Clojurians Log v2

Hey guys, I’m looking for a book on design patterns. I found this one: Design Patterns: Elements of Reusable Object-Oriented Software. Of course, it has OO in the title. Is it still useful for a young fledgling clojure dev? What do you guys recommend?

Most of those patterns can be replaced in Clojure with just using a function

So, not that useful imo

really great talk on this topic: https://www.youtube.com/watch?v=E8I19uA-wGY

Can recommend this talk, it got me interested in FP

@c.westrom that book is still pretty useful to understand the patterns, but don't try to do it that way in Clojure. I have it and I refer to it occasionally for my day job using Typescript

much appreciated thank you

@c.westrom I believe SICP Structure and Interpretation of Computer Programs is a classic

Not really a "design patterns" book though... but good for FP if you haven't already read it.

I like to point folks to this http://mishadoff.com/blog/clojure-design-patterns/ when they're asking about "classic" design patterns @c.westrom

This is quite a good preso https://www.infoq.com/presentations/Clojure-Design-Patterns/

I'm getting an error when I modify some code related to a deftype/defprotocol. It works on first load, but after modification, I get:

1. Unhandled java.lang.IllegalArgumentException
   No implementation of method: :as-map of protocol:
   #'com.owoga.tightly-packed-trie.core/ITrie found for class:
   com.owoga.tightly_packed_trie.core.Trie

          core_deftype.clj:  583  clojure.core/-cache-protocol-fn
          core_deftype.clj:  575  clojure.core/-cache-protocol-fn

^ Cancel! Realized I had a defonce instance of the thing I was refactoring... 😳

@robertfrederickwarner yeah I used :insecure? to false and it worked for me,

I think at this point the can of worms has been fully opened lol Double byte-array + transient for filter output is a neat way to get around the bottlenecks of either approach Curious though, I wonder how close these implementations are getting to bare metal Java solutions

set to false? I would have expected it to be set to true to allow insecure certs

ya sorry, I rechecked it ..i set it to true

Groovy. Glad that got you off the ground. Just be wary of that :insecure? setting - it does what it says on the tin, and makes things less secure. Fine for development but if you are putting things into production I'd recommend either getting a properly signed cert, or looking into the :keystore options

yes

anyone gone through the web-development-with-clojure book and had problems with chapter 5 replacing cljsbuild with shadow-cljs? Getting kicked hard right now

Which edition of the book do you have? Which errors do you get?

I have the third edition. I have attached a screenshot of the errors

I see a typo in a namespace in the error:

Sorry I just realized I was missing a "src/cljs" source path

actually I still get the same error

I'm sorry how so?

I see it not, sorry I managed to fix the typo and looks like I have a couple more issues

Oh, I meant’ “geustbook” instead of “guestbook”. Did the error messages change?

Thank you so much I'm just getting warnings now that I am worried about

It seems like get-messages requires a parameter, and your code calls it without one

Hi team, how can I delete maps in vector? for example how can I delete a map if :name is "a" or "c" from given vector want to get

{:name "b" :age 23}

[{:name "a" :age 32} {:name "b" :age 23} {:name "c" :age 23}]

(vec (filter #(contains? #{"a" "c"} (:name %)) [{:name "a"} {:name "b"} {:name "c"}])) @vnazaryan

great thank you

I have "messages" as a parameter.

The error messages show different code. Maybe you have not saved the file?

It is only when I remove the parameter that the warning goes away

Does the app work as expected, it’s just the warnings?

Yes when I open the app on port 3000 is works just fine, I was just worried that the warnings have introduced an issue into the app. I am yet to open the app on port 7002

hey sorted it out thank you so much

Good to hear 🙂 What did you change to sort it out?

I think I have lessons gained in my optimizing of the Java-ish solution that I can bring over to my more Clojuresque solutions. Maybe there are at least two classes to this hunt?

What’s a simple static file server in clojure? I want to move from local hosting my oz viz to exporting to html and server more widely (to my LAN)

Not sure if this is what you are looking for, but deployment to Heroku is pretty straightforward: https://devcenter.heroku.com/articles/getting-started-with-clojure

Honestly, for purely local, static stuff, it's hard to beat just typing python -m http.server <port> at the command line in the dir you want to publish. If you don't need to make API calls to a Clojure backend and are just serving static files, that's the route I'd go.

See also:

I created with golang in the past.. https://github.com/damesek/golang-clojurescript if you have exported html/js version. Quite ok, I didn’t implement the ‘faster go http server’ (fasthttp) but you can shutdown the clojurescript process gracefully

Yep, though I already willi have a clojure daemon running

One really cool thing I like about Clojure's built-in map function is that you can pass it multiple lists. As it maps through, it will take the nth item from each list and pass it to your function:

(def vector-one ["hello " "goodbye "])
(def vector-two ["friend" "buddy"])
(map (partial apply str) vector-one vector-two)
; -> ("hello friend" "goodbye buddy")

(def vector-one ["hello " "goodbye "])
(def vector-two ["friend"])
(map (partial apply str) vector-one vector-two)
; -> ("hello friend" "goodbye friend")

Use an infinite sequence of “friend” for vector-two

map stops when it runs out of a seq input

What's the best way to do this sort of thing (first (for [i items j (expensive-fn i) :when (pred j)] j)) without computing expensive-fn unnecessarily due to chunking? Is there an unchunked version of for?

(imagine there's more layers to the for)

If you want control, use loop recur

Here comes the next step in building up my "Clojure brain." Great suggestion, thank you!

In general, if you care about exactly how many things get evaluated, you should not be using lazy seqs

Fair point 🙂

for is just so nice and readable

A common pattern for initializing maps is to zipmap finite keys with (repeat 0) or whatever the initial value is (similar idea)

(def scores (zipmap [“Joe” “Anna”] (repeat 0)))

Naw, I want to host on my raspberry pi. Basically my Pi is taking various measurements of sensors and shoving it in a DB. I use oz to display it, but it normally opens a websocket to the front end which is on localhost. I want to make a bit of a dashboard

You can compile to Raspberry PI with my solution, with To build it for the Raspberry Pi, we use: env GOOS=linux GOARCH=arm GOARM=7 go build. command. i think you could do with that, eg what you can with shadow-cljs. I updated a little bit the repo, maybe in this way could be helpful.

You can create w/ V8 cli apps too, or with Babashka/ Graalvm.

Here’s a version of that last loop w/ transients solution, where I parallelize the collection of the sieved indexes.

(defn pez-ba-loop-transient-parallel-sieve [^long n]
  (let [primes (boolean-array (inc n) true)
        sqrt-n (int (Math/ceil (Math/sqrt n)))]
    (if (< n 2)
      '()
      (loop [p 3]
        (if (< sqrt-n p)
          (let [num-slices (if (and (even? n)
                                    (> n 1000))
                             50
                             1)
                slice-size (quot n num-slices)
                futures (mapv (fn [^long slice-num]
                                (future
                                  (let [start (inc (* slice-num slice-size))
                                        end (dec (+ start slice-size))]
                                    (loop [res (transient [])
                                           i start]
                                      (if (<= i end)
                                        (recur (if (aget primes i)
                                                 (conj! res i)
                                                 res)
                                               (+ i 2))
                                        (persistent! res))))))
                              (range num-slices))]
            (concat [2]
                    (drop 1 (into []
                                  (mapcat deref)
                                  futures))))
          (do
            (when (aget primes p)
              (loop [i (* p p)]
                (when (<= i n)
                  (aset primes i false)
                  (recur (+ i p p)))))
            (recur  (+ p 2))))))))