Partial application with a C++ lambda?

Question

EDIT: I use curry below, but have been informed this is instead partial application.

I\'ve been trying to figure out how one would write a curry function in C++, and i a

Answer 1

Your curry function is just a scaled down inefficient subcase of std::bind (std::bind1st and bind2nd should not be used anymore now that we have std::result_of)

Your two lines read in fact

auto f5 = std::bind(f, 5, _1);
auto g2 = std::bind(std::multiplies(), 2, _1);

after having used namespace std::placeholders. This carefully avoids the boxing into std::function and allows the compiler to inline more easily the result at the call site.

For functions of two arguments, hacking something like

auto bind1st(F&& f, T&& t) 
    -> decltype(std::bind(std::forward(f), std::forward(t), _1))
{
    return std::bind(std::forward(f), std::forward(t), _1)
}

may work, but it is difficult to generalize to the variadic case (for which you'd end up rewriting a lot of the logic in std::bind).

Also currying is not partial application. Currying has "signature"

((a, b) -> c) -> (a -> b -> c)

ie. it is the action to transform a function taking two arguments into a function returning a function. It has an inverse uncurry performing the reverse operation (for mathematicians: curry and uncurry are isomorphisms, and define an adjunction). This inverse is very cumbersome to write in C++ (hint: use std::result_of).