Clojure: How to get a function docstring?

Question

I am trying to get ONLY the docstring of a function in Clojure, nevertheless I have encountered several problems as all the functions that I find actually print the function signature + docstring.

So for example (doc map) will actually print something like.

clojure.core/map

([f coll] [f c1 c2] [f c1 c2 c3] [f c1 c2 c3 & colls])

Returns a lazy sequence consisting of the result of applying f to the ...

I am only interested in getting the docstring not printing it nor having its namespace or arity. What I am looking for is something like (get-doc function-name) which would return a string with

"Returns a lazy sequence consisting of the result of applying f to the ..."

Is this possible in Clojure?

bsvingen · Accepted Answer · 2015-08-19 17:13:55Z

16

You can do this:

(:doc (meta #'map))

map itself is just a symbol, that is, a name. This symbol resolves to a var, which is accessed by the special form #'map. The value of this var is the actual function, and the docstring for the function is stored as metadata on the var.

Therefore, #'map gives you the var (this can also be done using (var map)), meta gives you the metadata for that var, and :doc extracts the docstring.

For more information, have a look at var, metadata, and special forms.

edited Aug 19, 2015 at 17:13

answered Aug 19, 2015 at 13:08

bsvingen

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2 Comments

carocad Over a year ago

Hey @bsvingen, your answer is definitely correct :) Thanks a lot, but could you expand on it? I really dont get what var does :/ I was always trying using meta directly but always run into errors. Could you explain it to me please?

carocad Over a year ago

yes, I think it is clearer now, Thanks. From what I understand this has to do with the separation in Clojure between identity, name and state, right? So on runtime the symbol is resolved to the actual function and then executed?

Rovanion · Accepted Answer · 2017-04-17 12:19:46Z

4

Based bsvingen's answer we can define a macro which returns the docstring like:

(defmacro docstring [symbol]
  `(:doc (meta (var ~symbol))))

If we specifically want it to be a function, e.g. for use with map, you can write it as

(defn docstring [symbol]
   (:doc (meta (resolve symbol))))

edited Apr 17, 2017 at 12:19

answered Apr 17, 2017 at 11:59

Rovanion

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