ordered provides sets and maps that maintain the insertion order of their contents.

Sets

(use 'flatland.ordered.set)

(ordered-set 4 3 1 8 2)
=> #ordered/set (4 3 1 8 2)

(conj (ordered-set 9 10) 1 2 3)
=> #ordered/set (9 10 1 2 3)

(into (ordered-set) [7 6 1 5 6])
=> #ordered/set (7 6 1 5)

(disj (ordered-set 8 1 7 2 6) 7)
=> #ordered/set (8 1 2 6)

Maps

(use 'flatland.ordered.map)

(ordered-map :b 2 :a 1 :d 4)
=> #ordered/map ([:b 2] [:a 1] [:d 4])

(assoc (ordered-map :b 2 :a 1 :d 4) :c 3)
=> #ordered/map ([:b 2] [:a 1] [:d 4] [:c 3])

(into (ordered-map) [[:c 3] [:a 1] [:d 4]])
=> #ordered/map ([:c 3] [:a 1] [:d 4])

(dissoc (ordered-map :c 3 :a 1 :d 4) :a)
=> #ordered/map ([:c 3] [:d 4])