Why does it need generics? There's a great blog post about how you can replace a lot of trait behaviour with just functions. Maybe something like that can be done for generics

the comment is wrong, what Gleam lacks is interfaces.

Which feels super strange, but doesn't seem to really be a problem, e.g. imagine a language where you'd write

    fun sum_all_numbers(Iterable<T> it) { it.fold(...) } # an interface
    sum_all_numbers(a_list) # a list implements iterable

    fun sum_all_numbers(Iterator<T> it) { it.fold(...) } # a concrete type
    sum_all_numbers(a_list.iterator) # get the caller to build the right object