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clojurians | clojure | on can’t “break out” of reduce. one has basically to walk though the entire collection… | 2017-12-26T18:03:08.000042 | Marcel |
clojurians | clojure | well, it's actually possible to break out of a reduce | 2017-12-26T18:03:30.000050 | Ambrose |
clojurians | clojure | because clojure provides a special way to signal that you want to break out early | 2017-12-26T18:04:01.000160 | Ambrose |
clojurians | clojure | but I'd avoid that until you're more comfortable with reduce and FP in general | 2017-12-26T18:04:27.000090 | Ambrose |
clojurians | clojure | `reduced`? | 2017-12-26T18:04:33.000016 | Marcel |
clojurians | clojure | yep | 2017-12-26T18:04:35.000096 | Ambrose |
clojurians | clojure | loop/recur's name is a bit unlucky, since newcomers often think it's similar to an imperative loop | 2017-12-26T18:08:32.000137 | Ambrose |
clojurians | clojure | it’s an end-tailed recursion, right? | 2017-12-26T18:08:49.000089 | Marcel |
clojurians | clojure | yeah | 2017-12-26T18:08:58.000135 | Ambrose |
clojurians | clojure | you can `recur` without `loop`, too | 2017-12-26T18:09:08.000118 | Ambrose |
clojurians | clojure | in which case it'll just recurse from the beginning of the function | 2017-12-26T18:09:25.000097 | Ambrose |
clojurians | clojure | *tail recursion | 2017-12-26T18:09:27.000094 | Marcel |
clojurians | clojure | oh what | 2017-12-26T18:09:46.000012 | Marcel |
clojurians | clojure | but without the tail optimization, correct? stack or heap would fill up | 2017-12-26T18:10:32.000003 | Marcel |
clojurians | clojure | *with the optimization, you mean? | 2017-12-26T18:10:55.000141 | Ambrose |
clojurians | clojure | oh, I see | 2017-12-26T18:11:14.000037 | Ambrose |
clojurians | clojure | recur tells clojure to use tail optimization | 2017-12-26T18:11:33.000001 | Ambrose |
clojurians | clojure | just calling recur would omit optimizations | 2017-12-26T18:11:34.000032 | Marcel |
clojurians | clojure | ah | 2017-12-26T18:11:36.000071 | Marcel |
clojurians | clojure | what does loop do then? | 2017-12-26T18:11:48.000106 | Marcel |
clojurians | clojure | if you just called the function itself you'd fill up the stack | 2017-12-26T18:11:52.000070 | Ambrose |
clojurians | clojure | loop just localizes it | 2017-12-26T18:11:57.000009 | Ambrose |
clojurians | clojure | ah loop is just the jump-point for recur? | 2017-12-26T18:12:00.000129 | Marcel |
clojurians | clojure | yep | 2017-12-26T18:12:03.000077 | Ambrose |
clojurians | clojure | for when you don't want to go all the way back to the beginning of a function | 2017-12-26T18:12:17.000038 | Ambrose |
clojurians | clojure | also you can recur to a function - loop is just a convenience if the loop bindings shouldn't be your function args | 2017-12-26T19:38:52.000161 | Margaret |
clojurians | clojure | The key thing is that `recur` may only appear in a tail position -- and therefore it _is always optimized_. The compiler won't allow you to `recur` in a position that couldn't be optimized. | 2017-12-26T19:59:48.000044 | Daniell |
clojurians | clojure | Hi, just wondering, how do you guys use spec for data validation?
Using `:pre` in `defn` helps in a way to ensure that the function can't be called with unsuitable arguments. But the resulting AssertionError is not really helpful for composing error message to the user. I mean, I don't want to return "Assert failed: (spec/valid? ::email email)" as the error message to the user. Something like: "Invalid format for email" is good enough for me as of now. | 2017-12-27T03:07:02.000036 | Marvin |
clojurians | clojure | I came across this <https://groups.google.com/forum/#!topic/clojure/H9tk04sSTWE>
It gave me some clarity, but any thoughts here will still be appreciated :slightly_smiling_face: | 2017-12-27T03:19:24.000160 | Marvin |
clojurians | clojure | thank’s for explaining :slightly_smiling_face: | 2017-12-27T04:46:24.000048 | Marcel |
clojurians | clojure | the spec guide <https://clojure.org/guides/spec#_testing> has a snippet on how to test all spec'ed functions from an ns `(-> (stest/enumerate-namespace 'user) stest/check)`. Where should I add this in a classic clojure.test file? Adding it just like that produces 0 tests. Wrapping it in a deftest produces 1 tests with 0 assertions.. | 2017-12-27T04:52:54.000144 | Ahmed |
clojurians | clojure | ```
(counted? (float-array [1 2 3]))
(comment
false)
```
what is the constant time way to get the size of a float-array ? | 2017-12-27T06:54:30.000037 | Berry |
clojurians | clojure | it dousn't implement clojure.lang.Counted because it's not a clojure type | 2017-12-27T07:48:46.000003 | Margaret |
clojurians | clojure | it still supports count in constant time | 2017-12-27T07:48:54.000024 | Margaret |
clojurians | clojure | ```user=> (source counted?)
