consとconjの違い

(def x (cons (list 1 2) (list 3 4))) ; => ((1 2) 3 4)
(class x) ; => clojure.lang.Cons
(list? x) ; => false

(def y (conj (list 3 4) (list 1 2))) ; => ((1 2) 3 4)
(class y) ; => clojure.lang.PersistentList
(list? y) ; => true
````````````````

ソースをみてみる.

``````````````clojure
user=> (source cons)
(def
 ^{:arglists '([x seq])
    :doc "Returns a new seq where x is the first element and seq is the rest."
   :added "1.0"
   :static true}
 cons (fn* ^:static cons [x seq] (. clojure.lang.RT (cons x seq))))
```````````````

``````````````clojure
user=> (source conj)
(def
 ^{:arglists '([coll x] [coll x & xs])
   :doc "conj[oin]. Returns a new collection with the xs 'added'. (conj nil item) returns (item).  The 'addition' may happen at different 'places' depending on the concrete type."
   :added "1.0"
   :static true}
 conj (fn ^:static conj
        ([coll x] (. clojure.lang.RT (conj coll x)))
        ([coll x & xs]
         (if xs
           (recur (conj coll x) (first xs) (next xs))
           (conj coll x)))))