#clojure – 2015-09-11

2015-09-11

00:00	justin_smith	nowprovision: why not nth?
00:01	nowprovision	justin_smith, that seems better, im very rusty.. tahnks
00:01	justin_smith	nowprovision: it might read better if you bind the (iterate ...) in the let block, then use nth on that
00:10	nowprovision	okay now I have https://www.refheap.com/20d51c2bb7ea776d05824a862 any further thoughts
00:14	ska-fan	So (:a {:a 4}) is 4, but ("a" {"a" 4)) throws an exception - does key as a function just doesn't work for strings?
00:15	TEttinger	ska-fan: ah this is neat
00:15	TEttinger	so keywords like :a actually do more than just store text conveniently
00:15	tolstoy	But ({"a" 4} "a") is 4.
00:16	ska-fan	tolstoy: Ha! indeed. /me goes of simplifying.
00:16	nowprovision	a keyword is a function
00:16	justin_smith	ska-fan: clojure always calls the first thing after the paren
00:16	TEttinger	a keyword also implements IFn (meaning, it can be called as a function), but they are fns that can be called with a map as an arg (possibly other stuff too)
00:16	justin_smith	ska-fan: it just so happens that keywords are callable
00:16	justin_smith	,(:a :a :a)
00:17	TEttinger	maps also implement IFn and can be called with a key
00:17	clojurebot	:a
00:17	TEttinger	wha
00:17	TEttinger	,(:a :a)
00:17	clojurebot	nil
00:17	TEttinger	ha!
00:17	TEttinger	it's a get
00:17	TEttinger	,(:a :a :b)
00:17	clojurebot	:b
00:17	justin_smith	TEttinger: demonstrating that :a is callable, and it isn't something being done by the map
00:17	TEttinger	,({:a 5} :a)
00:17	clojurebot	5
00:18	TEttinger	,({"a" 5} "a")
00:18	clojurebot	5
00:18	TEttinger	maps are fns too, but like justin_smith is saying, the first thing after the '(' is what gets called
00:18	tolstoy	,({2 4} 2)
00:18	clojurebot	4
00:18	TEttinger	threeve_: is that nick a celebrity jeopardy reference?
00:26	devtrope	,(supers (class :a))
00:26	clojurebot	#{java.util.concurrent.Callable clojure.lang.IFn java.lang.Runnable java.lang.Comparable java.io.Serializable ...}
00:29	TEttinger	,(clojure.string/join " " (supers (class :a)))
00:29	clojurebot	"interface clojure.lang.IHashEq interface java.util.concurrent.Callable interface clojure.lang.IFn interface java.lang.Runnable interface java.lang.Comparable interface java.io.Serializable interface clojure.lang.Named class java.lang.Object"
03:13	deiodeiodeio	I want to be able to run my tests in parallel (selectively). Currently, I'm using midje, and my naive approach of wrapping parallelizable sections of my test code in futures seems to break it. What's a good way of doing this?
03:15	ordnungswidrig	deiodeiodeio: that's actually a good question. But why want you to run tests in parallel?
03:16	deiodeiodeio	I'm doing integration tests involving spinning up and taking down a lot of services
03:17	deiodeiodeio	naturally, this takes a while
03:17	ordnungswidrig	deiodeiodeio: I see. In which way do futures break it?
03:17	ordnungswidrig	deiodeiodeio: I'm assuming there are no race conditions or the tests influencing easch other
03:21	deiodeiodeio	ordnungswidrig: it doesn't seem to be my code, no..
03:22	ordnungswidrig	can you distill an example? just how you use midje and futures?
03:22	deiodeiodeio	yeah, sorry, I'm working on it
03:29	deiodeiodeio	ordnungswidrig: basically, I did something along the lines of (facts (future (fact 1 => 0)) (future (fact 1=> 0) ...)), and got a bunch of Exception in thread "main" java.lang.AbstractMethodError: clojure.core$promise$reify__6363.invoke()Ljava/lang/Object
03:30	ordnungswidrig	deiodeiodeio: oh weird
03:30	deiodeiodeio	ordnungswidrig: yeah. but I'm now not entirely convinced it's midje's fault. if it is, it seems to be flaky
03:30	deiodeiodeio	so I guess I'll have to investigate it a bit closer
03:30	ordnungswidrig	deiodeiodeio: I would macroexpand the (facts) expression
06:30	namra	j/quit
07:30	deiodeiodeio	what's a good, simple way of doing concurrent printing without using core.async or a logging library?
07:30	deiodeiodeio	(i.e. without multiple lines printing concurrently)
07:40	mnngfltg	deiodeiodeio, using an agent perhaps?
07:40	luma	yep, create an agent and then send each printing to it
09:19	galaux	I can't find some kind of "fail" method for Clojure unit tests …
09:19	galaux	Does it exist somewhere?
09:21	snowell	Wouldn't you generally want to assert the opposite of what's happening?
09:21	galaux	well: nothing is happening, that's the idea
09:21	snowell	What are you testing for?
