(I guess there's a small chance that -> form is incorrect because ($ 1) or ($ :type) might not be a map lookup, but I find it unlikely it would be anything else in context)

Also (since this is one of my "pet peeves"), as-> is designed to be used inside -> for cases where the value you're passing in is neither the first nor last argument (for the latter case you can nest ->> inside ->). So it is more normal to see:

(-> exp
    (f 2 3)
    (as-> x (g 1 x 3))
    (h 2 3)
    (->> (map foo)))

@noisesmith Yes, that was an example from the Clojure docs.

http://Clojuredocs.org are not official clojure docs, so you need to be dubious of what you find there

A lot of what is there is good, but the quality does vary

In Python one can strip characters from the end of a string with 'foo/'.rstrip('/'). Is (clojure.string/replace "foo/" #"/$" "") the Right Way to do that in Clojure?

If you only want to strip one / off, that would work. #"/+$" would match one or more / at the end of the string.

I don't know whether I'd say regex is the Right Way but it's either that or checking (str/ends-with? s "/") and then returning (subs s 0 (dec (count s))) which may be clearer or not 🙂 but might well be slower.

Looks like the if / ends-with? / subs approach is faster if that matters @clojurians-slack100?

user=> (time (dotimes [n 100000] (str/replace foo #"/$" "")))
"Elapsed time: 91.607793 msecs"
nil
user=> (time (dotimes [n 100000] (if (str/ends-with? foo "/") (subs foo 0 (dec (count foo))) foo)))
"Elapsed time: 33.313469 msecs"
nil

(I ran it several times and that's about the average -- but all the usual caveats about micro-benchmarks apply 🙂 )

Very cool, thanks @seancorfield!

I tend towards the more readable one for single cases, so I guess I'll stick with str/replace 🙂

@adamfranzen check if you're in the same namespace as the one you defined foo in

which channel will be a proper one to ask java memory model question?

@nxtk here

Just need a confirmation that JMM is weakly ordered and such order of reads is allowed for a non-synchronized code.

if t1 runs test concurrently with t2 writing v, t1 can get the old value

but you can easily fix this using the stack, e.g return (r.v = v);

@leonoel the question is can test's return value be older than r.v

if v was changed by other thread, before test run

t1 v = 1
t2 return v:0
t2 r.v = v:1

yes

yup ty

Hi Clojurians, I have a simple problem for which I’m trying to find an idiomatic solution - basically transforming a map of maps into a vector of vectors

(fun {{:a 1} {:b 1}} )
;;=> [[:a 1] [:b 1]]

(fun ({:a 1} {:b 1}))

When reading clojure code I don't seem to see any explicit error handling like try/catch or whatever (I'm really naive on this stuff for any language, not just clojure). I've explored using :pre and :post conditions a little bit.

Looking for some regex help (I think). I want to split a string like "2AB3cD4e" into ["2A" "B" "3c" "D" "4e"] so with some repl experimentation I have (re-seq #"\d[a-zA-Z]" text) but that leaves out all single letters like "B" or "D". Various other attempts give me different things too but I can't quite get what I want. Any help? Would you approach this altogether differently?

(re-seq #"\d?[a-zA-Z]" text) ?

?!!! Thanks. Man, regexes kick my butt sometimes.

So regex is pretty universal across languages, right? If I find a general regex tutorial on the interwebs it should be directly applicable or should I learn a specific java way?

the basics are pretty universal, the details or advanced usage usually depend on which flavor you're using

but Clojure just re-uses Java's so that is the one to look at

https://docs.oracle.com/en/java/javase/13/docs/api/java.base/java/util/regex/Pattern.html

top part of that page is the reference for the Java api

thank you! ? seems to be a "once or not at all" pattern.

I am not an authority on this, but having seen quite a few regex languages over the years, the meanings of these characters is good to learn, and common across all or most of them: [ ] + * ? | . After that things like \s \S \d I use most commonly. After that I don't trust that I will be doing enough with that one regex library that I will remember what is common across them and what is not.

This web site has way more detail than I ever want to learn on the subject, but is probably a good resource if you want to (a) learn the basics, (b) find some cool tools that show interactive color highlighting of a regex against sample text, to more quickly debug your regexes, and (c) dig into the gory details of the differences between different libraries, if you want to. https://www.regular-expressions.info/

awesome. I'll bookmark it. I also was recently suggested this one: https://regexone.com/ and it looks good too.

As I may have already strongly hinted at, I would recommend learning the basics of regex's first, and if you start getting into things where you are using other features, e.g. lookahead, lookbehind, etc., consider instead using a more powerful parser, e.g. for Clojure something like instaparse

Howdy y'all, anybody got a problem? 😄

How hard of a problem are you looking for? 🙂

hmm, what's your hardest one?

