Re: [boost] Final lightweight monad, next gen futures and upcoming AFIO review

Subject: Re: [boost] Final lightweight monad, next gen futures and upcoming AFIO review
From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2015-06-29 04:05:07

2015-06-29 8:37 GMT+02:00 Vicente J. Botet Escriba <vicente.botet_at_[hidden]
>:

> Le 26/06/15 13:00, Niall Douglas a écrit :
>
>> On 26 Jun 2015 at 10:42, Andrzej Krzemienski wrote:
>>
>>  monad is now space optimal, consuming as little as two bytes
>>>> depending on configuration. monad<void> is now working, plus these
>>>> new specialisations were added:
>>>>
>>>> * result<T>: empty/T/error_code (no exception_ptr).
>>>>
>>> To what run-time condition does an empty state correspond here? I used to
>>> thing that you either have a result (T) or a reason why you do not have
>>> one
>>> (error_code), but what does it mean that you have neither?
>>>
>> Semantically speaking, after feedback from this list, and having
>> attended Charley's C++ Now Presentation on ternary logic programming
>> "Your CPU is Binary", I realised that it's worthwhile to formally
>> specify future/monad/result as ternary logic primitives with ternary
>> logic operators. option<T> remains boolean. This gives the following
>> logic table:
>>
>> Empty => False (future/monad/result/option)
>> Errored/Excepted => Indeterminate (future/monad/result)
>> Value => True (future/monad/result/option)
>>
> The meaning of empty in optional/option and future is not the same. For
> the fist is a valid state, for the second is an invalid state.
>

If "empty" means something different in the case of three-type "result",
perhaps it deserves a different name?

> In addition asynchronous types have an additional state not-ready, e.g.
> future can be invalid, not-ready, exceptional or valued.

So it looks like you have two sets of error codes:
1. The one represented by E in result<T, E>
2. A set of error conditions inherent to asynchronous state processing:
"invalid", "not ready" (maybe also "already retrieved").

Regards,
&rzej