(defn counted?
"Returns true if coll implements count in constant time"
{:added "1.0"
:static true}
[coll] (instance? clojure.lang.Counted coll))
nil
``` | 2017-12-27T07:49:19.000226 | Margaret |
clojurians | clojure | <@Daniell> does the compiler similarly optimize non-`recur` recursion when it's in the tail position ? | 2017-12-27T09:32:24.000056 | Beulah |
clojurians | clojure | no, this feature is intentionally missing | 2017-12-27T09:35:33.000365 | Margaret |
clojurians | clojure | explicit is better | 2017-12-27T09:37:38.000090 | Beulah |
clojurians | clojure | <@Margaret> actually, shouldn't `recur` be called `iterate` (I know `iterate` has been used) ? it's not recursion when it's in the tail-position | 2017-12-27T09:39:45.000235 | Beulah |
clojurians | clojure | it's still recursion, a tail recursion is trivially translated into a goto | 2017-12-27T10:12:42.000155 | Margaret |
clojurians | clojure | but that's an implementation detail - aside from stack usage the behavior is the same as direct recursion | 2017-12-27T10:13:09.000100 | Margaret |
clojurians | clojure | :wave: I recently converted a clojurescript project to use mostly cljc (to possibly move towards clojure), but now i'm getting a :boat: load of errors when I boot my cljs project:
`java.lang.RuntimeException: Unable to resolve symbol: defproject in this context, compiling:(project.clj:1:1)` usually starting with that :arrow_left: . Strangely enough everything still works. Sound familiar with anyone? | 2017-12-27T10:34:32.000354 | Huey |
clojurians | clojure | Looking for a working proxy middleware for ring. Have tried tailrecursion/ring-proxy but running into errors. Any recommendations? | 2017-12-27T10:37:22.000455 | Inocencia |
clojurians | clojure | More specifically looking for a proxy configuration that can work with figwheel: <https://github.com/bhauman/lein-figwheel/issues/634> | 2017-12-27T10:42:52.000039 | Inocencia |
clojurians | clojure | is your source path for cljs set up so it would find project.clj? | 2017-12-27T10:52:40.000014 | Margaret |
clojurians | clojure | I'm currently using the lein checkouts feature ... and I also have the third party lib cljc thing as a dependency... | 2017-12-27T10:58:56.000074 | Huey |
clojurians | clojure | ie. for my shared cljc lib I have run "lein install", and am now referencing that as a dependency as well as using the lein checkouts sym link features to make use of it. Everything _appears_ to work, but I am seeing these errors on boot. | 2017-12-27T10:59:45.000242 | Huey |
clojurians | clojure | the errors look like so:
```
Reloading Clojure file "/src/myproject/myfile.cljc" failed.
clojure.lang.Compiler$CompilerException: java.lang.IllegalAccessError: MY-FUNCTION does not exist, compiling:(src/myproject/myfile.cljc:1:1)
``` | 2017-12-27T11:01:00.000021 | Huey |
clojurians | clojure | Hi all, can you tell me why `tree-seq` is flattening my tree? My code is like this:
```
(defn to-tree [root]
(let [name (:name root)
reg @registry]
(tree-seq
#(some? (:childs (get reg %)))
#(:childs (get reg %))
name)))
```
`registry` is a giant atom map with `{"xxx" {:name "aaa" :childs ["yyy" "zzz"]}}` | 2017-12-27T11:09:33.000111 | Ross |
clojurians | clojure | I know, it isn’t very functional; I’m calling `(to-tree "xxx")` | 2017-12-27T11:09:39.000010 | Ross |
clojurians | clojure | but I get a flat sequence `("xxx" "yyy" "zzz") ` | 2017-12-27T11:10:43.000111 | Ross |
clojurians | clojure | > Returns a lazy sequence of the nodes in a tree, via a depth-first walk.