09:21	galaux	I'm testing for a particular function NOT to be called
09:22	galaux	This is a function I pass to some other function … I want to check it has not be called
09:22	galaux	So I thought I would just make this second method something like `(fail "Error")
09:23	snowell	I mean…you could always assert false ;)
09:23	galaux	yes …
09:23	snowell	Sorry that's not a whole lot of help
09:24	galaux	no but still it would work … even though a "fail" method would have been perfect (especially for handling a test failing messge)
09:24	galaux	snowell: thanks
09:25	snowell	I've not done much unit testing in clojure. When I have, it was with https://github.com/marick/Midje
09:26	dstockton	galaux: assert can take an option message
09:26	dstockton	(defn fail [message] (assert false message))
09:28	dstockton	or you could throw an exception
09:29	galaux	An exception is not a failing test
09:29	galaux	I don't want to crash it, just flag it as failed
09:29	galaux	but it would work in some way
09:32	galaux	I am going to go for `(is (true? false) "Something went wrong")`
09:32	galaux	snowell: thanks for the link,looks nice !
09:33	snowell	With both Midje and clojure.test, you can assert that exceptions are thrown/not thrown
09:34	snowell	So if you pass in a function that just throws an Exception, you can assert that said Exception isn't thrown
09:34	snowell	Without crashing the test execution
10:13	justin_smith	e
10:21	justin_smith	,0xDEADBEEFCAFEBADD
10:21	clojurebot	16045690984503098077N
10:21	justin_smith	I hear that number is prime
10:26	gfredericks	,(.isProbablePrime (biginteger 0xDEADBEEFCAFEBADD) 100)
10:26	clojurebot	true
10:33	troydm	which function should I use for lenghth of string in Clojure? .length or count?
10:41	justin_smith	well only one of those is a function
10:41	justin_smith	use count
12:52	mdeboard	Ok so in cider, I'm running this long-running async process in a goroutine. How the heck do I kill it?
12:59	justin_smith	mdeboard: write it such that it checks some condition you have control over, and it exits gracefully
12:59	justin_smith	or kill your vm
13:00	mdeboard	ok, that's what I figured (the last)
13:00	justin_smith	mdeboard: is it reading from some channel? closing the channel would help in that case
13:00	justin_smith	(I was being slightly glib)
13:00	mdeboard	Yeah I just added some logic to close
13:05	mdeboard	I assume the value of `(<! ch)` if there are no messages on the channel is `nil`, is that right?
13:08	justin_smith	no
13:08	justin_smith	it doesn't return to your process
13:08	justin_smith	nil is if the channel is closed
13:09	justin_smith	(which is why I mention that closing a channel could communicate to a go block that it should exit)
13:09	justin_smith	mdeboard: forgot to highlight you in my reply ^
13:10	mdeboard	I see
13:10	mdeboard	Hmm
13:10	mdeboard	Because I want to flush my buffered writer if there's nothing on the channel
13:10	mdeboard	so I don't have half a message in the log
13:10	mdeboard	just chilling, waiting for more data
13:11	justin_smith	mdeboard: check out alts!
13:11	justin_smith	then you can have a timeout, and flush if the timeout is hit
13:11	mdeboard	Cool
13:11	mdeboard	Very nice
13:12	justin_smith	like (alts! [ch (timeout 10000)]) either gets data from ch, or from the timeout after 10 seconds
13:12	justin_smith	and in the return value you can test which you got
13:13	mdeboard	Frustrated with Clojure's documentation atm.
13:13	mdeboard	As I have been since 2010 or something.
13:13	justin_smith	mdeboard: this is what makes our lovely community so valuable :)
13:14	justin_smith	mdeboard: the official core.async api is a bit disorganized maybe, but it is comprehensive https://clojure.github.io/core.async/#clojure.core.async/alts!
13:14	justin_smith	official core.async api docs, that is
13:17	mdeboard	yeah that's what I'm frustrated with :P
13:17	mdeboard	It's definitely exhaustive
13:17	mdeboard	Not sure how useful it actually is, but it's exhaustive
13:18	mdeboard	justin_smith, So where can I find a full example of this alts functionality
13:18	justin_smith	mdeboard: I think my skill as a developer has been helped quite a bit by my extensive experience reading postmodern literature - fragmented, odd points of view, strange aporias ...
13:18	justin_smith	mdeboard: hmm, maybe conj.io, checking
13:19	mdeboard	Is that another stab at community-curated docs?
13:19	mdeboard	Ah this is uh
13:19	justin_smith	mdeboard: if not i'll share a quick repl demo of it
13:19	mdeboard	Oh the guy lives here in Austin
13:19	mdeboard	Can't remember his name, but this is his thing
13:19	justin_smith	mdeboard: arrdem
13:19	mdeboard	arrdem, yeah
13:19	justin_smith	I thought he had core.async on here but I can't find it
13:20	mdeboard	Here's my function https://gist.github.com/mattdeboard/ecd0d033d1977bf6da78
13:21	mdeboard	I think the alts! call would go on like line 7 (and I'd need to refactor a little to remove the arg to recur
13:21	mdeboard	)
13:23	justin_smith	mdeboard: working demo of alts! from the repl https://www.refheap.com/109440
13:23	justin_smith	mdeboard: you can test via the second item in that returned vector which channel the value came from
13:23	justin_smith	mdeboard: paste updated to show this fact https://www.refheap.com/109440
13:25	justin_smith	mdeboard: yeah, I would put the alts on line 7, and if the channel the value comes from does not = ch, then flush, otherwise use the value
13:26	justin_smith	mdeboard: using my own repl example of alts as a basis for that should be easy enough
13:34	mdeboard	Nice, thanks
13:35	mungojelly	why do i need to say var# to get unclobbered variables in macros, do y'all also use macros to intentionally clobber variables?
