adamc@211: class default t = t
adamc@211: 
adamc@211: val string_default : default string = ""
adamc@211: val int_default : default int = 0
adamc@211: 
adamc@211: val default : t :: Type -> default t -> t =
adamc@211:         fn t :: Type => fn d : default t => d
adamc@211: val empty = default [string] _
adamc@211: val zero = default [int] _