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clojurians | clojure | ```
(defn reposition [planets]
(map (partial new-position planets) planets))
```` | 2017-12-15T11:18:16.000582 | Jami |
clojurians | clojure | but you have to define `new-position` to take the list of planets first | 2017-12-15T11:18:36.000513 | Jami |
clojurians | clojure | no, using map is not correct | 2017-12-15T11:19:36.000334 | Kareen |
clojurians | clojure | note that in <@Kennith>'s js version, each invocation of newPosition takes the updated planets map, not the original one | 2017-12-15T11:19:53.000300 | Kareen |
clojurians | clojure | good point. | 2017-12-15T11:20:52.000189 | Willow |
clojurians | clojure | reduce is the natural way to express this in clojure | 2017-12-15T11:21:06.000728 | Kareen |
clojurians | clojure | <@Kareen> <@Willow> agreed, I though the planet object did not change after each iteration | 2017-12-15T11:22:12.000559 | Jami |
clojurians | clojure | <@Kareen> Yes, that is correct. This is actually what tripped me up. Planets is a vector of maps, but reduce-kv works anyway as far as I can tell. | 2017-12-15T11:22:21.000119 | Kennith |
clojurians | clojure | yeah reduce-kv supports vectors | 2017-12-15T11:22:49.000492 | Kareen |
clojurians | clojure | `reduce` is the traditional solution for `state` + `rules for state change` => `new state` <@Kennith> | 2017-12-15T11:24:58.000833 | Daniell |
clojurians | clojure | (for a given set of events -- in this case the set of planets acts as both the initial state and the set of "events" that trigger state change) | 2017-12-15T11:27:14.000415 | Daniell |
clojurians | clojure | <@Daniell> Yes, I was missing the idea of using planets as both the accumulator and collection over which to reduce, as mentioned by <@Kareen>. | 2017-12-15T11:37:25.000148 | Kennith |
clojurians | clojure | <@Kennith> are you doing gravitational dynamics? | 2017-12-15T12:11:55.000054 | Priscilla |
clojurians | clojure | because if so you're making it unnecessarily difficult from a programming standpoint | 2017-12-15T12:13:35.000390 | Priscilla |
clojurians | clojure | since from a physics standpoint you'd like to do one pass over the planets and calculate force | 2017-12-15T12:14:00.000667 | Priscilla |
clojurians | clojure | and then another pass to update momentum | 2017-12-15T12:14:20.000695 | Priscilla |
clojurians | clojure | and another pass to update position | 2017-12-15T12:14:25.000067 | Priscilla |
clojurians | clojure | although for speed probably the best thing to do is to solve for the gravitational potential on a grid and then interpolate to get forces, depending on how many planets you have | 2017-12-15T12:16:13.000338 | Priscilla |
clojurians | clojure | i doubt there's a good poisson library in javascript, haha | 2017-12-15T12:16:31.000341 | Priscilla |
clojurians | clojure | <@Priscilla> I am, I am trying to reimplement this: <https://github.com/raisoman/de-for-children/blob/master/processingjs/p5/mars-trip.html> in cljs. | 2017-12-15T12:17:23.000155 | Kennith |
clojurians | clojure | ya, from a physics POV, that code would be better if it accumulated `xpp` and `ypp` in arrays | 2017-12-15T12:21:19.000672 | Priscilla |
clojurians | clojure | and only actually moved the planets after it had calculated that for all of them | 2017-12-15T12:21:51.000210 | Priscilla |
clojurians | clojure | splitting hairs, probably; the errors from doing it as linked take many orbits to be visible | 2017-12-15T12:22:33.000221 | Priscilla |
clojurians | clojure | `(comp (map #(update-position planets)) (map get-force))` | 2017-12-15T12:24:09.000199 | Priscilla |
clojurians | clojure | would give you pretty much what you need | 2017-12-15T12:24:25.000681 | Priscilla |
clojurians | clojure | <@Priscilla> I also had a sneaking suspicion that my original was actually more correct, but the constants are calibrated to work with the js version, which is quite sensitive to starting conditions since it is inserting a tiny space-ship into orbit around mars. Not that I really understand the physics very well :slightly_smiling_face: | 2017-12-15T12:27:32.000343 | Kennith |
clojurians | clojure | ```
(def queue (agent []
:error-mode :continue
:error-handler (fn [a ex]
(l/error ex "slack agent failed"))))
```
Is there easy and simple way to achieve `:error-mode :retry` ? :slightly_smiling_face: Just from time to time sending messages to slack fail and I don’t want lose them.
