Thanks @andy.fingerhut! (flush) did the trick

Hey All. When I do (map (fn [nr] '(nr)) [1 2 3]), the result I get from my REPL is ((nr) (nr) (nr)), why isn’t this ((1) (2) (3)) ?

quote is recursive, so it will quote everything inside the list

try (list nr) instead

oh wow yeah that works, I don’t understand exactly why though. Is the quote character somehow telling the compiler to take everything inside of it literally?

precisely! when you see quote, everything inside whatever you’ve quoted will be returned exactly as it looks

@tim.degroote yes, the quote special form (which ' maps to), tells the compiler to stop evaluation for the next form

there is also the syntax-quote form (the backtick), which accepts "unquoting" via ~ and "unquote splicing" via ~@

so you can do for example

`[a b ~c d]

this is rougly equivalent to ['a 'b c 'd] (except syntax-quote also namespace qualifies symbols)

oooh interesting, didn’t know this! This cleared it up for me, thanks a lot for the help @schmee @bronsa!

you can read a bit more about syntax-quote here https://clojure.org/reference/reader#syntax-quote

Is there something like resolve that, rather than returning the var, returns the fully qualified symbol name?

e.g. (symbolic-resolve '+) => clojure.core/+

in 1.10 that's just (comp symbol resolve)

but you can use syntax-quote for that

if you can do that at read-time

doh. perfect. thanks

yeah, i need a function since I am handling this at macroexpansion time

and quasiquote is ruining my symbol equality tests 😉

hmm. no not quite right. (comp resolve symbol) returns a var again. I need the fully qualified symbol

check what I wrote :)

you want to transpose those two functions

symbol resolve, not resolve symbol

ah, but .. hm. swapping that fails for me

((comp symbol resolve) '+) ClassCastException clojure.lang.Var cannot be cast to java.lang.String clojure.core/symbol (core.clj:579)

well yes, unless you're on 1.10

it's a new feature

ooh, doh. sorry i misread 1.10 as some incredibly old version of clojure...

if you're on 1.9 you'll have to do it manually by accessing the .sym and .ns fields of the var

ahh, secret hack.

you read 1.1 == 1.10. simple and understandable mistake 🙂

😄 I suppose I did

one sec, I'll link you the impl

ah thanks

(defn var->sym
  [^clojure.lang.Var v]
  (symbol (str (.name (.ns v)))
          (str (.sym v)))
  )

this is the usual impl pre 1.10

that's perfect, thanks!

Hello guys! I’m writing a small program that solves n-puzzle problem with a* algorithm. The main function iterates over different states of the puzzle to find a path towards the goal state. I used atoms to hold some local state in the function and it worked just fine, but I feel maybe there is a better (more performant or idiomatic) way to do it. I understood that atoms are used for synchronous concurrent state. In my case I don’t have any concurrency involved. I’ve been thinking maybe :^dynamic vars with binding and set! can be a solution. Here is the code:

(defn solve [pzl heur]
  (let [target (generate (count pzl))
        a*-eval (partial puzzle/a*-eval heur)
        open-set (atom (priority-map pzl (a*-eval pzl)))
        closed-set (atom #{})]
    (loop [cur (first (peek @open-set))]
      (swap! open-set pop)
      (swap! closed-set conj cur)
      (if (not= cur target)
        (do
          (doseq [neighbor (get-neighbors cur)]
            (let [neighbor-cost (a*-eval neighbor)]
              (when-let [neighbor-cost-in-open-set (@open-set neighbor)]
                (when (< neighbor-cost neighbor-cost-in-open-set)
                  (swap! open-set dissoc neighbor)))
              (when-let [neighbor-in-closed-set (@closed-set neighbor)]
                (when (< (puzzle/count-parents neighbor)
                         (puzzle/count-parents neighbor-in-closed-set))
                  (swap! closed-set dissoc neighbor)))
              (when-not (or (contains? @open-set neighbor)
                            (contains? @closed-set neighbor))
                (swap! open-set assoc neighbor neighbor-cost))))
          (recur (first (peek @open-set))))
        cur))))

why are you using atoms?

to change value of the queue and closed set. I didn’t take much time to come up with a recursive algorithm

you are paying a perf overhead for using atoms where there's no data races, and the idiomatic version would be to return new values for open-set and closed-set from each step that can alter them

including making open-set and closed-set args to the loop/recur

also, in code that actually used the atoms for concurrency, your usage of the atoms would have a race condition

ok got it, I would reformulate the code. can you briefly describe the last point?

