Builtins.lazy for lazy arguments

Ideas
102

Still compiling use cases. But I will use your (@blhsing) suggestion from another thread and do pros and cons of deferred evaluation attempts

So there have been several deferred proposals/paths explored:

1. Lazy object based deferred evaluation

Progress:

  1. I have experimented with Python level implementations for a while
  2. They had drawbacks, but Backquotes for deferred expression has fixed them
  3. It hit the wall of functioning at C level and hasn’t moved forward yet

2. Lazy evaluation via Type Annotations

Progress:

  1. Lazy evaluation of expressions

3. Lazy defaults via extra parameter

Already available

4. “Just use lambda”

Already available

5. this - lazy object for signalling, but explicit handling is needed

Progress:

  1. Been using this approach in various places for a while without any issues

Pros/Cons

|   Pros                 Cons
+-------------------------------------------
(1) Implicit             Complex
    Intuitive            Uncertain if can be implemented without Python 4
    Nesting              Too complex and advanced given current actual needs

(2) Implicit             Complexity at parser level
                         Breaks conventions in undesirable manner
                         Adds undesirable weight on parser
                         No attempt at implementation has been made yet
                         Unlikely to work for extensions

(3) Explicit             Verbose
    Already exists       Inconvenient
                         Noone uses it despite being available
                            e.g. why does not `dict.get` have
                            extra argument for lazy default?
                         Does not ensure consistent standard
                            e.g. parameter naming
                         Extra parameter might be troublesome for some cases
                            e.g. `assert`
                         Needs Explicit Handling that
                            developers need to implement for each case

(4) Explicit             Various issues mentioned in
    Already Exists          https://discuss.python.org/t/builtins-lazy-for-lazy-arguments/86577/67
                         Just think about issues enabling `dict.get`
                            to accept lambda as lazy argument
                         Simply unsuitable to be "one way to do it"
                         Needs Explicit Handling that
                            developers need to implement for each case

(5) Explicit             Needs Explicit Handling that
    Simple                  developers need to implement for each case
    Easily Achievable    Relies on mutual agreement to use the same object
    Imposes desirable
        consistency
    Does not have issues
        mentioned in
        https://discuss.python.org/t/builtins-lazy-for-lazy-arguments/86577/67
    Maintains good enough
        performance
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