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defmostly

Multimethod-like dispatch leveraging Clojure Spec.

Clojure's multimethods (defmulti) require the dispatch function to produce an exact match for one of the registered defmethods.

defmostly takes a looser approach that levarages specs and their specificity.

Specificity.. What is it? Currently a recursive count of spec predecates. For example (s/def ::user (s/keys :req-un [::id ::email])) has a specificity of 2.

During definition defmostly determines the specificity of the passed in spec.

During dispatch defmostly reduces over the specs, narrowest (highest specificity) first, running s/valid? with passed argument. Upon the first valid result, it shortcircuits and invokes the argument with the registered function.

defmostly is an idea-sketch and should not be used in production.

Usage

(ns my-ns
  (:require [den1k.defmostly :refer [defmostly]]))
  
(defmostly auth ::logged-out-user
  [user]
  (println :login! user))

(defmostly auth ::logged-in-user
  [user]
  (println :logout! user))

(auth {:db/id #uuid "84a4afff-8816-401f-a09e-8d4325801f86"})

;=> :login! #:db{:id #uuid "84a4afff-8816-401f-a09e-8d4325801f86"}

(auth {:db/id #uuid "84a4afff-8816-401f-a09e-8d4325801f86"
       :user/session {:session/key "foo"}})

;=> :logout! {:db/id #uuid "712fcc62-77e6-4811-86f9-6db8528f69eb"
;             :user/session #:session{:key foo}}

Todo

  • CLJC compatability
  • benchmarks & performance improvements

License

Copyright © 2019 Dennis Heihoff

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