Peter Dimov wrote:
Steven Watanabe:
Joel de Guzman wrote:
Yep. Phoenix can do that. A local variable may hide an outer local variable. Here, we just reuse the locals for arguments to the lambda as well. So, in current terms, this:
lambda( _x, _y )[ _x + _y ]
is just this:
lambda( _x = _1, _y = _2 )[ _x + _y ]
Am I misunderstanding something? I thought that this would give lambda( _x = _1, _y = _2 )[ _x + _y ] (1, 2)() == 3 instead of lambda( _x = _1, _y = _2 )[ _x + _y ] ()(1, 2) == 3
Under the model I have in mind:
lambda( _x, _y )[ _x + _y ] ( 1, 2 ) == 3
That is, lambda is not lazy, and it doesn't compose further.
lambda( _x )[ _x ] + _1
doesn't compile; there's no operator+ taking a lambda.
Again, there's a problem with this behavior and the higher-order argument ala for_each. But maybe not. I'm starting to investigate. There was a time that this was allowed: phx::for_each(_1, std::cout << _1 << std::endl) (vec) The f is an implicit lambda. Not saying that this is good, but just to show that it's possible to detect the scope of the _1 on the left and on the right. Explicit lambdas would be the same, me thinks.
I don't think it is quite the same if you use an arbitrary expression instead of _x + _y. For instance, what should this mean:
lambda(_x, _y) [ _x + _y + _1 ]
If we're allowed to not think about backward compatibility, I'd say that _1 would no longer exist. Not even at top level.
Right! _1 would not make sense because essentially all the arguments are declared already in the lambda declarator (_x, _y). Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net