Reduce in a Direction

import Linear exposing (Direction(..))
import Set


Set.fromList [ 'i', 'l', 'a', 'g' ]
    |> Set.Linear.foldFrom "" Up String.cons
--> "liga"


Set.fromList [ 'i', 'l', 'a', 'g' ]
    |> Set.Linear.foldFrom "" Down String.cons
--> "agil"