13:42	sdegutis	Is there a simpler way of mapping characters in a string to their line/char position than this? https://gist.github.com/sdegutis/ff476b6efef23e7a5a1d
13:42	sdegutis	This function seems overly complex.
13:42	mdeboard	justin_smith, Sorry if I'm being a huge dunce but the alts! syntax doesn't make sense to me. it takes an array of "ports", and does what?
13:43	mdeboard	It says it "does at most one of several channel operations"
13:43	mdeboard	What operations is it talking about?
13:43	snowell	mdeboard: It accepts any number of channels and performs a take on whichever one of them first returns a value
13:43	mdeboard	Oh
13:43	mdeboard	What the hell?
13:44	mdeboard	wth @ the docs
13:44	arrdem	mdeboard: o/
13:44	mdeboard	that's 100% impenetrable
13:44	arrdem	are we on about docs again
13:44	mdeboard	and also just seems inconsistent with actual functionality?
13:44	mdeboard	arrdem, lol
13:44	mdeboard	I don't want to get you in any legal trouble
13:45	mdeboard	or something (recalling some blog post about something like that)
13:45	snowell	I do. I'd love an excuse to go back to Austin ;)
13:45	mdeboard	"Completes at most one of several channel operations." <-- actually means "Performs a take on at most one of several channels"?
13:46	mdeboard	Ok now that I understand alts! because of the explanation in IRC, the docs make sense. That's not how docs are supposed to work.
13:47	arrdem	welcome to Clojure
13:48	mgaare_	mdeboard: actually that's not what it means. because you can also do a put inside of alts!
13:48	mdeboard	Yeah was just saying this has been constant source of irritation for like 5 years
13:48	mdeboard	mgaare_, Yeah I see that now
13:48	mdeboard	I'm tempted to do a PR to improve that docstring
13:48	snowell	Sorry…I knew there was a chance I only partially understood it :/
13:49	mdeboard	but by "several" it just means "two" right? Either put or take?
13:49	mgaare_	that's why it says channel operations.
13:50	snowell	"several" refers to its args
13:50	mdeboard	wat
13:50	clojurebot	Titim gan éirí ort.
13:51	snowell	You pass in several operations, it will perform at most one of them
13:51	mdeboard	Ok, maybe I am misunderstanding the word operation.
13:53	mgaare_	operation in this context is the combination of action + channel. So "put on channel x" is an operation, "take from channel y" is an operation, and you can have an arbitrary number of these in what you pass to alts!
13:54	seancorfield	clojars.org seems to be struggling... very very slow to respond / occasional 500 server error messages
13:54	mdeboard	ok so you can do like `(alts! [ch-foo [ch-bar 1] ch-baz [ch-qux 2]])` ?
13:55	mgaare_	mdeboard: that's right
13:55	mdeboard	Ok. Thanks for the clarification
13:55	mdeboard	Does it just iterate left-to-right looking for the first valid operation?
13:56	mdeboard	and a put is invalid only if the channel is closed?
13:57	mgaare_	mdeboard: if you pass :priority true as an opt, then they will be tried in order, otherwise there is no order guarantee. a put will only succeed if the channel is open and not blocked
13:58	mdeboard	Understood, thank you
13:59	mungojelly	why the ! does it change something
14:03	_alejandro	it modifies the channel it reads from / writes to
14:12	mdeboard	That's just a freaking hard function to explain. Takes more than the dry matter-of-fact tone of docstring.
14:12	mdeboard	(I'm sitting here trying to write better documentation.)
14:14	geet	Hi! I'm new to Clojrue, I'd like to start contributing. Where would you suggest I do?
14:15	mungojelly	hmm so you only get tail-call optimization if you ask for it with "recur"?
14:17	arrdem	mungojelly: correct
14:18	mungojelly	ok thanks well that's clear enough anyway. what do you want to contribute to what, geet, i don't understand?
14:19	arrdem	note that the JVM itself doesn't have TCO yet due to reliance on stack frame counting for some security stuff
14:22	geet	Contributing to clojure
14:22	geet	mungojelly:
14:23	mungojelly	personally what i think it needs is more toys
14:24	mungojelly	i'm learning by poking at lists of meaningless numbers, i'm bored, someone hand me a toy
14:25	mdeboard	Is there any kind of proscription against calling `recur` in a `do` block
14:26	justin_smith	mdeboard: only that it needs to be in the tail position (that would always be the end of a do block, or the end of a branch in a do block)
14:26	mdeboard	Alright, cool
14:34	mdeboard	I think this will do what I am wanting but not entirely sure https://gist.github.com/mattdeboard/ecd0d033d1977bf6da78
14:34	mdeboard	It didn't, actually. I wonder if it closed too quick or something.
