Re: [boost] [next gen futures] Lightweight monad ready for inspection

Subject: Re: [boost] [next gen futures] Lightweight monad ready for inspection
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2015-06-21 20:43:17

On 21 Jun 2015 at 9:07, Vicente J. Botet Escriba wrote:

> Le 19/06/15 19:03, Niall Douglas a écrit :
> > Some may remember the thread starting from
> > http://boost.2283326.n4.nabble.com/next-gen-future-promise-What-to-cal
> > l-the-monadic-return-type-td4676039.html and that I would firstly
> > prepare an optimally lightweight monad<T> for review here before
> > going on to base a next-gen lightweight future-promise on that
> > monad<T>.

Firstly Vicente your three emails contained a ton of gold quality 
observations. From those I have generated this task list:

Boost review feedback work items:
 - [x] Documentation incorrectly says exceptions thrown are 
future_error when they are in fact monad_error.
 - [ ] Add template aliases for different configurations of monad<T> 
(one of maybe, result, holder, value, retval, potential, likely). Add 
two additional aliases, one for a monad without exception_ptr, and 
another for a monad with neither error_code nor exception_ptr 
(option<T>?).
 - [ ] Make how error_type is converted into exception_type 
configurable.
 - [ ] Make the tribool nature of monad<T> much more formally 
obvious.
 - [ ] In addition to value_or(), error_or() etc add value_and(), 
error_and() etc.
 - [ ] As .then() is defined in a future as executing the callable 
when the value is set, and monad<T>.then() executes immediately and 
does not execute when the value is next changed, does this make 
monad<T>.then() deceptively named? (I think yes). Perhaps and() is a 
better name for then()? What about simply operator() i.e. make the 
monad callable? What about operator[]?
 - [ ] Add match() function which visits a callable on the contents.
 - [ ] Look into member operator overloads for bind() and map() e.g. 
monad<int> &m; auto r = m >> [](int a){return a;}; Can't use operator 
>>=() from Haskell as has same precedence to operator=().

Thank you *hugely* for your feedback Vicente. It was extremely 
valuable to me.

Niall

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