Can someone help me figure out a probably-stupid oops? I'm trying to avoid blowing the call stack on a non-recursive function (calculating triangular numbers) by leveraging memoize + laziness. This code works, and prints 28 as expected:

(defn tri [num]
  (if (= num 1)
    1
    (+ num (tri (- num 1)))))
(def triangulate (memoize tri))
(println (triangulate 7))

(def triangles (map triangulate (range)))

(println (take 7 triangles))

the self call doesn't go back and call the memoized version

oh, that would make a difference rather

I'm an idiot

hah

(def triangulate (memoize (fn tri [num] (if ... (+ num (triangulate (dec num))))))

back references to a def you are inside are allowed

I knew it would be a dumb mistake... 🙂 thanks @noisesmith !

hmm. even the properly memoized version still blows the call stack though.

(def triangulate
  (memoize
   (fn tri [num]
    (if (= num 1)
      1
      (+ num (triangulate (dec num)))))))

(def triangles (map triangulate (range 7)))

(println (take 2 triangles))

oh wait.

I'm still stupid.

that's because the range starts at 0. oooops

is there a blush emoji here somewhere? this works 😱

this might be take a nap time. 🙂

is it well defined what #?(:cljs 1) evaluates to in clojure ? is it 'nil', nothing-at-al--since-stripped-awway-by-reader, or undefined

> If no tags match and :default is not provided, the reader conditional will read nothing (not nil, but as if nothing was read from the stream at all).

https://clojure.org/guides/reader_conditionals

@gowder FWIW, memoizing a function does not prevent a stack overflow .. if the function is called recursively many times when no memoized values are available yet, it will still blow up.

Every time I use partition I think it is going to behave like partition-all…. until awhile later tiny parts of data are missing everywhere and I remember my nemesis

Do we have list of functions like into which works with transducers?

how to do sql in in clojure.java.jdbc?

Is that I have to write in (?, ?, ?) and provide 3 values.

Do you see here place for transducer? https://pastebin.com/ABd9rYAr

how can i call a java function that expects a primitive float? (f 0.5) won't work because 0.5 is read as a java.lang.Double

(f (float 0.5)) ?

(type (float 0.5)) yields java.lang.Float

that's because type expects an Object so the primitive float will get boxed again

but in contexts where a primitive float is accepted, (float 0.5) will do the job

nonetheless, (f (float 0.5)) doesn't work. f is a constructor and i'm getting No matching ctor found for class

if i do (f 1) it works because there's a constructor for ints

but i can't call the one for floats

found a solution. The full signature of f was (f float float float float). calling this in Java with f(1, 1, 1, 0.5) works fine because the ones get coerced

in clojure i have to write (f (float 1) (float 1) (float 1) (float 0.5)) to get the same effect

i was only trying (f 1 1 1 (float 0.5))

so i'm trying to implement an abstract class using proxy and i want to set a protected field during an init method. using set! seems to fail because of the visibility restriction

even packageprivate won't work even though it's the same package in my test case

i can only set the field if it's public

@hoff write a subclass in Java that exposes whatever you need?

Is it expected that executing java -jar mystandalone.jar from the command line returns focus back to the user when the main function is finished? When I execute the jar file my main function runs, gives the output, and then it just hangs

i think i fixed it by adding (System/exit 0) at the end of my main function

@michaellindon Instead try shutdown-agents, which might address the root cause

There's a 60 seconds delay on the agent threadpool or something like that; shutdown-agents bypasses that.

https://clojure.org/guides/faq#agent_shutdown

thanks guys

Thank you, Alex!

hi I have a ‘flattening’ question I have a list like this (def listoflists [[1 2 3 4] [5 6 7 8]]). I’d like to build a new list that’s something like [ 1 [1 2 3 4] [5 6 7 8]] by doing [1 something(listoflists)] . (flatten) is ‘greedy’ Doing it on the entire collection gives me [ 1 1 2 3 …] just on listoflists results in [1 (1 2 3 ..)]. I’d found some notes that indicated that either (apply concat listoflists) or (mapcat identity listoflists) would do what I want, but they both seem to essentially do a flatten

