I have a big non-specific question/topic for which I apologize in advance... I am trying to get my project off my laptop into the cloud, and I'm finding the whole thing daunting... there's kubernetes and all its providers, AWS EC2 and Elastic Beanstalk, just renting a VPS... so many possibilities. Does anyone have suggestions for a workflow for how to develop locally and then deploy into a persistence backed situation without scp'ing jars around (although that's on the table, absolutely, too)... thoughts, suggestions, counseling?

no database?

yes, postgres currently.

that makes things a bit more complicated, definitely.

yes, backup requirements come into play if any

AWS RDS and EC2 might the simplest way to start (but not the cheapest)

it really depends on so many things...

that's the direction I've been going in... I was a bit dismayed at how quickly the costs can add up for a hobby project... RDS can be stopped for 7 days and then it automatically wakes up and starts running up a bill.

AWS kills you on traffic, a digitalocean VPS with backups enabled and an attached volume for the database (with some rsync cron jobs) may be good enough (and way cheaper) depending on your case, if you don't mind setting up postgresql yourself and doing some little ops

also, look at heroku

they have a free tier

and managed postgres

oh wow, I was already having sticker shock and I hadn't even thought about the traffic.

I'll look at DigitalOcean... great idea.

and they have a new kubernetes thing, which means I could run postgres from a docker container, theoretically. but the whole K8 thing could be a rabbit hole.

start with the basics 😉

sounds good... I'll look at DigitalOcean... the postgres setup will be a learning thing there, but sounds like a solid plan. 😊

Is there a Clojure core function that splits a list into two lists: 1. items that pass a predicate 2. items that fail the predicate?

Group by

I ended up using partition by

has anyone run into a lein repl error out with Exception in thread "main" java.lang.AssertionError: Assert failed: transport-fn? It seems to be a result of the latest macos mojave point update

https://stackoverflow.com/questions/53771488/lein-repl-results-in-java-lang-assertionerror-transport-fn

happened to me right after I did the update to macos 10.14.2 today. I've tried java 8 and 11

@langmartin https://github.com/technomancy/leiningen/issues/2497 if you’re in a project you can add the nrepl dep to your profiles.clj, downgrade to lein 2.8.1 via lein upgrade 2.8.1 or git clone master branch and run lein bootstrap

I noticed that all of the channels here only go back about five days. Are older messages archived somewhere?

@jayzawrotny split-with

Oooh perfect thanks!

(defn separate-dirs-from-files
  [files-list]
  (reduce (fn [[dirs files] file]
            (let [name (.getName file)]
              (if (directory? file)
                [(conj dirs name) files]
                [dirs (conj files name)])))
          []
          files-list))

Haven't run it but...

(defn separate-dirs-from-files
  [nodes]
  (let [g (group-by directory? nodes)]
  	[(get g true []) (get g false [])]))

Also, @jayzawrotny split-with gets you a vector of stuff that succeeds until first failure, and stuff that fails until first success. It is equivalent to #(vector (take-while % %2) (drop-while % %2)). Code was more concise and readable that my description of it 😅

Thanks for the explanation. That makes sense but the tricky part is getting the name of each node, that’s why I went with reduce, otherwise I would have to map over them again.

hey guys, how to use env file in my clojure project whithout extern libs please?

or a better way to pass env to my clojure project

Probably wouldn’t be too difficult to write a function that reads each line of an env file, splits it by = VAR_NAME=VALUE, then populates a map. Then you can design a general function for retrieving data from that map or System/getenv but at this point you probably just reinvented the wheel. This solution may suit your needs though https://stackoverflow.com/questions/32323572/is-there-a-way-to-set-system-properties-in-leinegen

can you guys tell me here difference between lein-2.7.1-alpine-onbuild and lein-2.7.1-alpine please?

(first
   (filter #(do (println %) (even? %))
           [1 2 3]))

you can use one of the many unchunk fns around

better would be not to use a lazy-seq I guess, but maybe you don't have a choice

(reduce #(when (even? %2) (reduced %2))
          []
          [1 2 3])

Not sure I fully understand what you mean by not using a lazy-seq, the vector isn't lazy but filter makes it lazy, no?

filter returns a chunked lazy-seq

filterv would return a vector

if you have more complex stuff going on per iteration you can also think about using tranduce + halt-when

but in you example it seems not necessary

interesting, didn't know about halt-when

an eduction would work too

(eduction (comp (map #(doto % prn)) (halt-when even?)) [1 2 3])

meh

I forgot that filterv exists in the stdlib 😄 Are you suggesting that this should work?

