#clojure – 2016-03-10

2016-03-10

06:43	amoe_	it seems strange to me that (def blah nil) (blah) => NullPointerException. I mean, it totally makes sense, but I wonder why there is not a more specific error message.
06:55	tdammers	amoe_: because clojure doesn't abstract away all the JVM peculiarities
06:55	tdammers	for the same reason, you'll also see the underlying Java class names and such in stack traces instead of their clojure appearances
08:08	faxmodem	I've been successfully using lein try a lot and it's awesome
08:08	faxmodem	how can I use it for a local project?
08:08	faxmodem	e.g. 'lein try .'
08:15	ridcully_	faxmodem: isnt that just lein repl then?
08:17	faxmodem	ridcully_: I guessed the same
08:17	faxmodem	but then the deps arent' being fetched
08:17	faxmodem	so I guess I'm just looking at the lein command to do that :)
08:19	ridcully_	oh you mean you want to temporarily try it out with an existing project
08:19	ridcully_	i either add it then or use lein plz. i only ever used try without projects
08:37	faxmodem	yes
08:38	faxmodem	lein plz is that shipped with leiningen?
08:40	tdammers	lein is leiningen
08:40	ridcully_	plz is another plugin
08:40	tdammers	oh nm
09:08	faxmodem	tdammers: then 'lein deps && lein repl' should be enough to get started?
09:08	faxmodem	s/tdammers/ridcully_/
09:15	ridcully_	faxmodem: yep (even without the deps first)
09:15	ridcully_	your project.clj should contain the deps beforehand
09:22	faxmodem	ridcully_: I thought it did :)
09:22	faxmodem	ridcully_: so lein repl should run deps
09:40	faxmodem	so when I run lein deps, where do the deps get stored?
09:42	schmir	faxmodem: ~/.m2/
09:42	faxmodem	thanks!
09:59	sdegutis	I'm about to use reduce-kv for the first time ever!
10:10	fod	https://www.youtube.com/watch?v=-W6as8oVcuM
13:20	backnforth	Hello, can someone explain to me how to short snipper of code works: http://pastebin.com/y8tHJ47Z . Really I'm trying to understand how "i" and "y" obtain their values, how does the "?" work, and how does filter, identiy, and map-indexed work? And whether it was right for me to add a println to the main when calling the questioned function.
13:21	hiredman	? isn't anything special
13:21	hiredman	,(let [x?y?z 1] x?y?z)
13:21	clojurebot	1
13:22	hiredman	filter, identity, and map-indexed all have docs you can read on clojure.org
13:23	backnforth	,(let [x?y?z? 1] x?y?z?)
13:23	clojurebot	1
13:23	hiredman	when you added the println, you replaced the call to listread with the call to println
13:24	backnforth	How should the return of the function be printed?
13:42	backnforth	I'm having a hard time understanding how "filters" how.
13:44	backnforth	Oh, so it returns a lazy sequence for which the "pred" holds true,
13:51	backnforth	Anyone know where I may find a Clojure tutor?
13:52	justin_smith	backnforth: have you checked for nearby clojure meetups?
13:52	backnforth	None unfortunely.. I would even be willing to pay for a tutor.
13:53	justin_smith	if remote tutoring is an option, maybe you can find someone here, or on the clojurians slack channel
13:54	backnforth	I would prefer remote tutoring
13:54	backnforth	I'll also check the slack channel
13:55	rhg135	We don't talk about that place
13:55	justin_smith	I'd offer but I'm very busy with the day job at the moment (though I do make time to check in and answer questions here)
13:55	justin_smith	haha
13:56	backnforth	I have all day, justin_smith. If you'd like to help me later I could try to have a session prepared for then.
13:56	backnforth	Or possibly another day.