14:35	justin_smith	mdeboard: (if (nil? entry) ...) should be (if (nil? (first entry)) ...)
14:35	justin_smith	mdeboard: remember alts returns a two part vector
14:35	justin_smith	even better, it could be (if-not (= ch (second entry)) ...)
14:36	justin_smith	mdeboard: similarly with your other usages of entry I think you want (first entry) to actually get the data, rather than the data/channel pair
14:37	justin_smith	mdeboard: or, perhaps the easier change is (let [[entry source] (async/alts! ...) ...] ...) and then the rest of the code can stand unchanged
14:37	mdeboard	Are you sure about the vector thing?
14:37	mdeboard	https://gist.github.com/mattdeboard/f15ff4454ffd1c570ca2
14:37	justin_smith	mdeboard: absolutely sure
14:37	justin_smith	mdeboard: it's not timeout that returns the vector
14:38	justin_smith	it is alts! that is returning a vector
14:38	mdeboard	Oh!
14:38	mdeboard	Ok.
14:38	justin_smith	mdeboard: see my example - no matter which data source is acessed, you get a two element vector of the data and the channel it came in on
14:38	justin_smith	alts! would not be very useful without that feature
14:38	mdeboard	Why is this so hard for me to grok
14:39	justin_smith	mdeboard: it's new?
14:47	mdeboard	Nice, it works
14:47	mdeboard	Thanks for the help all youse
14:48	justin_smith	cool
14:50	mdeboard	Hm maybe not.
14:51	mdeboard	This is really hard to troubleshoot, the asynchrony. Feel like I'm doing JavaScript
14:52	mdeboard	Writing javascripts*
14:53	justin_smith	jabbyscraps
14:54	justin_smith	yes, core.async can be weird to figure out when misbehaving
16:52	ben_vulpes	so i'm wiring a figwheel server setup into my clojure projects own reloaded flow, and i've bumped into an issue managing the figwheel server's state
16:52	ben_vulpes	i new up a figwheel server, stop it, and then bind the result to fig-server
16:53	ben_vulpes	pass that into the watcher as (fig/autobuild* {... :fig-server fig-server})
16:53	ben_vulpes	call (fig/stop-server ...) on the value for the :fig-builder key in my system object
16:54	ben_vulpes	get a repl print line that claims that the fig-server has been started on :3449
16:54	ben_vulpes	but then i simply get websocket errors in the browser, a la 'ws://localhost:3449/figwheel-ws/dev failed' ERR_CONNECTION_REFUSED
16:56	nooga	I just had the weirdest node.js like experience with clojure
16:56	ben_vulpes	oh fascinating. it's not even recompiling the cljs.
16:56	mdeboard	ben_vulpes, Is your project.clj set up right?
16:57	nooga	timbre was throwing an exception because something inside manifold returned an exception instead of a value I wanted to log
16:57	mdeboard	Here's a year-old project.clj of mine from a cljs project I was working on that uses figwheel and all that https://github.com/mattdeboard/dots/blob/master/project.clj
16:57	nooga	and I saw manifold's exception with meaningless timbre call stack
16:58	nooga	took me a while
16:58	mdeboard	ben_vulpes, figwheel used to be super, super hard to set up then... something changed that I can't remember
16:59	mdeboard	maybe I just stopped being dumb
16:59	nooga	heheh
16:59	mdeboard	Gosh darnnit I hate that i have to have the source code ordered correctly in order to compile
16:59	mdeboard	like if function A calls function B, function B has to be physically above function A in the source
17:00	mdeboard	is that unavoidable?
17:07	oddcully	,(doc declare)
17:07	clojurebot	"([& names]); defs the supplied var names with no bindings, useful for making forward declarations."
17:08	nathanmarz	Clojurescript question for any of the experts here
17:09	nathanmarz	Trying to implement IFn protocol for more than 20 arguments, but this isn't working: https://gist.github.com/nathanmarz/e932e11c523fe90b1850
17:10	nathanmarz	when I invoke with 21 args it just binds "rest" to the 21st arg (instead of a seq), and when I bind with more it gives an arity exception
17:11	nathanmarz	@dnolen any ideas?
17:14	ben_vulpes	mdeboard: no clue, boss.
17:14	ben_vulpes	i've fallen back to using lein-figwheel
17:14	ben_vulpes	but now it's not watching files
17:16	ben_vulpes	clean-builds and build-once work handily from the repl, but figwheel is refusing to reload changes.