* It can be achieve in whatever way. `:retry` example was to easy describe my needs. | 2017-12-15T12:40:55.000124 | Gladys |
clojurians | clojure | `(send-off ... (retry fn) ...)` | 2017-12-15T12:51:46.000162 | Rebeca |
clojurians | clojure | ```
(defn retry [f] (fn x [& args] (try (apply f args) (catch Throwable t (apply x args)))))
``` | 2017-12-15T12:53:02.000028 | Rebeca |
clojurians | clojure | there’s a gotcha also if you use defrecord, defprotocol, gen-class etc. because that creates classes in the default package which is poorly behaved on the jvm right? | 2017-12-15T13:09:40.000144 | Margaret |
clojurians | clojure | or are clojure’s classes exempt from those problems? | 2017-12-15T13:09:53.000287 | Margaret |
clojurians | clojure | eg. class loading problems if two deftypes both use the default package… | 2017-12-15T13:13:19.000654 | Margaret |
clojurians | clojure | I just tried, using deftype and gen-class with namespaces producing items in the default package and yeah it works (likely would have caused problems if I tried to use import though) | 2017-12-15T13:30:39.000220 | Margaret |
clojurians | clojure | inside a (fn [] .... ) is there a way to "refer to self, i.e. the function being defined" -- and this is not via recur | 2017-12-15T14:16:27.000354 | Berry |
clojurians | clojure | Why are you not able to use recur? | 2017-12-15T14:17:24.000347 | Erlene |
clojurians | clojure | you can name a fn (fn f [] …) | 2017-12-15T14:17:41.000393 | Felix |
clojurians | clojure | because I need to call the function two/three times, in a tree like fashion, it's not a loop | 2017-12-15T14:23:25.000463 | Berry |
clojurians | clojure | yeah, that’s why the `(fn f [] ...)` syntax exists, it’s the straightforward way to do this | 2017-12-15T14:24:01.000257 | Margaret |
clojurians | clojure | though if two functions need to do this mutually, `letfn` exists for that purpose and no other | 2017-12-15T14:24:26.000167 | Margaret |
clojurians | clojure | ah, the `(fn f [] ...)` syntax gives it a name I can refer to it by; no idea howI missed it all these years; thanks! | 2017-12-15T14:24:57.000354 | Berry |
clojurians | clojure | extra bonus - when you use (fn f [] …) the name “f” will show up in a stack trace | 2017-12-15T14:25:19.000447 | Margaret |
clojurians | clojure | sometimes I name my fn even if it doesn’t self call just so my stack traces will make a little more sense | 2017-12-15T14:25:44.000008 | Margaret |
clojurians | clojure | it makes me want versions of partial and comp and complement and fnil etc. that take a “name” parameter too frankly | 2017-12-15T14:26:23.000407 | Margaret |
clojurians | clojure | How does the keyword-as-accessor syntax actually work in the language? E.g. `(:b {:a 1, :b 2})` Is this just special syntax built into the language or is there some reason why keywords can act as functions in this way? | 2017-12-15T14:52:25.000211 | Thu |
clojurians | clojure | it is not a syntax, keywords are functions | 2017-12-15T14:52:38.000151 | Margaret |
clojurians | clojure | symbols, hash-maps, sets, and vectors are also functions | 2017-12-15T14:52:56.000412 | Margaret |
clojurians | clojure | at one point they argued about making regexes functions too but they opted not to do that | 2017-12-15T14:53:22.000502 | Margaret |
clojurians | clojure | specifically, keywords implement IFn | 2017-12-15T14:53:34.000307 | Myles |
clojurians | clojure | ah? do you remember when ? | 2017-12-15T14:53:45.000343 | Kareen |
