filter doesn't know that the predicate you give it will never return true again

so an infinite sequence input to filter results in a sequence that in theory is finite, but never arrives at its end, so last can never know when it has arrived at the last element to return

you likely want something like take-while

Or drop-while and first (instead of last)?

(and a reversed condition)

your (range ) function is empty so it uses the defaults, this implies (range INF), also why without the loop it is an infinite loop

where start defaults to 0, step to 1, and end to
infinity.

A constant holding the maximum value an int can have, 2^31-1.

something to keep in mind is you are dealing with binary integers, so there may be a faster way to find the next smaller power of two using bit twiddling

there may even be a method on Long that returns such a thing

Thanks @U0NCTKEV8 take-while worked. There is such a small wording difference in their documentation. Thanks @U04V70XH6 will try drop-while as well. @U03GLUMEQSF Thanks for responding, I already understood the part why it was failing, just curious if there is an alternative to filter which works.

I don't know if this is a good solution, but it is definitely a solution:

(def pow2s (map #(int (Math/pow 2 %)) (range)))

(defn just-smaller-pow2 [value]
  (some (fn [[k v]]
          (when (> k value) v))
        (map (fn [k v] [k v])
             pow2s
             (cons 0 pow2s))))

(just-smaller-pow2 5)
; =>
4

(let [l2 (Math/log 2)]
  (defn log2 [x]
    (/ (Math/log x) l2)))

(defn your-fn [x]
  (long
   (Math/pow 2 (Math/floor (log2 x)))))

actually depending on how you want the actual powers of 2 to break…

(defn your-fn [x]
  (if (zero? x)
    x
    (Long/highestOneBit (dec x))))

(defn your-fn [x]
  (Long/highestOneBit x))

Ok using Sean's tip but with take-while...

I haven’t tried that so don’t have answer to your exact question. But Exercism is pretty good along with book Programming Clojure. At this point I am able to read other people’s solutions on Exercism and can appreciate really elegant solutions 😛

Huh cool!

I haven't heard of Exercism before

It doens't seem to be too featured. I will definitely do it though if its free

lucky you! I hear Uncle Bob is a big Clojure fan. I am not familiar with Clean Coders. You might like Paul Graham's "On Lisp" when it comes to Lisp-y coding. Free PDF: http://www.paulgraham.com/onlisptext.html

> It doens’t seem to be too featured. I will definitely do it though if its free Yeah but their CLI is free and their questions are fairly simple for beginners. They also have a VSCode plugin which helps you with test run and quick submission.

https://github.com/oxalorg/4ever-clojure There's also the venerable 4clojure series, which if you haven't already seen, is a good way to familiarize yourself with the standard library and its idioms.

I’m sorry you’re having issues. I don’t know how to use calva (but lots of people do, it’s very popular). I’m sure you can find some help by asking this question in #CBE668G4R where lots of people will be able to point out what’s going on

Thank you very much... Doing it just now!

Here works fine, @U04LNEP9KC6, and of course you are also welcome to the #CBE668G4R channel!

I can't get it working...

I'm trying to understand why this happens. Saw an issue on Github about it too this morning. Maybe that was you, I now realize.

yes, it was me... 🙂

Is the deps.edn really in a subdirectory time?

yes, it is... what I noticed is that the call to clojure doesn't starts with "java -jar '/root/.vscode-server/extensions/betterthantomorrow.calva-2.0.326/deps.clj.jar' -Sdeps '{:deps {nrepl/nrepl ..." as when I first used the fire up Getting Started

it is like it's not linked to calva...

Astute observation! The Getting Started REPL assumes clojure is not installed.

deps.edn should be in the root. Check if that helps. If it does then we need to fix a better UI in Calva.

nope 😞

it is in the root of the project...

What's the content of deps.edn?

{:deps {clojure.java-time/clojure.java-time {:mvn/version "1.1.0"}}}

Cool. That should work. Let me try this and see what I get.

One complication is that I am testing on a devcontainer but the Getting Started worked perfectly...

I see. Maybe that could be a clue. I'll try both.

Thank you very much!

Which version of clojure are you using?

clojure --version

clojure --version Execution error (FileNotFoundException) at http://java.io.FileInputStream/open0 (FileInputStream.java:-2). --version (No such file or directory) Full report at: /tmp/clojure-12876054732791771324.edn [email protected]:/workspaces/clojure# clojure Clojure 1.10.1 user=>

1.10.1, but there was an error trying to get the version directly

That doesn't look like I expect it to.

Do you know where it is installed? If so you could try rename it so that Calva doesn't find it, and try if it works then.

I can set the full project in a git repo if that helps...

clojure is in bin: /usr/local/bin/clojure

With devcontainer and all? That would be great. I don't think it is about the devcontainer anymore, now that it seems it is the clojure executable that is funny. But a repo with your setup would be good anyway.

yes, sure...

I now see that Calva has a setting for using old clojure versions. Search for ”Calva deprecated” in VS Code setting and enable Use Depecrated Alias Flag

Just to see if that works. The real fix is probably that you update clojure.

Calva version: v2.0.327

found the setting, and it worked!!

great!!

Cool! Don't hesitate to reach out should Calva be acting up on you more.

Thank you very much!! Really appreciated!! And... I will, I am super excited to work with clojure/calva!!

btw, a more standard structure of the project is: • deps.edn • src ◦ some_app_namespace ▪︎ time.clj Making the ns form in time.clj be:

(ns some-app-namespace.time)

great!! thank you!