17:18	dnolen	@nathanmarz probably just a bug
17:19	dnolen	@nathanmarz oh right, but there's no support for this at the protocol level in ClojureScript (and unlikely unless somebody else wants to do the work)
17:19	ben_vulpes	(i'm a derp, disregard)
17:20	nathanmarz	@dnolen: ok
17:20	dnolen	JavaScript doesn't support variadic methods in the nice way that Java does
17:20	dnolen	so you will need a fn to pull apart the args for you (fns produce a bunch of dispatching logic)
17:20	nathanmarz	@dnolen: I though that 21 arity version of -invoke (not including the "this" param) handled that case
17:20	dnolen	but this completely undesirable at the protocol level for perf reasons
17:21	dnolen	protocols are at the very bottom
17:21	dnolen	they are literally nothing but the host
17:21	dnolen	i.e. JavaScript methods
17:21	Bronsa	dnolen: isn't this the same for clojure on the jvm? IFn vs RestFn
17:22	nathanmarz	@dnolen: ok
17:22	dnolen	Bronsa: but Clojure separated these things out, Java doesn't have functions
17:22	nathanmarz	@dnolen: why to functions like assoc and + allow for more than 20 args?
17:22	dnolen	JavaScript does
17:22	dnolen	nathanmarz: var args support at the compiler level
17:22	dnolen	every function emits dispatching code to handle this stuff
17:23	nathanmarz	oh i see
17:23	dnolen	this code is not expressed at anything shareable (via a class)
17:24	dnolen	but also protocols do not support var args, neither Clojure nor ClojureScript
17:24	dnolen	IFn in Clojure is a Java thign
17:24	nathanmarz	yea, IFn in clojure has applyTo
17:25	nathanmarz	I thought the -invoke definition in cljs was the equivalent, but it just gets interpreted as a 21 artity invoke
17:25	dnolen	nathanmarz: nope
17:25	dnolen	the 21st arity is just to support fns that dispatch to protocols
17:26	dnolen	which will have already pulled apart the args
17:27	dnolen	@nathanmarz there's probably some way to make this work, but I'm not going to stick my brain there right now
17:27	nathanmarz	oh I just mean for my own extension of IFn to my own type
17:27	nathanmarz	yea it's not that big of a deal
17:30	dnolen	nathanmarz: Bronsa: actually scratch everything I just said
17:30	dnolen	I'd just forgotten how this worked (I did this so long ago)
17:30	dnolen	it's a simple bug
17:31	dnolen	nathanmarz: http://dev.clojure.org/jira/browse/CLJS-1447
17:31	dnolen	not sure when I'll get around to this though
17:34	nathanmarz	@dnolen: I'll keep my test for this commented out in the meantime ;)
17:36	dnolen	nathanmarz: yeah ok now I remember the issue :)
17:36	dnolen	so ClojureScript functions are just JavaScript functions, there is no arity limit
17:36	dnolen	but this of course doesn't make sense for the IFn protocol, the change is actually pretty simple, the ticket is updated with some simple details on how to do it
17:54	berns_	When I merge maps with merge-with, is there any way to maintain the order of the values?
17:54	amalloy	what do you mean, the order of the values?
17:55	eklo	Hello, I'm working on a recursive fn for counting the number of solutions to the n-queens but it seems slower then it should be. I'm just trying to learn if I used the correct structure for recursing and stopping branches early. https://www.refheap.com/109449
17:59	berns_	amalloy: ({:foo 1} {:foo 2} {:bar "a"} {:foo 3}) -> {:foo (1 2 3) :bar "a"}
17:59	amalloy	as opposed to...?
17:59	berns_	{:foo (3 1 2) :bar "a"}
18:00	amalloy	the function that you give to merge-with will receive the values it needs to merge in the same order that they are present in the map you give to merge-with
18:01	amalloy	eklo: it looks reasonable enough to me
18:02	berns_	but if I merge with conj, it prepends. If I merge with vector, it does [1 [2 3]]
18:03	amalloy	berns_: if you merge with conj it doesn't work at all, because (conj 1 2) is an error
18:03	nooga	btw. what is the best place to start learning about cljs compiler? (I mean the code, obviously, but it's a big program and it's hard to understand its structure eight away)
18:03	nooga	right*
18:58	seako	hello fellow clojurians, i'm wondering if anyone has any wisdom to share re: tuning garbage collection and jvm options or articles they can point me to? as i'm new to the jvm, nothing is too elementary.
18:59	tcrayford____	seako: I was just reading just the thing!
18:59	tcrayford____	http://insightfullogic.com/2013/Feb/20/garbage-collection-java-1/, http://insightfullogic.com/2013/Mar/06/garbage-collection-java-2/, http://insightfullogic.com/2013/May/07/garbage-collection-java-3/, http://insightfullogic.com/2013/Jun/24/garbage-collection-java-4/
19:00	seako	thanks!
19:00	tcrayford____	that's for GC at least. RE JVM options, I mention them a bit in a talk I gave at euroclojure this year: http://yellerapp.com/posts/2015-06-29-performance-and-lies.html
19:00	tcrayford____	(there's a table in the slides that you can skip to, but it ain't useful without me talking over it)
19:01	seako	thanks so much, really appreciate it!
19:02	tcrayford____	s'cool. Feel free to PM me on freenode if you have questions, I have done a lot of stuff with the JVM and perf/tuning/etc (I have an irc bouncer so I may not reply immediately, but I will get your message and reply eventually)
19:04	seako	super generous of you, i just might take you up on that :)
20:39	felipedvorak	http://pastebin.com/EWqrjtBs can somebody help me with that? It's ultra basic baby so probably won't take more than a few seconds of your time. I'm trying the classic "get me the odd numbers out of this sequence". What am I doing wrong?
