Function join

include_all_in_one/include/fplus/fplus.hpp:4766–4769

template <typename Container,
    typename X = typename Container::value_type>
X join(const X& separator, const Container& xs)
{
    return concat(intersperse(separator, xs));
}

// API search type: join_elem : (a, [[a]]) -> [a]
// fwd bind count: 1