car, cdr, cadadr and friends in clojure

car.clj

(ns car
  "The sixties are back!"
  (:require
   [clojure.math.combinatorics :as combo]))

(defn ad-combos [n]
  (distinct
   (mapcat (fn [i]
             (combo/selections '[a d] i))
           (range 1 (inc n)))))

(defn make-name [combo]
  (symbol (str "c" (apply str combo) "r")))

(def ad->fn
  {'a `first, 'd `next})

(defn make-fn [combo]
  `(comp ~@(map ad->fn combo)))

(defmacro defcadrs
  ([] `(defcadrs 4))
  ([n]
   (vec (for [combo (ad-combos n)]
          `(defn ~(make-name combo)
             [~'coll]
             (~(make-fn combo) ~'coll))))))

(defcadrs 6)

(comment
  ;; Yay, super readable code!
  ;; Can you guess what each one evaluates to?

  (caddar '((peas carrots tomatoes) (pork beef chicken) duck))

  (cadadr '((peas carrots tomatoes) (pork beef chicken) duck))

  )