20:40	justin_smith	felipedvorak: when would tail be 0?
20:40	justin_smith	,(rest ())
20:40	clojurebot	()
20:41	felipedvorak	hmmm
20:41	felipedvorak	would (nil? tail) work?
20:41	justin_smith	also why (into () resul) - you could just conj the items onto () in the first place if you want a reversed list instead of an in-order vector
20:41	justin_smith	felipedvorak: no
20:41	amalloy	also, this looks like you are trying to do the classic CL/scheme "accumulate a list and then reverse it"
20:41	justin_smith	err, maybe
20:42	justin_smith	but empty
20:42	felipedvorak	amalloy: I don't really know what I'm doing hehe
20:42	amalloy	nil? would be fine
20:42	justin_smith	oh, yeah he is using destructuring and not rest
20:42	amalloy	although uh, you then lose the last element of the sequence
20:42	amalloy	you can't just check the tail of the list and then ignore the head
20:43	justin_smith	felipedvorak: also, this is very much common-lisp style imperative code, and we have much simpler ways to do operations like this (but I trust if you stick to clojure you'll learn those eventually)
20:44	felipedvorak	I hope so, I'm only a few days in
20:46	felipedvorak	I still don't get it though
20:46	dbasch	felipedvorak: you probably want to start by looking at some of the built-ins that come with clojure http://clojure.org/cheatsheet
20:46	justin_smith	felipedvorak: rule of thumb, if what you are doing involves going through a sequence one item at a time, clojure probably has something much nicer than loop you can use for that
20:47	dbasch	felipedvorak: e.g. in this particular case, odd? and even?
20:47	justin_smith	felipedvorak: which part don't you get?
20:47	xzilend	noob question, I have a {:email ".." :password ".."} map. I'd like a validation function to add: {:errors ["error 1"]} to the initial map. I currently have (update-in creds [:errors] conj "error 1"), but that creates {:errors ("error 1")}, is there anyway I can enforce a vector instead?
20:47	justin_smith	xzilend: (fnil conj [])
20:47	felipedvorak	dbasch: I have that on my bedroom wall hehe will check it more often
20:48	justin_smith	,((fnil conj []) [] :a)
20:48	clojurebot	[:a]
20:48	justin_smith	,((fnil conj []) nil :a)
20:48	clojurebot	[:a]
20:48	dbasch	felipedvorak: I haven’t read your code but it sounds like you want (filter odd? your-seq)
20:48	justin_smith	dbasch: I think he still could learn a few things by making the loop work (though your version is canonical, of course)
20:49	dbasch	justin_smith: agreed
20:50	felipedvorak	lol, (filter odd? sequence) looks beautiful. Must love this language.. I'll try to fix this code for learning purposes
20:53	xzilend	justin_smith: thanks!
20:53	justin_smith	xzilend: fnil is almost as awesome to use as it is to say
20:53	justin_smith	fnil
20:53	justin_smith	rolls right off the tongue
20:55	oddcully	close to fna
20:56	lodin-	justin_smith: There's also a more esoteric solution, and that's to use a lens library and do (update creds (lookup :errors []) conj "error 1") where lookup is the lens with default value [].
20:57	justin_smith	one of my first experiences with my new job was introducing my coworkers to fnil, only to have them laugh at the word
20:57	justin_smith	lodin-: I was once talked out of trying to use lenses in clojure, do you think it's worth it?
20:57	xzilend	lodin-: thanks! I'll keep that in mind :D
20:58	lodin-	justin_smith: Yes!
20:59	lodin-	justin_smith: I really miss a solid lens library though. One day I might find the time to write one myself.
21:01	felipedvorak	hmm, and now hehe still get an error, I believe it may have to do with conj? (trying te primitively read the error output)
21:01	felipedvorak	http://pastebin.com/4M78iwvJ
21:01	justin_smith	felipedvorak: yeah, your args to conj are flipped
21:01	lodin-	justin_smith: I benched the functor implementation of lenses (my own, adapted from https://speakerdeck.com/markhibberd/lens-from-the-ground-up-in-clojure), against a 100 keys deep get-in. Lenses were faster. Blew my mind. I still believe the benchmark was wrong.
21:02	justin_smith	felipedvorak: it will still have the issue amalloy_ mentioned where if the last item is odd it will throw it away erroneously
21:02	felipedvorak	lol, now it gives me (6) as a result, but at least it runs
21:03	lodin-	Or was it update-in? Don't remember.
21:03	justin_smith	felipedvorak: oh, you flip the input and the result in your recur too
21:03	justin_smith	(in the first recur that is)
21:05	lodin-	justin_smith: Anyway, the point is that you don't need to worry about overhead, which leads us to the benefits.
21:06	felipedvorak	I still don't get why I loose the last item
21:06	lodin-	justin_smith: The biggest benefit is not actually lenses, but traversals.