(def listoflists [[1 2 3 4] [5 6 7 8]])
=> #'user/listoflists
(pprint [1 listoflists])
[1 [[1 2 3 4] [5 6 7 8]]]
=> nil
(pprint [1 (apply concat listoflists)])
[1 (1 2 3 4 5 6 7 8)]
=> nil
(pprint [1 (mapcat identity listoflists)])
[1 (1 2 3 4 5 6 7 8)]

@eoliphant if [1 [1 2 3 4] [5 6 7 8]] is not a typo, the answer is (cons 1 listoflists)

Is there a way to get clojure.test/are to report the values for which it failed on failure

it doesn’t seem like you actually want flattening at all

ah heck didn’t really think about it that way

yeah i’m dynamically building up a Datomic transaction

and have lists of adds and retracts

thx

going to restructure it

if it needs to remain a vector for datomic, you can use (into [1] listoflists)

is there an idiomatic implementation of binary trees to be found anywhere? I cannot seem to find much content on binary trees in clojure -> it makes me believe that the standard was of delclarying a node object with key left and right is not idiomatic in clojure

a clojure sorted-set is a binary tree iirc

it’s red/black

ClojureScript has CLJS ports of the Clojure datastructures, including the PersistentTreeMap, which is the red/black tree used for sorted-map and sorted-set https://github.com/clojure/clojurescript/blob/master/src/main/cljs/cljs/core.cljs#L7649-L8364

There you have node objects RedNode and BlackNode, defined with deftype and having left and right fields

data.avl also uses deftype to define AVLNode: https://github.com/clojure/data.avl/blob/master/src/main/clojure/clojure/data/avl.clj#L159

this looks good, let me check some of these out, thanks

🙂

So I have a project running in both boot and lein. Under lein it runs fine, but under boot I get a ClassNotFoundException: org.jboss.vfs.VirtualFileFilter. Both projects have the exact same dependencies. Why would boot faile to load JBoss properly?

boot does classloader jiggery pokery after the jvm has started, lein starts the jvm with the classpath set

does this eastwood message mean anything? I didn’t get a warning

dbg wrong-pre-post: condition=(:exec game-record) line=103 test-ast :op=:keyword-invoke

just wondering if anyone here uses clojurewerkz/neocons on a semi regular basis?

in case someone picks this up later, i find myself writing a lot of cypher queries and executing them via tquery, but i'm constantly mapping through results to pluck the :data values and ignore all the other stuff i don't care about (incoming relationships, meta properties, etc.). i'm now resorting to spectre to stay sane. is there a better way?

in a *.cljc file, I should be able to just do: (:require [clojure.core.match :refer [match]]) and it all works right? or do I have to #?(:cljs ... :clj) separate lines ?

you probably need to escape the vector (`'[clojure.core.match :refer [match]]`)

not sure beyond that

but it's insided the ns part

(ns ...
  (:require ... ))

right, you don't. Sorry about that

effort is apprecaited

this latest "some stuff is magical clj/cljs is confusing me"

@qqq I think this should work.

(ns foo.bar
  (:require
   [clojure.core.match :refer [match] #?@(:cljs [:include-macros true])]))

https://github.com/clojure/clojurescript/wiki/Differences-from-Clojure#namespaces

You may get away with not including the include-macros thingy, and just :requiring normally, but it depends on how the namespace you're requiring is written.

http://blog.fikesfarm.com/posts/2016-03-01-clojurescript-macro-sugar.html#implicit_sugar

hrm, there really is no way to override hashCode for a defrecord, huh?

I’ve got an issue with that, I have a defrecord that contains a derived map from potemkin, but which one of the “keys” of the derived map is null

which causes hashCode to throw a NullPointerException