Explore the implementation of variant visitation using lambdas in C++17 through this comprehensive ACCU 2017 conference talk. Delve into the intricacies of std::variant and its role as a type-safe sum type in the STL. Learn about traditional and lambda-based visitation techniques for both non-recursive and recursive variants. Discover how to create an "overload set" generator and implement a "Y-Combinator" for recursive visitation. Gain insights into callable object arity deduction techniques to enhance user interface elegance. Suitable for developers familiar with C++11 and C++14 core language features, this talk covers topics such as variant types, visitation techniques, overload sets, recursive variants, and grammar constructors.