Proto for Boost mailing list page: Re: [proto] proto-11 progress report

Subject: Re: [proto] proto-11 progress report
From: Eric Niebler (eric_at_[hidden])
Date: 2012-06-25 17:30:56

On 6/25/2012 12:21 PM, Mathias Gaunard wrote:
> On 24/06/2012 01:10, Eric Niebler wrote:
> 
>> As for what is not changing:
>>
>> Grammars, Transforms and Algorithms
>> ===================================
>> It would be wonderful if there were a more natural syntax for describing
>> proto algorithms rather than with structs, function objects, proto::or_,
>> proto::when, and friends. If there is one, I haven't found it yet. On
>> the up side, it means that many current proto-based libraries can be
>> upgraded with little effort. On the down side, the learning curve will
>> still be pretty steep. If anybody has ideas for how to use C++11 to
>> simplify pattern matching and the definition of recursive tree
>> transformation algorithms, I'm all ears.
> 
> There is a function which is very simple and that I found to be very
> useful when dealing with expression trees.
> 
> unpack(e, f0, f1) which calls
> f0(f1(e.child0), f1(e.child1), ..., f1(e.childN))
> 
> I can do recursion or not with the right f1, and I can 'unpack' an
> expression to an n-ary operation f0.
> 
> Here f0 is typically a function that uses its own overloading-based
> dispatching mechanism.

OK, thanks for the suggestion. Where have you found this useful?

Along those lines, I've been thinking about adding a kind of transform
that gives an exploded view of an expression, kind of like what
evaluation contexts give you. If you tell me your use case, I can try to
make the new transform support it.

For the record, I'll be killing off evaluation contexts completely in
proto.next.

>> It needs clang trunk to compile.
> 
> Why doesn't it work with GCC?

The big missing feature is ref qualifiers for member functions (n2439).
AFAIK, clang is the only compiler that has implemented it.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com