Establishes a parent/child relationship between parent and tag. Parent must be a namespace-qualified symbol or keyword and child can be either a namespace-qualified symbol or keyword or a class. h must be a hierarchy obtained from make-hierarchy, if not supplied defaults to, and modifies, the global hierarchy.
; clojure/core.clj:3337 (defn derive ([tag parent] (assert (namespace parent)) (assert (or (class? tag) (and (instance? clojure.lang.Named tag) (namespace tag)))) (alter-var-root #'global-hierarchy derive tag parent) nil) ([h tag parent] (assert (not= tag parent)) (assert (or (class? tag) (instance? clojure.lang.Named tag))) (assert (instance? clojure.lang.Named parent)) (let [tp (:parents h) td (:descendants h) ta (:ancestors h) tf (fn [m source sources target targets] (reduce (fn [ret k] (assoc ret k (reduce conj (get targets k #{}) (cons target (targets target))))) m (cons source (sources source))))] (or (when-not (contains? (tp tag) parent) (when (contains? (ta tag) parent) (throw (Exception. (print-str tag "already has" parent "as ancestor")))) (when (contains? (ta parent) tag) (throw (Exception. (print-str "Cyclic derivation:" parent "has" tag "as ancestor")))) {:parents (assoc (:parents h) tag (conj (get tp tag #{}) parent)) :ancestors (tf (:ancestors h) tag td parent ta) :descendants (tf (:descendants h) parent ta tag td)}) h))))
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