Re: [boost] [proto] transform for flattening an expression - how?

From: Larry Evans (cppljevans_at_[hidden])
Date: 2008-03-18 00:45:44

On 03/17/08 17:55, Eric Niebler wrote:
> Larry Evans wrote:
>> Me too!  
> 
> I couldn't tell from your email -- what are you me too-ing?

flattening a sequence of binary operators into one list
with a tag indicating the operator to be applied between
elements in the list.

> 
>> In general, there should be an n-ary version of all the
>> binary ops. 
> 
> Do you mean, you'd like to create an expression expr<tag::plus, 
> args4<A,B,C,D> > ? There's nothing stopping you from doing that today.
> 
>    make_expr<tag::plus>(1,2,3,4)
> 
> The only problem is that default_context won't know what to do with it, 
> but that's not big a problem ... just write your own context.

Actually, I was thinking an n-ary expression with a tag like:

reduce<BinOp>

For example, make_expr<reduce<tag::plus> >(1,2,3,4).  The reason
for the name "reduce" is that what apl uses.  Or maybe fold<BinOp>,
since that's what other boost libraries use.

> 
>> This should also be extended to the or_ also.
>> I remember having a problem with folding or_ because it was
[snip]
> IIRC, your problem was that or_ requires at least 2 parameters. I had 
> agreed to change that, but haven't yet.
> 

Yep, now I remember.