CLasp is the OG Lisp/C++ combo, but its interop is nowhere near seamless. Last I checked, Clasp requires that functions, types, and values must be registered, from C++, before being accessible in Lisp. This requires you to build a bridge between these two worlds, in C++ code. That's a huge seam.

In jank, you just require the C++ headers, like you would in C++, and then you access whatever you want from them, like you would in C++. jank's type system is the C++ type system. jank also compiles to C++. jank includes a Clang-based JIT C++ compiler to make all of this possible.