Re: Capabilities interact nicely with Substructural Types and Reactivity

This is a difference from E. This paper shows how to leverage Joe-E's
Immutable to determine purity. This is cool and there isn't anything like
it in E.


On Thu, Sep 12, 2013 at 5:29 PM, David Wagner <[email protected]> wrote:

> On Thu, Sep 12, 2013, at 04:13 PM, David Barbour wrote:
> > If you know an object isn't stateful - i.e. that it cannot remember its
> > past inputs - then whole classes of security, consistency, and
> > correctness
> > issues can be eliminated. One can prevent time-bomb behaviors that might
> > be
> > resistant to basic testing and analysis.
>
> I'm on board with this goal.  Joe-E's mechanisms allow you
> achieve this goal -- indeed, that was one of the major goals
> when we designed the language, and we wrote an entire paper
> on the subject.  You should read it. :-)
>
> May I encourage you to take a look at how Joe-E achieves this
> and see if it changes your views at all about the adequacy
> of DeepFrozen/Immutable for this purpose?
>
> The very short version is that if an object is Immutable, then
> you know it cannot remember state; and if you know that all of
> a method's parameters are Immutable, then (in Joe-E) you are
> entitled to deduce that the method is pure and cannot remember
> its past inputs.  This provides a simple, local check to verify that
> a method is pure (isn't stateful).  Joe-E was designed to ensure
> that this inference would be sound.  (The implicit "this" parameter
> must be treated as one of the method's parameters, for purposes
> of this condition.)  But read the papers for a detailed explanation.
>
> -- David
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-- 
Text by me above is hereby placed in the public domain

  Cheers,
  --MarkM

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