Ordered sets and maps, implemented in pure clojure
Clojure
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README.md

lein dependency

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)

;; Adding an element already in an ordered set does not change its
;; position in the order.
(conj (ordered-set 4 3 1 8 2) 8)
=> #ordered/set (4 3 1 8 2)

;; Removing an element, then adding it back in, puts it at the end,
;; just as it would if it were never part of the set.
(-> (ordered-set 4 3 1 8 2) (disj 8) (conj 8))
=> #ordered/set (4 3 1 2 8)

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])

;; Adding a key already in an ordered map does not change its position
;; in the order.
(assoc (ordered-map :b 2 :a 1 :d 4) :b 7)
=> #ordered/map ([:b 7] [:a 1] [:d 4])

;; Removing a key, then adding it back in, puts it at the end, just as
;; it would if it were never part of the map.
(-> (ordered-map :b 2 :a 1 :d 4) (dissoc :b) (assoc :b 7))
=> #ordered/map ([:a 1] [:d 4] [:b 7])

Repositories

These two repositories are usually identical:

The first is the canonical one. Fixes tend to appear there first, and that is the preferred repository for filing issues on Github. Fixes are backported to the second one periodically.