NB: It should be underscores separating the words in some_app_namespace in the directory name, and dashes in the ns form. ( Super easy mistake to do to use dashes in the filename. I actually wrote it wrong first and updated the comment...)

Wow!! this is subtle... 🙂 thank you!

https://clojurians.slack.com/archives/C053AK3F9/p1674650262679479?thread_ts=1674649902.788459&cid=C053AK3F9

What should be the result for search for "d"?

nil empty list

Can one element have more children? Something like:

(def data
  [{:name "a" :children [{:name "b" :children [{:name "c" :children []}]}
                         {:name "d" :children []}]}])

yes

First attempt:

(def data
  [{:name "a" :children [{:name "b" :children [{:name "c" :children []}]}
                         {:name "d" :children []}]}])

(defn in-tree? [data item]
  (.contains (tree-seq associative? identity data)
             [:name item]))

(defn search-name [{:keys [name children] :as data} searched-name]
  (if (= name searched-name)
    (assoc data :children [])
    (assoc data :children [(->> children
                                (filter #(in-tree? % searched-name))
                                (#(search-name (first %) searched-name)))])))

(defn search [data searched-name]
  (when (in-tree? data searched-name)
    (search-name data searched-name)))

(search (first data) "a")
=> {:name "a", :children []}
(search (first data) "b")
=> {:name "a", :children [{:name "b", :children []}]}
(search (first data) "c")
=> {:name "a", :children [{:name "b", :children [{:name "c", :children []}]}]}
(search (first data) "d")
=> {:name "a", :children [{:name "d", :children []}]}
(search (first data) "e")
=> nil

Second attempt (example calls are the same):

(defn in-tree? [data item]
  (.contains (tree-seq associative? identity data)
             [:name item]))

(defn search [{:keys [name children] :as data} searched-name]
  (when (in-tree? data searched-name)
    (if (= name searched-name)
      (assoc data :children [])
      (assoc data :children [(into {} (mapcat #(search % searched-name) children))]))))

wow that's much simpler!

Something to keep in mind is using .contains is a linear search

depending on what else you’re trying to do, clojure.zip might be useful to edit and navigate the tree

@U1Z392WMQ thank you for a hint 🙂 After playing around with the code I had lower my desired requirements. Now just want to check if tree of tags str/includes? substring. e.g Can I use tree-seq for this? For a real use case of this functionality see my site https://culturevein.com/tags So far I have this: (def data [ {:name "a" :children [ {:name "b" :children[]} {:name "c" :children [ {:name "d" :children []}]}]}]) (defn includes-in-tags-tree? [tags substr] (loop [tag tags] (if (and (:name tag) (clojure.string/includes? (:name tag) substr)) true (if-let [child (first (:children tag))] (recur child))))) (includes-in-tags-tree? (first data) "a") ;; => true (includes-in-tags-tree? (first data) "b") ;; => true (includes-in-tags-tree? (first data) "c") ;; => nil -> should be true (includes-in-tags-tree? (first data) "d") ;; => nil -> should be true

it doesn’t look very idiomatic IMO, but another powerful option is https://github.com/redplanetlabs/specter

I'm newbie in clojure 😉 thx for another hint I will check this out 😄

Something like this?

(defn includes-in-tags-tree? [tags substr]
  (->> (tree-seq associative? identity tags)
       (some #(and (map-entry? %)
                   (let [[k v] %]
                     (and (= k :name)
                          (str/includes? v substr)))))))

(includes-in-tags-tree? (first data) "a")                   ;; => true
(includes-in-tags-tree? (first data) "b")                   ;; => true
(includes-in-tags-tree? (first data) "c")                   ;; => true
(includes-in-tags-tree? (first data) "d")                   ;; => true

thank you @U01RL1YV4P7 you are very kind and helpful

that's really elegant solution. But I'm a little surprised with 'and' condition (some #(and (map-entry? %) and (and (= k :name) I would use 'if'. Is this is the way to do it or personal preference ? @U01RL1YV4P7

So, you want to write something like (if ... true false)? You shouldn't do that- see https://github.com/bbatsov/clojure-style-guide#converting-something-to-boolean.

I would write : (defn includes-in-tags-tree? [tags substr] (->> (tree-seq associative? identity tags) (some #(if (map-entry? %) (let [[k v] %] (if (= k :tag_name_lowercase) (str/includes? v substr)))))))

hmm... I'm not sure this the right case 'Converting Something to Boolean'. I understand code this way. with 'and': 1. check - (map-entry? %) - if true proceed to next form, 2. check - can bind key & value to symbol k & v - if true then whole 'and' is true and will proceed further But I understand that '(let [[k v] %]' will be always true, it is always possible, if '(map-entry? %)' is true. So I would use just 'if' => '(if (map-entry? %)' then just bind symbols, don't need to check if CAN bind those value and return true if can.

That will work, I'm just more used to and and or (and some expects some predicate, and small predicates joined with and look more like predicate) ... and and and or are macros and expand to nested ifs, so it actually doesn't matter.

https://groups.google.com/g/clojure/c/b2safKndrTM/m/_lkj391LBQAJ

and an example from clojure.java.shell https://github.com/clojure/clojure/blob/master/src/clj/clojure/java/shell.clj#L52

Hideous, but it works 😛