Peter Dimov wrote:
Joel de Guzman:
Maybe you want:
let(_a = 0)[ ++_a ]
Maybe I do. :-)
phx::for_each(_1, lambda[std::cout << _1 << std::endl])
Notice that like protect, there are two function invocations happening here.
The confusion here comes from the fact that the above would work if lambda[] had "unlambda" semantics, that is, if it returned a function object that was not a phoenix expression.
No, that is not the "unlambda" semantics. There needs to be 2 function application there: 1) the one that substitutes the stl container for _1 (the leftmost _1) and 2) the one that substitutes the container's element for _1 (the rightmost _1). The key point here is that phx.lambda (and BLL protect), *returns a lambda-functor that returns a lambda-functor*. unlambda OTOH simply returns a plain functor (non-actor). A plain functor can only do one function application (bear in mind that this is phoenix for_each (lazy), not std::for_each (eager)). Here's the crucial difference (using BLL) highlighting the difference: { int x = 5; int r = bind(_1, _2)(unlambda(_1), x); BOOST_TEST(x == 5); } { int x = 5; int r = bind(_1, _2)(protect(_1)(), x); BOOST_TEST(x == 5); } Notice that protect *requires* the additional function application: protect(_1)() I'm CC'ing Jaakko for clarification. It's also plausible that I am confused. Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net