate x() for its side effects". >> > >
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