that seems to be what it promises? perhaps you want something in `clojure.walk`? | 2017-12-27T11:32:27.000242 | Willow |
clojurians | clojure | I was hoping to get something like `("xxx" ("yyy" "zzz" (...))` | 2017-12-27T11:37:53.000175 | Ross |
clojurians | clojure | I don’t have any help for you but just want to say thank you for working on this. This feature would be very helpful. | 2017-12-27T11:48:44.000014 | Thu |
clojurians | clojure | yeah, you want clojure.walk/post-walk for that likely | 2017-12-27T12:59:10.000144 | Margaret |
clojurians | clojure | tree-seq is useful if you have no assumptions about the shape of the data, but you know what the thing you want looks like (so you can filter and find it) | 2017-12-27T12:59:39.000199 | Margaret |
clojurians | clojure | post-walk / pre-walk / walk are for doing a transformation in the shape of the original collection | 2017-12-27T12:59:55.000243 | Margaret |
clojurians | clojure | When is the 2017 Clojure survey? | 2017-12-27T14:16:00.000214 | Johana |
clojurians | clojure | <@Sonny> ^ ? Last year it was opened in early-ish December (12th) and the results came out in early February (7th). | 2017-12-27T14:32:46.000131 | Daniell |
clojurians | clojure | Folks, what is the better/more idiomatic/shorter way to sort+print a vector of elements than ``` (doall (map #(-> %
format-value
println)
(sort-by some-fn some-vector)))```? | 2017-12-27T15:21:57.000123 | Maryann |
clojurians | clojure | drop the 'doall' and replace 'map' with 'run!'? | 2017-12-27T15:23:21.000027 | Bibi |
clojurians | clojure | also consider `(doseq [value (sort-by some-fn some-vector)] (println (format-value value)))` | 2017-12-27T15:26:19.000289 | Margaret |
clojurians | clojure | also, if using map instead of run! (eg. for clojure version reasons or to take extra args like map does) use dorun instead of doall, since the value returned is not something you want or need (just a sequence of nils) | 2017-12-27T15:27:12.000179 | Margaret |
clojurians | clojure | `(run! #(println (format-value %)) (sort-by some-fn some-vector))` looks better, thanks. | 2017-12-27T15:33:24.000026 | Maryann |
clojurians | clojure | for fancy fp-gangsta points you can replace that function with the equivalent `(comp println format-value)` | 2017-12-27T15:37:52.000319 | Margaret |
clojurians | clojure | ```
(->>
some-vector
(sort-by some-fn)
(mapv (comp println format-value)))
``` | 2017-12-27T15:39:57.000257 | Ambrose |
clojurians | clojure | run! is much better than mapv here | 2017-12-27T15:40:22.000304 | Margaret |
clojurians | clojure | agreed | 2017-12-27T15:40:38.000050 | Ambrose |
clojurians | clojure | ```
(defn get-data []
(<http://clojure.java.io/make-parents|clojure.java.io/make-parents> (str (mnist-config :data-dir) "foo"))
(doseq [[k url] (select-keys mnist-config [:train-images :train-labels :t10k-images :t10k-labels])]
(with-open [in (java.util.zip.GZIPInputStream. (<http://clojure.java.io/input-stream|clojure.java.io/input-stream> url))]
(spit (str (mnist-config :data-dir) (name k)) (slurp in)))))
(get-data)
```
is there a better way to write this? in particular, the (spit ... (slurp ...)) seems redundant
We're downloading a bunch of *.gz files, gunziping thej,m, and writing it out to file | 2017-12-27T15:47:39.000226 | Berry |
clojurians | clojure | `<http://clojure.java.io/copy|clojure.java.io/copy>` perhaps? | 2017-12-27T15:48:07.000234 | Daniell |
clojurians | clojure | Oh wait, you're slurping an input stream... not sure if copy will do that... | 2017-12-27T15:48:27.000118 | Daniell |
clojurians | clojure | you can write an inputstream directly though | 2017-12-27T15:49:49.000141 | Margaret |
clojurians | clojure | that is, you can write it to an outputstream, and create the output stream in the with-open call as a second binding | 2017-12-27T15:50:54.000041 | Margaret |
clojurians | clojure | something vaguely like `(with-open [in …. out (io/output-stream (io/file (str …)))] (.write out in))` but probably also requiring a loop or a byte count on the write | 2017-12-27T15:51:50.000007 | Margaret |
clojurians | clojure | these files are only 60M, I'll deal with the 'memory inefficiency' then | 2017-12-27T15:52:42.000323 | Berry |
clojurians | clojure | it’s just a needless creation of a string, not a huge deal | 2017-12-27T15:53:16.000053 | Margaret |
