Clojurians Log v2

Oh I do care, the result is a side effect though (slack message)

I don't keep a reference to the future, nor do I wanna block on it

I very often get the following genre of error

actual: java.lang.IllegalArgumentException: Don't know how to create ISeq from: clojure.lang.Symbol
 at clojure.lang.RT.seqFrom (RT.java:553)
    clojure.lang.RT.seq (RT.java:533)
    clojure.core$seq__5387.invokeStatic (core.clj:137)
    clojure.core$empty_QMARK_.invokeStatic (core.clj:6206)
    clojure.core$empty_QMARK_.invoke (core.clj:6206)  clojure_rte.genus_spec$eval17078$_spec_to_rte__17079$strip_keys__17105.invoke (form-init10191085421504055651.clj:122) clojure_rte.genus_spec$eval17078$_spec_to_rte__17079$specify__17080$iter__17081__17085$fn__17086.invoke (form-init10191085421504055651.clj:103)
    clojure.lang.LazySeq.sval (LazySeq.java:42)
    clojure.lang.LazySeq.seq (LazySeq.java:51)
    clojure.lang.Cons.next (Cons.java:39)
    clojure.lang.RT.next (RT.java:709)

The https://clojuredocs.org/clojure.core/letfn`letfn` says I cannot put :pre and :post conditions on local functions. Is that intentional? I often use :pre conditions while debugging.

Hello, i am new to Programming overall i only know a bit JS and mediocre elisp since I am using alot of Emacs for Work. I plan to create a small to medium personal webproject - I dont know if Clojure is suited well for that but where would be a good starting point?

I do not see any mention of pre or post conditions at all in that documentation. It does not say you cannot. It does not say anything about them.

But agree they are absent from that documentation, from which one might guess they cannot be supplied.

It really only takes a minute or two to experiment and see whether they work or not, in a REPL.

In my several-minute experiment, they are supported inside of functions defined within leftfn

That error can occur with no destructuring occurring, too.

For example:

user=> (seq 'a)
Execution error (IllegalArgumentException) at user/eval184 (REPL:1).
Don't know how to create ISeq from: clojure.lang.Symbol

user=> (filter even? 'a)
Error printing return value (IllegalArgumentException) at clojure.lang.RT/seqFrom (RT.java:557).
Don't know how to create ISeq from: clojure.lang.Symbol

user=> (map identity 'a)
Error printing return value (IllegalArgumentException) at clojure.lang.RT/seqFrom (RT.java:557).
Don't know how to create ISeq from: clojure.lang.Symbol

Note that the symbol in question might not occur in your source code anywhere, e.g. it could be read from input.

Clojure works well for web-development. What kind of a project are you planning?

Hi, I am newbie in Clojure so my question might be very stupid. Suppose thread A wants to set an atom x to 5 and thread B wants to set it to 6. We expect the value to be 5 first and 6 after. Thread A though is blocked and retried after thread B, the value of x would then be 6 first and then 5. How is consistency assured with atom when a retry happens?

@francesco.losciale what do you mean by threads? i never use forking in clojureland

Compare and set is a common idiom to the point where most processors actually implement an equivalent instruction

The retry is not around the setting, but the entire operation

why do you expect the value to be 5 first then 6? the atom will ensure that the operations are applied atomically, but I don't see anything in your description that would imply or impose ordering

1. Read value 2. Apply function to get new value 3. Set new value if nothing has changed or go-to 1

Depends on how much you want to make from scratch and how much you want to use an existing template for... z

Luminus, Fulcro, are both options for applications You could also simply start with an http-server like clj/ring or http-kit and then build a website from a basic server with HTTP requests/responses

I am thinking of a use case in which the state can only be increased, for example. If it changes to 6 and then to 5, the first “thread” might run logic thinking the state is 6.

Is it implied the functions that change the state are always commutative?

oh, ok! here's the equivalent code

(def x (atom 4))

;; on thread A
(swap! x inc) 

;; on thread B
(swap! x inc)

you can find clojure's implementation https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/Atom.java#L34

public Object swap(IFn f) {
	for(; ;)
		{
		Object v = deref();
		Object newv = f.invoke(v);
		validate(newv);
		if(state.compareAndSet(v, newv))
			{
			notifyWatches(v, newv);
			return newv;
			}
		}
}

Hello, I'm starting the book Programming Clojure by Alex Miller. I'm trying to run (require '<http://clojure.java.io|clojure.java.io>') . I've started a repl using the lein repl command. I know little about Java and the error I'm getting hasn't been useful so far. Here's the error:

Could not locate clojure/java/io'__init.class, clojure/java/io'.clj or clojure/java/io'.cljc on classpath.

No single quote after http://clojure.java.io

It is not a string, but a symbol. A leading single quote in Clojure means that the following expression should not be evaluated.

Thank you so much!