Curious question I just thought of that I don’t really know the answer to. Does Clojure structural sharing mean that if I create copies of the same data structure in a larger data structure there is only one copy in memory, or does each copy take up more memory? e.g. (into [] (repeat 10 {:a "foo" :b "bar"})) is there 10 copies in memory or just one?

I'm not entirely sure, but I think there would be 10 copies. That said, both keywords and strings are interned in Clojure, so there's always only one copy of them

So like, irregardless of structural sharing, there is always only one copy of equal keywords and strings

But structural sharing doesn't share between equal elements, it shares parent node in the tree of changes

@didibus @sofra repeat will give you the same object N times, period

you'll have 10 pointers filling the [] of course, but the map itself is only created once

:thumbsup:

also you should write your code so the difference wouldn't matter :D

Oh right, that too. But I assumed the question meant more: (repeatedly #(identity {:a "foo"}))

even that, the clojure compiler only creates that hash map literal once, and identity doesn't touch it, just returns it

thanks @noisesmith, I think that clears it up

but agreed with @didibus that this isn't structural sharing - it's just normal behavior

Hum, true true, because the literal can be treated as a value. Okay so: (repeatedly #(hash-map :a "foo"))then

(though behavior that you're less likely to take advantage of in a language where data isn't immutable)

that would create new hash maps yeah

In which case structural sharing would not dedupe these correct?

because hey, you might redefine hash-map in the middle of realizing that lazy seq, and clojure promises to role with that

(please dont' redefine hash-map in the middle of a lazy-seq or otherwise)

🙂

@didibus right, none of these examples so far are structural sharing

Cool, I wonder how all this plays with regards to performance and cache hits

If you want to see whether structural sharing is occurring, and exactly how, in Clojure/Java (not ClojureScript), I have a little library that graphically draws the JVM objects in memory used to represent Clojure values. I included a little gallery of example images it created in the docs for the library here: https://github.com/jafingerhut/cljol/blob/master/doc/README-gallery.md

That gallery does not currently contain any examples of structural sharing, but it would be easy to add some.

would be super useful to have in CLJS too! 😄

Hi everyone, I'm using ring-swagger + spec-tools and trying to send array-like query param to the server from Swagger UI: What I want to see: `orders?status=NEW&status=PROGRESS`, but the request was sent in comma-separated form: `orders?status=NEW,PROGRESS` How can I fix it? Seems like I need to add `explode true` in serialization params... Thanks in advance!

Is there some way to have maps printed with clojure.tools.logging be pretty-printed?

If I have a symbol 'foo/bar where foo is an aliased ns, how can I find out the full, un-aliased ns?

resolve

I guess resolve will give you the var, you may be asking for the alias resolution particularly?

yea hthat only works if foo/bar is an existing var

you can use ns-aliases to resolve aliases

@alexmiller resolve, of course. thanks

user=> (alias 'foo 'user)
nil
user=> (ns-name ((ns-aliases *ns*) (symbol (namespace 'foo/bar))))
user

(.name (get (ns-aliases *ns*) 'foo))

jinx

using ns-name is better of course

(defn resolve-symb-alias [s]
  (symbol (str (get (ns-aliases *ns*) (symbol (namespace s))))
          (name s)))

that's what I had..

even had the answer in the name of the fn!

Dear all, I am new to Clojure. I am using Cursive on IntelliJ. I can Build my project but when I try to run it I get this error. Error running 'test (1)': failed to access class com.intellij.execution.impl.ProcessStreamsSynchronizer from class com.intellij.execution.impl.ConsoleViewRunningState (com.intellij.execution.impl.ProcessStreamsSynchronizer is in unnamed module of loader com.intellij.util.lang.UrlClassLoader @7f9a81e8; com.intellij.execution.impl.ConsoleViewRunningState is in unnamed module of loader http://com.intellij.ide.plugins.cl.PluginClassLoader @7b0d6c9c). Does anybody understand what I am doing wrong?

in terminal emacs, I just want to press a binding and see the ClojureDoc with examples for a symbol under the cursor and I want to see the results in emacs as opposed to having it launch the browser... I had this once but I think it became deprecated... also, it seems that cider has to be running for quite a few approaches to this, which is less than ideal for just reviewing/learning-from code I don't want to start a repl for. Any ideas?

I like terminal emacs so much, but it is so great to get instant docs for the methods of objects in most languages and editors. There has to be a way!

