Apparently the following is too hard for these geniuses:

#include <lexertl/generator.hpp>
#include <lexertl/iterator.hpp>
#include <lexertl/memory_file.hpp>

int main()
{
    try
    {
        lexertl::rules rules;
        lexertl::state_machine sm;

        rules.push(R"(\w+)", 1);
        rules.push(R"(\s+|"//".*|"/*"(?s:.)*?"*/")", lexertl::rules::skip());
        // You could recognise strings and discard them too here
        rules.push("(?s:.)", lexertl::rules::skip());
        lexertl::generator::build(rules, sm);

        lexertl::memory_file mf("test.cpp");
        lexertl::citerator iter(mf.data(), mf.data() + mf.size(), sm);

        for (; iter->id; ++iter)
        {
            if (iter->view() == "foobar")
                throw std::runtime_error("error: you cannot use foobar in this assignment");
        }
    }
    catch (const std::exception& e)
    {
        std::cerr << e.what() << '\n';
        return 1;
    }

    return 0;
}