Re: [boost] Interest for a perl6-like-junctions-class?

From: Rob Stewart (stewart_at_[hidden])
Date: 2005-08-05 08:25:40

From: Paul <elegant_dice_at_[hidden]>
> Rob Stewart wrote:
> > From: FlSt_at_[hidden]
> 
> If I read this correctly, Rob's interpretation of the set algebra is 
> slightly incorrect.
> 
> >>( any_of( a ) >= any_of( b ) ) <= any_of( c )
> >>
> >>Or if the comparison returns an container:
> >>
> >>any_of( any_of( a ) >= any_of( b ) ) <= any_of( c )
> > 
> > Why would you write those?  What do they mean?
> 
> any_of(a) >= any_of(b)
> would return a subset of values from 'a', where those items are >= than 
> any item in 'b'.

We have been discussing expressions that return a bool, not a
subset, for quite some time.  You snipped quite a bit of context,
so I'm not sure how old this discussion really is.

> You can't do this:
> 
> >    (any_of(a) >= min_element(b)) <= max_element(c)
> 
> because you are placing a total-ordering requirement on all sets.

I don't know what interpretation you're referring to; you
apparently snipped something from my reply.  Otherwise, I was
just questioning the value of such an expression.

> what if the sets only satisfy the partial-ordering definition?
> 
> Example, let there be b[i] < b[j], but a[k] < b[i] and a[k] > b[j].
> So the any_of/any_of variant's result would include a[k] (a[k] > b[j])
> but min_element won't, as a[k] < min_element (which is b[i])

Possibly so, but that's for a different library than we are now
discussing.

-- 
Rob Stewart                           stewart_at_[hidden]
Software Engineer                     http://www.sig.com
Susquehanna International Group, LLP  using std::disclaimer;