pred-get.clj

(defn pred-get
  "Steps through all the keys in pred-map, which are mutually exclusive
  predicates, finds the first one that returns true when passed expr, and
  returs the value associated with that predicate.
  
  (map #(pred-get {neg? -1, zero? 0, pos? 1} %) [5 -2 0]) => (1 -1 0)"
  [pred-map expr]
  (loop [preds (keys pred-map)]
    (when-first [pred preds]
      (if (pred expr)
	(get pred-map pred)
	(recur (rest preds))))))