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