21:09	xzilend	Can anyone tell me why I would prefer one of these over the other? (defn fun [s] (-> s f1 f2 f3)) or (def fun (comp f1 f2 f3))?
21:11	lodin-	xzilend: I opt for the first. The argument is explicit. (You have the order wrong in one of them though.)
21:13	xzilend	makes sense! thanks
21:13	lodin-	xzilend: Assuming the first version is correct, then it is clear that f1 takes just one argument. In the second, f1 could take any number of arguments.
21:15	lodin-	xzilend: I think linters like eastwood will help you out as well with the first, but not the second, if you do (fun x y) or (fun) etc. But I'm not sure.
21:18	xzilend	lodin-: good point! thanks :D was reading http://drboolean.gitbooks.io/mostly-adequate-guide/ and it's very keen on the (comp ..) (although in JS) form
21:20	justin_smith	xzilend: clojure definitely has its population of point-free fans
21:20	justin_smith	(point free programming being the style where you avoid named arguments, so frequently use constructs like comp or juxt)
21:21	lodin-	xzilend: At the top-level I think you should just spell out your function. Anonymous functions, like functions passed to e.g. filter, is another thing.
21:23	lodin-	xzilend: In practice, I find that I end up using #(-> % ...) anyway, since it's easier to do things like (get foo) there, rather than doing #(get % foo) in a comp.
21:25	lodin-	xzilend: If you do use comp a lot, I recommend using (defn => [f & args] #(apply f % args)) too. It will be cleaner.
21:25	lodin-	Especially since you can't nest #().
21:26	xzilend	lodin-: yeah those arguments definitely make sense
21:26	xzilend	I've been using -> since I started clojure about a month or two ago, hadn't really seen comp used anywhere
21:27	lodin-	I'm not sure, but I think point-free makes more sense in "curried" languages, i.e. where multiple arity is just sugar for nested unary functions.
21:51	felipedvorak	justin_smith: with reduce I managed to get a list of the odd items BUT they are not in the correct order :/ http://pastebin.com/RXjZxAcH
21:52	felipedvorak	hehe but I'm almost there
21:52	justin_smith	felipedvorak: if you want to keep the order, use [] instead of ()
21:52	justin_smith	also, '() is the same as (), you never need the former
21:52	felipedvorak	hmm
21:52	justin_smith	,(= () '())
21:52	clojurebot	true
21:53	felipedvorak	but if the answer must be given in a list format, I use `into`?
21:53	justin_smith	no, into will reverse the order
21:53	justin_smith	use seq if you need the result to be a list - but why do you need a list?
21:54	felipedvorak	justin_smith: because the 4clojure problem, as far as I understood, asks for a list output
21:54	justin_smith	felipedvorak: I doubt it will reject a vector
21:55	justin_smith	but wrap the whole thing in seq if it rejects the vector
21:55	justin_smith	,(= [:a :b :c] '(:a :b :c)) ; felipedvorak: in clojure lists and vectors are equal if they have the same content in the same order
21:55	clojurebot	true
21:56	felipedvorak	hmm, thats new to me
21:57	felipedvorak	justin_smith: must go out for a bit, thanks for your help, I'll keep trying when I come back
21:59	felipedvorak	it works! hehe thanks
22:37	pydave6377	Probably a stupid question, but is there a way of combining a HOF with the threading macro? Something like: (-> rtm-conn :start :users (filter :is_bot) first :id)
22:38	justin_smith	pydave6377: that works if you use ->> instead of ->
22:38	lodin-	pydave6377: You want to use ->> in front of filter.
22:38	justin_smith	since your collection needs to be the last arg
22:38	justin_smith	pydave6377: also, ->> can be used inside of -> if you need to combine the behaviors
22:40	justin_smith	,(-> {:a [1 2 3 4]} :a (->> (map inc)))
22:40	clojurebot	(2 3 4 5)
22:40	lodin-	pydave6377: Has nothing to do with HOF though.
22:40	pydave6377	justin_smith: lodin- This is fantastic! Thank you both so much! I always had trouble working out the difference between -> and ->> so I'm ecstatic to have finally learned! Thank you both again!
22:41	pydave6377	lodin-: apologies - perhaps I mispoke. Still getting the hang of FP!
22:42	lodin-	pydave6377: Ah, wait. Did you mean "partial"?
22:43	pydave6377	lodin-: partial would have been a much more apposite description.
22:45	lodin-	pydave6377: All the forms in -> and ->> are "partial". That's the point of ->. That's not always clear because you often see it with unary functions and symbols are rewritten to have a parenthesis around them.
22:45	pydave6377	justin_smith: sorry, took me a moment to grok that. I had no clue that was possible! Thank you
22:45	lodin-	pydave6377: In other words, (-> x foo bar) is really (-> x (foo) (bar)).
22:46	felipedvorak	How do I get a number, say 424 and interpret it like a list (1 2 3 4 5...) so I can iterate?
22:46	justin_smith	lodin-: it's not really partial application though, -> / ->> don't operate on runtime functions and values, the operate on compile time forms
22:46	lodin-	pydave6377: And (-> x (foo y)) is (foo x y).