(first
   (filterv #(do (println %) (even? %))
            [1 2 3]))

no, it will print 3 times

yeah ok, that's what I'm seeing too

(eduction (halt-when even?) [1 2 3]) is the nicest so far imho

then you need to feed it to something if you use it more than once otherwise you'd get bad surprises

hm, I can't get the eduction to return the value for which the predicate fn returns true

But thanks, I'll take a closer look at that 🙂

right, you want the value, not a coll with it

halt-when takes an optional second arg fn

That retfn gets both the halt-on val and the pred result

oh!

doesn't seem to work with eduction tho, but it's fine with transduce of course

(transduce (halt-when even? (fn [_ x] x)) conj [] [1 2 3]) -> 2

which kind of make sense given the ret value of an eduction, it's not the same purpose

Anyone have a “transducers for dumb people” or similar? I’ve tried a couple times to get it and it’s not stuck

hi I am trying such interesting dynamic dispatch but I have got some interesting compile errors.

(def backend
  (case database-backend-keyword
    :mysql 'importer.persistence.mysql
    'importer.persistence.dummy))

(def insert! backend/insert!)

(def delete! backend/delete!)

@masta Your backend var holds a symbol, not a namespace.

Try ns-resolve

But if I had to implement pluggable backends I would use a protocol.

Is there any way to update lein to use clojure 1.10?

what do you mean? In a project you can change your Clojure dependency to be a 1.10 version

and lein will pick it up

https://clojure.org/community/downloads The latest dev release is "1.10.0-RC5"

like if I run lein repl it runs 1.10

Thank you for the in-project dependency though

can I do a ~/.lein/profiles thing?

@seancorfield just saw your article on datafy/nav, very helpful and thanks! one thing wasn’t very clear though: how can you tell whether an id in a row or a result set is a foreign key to another table?

@gganley Leiningen consults a :repl profile if you define one, and yes you can do it in ~/.lein/profiles.clj (for reference: https://github.com/technomancy/leiningen/blob/3aad5ec7eb7eb91e9c5beb41aecf097c5d819472/src/leiningen/repl.clj#L363)

Oh I forgot I was getting this error ->

when I run lein repl this happens for some reason

Is lein repl supposed to use nrepl? I thought that was only a CIDER thing

this is a bug in lein 2.8.2 that was just released

downgrade to 2.8.1 for the moment

Ah ok

Thank you

brew switch leiningen 2.8.1, Thanks!

I made an example showing (well, hinting at) the power of bespoke datafy/nav https://github.com/stuarthalloway/reflector

@jayzawrotny I think you want group-by and not partition-by

Is it possible for lein's project.clj to look at a config file for certain values, like :version?

What’s wrong with this macro?

(defmacro uninterrupted [h & tail]
  (when h
    `(when-not (Thread/interrupted)
       ~h
       ~(uninterrupted tail))))

should be (uninterrupted ~tail)

oh wait, I should splice tail

~@ ?

that too

that too yes 🙂

the main thing is that you just can't use a macro in the "runtime" part of the macro definition

this should do it:

(defmacro uninterrupted [h & tail]
  (when h
    `(when-not (Thread/interrupted)
       ~h
       ~(when tail `(uninterrupted ~@tail)))))

don't think you need the innermost when

when I don’t do the when, the last uninterrupted gets called with 0 args 😕

ah yes :)

but now the return value is always nil 😕

a bit hacky to fix the return value:

(defmacro uninterrupted [h & tail]
  (when h
    `(when-not (Thread/interrupted)
       ~h
       ~@(when tail [`(uninterrupted ~@tail)]))))

(uninterrupted 1 2 3) => 3

you might want to consider how to handle InterruptedException too - if one of the expressions is blocked on something interruptible, it will throw InterruptedException as well

maybe it’s fine to just let that throw, but you could also catch/ignore. generally, you might think about how/whether to give feedback for if interruption occurred

I’m currently only cancelling futures in this piece of code and handling java.util.concurrent.CancellationException when reading them

but yeah, good idea

Glad to see another Vulfpeck fan in Clojureland, Alex. :the_horns::skin-tone-3:

I’m planning to see them at red rocks in May :)

Should probably take this to #off-topic though :)

huh. I never noticed...

user> (:foo (sorted-map "foo" "bar"))
Execution error (ClassCastException) at user/eval36355 (REPL:83).
java.lang.String cannot be cast to clojure.lang.Keyword
user> (contains? (sorted-map "foo" "bar") :foo)
Execution error (ClassCastException) at user/eval36357 (REPL:86).
java.lang.String cannot be cast to clojure.lang.Keyword

