libfn provides CMake targets:

    find_package(libfn CONFIG REQUIRED)
    target_link_libraries(main PRIVATE libfn::pfn)  # C++20 standard-library polyfills
    target_link_libraries(main PRIVATE libfn::fn)   # the functional library (C++20)

    # C++26 mode (std::type_order); use instead of libfn::fn, never both:
    target_link_libraries(main PRIVATE libfn::fn_cxx26)