clojurians | clojure | @chris right when I say “is a function” about clojure that means “implements IFn” | 2017-12-15T14:53:55.000391 | Margaret |
clojurians | clojure | no - I have seen discussion about it but forget the details | 2017-12-15T14:54:16.000117 | Margaret |
clojurians | clojure | But there must be something special about them because there are an infinite number of them and they spring forth whenever you use them | 2017-12-15T14:55:04.000548 | Thu |
clojurians | clojure | @Justin how’s that different from fn? | 2017-12-15T14:55:22.000540 | Margaret |
clojurians | clojure | is that different from how a function works? | 2017-12-15T14:55:27.000452 | Myles |
clojurians | clojure | haha | 2017-12-15T14:55:31.000478 | Margaret |
clojurians | clojure | or a symbol | 2017-12-15T14:55:35.000109 | Kareen |
clojurians | clojure | I've never seen serious discussion about it, just perennial whinging about how nice or how cool it would be if it was the case | 2017-12-15T14:55:38.000435 | Rebeca |
clojurians | clojure | the reader interns symbols/keywords | 2017-12-15T14:55:52.000366 | Kareen |
clojurians | clojure | yeah same | 2017-12-15T14:56:04.000231 | Kareen |
clojurians | clojure | but symbols can have metadata so they do something different about the interning right? | 2017-12-15T14:56:14.000285 | Margaret |
clojurians | clojure | yeah symbols just have their internal string interned | 2017-12-15T14:56:42.000153 | Kareen |
clojurians | clojure | actually since a few versions ago that might not be true, I can't remember | 2017-12-15T14:56:54.000228 | Kareen |
clojurians | clojure | one possible answer “pattern is a final class” <https://groups.google.com/forum/#!topic/clojure/LiWT7NIJOdQ> | 2017-12-15T14:57:16.000751 | Margaret |
clojurians | clojure | and interning has nothing to do with being used as a function | 2017-12-15T14:59:57.000518 | Rebeca |
clojurians | clojure | true, I was just answering how they "pop out of existence" | 2017-12-15T15:00:53.000048 | Kareen |
clojurians | clojure | `(foo a b c)` in clojure is something like `((IFn)foo).invoke(a, b, c)` in java | 2017-12-15T15:01:09.000131 | Rebeca |
clojurians | clojure | I previously just thought of them as identifiers that had some concrete unique representation that allowed them to be used as keys in a map. But then they can also be used in the first position in a list (which I think of as “function” position but I’m sure it has a more precise name). I suppose the point is that they are instantiated as lookup functions the moment the reader sees them and the reference to that lookup function is what is used as a key? | 2017-12-15T15:01:30.000144 | Thu |
clojurians | clojure | they are instances of clojure.lang.Keyword | 2017-12-15T15:01:53.000379 | Rebeca |
clojurians | clojure | which implements IFn | 2017-12-15T15:01:59.000025 | Rebeca |
clojurians | clojure | clojure.lang.IFn | 2017-12-15T15:02:08.000215 | Rebeca |
clojurians | clojure | oh right. okay got it | 2017-12-15T15:02:26.000205 | Thu |
clojurians | clojure | thanks all | 2017-12-15T15:02:29.000031 | Thu |
clojurians | clojure | @Justin also, regarding “allowed to use them as keys in a map” that’s true of literally any value in clojure | 2017-12-15T15:02:40.000258 | Margaret |
clojurians | clojure | as an aside | 2017-12-15T15:02:51.000187 | Margaret |
clojurians | clojure | `(:foo {:foo 1})` becomes something like `new Keyword ("foo").invoke ( {:foo 1 })` | 2017-12-15T15:03:14.000202 | Kareen |