@tomjack "foo" and :foo are not the same

indeed. I would've guessed nil and false

oh - it's because sorted-map needs to do sorting! you can't sort :foo into "foo" "bar"

now I get it

That is certainly a bit surprising on the face of it -- but kinda obvious when you think about sorting. I guess you can always use sorted-map-by with a custom comparator that lets you compare strings and keywords (however you want)...

we’ve had a couple tickets on this and behavior has changed in some cases over the last couple releases

https://dev.clojure.org/jira/browse/CLJ-2089 ;; Clojure 1.10

https://dev.clojure.org/jira/browse/CLJ-1242 ;; Clojure 1.9

https://dev.clojure.org/jira/browse/CLJ-2325 ;; unresolved

the behavior in the example above I looked at in context of 1242 (was originally in there I think, but that ticket was narrowed) - I ultimately decided the get/contains behavior matched Java’s behavior on sorted sets (throws) and thus was correct as is, but I think it’s pretty gray

So i've create a hello world project with lein new ___ and then ran lein jar. After unpacking the jar I see that the testing files are not included. Would anybody know why this is?

test files are usually not included in artifacts

Sorry in advance for the vague-ish question, but if a library has to manage an external connection, is it a general good rule that the library probably needs some sort of logging mechanism (tools.logging as a decent clojure default?) included to allow users of the library to log things relating to errors and such involving that connection? I'm about to release a very small library and not sure if I can get away with skipping a tool.logging dependency. The alternative is probably to add an error handling function to be passed as an argument in the library's connection api right?

Is ^:static still a thing? I can’t tell from the answers on the internet. 😕

it is not still a thing

is there any sugar for making keywords namespaced in the current ns followed by a suffix, then the key name? E.g., sitting in the foo.accounting namespace, and want to make a foo.accounting.user/age keyword?

no

I need to encode a logic of trying number of times wrapped into catch block. i.e. sending a request that may cause java.net.SocketTimeoutException and trying for 5 times until there’s no exception. Possible without storing results of the request in a atom?

doing something like this, doesn’t look pretty:

(let [resp (atom nil)]
  (loop [tries 5]
    (try
      (reset! resp (http-get url options debug? description))
      (catch java.net.SocketTimeoutException ex
        (reset! resp nil)))
    (when (nil? @resp)
      (recur (dec tries)))))

https://github.com/joegallo/robert-bruce

generally I find using trampoline to be the cleanest way to loop around a try/catch

without pulling in a library you can do something like (trampoline (fn f [] (try whatever (catch Exception e f ))))

hmm…. nice

how do you make the counter (number of tries) thing with the trampoline approach?

oh wait… I think I got it

@alexmiller @hiredman thanks.

It seems like the macroexpansion of if-not is lacking parity with when-not.

(macroexpand
 '(if-not foo
    bar
    baz))
;; =>
(if (clojure.core/not foo)
  bar
  baz)

Should just be

(if foo
  baz
  bar)

Why bother with emiting the not?

when-not OTOH emits what I’d expect

(macroexpand
 '(when-not foo
    bar
    baz))
;; =>
(if foo nil (do bar baz))

I’m not really sure that’s ticket worthy or not.

this has to do with where there are do forms i believe. your swapping of the if and else forms is not equivalent

Yeah it is.

ah i was thinking clojure had the do block around the else branch. that's other lisps

(= (if-not false :a :b)
   (if true :a :b))
;; => true

that test case is not sufficient to disprove what i was thinking but you are correct

Unless there’s some logical property I’m missing here I can’t see how the macroexpansion I’m proposing is incorrect.

It’s easily provable.

i was thinking of in a lisp where there's a do block on the else branch they would not be the same, right?

(if nil
    (message "it was true")
  (message "it was false")
  (message "second block of it was false"))

That’s not a valid if.

that's what i was confused about and what your test case there would not highlight i thought

I’m saying if-not does not need to expand literally into (if (not ,,,) ,,,) it can just expand into if with the then and else arms swapped.

(defmacro if-not*
  ([test then]
   `(if ~test
      nil
      ~then))
  ([test then else]
   `(if ~test
      ~else
      ~then)))

(require '[clojure.test.check.generators :as tc.gen])
(require '[clojure.test.check.properties :as tc.prop])

(every?
 :result
 (tc.gen/sample
  (tc.prop/for-all [falsey (tc.gen/elements [nil false true])]
    (= (if-not falsey :a :b)
       (if-not* falsey :a :b)))
  1000))
;; => true

i thought more lisps had an implicit do body on the else branch. that was my confusion. it seems to just be emacs lisp

😄

Ah, yeah. That’ll do it. 🙂

Your alternate macro-expansion of if-not looks correct to me, and would save a call to clojure.core/not.

Although code like that can I think be potentially in-lined if it gets hot in the JVM, depending on a bunch of JVM- and code-specific factors.