Consistent behavior of <?maybe

[keerts]

In the README, <?maybe is documented as take and throw errors, return value if it’s not a channel. The function itself does not mention the throwing errors part in it's docstring. If the function indeed was intended to throw in case of an error (which I actually use it for, cause that's great!) that might not be the consistent behavior of it.
In case you pass a chan, that's exactly what it does, cause that's what <? brings to the table with (throw-err).
In case you pass a promise, the (throw-err) functionality is missing. That could either be added in <?maybe, or in promise variant of <?, maybe <?p.

What do you think?

(defmacro <?maybe
  "Tries to await for a value, first if checks if x is a channel, if so will read
  on it; then it checks if it's a JS promise, if so will convert it to a channel
  and read from it. Otherwise returns x as is."
  [x]
  `(let [res# ~x]
     (cond
       (chan? res#)
       (<? res#)
       (promise? res#)
       (throw-err (<!p res#))   or   (<?p res#))       <-----------
       :else
       res#))

[wilkerlucio]

Hello, thanks for taking the time to write. About the promises, I think they don't need to change because the <!p already handles promise errors. It's a bit different than returning an error as a value, if you use a promise and want to fail it, you must reject the promise (which is the standard thing).

Here are the relevant functions of the process:

(defmacro <!p
  [promise]
  `(consumer-pair (async/<! (promise->chan ~promise))))

(defn promise->chan
  "Converts promise p in a promise-chan. The response of this channel should be consumed
  using `consume-pair`."
  [p]
  (let [c (async/promise-chan)]
    (.then p
      #(async/put! c {:success %})
      #(async/put! c {:error %}))
    c))

(defn consumer-pair
  "Consume promise channel result pair."
  [resp]
  (if (contains? resp :error)
    (throw (:error resp))
    (:success resp)))

Makes sense?

[keerts]

Just thought it was inconsistent, when passing it a chan, it does throw errors, when passing it a promise, it does not. I would expect that behavior to be the same, no matter if it a chan or a promise. But I can work with it as it is.

[wilkerlucio]

I still can't see the inconsistency, maybe I'm not understanding it. I wrote this example to demonstrate that the case of promise also throws the error:

(is (= (<! (wa/go-promise
             (try
               (wa/<?maybe (js/Promise.reject (ex-info "foo" {:bar "baz"})))
               (catch :default _ "error"))))
       "error"))

Can you show the code you expect to trigger an error that isn't doing so?