clojurians | clojure | also just to be clear making a string out of a 60 meg file that’s encoded with utf-8 is likely 120megs in memory because java strings are utf-16 | 2017-12-27T15:57:02.000276 | Margaret |
clojurians | clojure | and definitely don’t use slurp/spit for anything that isn’t text | 2017-12-27T15:57:50.000086 | Margaret |
clojurians | clojure | (I don’t know what those “images” in the name refer to just be aware that if they are image data as in bmp or jpeg slurp/spit will turn them into garbage) | 2017-12-27T15:59:08.000167 | Margaret |
clojurians | clojure | is anyone else able to watch <https://www.youtube.com/watch?v=5VAEXYYdfWY> (“Zippers - Episode 2”)? it’s not working for me. | 2017-12-27T17:49:35.000138 | Alline |
clojurians | clojure | oh, i get a better error message embedded here in slack, sorry! (“This video requires payment to watch”) | 2017-12-27T17:50:12.000070 | Alline |
clojurians | clojure | is there an easy way to list the requires for a given namespace? I was looking for something like ns-refers but for requires | 2017-12-27T18:29:15.000031 | Barbar |
clojurians | clojure | i didnt realize youtube red videos were part of regular youtube | 2017-12-27T18:31:22.000029 | Williemae |
clojurians | clojure | I have a lot of .cljc code I'd like to make into a library. Is there a way to make cross platform libraries without rewriting my code twice? | 2017-12-27T18:57:02.000002 | Giovanni |
clojurians | clojure | <@Giovanni> are you already using reader conditionals? | 2017-12-27T19:45:01.000006 | Barbar |
clojurians | clojure | (<https://clojure.org/guides/reader_conditionals>) | 2017-12-27T19:45:41.000076 | Barbar |
clojurians | clojure | Yeah I tested out my reader conditionals in a chestnut project and they worked in both runtimes. | 2017-12-27T19:45:44.000044 | Giovanni |
clojurians | clojure | I just never actually packaged a pure cljc project. Does the default lein template work fine for both runtimes? | 2017-12-27T19:46:21.000081 | Giovanni |
clojurians | clojure | that part i’m not sure about | 2017-12-27T19:48:39.000122 | Barbar |
clojurians | clojure | <https://github.com/stuartsierra/component> looks like a minimal example of a (not quite pure) .cljc library | 2017-12-27T19:50:18.000131 | Alline |
clojurians | clojure | I should have looked at Sierra's components. It never clicked that I had them on the back and the front with the same namespace. It looks like this library has a project.clj a lot like mine as well. Thanks much! | 2017-12-27T19:55:03.000014 | Giovanni |
clojurians | clojure | hey, has anyone successfully used a go block in clojure >=1.7.0? i am having trouble with it not closing over its scope properly, so `(let [c (chan)] (go (prn (<! c))))` gets me `Unable to resolve var: c` | 2017-12-27T20:59:38.000073 | Linn |
clojurians | clojure | this is right out of the tutorial, and it works in clojure 1.6 | 2017-12-27T20:59:55.000093 | Linn |
clojurians | clojure | but that seems like an awful long time for something so fundamental to be broken | 2017-12-27T21:00:05.000140 | Linn |
clojurians | clojure | so i’m open to it being totally my problem | 2017-12-27T21:00:12.000052 | Linn |
clojurians | clojure | the weird thing about that block of code is that core.async should treat it as a noop returning a channel that never delivers | 2017-12-27T21:00:55.000085 | Margaret |
clojurians | clojure | since nothing can possibly use c | 2017-12-27T21:01:02.000009 | Margaret |
clojurians | clojure | i mean, there’s a more complicated version of that code, which also fails with the same issue, which actually does do a real hello world with the channels, in the tutorial | 2017-12-27T21:01:34.000024 | Linn |
clojurians | clojure | but i stripped it down to just that being enough for it to fail with the same issue | 2017-12-27T21:01:44.000181 | Linn |
clojurians | clojure | ```Clojure 1.9.0
+user=> (require '[clojure.core.async :as > :refer [go chan <!]])
nil
+user=> (let [c (chan)] (go (prn (<! c))))
#object[clojure.core.async.impl.channels.ManyToManyChannel 0x1e5e2e06 "clojure.core.async.impl.channels.ManyToManyChannel@1e5e2e06"]
``` | 2017-12-27T21:02:11.000137 | Margaret |
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