A simple and generic command handler for clojure apps using core.match pattern matching.

commands.clj

(ns commands.core
  (:require [clojure.string :refer [split]]
            [clojure.core.match :refer [match]]))

(defmacro defcommand
  "Defines a command function that takes a context argument and any number of additional arguments.
  If the `name` symbol does not have explicit label metadata attached to it, the name of the symbol will be used as the label.
  The `context-binding` can be any valid `let` binding form. It will be bound to the context argument at execution time.
  The `patterns` are a variable number of [[clojure.core.match/match]] matching forms that represent the different arguments that
  can be passed to this command."
  [name context-binding & patterns]
  `(defn ~(if (contains? (meta name) :label) 
            name 
            (vary-meta name assoc :label (clojure.core/name name)))
     [~context-binding & args#]
     (match (vec args#) ~@patterns)))   

(defn commands 
  "Creates a map of label -> command based on the inputted command function vars."
  [& commands] 
  (zipmap (map :label (map meta commands)) commands))

(defn dispatch 
  "Finds and dispatches the correct command based on the given command map and input.
  Throws an [[IllegalArgumentException]] if no matching command could be found."
  [commands context input]
  (let [[label & args] (split input #"\s+")]
    (if-let [command (get commands label)]
      (-> command var-get (apply context args))
      (throw (IllegalArgumentException. (str "No matching command found for label " label))))))