How do I modify a :arglists to a Clojure fn or macro?

Question

How do I modify the :arglist attribute for a clojure fn or macro?

(defn tripler ^{:arglists ([b])} [a] (* 3 a))

(defn ^{:arglists ([b])} quadrupler [a] (* 4 a))

% (meta #'tripler) => 
  {:arglists ([a]), :ns #<Namespace silly.testing>, :name tripler, :line 1, :file "NO_SOURCE_PATH"}

% (meta #'quadrupler) => 
  {:arglists ([a]), :ns #<Namespace silly.testing>, :name quadrupler, :line 1, :file "NO_SOURCE_PATH"}

Ok, no luck there, so I tried doing the following.

(def tripler
  (with-meta trippler
    (assoc (meta #'tripler) :arglists '([c]))))

% (with-meta #'tripler) => 
  {:ns #<Namespace silly.testing>, :name tripler, :line 1, :file "NO_SOURCE_PATH"}

Hmm, so now the :arglists key is gone? Well, I give up, how do I do this? I would simply like to modify the value of :arglists. The examples above use defn, but I would also like to know how to set the :arglists using a macro (defmacro).

Answer 1

alter-meta! changes the metadata on a var. The metadata on the function is not relevant, only the var.

(alter-meta! #'tripler assoc :arglists '([b]))