fun sum [fs ::: {Unit}] (fl : folder fs) (x : $(mapU int fs)) = @foldUR [int] [fn _ => int] (fn [nm :: Name] [rest :: {Unit}] [[nm] ~ rest] n acc => n + acc) 0 fl x fun main () = return {[sum {}]}
{[sum {A = 0, B = 1}]}
{[sum {C = 2, D = 3, E = 4}]}