requires("0.8.2")
class dc dynamic
--  public string fred = "555" -- (predefine some fields if you like)
end class
dc d = new()

while 1 do
    string name = prompt_string("Enter name or press Enter to quit:")
    if length(name)=0 then exit end if
    bool bExists = (get_field_type(d,name)!=NULL)
--  bool bExists = string(d[name])  -- alt...
    string prompt = iff(not bExists?"No such name, enter a value:"
                   :sprintf("Already exists, new value[%s]:",{d[name]}))
    string data = prompt_string(prompt)
    if length(data) then
        d[name] = data
    end if
end while