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A Clojure hierarchical set.
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Library providing a "hierarchical set" data structure. The provided data structure is set of elements with a defined hierarchical relationship. An element is considered to be in the set either if it is provided as a primary set member or if it is a descendant of any such element. Lookup in the set not only determines set membership, but also finds all primary set members which are ancestors of the lookup element.

The hierarchical relationship is defined by the element sort-order and a separate containment predicate, with the following constraints:

  • elements must sort prior to any descendants; and
  • elements must contain all elements which sort between themselves and any descendant.

This is sufficient to represent simple hierarchical systems where the hierarchy is implicit in the entities involved, such as the Java package system, hierarchical filesystems, or IP networks. It is inappropriate for modeling complex, ad hoc hierarchies, such as the relationships between classes with multiple inheritance.


Add hier-set to the :dependencies list in your Leiningen project.clj:

[hier-set "1.1.2"]

Primary usage is then through the hier-set and hier-set-by constructor functions in the hier-set.core namespace. In addition to set lookup as described above, the hier-set.core/ancestors and hier-set.core/descendants functions also provide access to lazy sequences of the ancestors and descendants respectively of a provided key.


A trivial example:

(ns example.hier-set
  (:require [hier-set.core :as hs])
  (:use [hier-set.core :only [hier-set]])

(def with-starts? #(.startsWith %2 %1))

(def hs (hier-set with-starts? "ack" "foo" "" "quux")

(get hs "bar")              ;;=> nil
(get hs "foo")              ;;=> ("foo")
(get hs "")      ;;=> ("" "foo")
(hs/ancestors hs "bar")     ;;=> ()
(hs/ancestors hs "foo.baz") ;;=> ("foo")
(hs/descendants hs "foo")   ;;=> ("foo" "")


Copyright © 2012, 2014 Marshall Bockrath-Vandegrift.

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.

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