clojurians | clojure | any object on the jvm that doesn't replace Object's hashCode and equals with methods that throw execeptions | 2017-12-15T15:03:24.000093 | Rebeca |
clojurians | clojure | which is implemented roughly as `{:foo 1}.get(this)` | 2017-12-15T15:03:40.000638 | Kareen |
clojurians | clojure | clojure values just make better keys then most objects on the jvm | 2017-12-15T15:04:07.000338 | Rebeca |
clojurians | clojure | immutability is a good idea™ | 2017-12-15T15:04:48.000444 | Myles |
clojurians | clojure | ahh right- you can use a mutable thing as a key, but if the mutation changes the hash or equality you will have a bad time haha | 2017-12-15T15:05:32.000352 | Margaret |
clojurians | clojure | <@Margaret> Right that was phrased awkwardly. Keywords are a little interesting because unlike something like a let binding or a formal parameter, what you call the keyword actually changes something in memory. I guess that’s no different from a string literal but it has always felt unusual to me because a keyword looks like a formal name rather than data. | 2017-12-15T15:06:07.000684 | Thu |
clojurians | clojure | At least I think that’s right. | 2017-12-15T15:06:20.000370 | Thu |
clojurians | clojure | keywords are data, not labels | 2017-12-15T15:06:31.000610 | Kareen |
clojurians | clojure | just like a string or a number | 2017-12-15T15:06:48.000096 | Kareen |
clojurians | clojure | same with symbols | 2017-12-15T15:07:08.000067 | Rebeca |
clojurians | clojure | Thanks yea that’s important to remember. Because to my C/C++/JS mind they look like names. | 2017-12-15T15:07:24.000207 | Thu |
clojurians | clojure | (in fact they are listed under data_structures on <http://clojure.org|clojure.org>, <https://clojure.org/reference/data_structures>) | 2017-12-15T15:07:34.000347 | Rebeca |
clojurians | clojure | apart from reader macros, there's no labels or language syntax that's not reified as a value | 2017-12-15T15:08:14.000372 | Kareen |
clojurians | clojure | let bindings are sneaky to find, and even sneakier to do anything with as data haha but yeah <https://gist.github.com/noisesmith/3490f2d3ed98e294e033b002bc2de178> | 2017-12-15T15:10:54.000346 | Margaret |
clojurians | clojure | omg | 2017-12-15T15:11:35.000162 | Thu |
clojurians | clojure | Beyond the `(keys &env)` I wouldn’t really consider let-bindings to be “reified” (officially) in clj | 2017-12-15T15:12:15.000329 | Petronila |
clojurians | clojure | right - but that snippet proves they are reified | 2017-12-15T15:12:34.000218 | Margaret |
clojurians | clojure | sort of | 2017-12-15T15:12:42.000100 | Petronila |
clojurians | clojure | hah | 2017-12-15T15:12:42.000420 | Petronila |
clojurians | clojure | no | 2017-12-15T15:12:42.000454 | Rebeca |
clojurians | clojure | you are reading compiler state using the macro and generating code to reproduce it at runtime | 2017-12-15T15:13:10.000104 | Rebeca |
clojurians | clojure | oh… that is different OK | 2017-12-15T15:13:30.000012 | Margaret |
clojurians | clojure | what bronsa meant is `(let [a 1] a)` is not "syntax" as such, it is a list containing a symbol, a vector, and another symbol | 2017-12-15T15:14:04.000290 | Rebeca |
clojurians | clojure | ```
user=> ((fn [x] ((x {:a {:a 1}}) x)) :a)
1
user=>
``` might be interesting to puzzle out when learning about keywords | 2017-12-15T15:19:43.000181 | Rebeca |
clojurians | clojure | anyone know why ```:1``` is a valid keyword but ```:foo/1``` is not? | 2017-12-15T15:31:04.000518 | Tuyet |
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