2025-04-07 squint | Clojure Slack Archive

squint 2025-04-07

Jonas Östlund 2025-04-07T14:04:44.087919Z

Hi again, thanks for the great work with Squint. I have run into an issue regarding the fact that JavaScript has both null and undefined to represent the absence of a value. It is a subtle issue and I can easily work around it, but I nevertheless would like to bring it up in case there is something I can improve inside Squint to make it generate better code. The following snippet of code represents the issue. The unit test is written so that it all the expectations pass with the current implementation of Squint:

(defn my-fn []
  (if false
    119
    nil))

(test "my-fn-test"
      (fn []
        (-> (expect (if false
                      119
                      nil))
            (.toBe nil))
        (-> (expect (my-fn))
            .-not
            (.toBe nil))
        (-> (expect (my-fn))
            (.toBe undefined))))

What this code highlights is that if I have a function, my-fn, that contains an if-form with one branch explicitly returning nil, the return value of that function becomes undefined instead. But if I test the expression directly without wrapping it in a function, it evaluates to nil. Is the best advice here to write my code so that it is invariant to whether an expression evaluates to undefined or nil , or is there anything I can do to improve the code generated by Squint here? I see saw the implementation (defmethod emit-special 'if ... in compiler_common.cljc .

✅ 1

borkdude 2025-04-07T14:28:52.925469Z

I don't think CLJS in general cares much about the difference between js/undefined and nil . e.g. the nil? function returns true for both of them

borkdude 2025-04-07T14:30:07.776389Z

we could add an explicit return null of course.

borkdude 2025-04-07T14:30:46.667329Z

I'd recommend checking what CLJS does: http://app.klipse.tech/ If there is a difference between an empty fn body, if, etc. and squint we could try to align it

borkdude 2025-04-07T14:30:58.925769Z

feel free to post an issue about this with examples

Jonas Östlund 2025-04-07T14:36:07.958729Z

Thanks! I will give this some more thought, and if I come up with something I can post an issue.

borkdude 2025-04-07T14:37:49.804939Z

I see there is a bug here: https://squint-cljs.github.io/squint/?src=KGlmIHRydWUgbmlsIDEp The nil case doesn't have a return

borkdude 2025-04-07T14:38:04.089689Z

that one is easy to fix probably and might also fix the other issues

borkdude 2025-04-07T14:38:20.931999Z

the empty function already returns null

borkdude 2025-04-07T14:38:33.827639Z

let me quickly solve the if case