Clojurians Log v2

that is a good idea.

will try that.

Is there a better way to write this?

(def urls {:yahoo "<https://www.yahoo.com>"
           :google "<https://www.google.com>"})

(defn getter [url]
  (future (slurp url)))

(reduce-kv (fn [acc name url] (assoc acc name (getter url))) {} URL)
;; write a another reduce to deref the futures.

I am trying to get this format output {:yahoo "...." :google "...."}

That reduce-kv is fairly idiomatic to update all the map values; some projects end up with a helper that is named ala map-vals (see e.g. https://weavejester.github.io/medley/medley.core.html#var-map-vals for a more "verbose" version with support for transients)

When you're going to reduce over a second time to deref the futures, you're going to be blocked by the slowest request; which I guess is OK, since you want all the return values together in one map

Which brings me to the elephant in the room - if you're writing some kind of "web scraper", slurp is a really small hammer; most of the http client libraries (e.g. clj-http , aleph , etc.) support things like persistent connections, threadpooling, retries, better support for headers, etc. Things you'll probably need. The way it is written, if a single http request fails, the entire operation will fail and even if you try/catch the result, you will only get back a partial result (as far as you reduced; perhaps other requests finished but you didn't know about it)

This may be of interest too https://practicalli.github.io/clojure-webapps/

what is the clojure way to implement a function that does slightly different things based on a single argument to it being either a keyword or a function?

defmulti

thank you

(defmulti function (fn [arg]
                     (cond
                       (keyword? arg) :keyword
                       ((some-fn ifn? fn?) arg) :function)))

(defmethod function :keyword [arg] )

(defmethod function :function [arg] )

(defmethod function :default [arg]
  (ex-info "Unexpected argument" {:arg arg}))

That's very helpful, thank you! I am reading the docs now and will experiment with it.

fwiw, I knew defmulti should be but I didn't realize I can't just ask type on the argument but have to explicitly create another function to categorize the arguments and dispatch based on that other function instead of type

so I almost got sidetracked before your example cleared it up, thanks again

there is also nice addition to defmulti for repl-driven development

(defn dispatch-fn [& args])

(defmulti function #'dispatch-fn)

...

without it, changes in dispatch function of that form (defmulti function (fn … will not be taken in account unless you explicitly eval something that overwrite function var.

can't use repl driven development yet

so I am not sure what the whole thing is about since I have never seen anyone do what I do using repl driven development and I haven't done anything backend side with clojure. Are you saying that using the above pattern, if I change the defmulti form, that will update how the function works? I understand at least why I would have to eval something that overwrites function usually.

How do people layout cond ? Do do you:

(cond foo?
      stuff
      bar?
      other-stuff
      :else
      do-else-thing)

(cond foo? stuff
      bar? other-stuff
      :else do-else-thing)

Thank you. clj-http looks a lot better.

https://guide.clojure.style/#else-keyword-in-cond

thanks, i wasn't aware of that guide

you should also get a lint/formatter for you editor which can do this for you.

Actually reading that, it seems like my cond should be a condp

Hi, I'm trying to create a selmer filter that can take multiple params.

maybe use split and pass them in with commas? or semicolons? kinda what i'm thinking

If it gets really large and unwieldy, I sometimes do:

(cond
  pred?
  stuff

  bar?
  other-stuff

  :else
  do-else-thing)

Is their a nicer way to do this?

(defn get-source-line-numbers [source]
  (:line-nos (reduce (fn [{:keys [cur line-nos] :as acc} i]
                       (if (or (= "" i) (clojure.string/starts-with? i ";"))
                         (assoc acc :line-nos (str line-nos "\n"))
                         (-> acc
                             (assoc :line-nos (str line-nos cur "\n"))
                             (update :cur inc))))
                     {:cur 0 :line-nos ""}
                     (str/split-lines source))))

Guess what I'm asking is if there is a way to do reduce but with a counter rather than create a map like I've done

In clojurescript, if I have a string stored in a variable, is it possible to get an element from that object based on that what's in that string? Like, say say:

(let [x "color"]
  (. js/window -x))

I know I could use something like eval to make it work, but it seems like that's way overkill in this situation.

Ah, oops, aget is probably what I want.

(And aset)

hmmm have you checked out reduce-kv ? not sure if it's helpful

If you’re accessing an object, use goog.object/get instead.

aget happens to work on objects too but should only be used on arrays

Oh interesting, okay. I wonder why that is.

Is there also goog.object/set?

You bet there is one :) https://google.github.io/closure-library/api/goog.object.html

Ah, there's the api, thanks. 🙂

May I ask why this is preferred over aget/`aset`?

I mean, I see that the docs say its for arrays. But I'm kind of curious about what differences there are (other than just style).

https://clojurescript.org/news/2017-07-14-checked-array-access

One problem that this creates is a challenge in further evolving aget to match its intended purpose. A few examples that come to mind include: • In Clojure, if you pass a non-integer array index to aget, it will round down to the nearest integer. It would be nice to make ClojureScript’s aget match this behavior. This is easily achievable by employing int in the implementation, causing the emitted JavaScript to look like array[ndx|0]. But this would break existing code that uses aget for object property access. • In Clojure, if you pass a negative array index, or one that is otherwise out-of-bounds, you’ll get an exception. It would be nice to consider adding such safety mechanisms to ClojureScript’s aget. But again, any attempt to blindly treat the indices as numbers would run afoul of aget being passed string indices. • In the future, perhaps core library functions will have specs written for them. The same issues arise: The indices passed to aget should satisfy the number? predicate, but if that were done, lots of code in the wild would be deemed non-conformant.

Ah, that makes sense, thanks. 🙂