Does Clojure program source code metadata exist and can it be easily accessed?

Question

My question is does Clojure program source code meta data exist, and is it easily accessible?

I was thinking of writing a function wrapper that would accept a function to call, a debug flag, and arbitrary text (location of the call in the source code, for example) to print when the debug flag is set. When clear, only the function would be called.

Rather than hard-code a position, I was wondering if that could be gleaned from the current function running. I do not know if such information is available. Otherwise, I can certainly supply arbitrary location information wherever the function is called.

Here is an example of such a function:

(defn test-fn
    []
    (println "This is a test function."))

(defn fn-call-loc
    [fn dbg-flag & locate-info]
    (if (= 1 dbg-flag)
        (println locate-info))
    (fn))

repl-test.core=> (fn-call-loc test-fn 1 "Called from main.")
(Called from main.)
This is a test function.
nil
repl-test.core=>

My question is rather than my hard-coding "Called from main.", is there available meta data about the position at the location of the call to fn-call-loc?

Thanks.

Could you please provide some pseudo code that can help to know what exactly you are trying to do as the question is not clear. — Ankur
– Ankur, Commented Jun 4, 2012 at 4:05
Is something like github.com/clojure/tools.trace helpful to what you're trying to achieve? — Swaroop C H
– Swaroop C H, Commented Jun 4, 2012 at 7:47

A Sammich · Accepted Answer · 2015-02-19 03:24:10Z

There is the Metadata clojure.org docs page that talks about metadata. To do what you would like I would change fn-call-loc like this:

(defn fn-call-loc
  [fv dbg-flag]
  (if dbg-flag
    (let [n (-> (:ns (meta fv)) (.getName))
          f (:name (meta fv))
          l (:line (meta fv))]
      (println (str "Called from " n "/" f " which is defined on line " l))))
  (fv))

And you call it like this:

(fn-call-loc #'test-fn true)

or this:

(fn-call-loc (var test-fn) true)

There are some gotchas though.

Change all instances of 'fv' to 'fn' in fn-call-loc and your results will probably be from clojure.core, not your namespace.
If you pass a symbol directly you'll get an exception. The Var object is needed see the (var symbol) clojure.org docs and the Var-quote in the reader docs pages.
Probably some more I can't think of right now.

This might be a good place for a macro but I think that's another question.

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