Prove that P=NP, or that P!=NP 🙂

i meant a useful problem

But I'll try to show that P = NP.

That would be cool.

I wonder why they decided to make clojure map destructuring work like “value key, value key” instead of the arguably more intuitive “key value key value”:

user=> (let [{a :a b :b c :c} {:a 1 :b 2 :c 3}] [a b c])
[1 2 3]

user=> (let [{:a a :b b :c c} {:a 1 :b 2 :c 3}] [a b c])
[1 2 3]

user=> (let [{:a a :b b :c c} {:a 1 :b 2 :c 3}] [a b c])
Syntax error macroexpanding clojure.core/let at (REPL:1:1).

Because bindings typically have symbol then expression.

(I think that's why)

If all the keys match the symbols you want, you can use (let [{:keys [a b c]} ,,,] ,,,)

thanks

at first I thought it was so that you could put any function on the right hand side, that keywords were just a special case, but:

user=> (let [{a :a b :b c :c size count} {:a 1 :b 2 :c 3}] [a b c size])
[1 2 3 nil]

user=> (let [{a 'foo b :bar c "quux"} {'foo 42 :bar 13 "quux" 99}] [a b c])
[42 13 99]
user=> 

Most maps have keys that are keywords -- but you can have symbols and strings too.

(Disclaimer: i'm a newb so, school me) P = NP. or why the equals sign doesn't make sense in asking about the equality of transformational potential. We have a question of results from transformations and their equality. Computer Science is fundamentally about naming and counting. When we count the number of motions required to achieve a transformation, we are reifying certain subsequences of the transformation. Due to physical necessity, counting requires a drawer or a register in which to store a value. However, in philosophy, the question of transformation is much cleaner: Can the water that become the ice also become steam? However, it seems obvious that a robot could tie shoes so tightly and so complexly (in a complex fashion) that it would be nigh impossible to untie. However, the exact transformation that got us there is also the exact reverse transformation that can get us out. In one-way mathematical transforms over fields, the question of information entropy is alive and well, although deteriorating like swiss cheese. However, no matter how complex the tying of the shoelace, it is still a shoelace. In this way, no matter what we do to transform the data, we end up with data. Can we reintegrate data when meaning has been obscured? It's not clear if all complex transformations have more than one solution mapping, but because they all have at least one solution mapping (it has never been shown that a problem has zero solution mappings) then P must equal NP. Only if someone were able to demonstrate that there is absolutely no way to map between the two domains for a given problem could we say they are distinct sets, but to my knowledge this is yet to occur, and unlikely to be the case, even if so at first glance.

And just like {:keys [,,,]} you can have {:strs [,,,]} or {:syms [,,,]} @joshlemer

destructuring always tries to put the symbol being bound on the "left" side of the let

@joshlemer consider {{:keys [a b]} :top {c :C_IS_POORLY_NAMED} :top}

it's useful and legal to use the same value twice in hash-map values

it isn't legal to use them twice as keys - the reader rejects it

I would say the mnemonic of "key value, ..." leads you in the wrong direction - it should be "binding value, binding value, ..."

@noisesmith seems like it would be more useful to just combine those though

ahh, they can be combined, true

I vaguely recall a valid and interesting usage of the same key twice in a destructure, used in different ways, but the example is clearly escaping me (or I missed something the first time around as you point out)

ok I see so it’s that they chose to be consistent with other places bindings happen, rather than try to be consistent with how maps look. Nice!

yes

sequential destructuring leads you into thinking about it as a pattern or template, but that's not a correct model

it's about describing structural binding

Topic change: I find transducers really cool in how they decouple the transformation from the underlying “sources”/“sinks”. But do they handle only the single-input single-output case such as collection operations, or can they encode multi-input/multi-output transformations as well, like fan-in/fan-out/routing?

generally, no

in the very special case of map in sequence context, the map transducer can take multiple input streams

the arities in this case fight with a lot of other uses so it's not done anywhere else

the "pull" model of how transducers are implemented means that multi-out or fan-out are not a good match (unless you are packing multiple outputs into a single output collection)

that said, core.async does have all those kinds of things and allow transducers on individual pipes (by embedding them in channels, or by using multi-threaded transducible pipelines)

oh okay thanks I’ll have an other look

Hi everybody, I am trying to get an existing project setup in InteliJ/Cursive. I created a Leiningen configuration, I am getting " Run Configuration Error: The Clojure jar is not attached to this module" . Does anybody have direction to help me out ? Any help is greatly appreciated.