[boost] Re: Fusion plan [was Re: tuple patch (constructing from apair)]

From: Larry Evans (cppljevans_at_[hidden])
Date: 2005-04-29 10:28:00

On 04/29/2005 08:32 AM, David Abrahams wrote:
> Larry Evans <cppljevans_at_[hidden]> writes:
> 
> 
>>Since the ForwardOp, as defined here:
>>
>>http://www.boost.org/libs/mpl/doc/refmanual/fold.html
>>
>>is pretty equivalent to a cons operation when it's defined as:
>>
>>template<class Head,class Tail>
>>struct forward_op_cons
>>: Tail
>>{
>>    Head value;
>>};
> 
> 
> ??  That's not a binary lambda expression.
> 
In fold_seq_test.zip in the vault under cppljevans/mpl there's the code:

       typedef mpl::fold_seq
         < types
         , start_state
         , my_node< _2, _1>
         >::type

where my_node is essentially the above forward_op_cons:

template<class L, class R>
struct my_node
{
     typedef my_node partial_type;
};

OK, I guess to be precise, I should have said the 2nd arg to
fold (or fold_seq) is the lambda expression:

   forward_op_cons< _2, _1>

where forward_op_cons is defined as:

   ...

I now see how this was unclear.