And, of course, it needs to be ClojureDocs as I can't really understand a lot of the official docs for functions.

the official docs for 'get' state that it

Returns the value mapped to key, not-found or nil if key not present.

(get ["foo" "bar"] 1)

is 1 an implicit key or something?

it seems that the docs are saying get works on maps, not vectors, via keys.

@patrickanium when get is used on a vector it uses the key you pass as the index. In this case that returns “bar”

If you passed 0 it would return “foo”.

it is interesting this is not at all indicated in the docs. or am I supposed to understand this from the docs?

(thank you for the answer!)

mapped can mean different things

in the case of a map, a key is mapped to a value

for a vector an index is mapped to a value

I still can't figure out if I'm just too dense to understand the official clojure documentation, or if it's somehow scant.

in this case, now I'm lined out (and grateful for the explanation)

similar for strings, a index is mapped to a character

user=> (get "foo" 1)
\o
user=>

nice, ok.

The official Clojure docs are (in)famously terse.

man, can't help with getting people into the language.

I feel like if I could understand them, I'd rock.

like, read one line, understand the function.

There is http://ClojureDocs.org as you know, and books, tutorials, etc.

but in the 'get' example above... not sure I could/would have realized that it works on vectors, etc.

actually, I'm want to know what I would have to know to be able to deduce how it behaves on other things than maps.

Anyone is free to write and publish docs for all 600+ built-in functions that they like better, of course. Except for http://ClojureDocs.org and books like Clojure: The Essential Reference (which probably took many person-years to write), no one has volunteered.

I know, but as someone learning the language... I'm not sure I'm up for writing docs... I need to read them! ;-D

The simple answer is: Don't rely only on the built-in doc strings. Find other sources that help you, too.

ah, ok... I got used to languages like JavaScript where you just casually move through the code and an intelligible explanation appears...

(multiple) browser trips for every new function is pretty brutal.

Does the text for get on http://ClojureDocs.org make it any clearer for you? If so, your project to make that quickly accessible in your IDE is a very good recommendation that you are already following.

that's what I'm working on ATM... I can get it via cider, it seems.

and thank god for http://clojuredocs.org.

Thank the contributors. They made it happen. God had nothing to do with it 🙂

haha indeed.

let's be clear, though... y'all are gods to me.

a pantheon.

Some people find the Clojure cheatsheet useful, not because it provides better docs, but because it organizes (most, not all) of Clojure's built-in functions and macros into related groups: https://jafingerhut.github.io

oh sweet!

this is very helpful. a map of sorts.

Why does halt-when not appear to work with sequence?

(sequence (halt-when odd? vector) [2 2 1 2])
=> (2 2)

certain transducible contexts (chan/sequence/into) do not expose the completed value

It doesn't make sense in the sequence or chan case I think it's a bug that #'into doesn't gel with halt-when

https://clojure.atlassian.net/browse/CLJ-2556

I think it could make sense to expose it. I would like a lazy sequence of results and a secondary value that contains an error, if one occurred.

I don't see how that would work with sequence

an example would be helpful

The result of halt-when's retf would be the end result. Something like this is the alternative, I think.

(def my-seq (sequence xf my-seq))
(doseq [item (filter #(not (error? %)) my-seq)]
  (process-item item))
(some error? my-seq)

It requires iterating my-seq twice.

you've hidden the return values of sequence

(sequence (halt-when odd? vector) [2 2 1 2]) what would this return?

Presumably [the-sequence failing-val], though, perhaps this is what you're getting at, failing-val may not have been realized yet.

you can't check the predicate without realizing the value

Right. Thus you saying "It doesn't make sense in the sequence or chan case"

it doesn't compute not because of the realization aspect, but because of the nature of those transducible contexts

channels' "step" is putting an item in a channel

can't have the completion function synthesizing things that weren't there and putting them in the channel (Flushing something like partition-all is different)

sequence's "step" is adding to the rest part of an ISeq

demand-driven iteration

Anything that is iterative/step based therefore will not work with halt-when, right? It only works for eager reduces.

halt-when is no different than take in that it chooses to abort the stepping process

(sequence xf coll) and (chan buf xf) do not expose the completed value

no matter the xform

here is the internal "step" of sequence https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/TransformerIterator.java#L39-L50

I posted a debug to my cider-clojuredocs issue to #cider if anyone is able to look at it https://clojurians.slack.com/archives/C0617A8PQ/p1588888419018300