Sequence iterator

local function split(test, f, s, v)
    local bridge = v
    local function filter(...)
        bridge = ...
        if test(...) then
            return nil
        else
            return ...
        end
    end

    local function head(s, v)
        return filter(f(s, v))
    end
    return function() return head, s, v end, function() return f, s, bridge end
end