foldl#3 x2 Nil x2 foldl#3 x16 Cons x24 x6 foldl#3 Cons x24 x16 x6 main x1 foldl#3 Nil x1 foldl#3 2 Nil 0 Cons 2 main 1 INNERMOST hoca/rev-foldl.trs