How to print a source of a function passed as a parameter

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4

It’s totally hacky but something like this could work:

(defn var-source
  "This is almost an exact copy of `clojure.repl/source-fn` but
  accepting var instead of symbol in current ns (*ns*)."
  [v]
  (when-let [filepath (:file (meta v))]
    (when-let [strm (.getResourceAsStream (clojure.lang.RT/baseLoader) filepath)]
      (with-open [rdr (java.io.LineNumberReader. (java.io.InputStreamReader. strm))]
        (dotimes [_ (dec (:line (meta v)))] (.readLine rdr))
        (let [text (StringBuilder.)
              pbr (proxy [java.io.PushbackReader] [rdr]
                    (read [] (let [i (proxy-super read)]
                               (.append text (char i))
                               i)))
              read-opts (if (.endsWith ^String filepath "cljc") {:read-cond :allow} {})]
          (if (= :unknown *read-eval*)
            (throw (IllegalStateException. "Unable to read source while *read-eval* is :unknown."))
            (read read-opts (java.io.PushbackReader. pbr)))
          (str text))))))


(defn fn-source
  [f]
  (let [[ns-name sym-name]
        (-> (str f)
            (clojure.repl/demunge)
            (clojure.string/replace #"@.*$" "")
            (clojure.string/split #"/"))
        ns (the-ns (symbol ns-name))
        fn-var (ns-resolve ns (symbol sym-name))]
    (var-source fn-var)))

(comment
  (fn-source tap>)
;; => "(defn tap>\n  \"sends x to any taps. Will not block. Returns true if there was room in the queue,\n  false if not (dropped).\"\n  {:added \"1.10\"}\n  [x]\n  (force tap-loop)\n  (.offer tapq (if (nil? x) ::tap-nil x)))"
  )
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