(let [foo (peek @a)] (swap! foo pop)) - this is a race condition because the two usages of foo to peek and pop are not coordinated

two blocks could peek the same value, and then pop two different values

thus using one value twice, and dropping another value on the floor

basically any pair of operations on the same atom that mix a read and a write are probably a race

got it, thank you a lot!

in your case the race never happens because the code is known to be single threaded

but it's good to recognize patterns like that

absolutely, I’ve been thinking how to parallelize the algorithm to get better performance, but that maybe the next step after refactoring to recursion

the pattern you'll likely end up with: (let [[open-set closed-set] (op open-set closed-set) [open-set closed-set] (op2 open-set closed-set) ...] [open-set closed-set])

it becomes simpler if you group the data that gets changed together into one map with keys for each valaue

so (-> {:open open-set :closed closed-set} (op) (op2) ...)

then you rewrite each of the nested conditional ops into separate functions you can place into that chain

thanks a lot!

the conceptual approach is changing each "thing" that changes some object into a function that takes the object and returns a replacement

this is part of why vectors and maps are so ubiquitous in our code - we need to keep track of multiple updated values if a function needs to update more than one piece of data

Hello there, i have a short question. Do I understand it correct that if i use cond all expressions are evaluated?

no

(cond (do (prn "eval test 1") false) (prn "result 1")
      (do (prn "eval test 2") true)  (prn "result 2"))

note which tests are evaluated and which consequences. change up true and false as well

Ok thank you very much! I was confused, because i thought it would always evaluate all expressions 😆

Heya, my google fu is failing me, lets say I have a core async channel with collections of values, is there a simple function to put those values one-by-one on that channel?

so, visually I have something like this: ... -> [a b c] -> [d e f] -> [g h i] -> ..., and I want to go to ... -> a -> b -> c ... -> g -> h -> i -> ...

you could use a (mapcat identity) transducer on the channel

or actually maybe just cat

can’t say I’ve ever done that but might be just right

yeah, I was googling for transducers but couldn’t wrap my head around how that would work ‘the other way around’ so to say. Will try, thanks!

yeah, that should work fine

(def c (chan 100 cat))

Cool, thanks for verifying

oh huh how does that work with buffers

there's also onto-chan that you can read the docstring of to see if it helps here or in other similar situations

core.async is a … bit to get my head around haha

I am writing a spec for a tuple. The only condition is that both positions in the tuple have to be the same data type. For example,

[1 45] ; good 
["hello" "blah"] ; good 
[:hello :blah ] ; good
[1 :hello] ; bad 

a spec is a predicate, so can you write a predicate that given some data returns true if it matches your criteria and false otherwise?

to ensure same type, you’ll need some custom predicate

but you can either write your own or combine with something like s/tuple or s/coll-of

troubleshooting figwheel hanging on compile?

(print-config id ...)           ;; prints out build configurations
          (fig-status)                    ;; displays current state of system
          (figwheel.client/set-autoload false)    ;; will turn autoloading off
          (figwheel.client/set-repl-pprint false) ;; will turn pretty printing off
  Switch REPL build focus:
          :cljs/quit                      ;; allows you to switch REPL to another build
    Docs: (doc function-name-here)
    Exit: :cljs/quit
 Results: Stored in vars *1, *2, *3, *e holds last exception object
Prompt will show when Figwheel connects to your application
[Rebel readline] Type :repl/help for online help info

... never goes anywhere

i even started a fresh project via lein new macchiato app ;_;

what is in your ~/.lein/profiles.clj

is it possible to use require with a wildcard? something like (require 'foo.bar.*)

no

k thx

vas$ cat profiles.clj
{:user {:plugins [
	 	  [lein-ancient "0.6.10"]
		  [http-kit/lein-template "1.0.0-SNAPSHOT"]
                  ]}}

do i need figwheel in my plugins? o.o

no, but I would try commenting out all the plugins in profiles.clj

Thank you

for now I try with commenting out lein-template and see how it goes.

strangely, my app was compiling yesterday. so i don't know what i changed that caused it to no longer function. and there's no errors... so yeah, probably something weird in the dependency chain

the macchiato template looks insanely complicated

hey that may be so, but i can use cljs and make a node server so... it's nice [when working]

did you use it with rebel readline yesterday?

no i don't even know what rebel readline is

just making sure that's not the new part

i think that was there yesterday, that helps color code the repl iirc

and i had color coding so

ok. just making sure that wasn't the variable

thanks. i may try disabling it... it's not actually getting me to a repl

the last time I did any cljs stuff I wrote a little script that called the cljs compiler and generated some js from some cljs code, which node was pretty happy with, without all that stuff

hmm

you're saying maybe do it from scratch without macchiato?

I dunno, maybe the cure is worse than the disease

haha

yeah. i could just make an empty figwheel project using rum that also compiles a javascript file for a node server...

;_;

@sova did you start the node process?

i can't start the node process until the javascript is compiled, and that step never completes.

i really don't know what i did, but it just hangs on compilation

hangs on launching CLJS repl

i guess the JS is compiled... lemme try firing up that npm process

how are you launching the REPL?

How to simplify (remove nil? (remove my-map atts))?

doh! @lilactown launching the npm process was the answer!

^_^ thank you

wishing i hadn't undone about ~2 hours of commits eaarlier but heyyy live and learn

lol

been there 😛

Hey everyone, how can I get some useful information from errors thrown during tests run by shadow-cljs using cljs.test? For the following:

(deftest test-nonsense
  (doall (map identity identity)))

ERROR in (test-nonsense) (Error:NaN:NaN)
Uncaught exception, not in assertion.
expected: nil
  actual: #object[Error Error: function cljs$core$identity(x){
return x;
} is not ISeqable]

Also, I'm on nodejs, so I can't use the devtools extensions and such (or can I?)

I guess more specifically, I'd love to have a sourcemapped trace.

Is there a simple way to create a new vec with an element inserted after an index?