22:47	justin_smith	,'(-> x (foo y))
22:47	clojurebot	(-> x (foo y))
22:47	lodin-	justin_smith: Yeah, I know. But you could say that the form is partial.
22:47	justin_smith	,(macroexpand1 '(-> x (foo y)))
22:47	clojurebot	#error {\n :cause "Unable to resolve symbol: macroexpand1 in this context"\n :via\n [{:type clojure.lang.Compiler$CompilerException\n :message "java.lang.RuntimeException: Unable to resolve symbol: macroexpand1 in this context, compiling:(NO_SOURCE_PATH:0:0)"\n :at [clojure.lang.Compiler analyze "Compiler.java" 6704]}\n {:type java.lang.RuntimeException\n :message "Unable to resolve symbol:...
22:47	justin_smith	err
22:47	lodin-	pydave6377: And (->> y (foo x)) is (foo x y).
22:47	pydave6377	lodin-: that's really interesting. I've been using it the whole time as a substitute for (bar (foo (x)))
22:47	justin_smith	,(macroexpand-1 '(-> x (foo y)))
22:47	clojurebot	(foo x y)
22:51	sotojuan	kool
22:51	lodin-	pydave6377: The name comes from how you do stitches with a needle. Thread, as in yarn.
22:55	pydave6377	lodin-: that's just made everything so much clearer. I've never thought of it like that. You guys have been incredibly helpful. Thank you so much!
22:57	lodin-	pydave6377: But don't start abusing it. :-)
22:57	lodin-	,(->> n dec f (* n) (if-not (pos? n) 1) (defn f [n]))
22:57	clojurebot	#'sandbox/f
22:57	lodin-	,(f 5)
22:58	clojurebot	120
22:58	justin_smith	oh my god that's terrible
22:58	justin_smith	haha
22:58	lodin-	justin_smith: This is how I write all my code. ;-)
22:59	kavkaz	D:
23:00	pydave6377	lodin-: that's the most egregious abuse of a well-intentioned feature that I have ever seen.
23:00	pydave6377	(inc lodin-)
23:14	justin_smith	this article about fortran covers clojure, and has some invalid common lisp code in it too http://arstechnica.com/science/2014/05/scientific-computings-future-can-any-coding-language-top-a-1950s-behemoth/
23:15	felipedvorak	What is the clojure equivalent of (i = 1; i < 1000; i++) ?
23:15	lodin-	felipedvorak: Depends on what you want to do, but probably (range 1 1000).
23:16	justin_smith	felipedvorak: (loop [i 0] (if (> i 999) nil ...) (recur (inc i)))
23:16	justin_smith	your code goes in the ... part
23:16	justin_smith	lodin-: I guess we interpreted that differently
23:17	justin_smith	another possibility is (doseq [i (range 1000)] ...)
23:17	lodin-	justin_smith: I'd doseq instead.
23:17	lodin-	Yeah.
23:17	felipedvorak	hmm
23:17	justin_smith	felipedvorak: what are you actually trying to do?
23:17	lodin-	But using range with doseq or what-not only works if you don't plan to change i in the loop.
23:18	felipedvorak	get as input a number and use it as a list to check each number for a condition
23:19	felipedvorak	also known as project euler problem 1 hehe
23:19	justin_smith	felipedvorak: what happens to the numbers you check?
23:19	justin_smith	do you return some of them?
23:19	justin_smith	do you print them?
23:19	felipedvorak	yeah
23:19	felipedvorak	if a number is multiple of 3 or 5
23:20	justin_smith	yeah, use doseq with a print inside
23:20	lodin-	I'd first filter and then doseq over the ones I want to print.
23:20	felipedvorak	my prowess is still very basic, I still don't know doseq
23:20	felipedvorak	let me check it
23:21	justin_smith	,(doseq [i (range 10)] (println i))
23:21	clojurebot	0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n
23:21	felipedvorak	in the end you must output the sum of the numbers
23:21	justin_smith	ahh, so you need to keep track and sum, you'll want more than just doseq for that yeah
23:21	felipedvorak	^ what is this output?
23:21	lodin-	felipedvorak: Then let me point you towards reduce.
23:22	lodin-	felipedvorak: You can use a combination of reduce, filter, and range.
23:22	justin_smith	yeah, that's probably the best bet
23:23	felipedvorak	i'll try that, thanks
23:25	lodin-	felipedvorak: The "easy" solution if you are used to using loops is to use loop/recur, but resist the temptation. :-)
23:25	felipedvorak	wouldn't reduce be even easier?
23:25	justin_smith	felipedvorak: simpler vs. more familiar
23:25	lodin-	felipedvorak: Simple vs easy. ;-)
23:26	felipedvorak	I'm really looking for the hard but still "clojury" solution hehe
23:26	kavkaz	Not Clojure related but I'm expecting I'll have a quick answer, is there a MELPA package I need to download for emacs to enable spellcheck?
23:27	justin_smith	kavkaz: ispell comes with emacs, flyspell-mode is a nice way to use it
23:31	kavkaz	justin_smith: Ah cool, thanks