14:04	justin_smith	backnforth: what I meant was I can probably answer one-off questions on this channel on a case by case baisis but can't promise to do one on one tutoring right now
14:04	justin_smith	but maybe someone else here is available
14:05	justin_smith	backnforth: in my experience if you share a link to some code and say "what's wrong with this code" you'll probably get a lot of good advice
14:06	backnforth	ok
14:30	backnforth	Why do variables often have ":" added in front of them?
14:31	justin_smith	backnforth: :foo is not a variable, it is a keyword
14:31	justin_smith	backnforth: keywords are a special type that is self evaluating
14:31	backnforth	A keyword to the function? And the functions should know how this keyword matches?
14:31	justin_smith	backnforth: wat
14:32	backnforth	How might they be self evaluating?
14:32	justin_smith	,:foo
14:32	clojurebot	:foo
14:32	justin_smith	that's what I mean - they always stand for themselves
14:32	amalloy	backnforth: :charles is a constant value, just like 5 is a constant value
14:32	justin_smith	right, that might be a clearer way to say it
14:33	amalloy	whereas there are other structures that don't evaluate to themselves. lists, for example: the list (+ 1 2) doesn't evaluate to the list (+ 1 2), it evaluates to 3
14:34	backnforth	,(= :charles :charles)
14:34	clojurebot	true
14:34	backnforth	,(= :charles charley)
14:34	clojurebot	#error {\n :cause "Unable to resolve symbol: charley in this context"\n :via\n [{:type clojure.lang.Compiler$CompilerException\n :message "java.lang.RuntimeException: Unable to resolve symbol: charley in this context, compiling:(NO_SOURCE_PATH:0:0)"\n :at [clojure.lang.Compiler analyze "Compiler.java" 6688]}\n {:type java.lang.RuntimeException\n :message "Unable to resolve symbol: charley i...
14:35	backnforth	,(let :charles 3)
14:35	clojurebot	#error {\n :cause "let requires a vector for its binding in sandbox:"\n :via\n [{:type java.lang.IllegalArgumentException\n :message "let requires a vector for its binding in sandbox:"\n :at [clojure.core$let invokeStatic "core.clj" 4333]}]\n :trace\n [[clojure.core$let invokeStatic "core.clj" 4333]\n [clojure.core$let doInvoke "core.clj" 4325]\n [clojure.lang.RestFn invoke "RestFn.java" 467...
14:35	justin_smith	and charley is not self-evaluating - clojure looks for a binding (and throws an error if it does not find one)
14:35	justin_smith	backnforth: for the top level you need def, and keywords are not valid bindings
14:35	backnforth	So i assume I can't assume values to :charles considering :charles is its value.
14:35	justin_smith	backnforth: what does that mean?
14:36	justin_smith	you can't bind a value to :charles because it always is just :charles if that's what you mean
14:36	backnforth	Yes, thank you.
14:36	justin_smith	unlike charley which can be bound
14:36	justin_smith	,(def charley "just some guy")
14:36	clojurebot	#'sandbox/charley
14:36	backnforth	It's so simple.
14:37	justin_smith	I like to think so, heh
14:42	backnforth	,(= poopy poopy)
14:42	clojurebot	#error {\n :cause "Unable to resolve symbol: poopy in this context"\n :via\n [{:type clojure.lang.Compiler$CompilerException\n :message "java.lang.RuntimeException: Unable to resolve symbol: poopy in this context, compiling:(NO_SOURCE_PATH:0:0)"\n :at [clojure.lang.Compiler analyze "Compiler.java" 6688]}\n {:type java.lang.RuntimeException\n :message "Unable to resolve symbol: poopy in this...
14:42	backnforth	,(= :poopy :poopy)
14:42	clojurebot	true
14:55	TMA	,(= 'karlos 'karlos) ; backnforth
14:55	clojurebot	true
14:57	justin_smith	,(apply = (map (comp symbol name) ["foo" :foo 'foo]))
14:57	clojurebot	true
14:57	backnforth	,(= 'karlos 'karlos)
14:57	clojurebot	true
14:59	TMA	backnforth: 'thing prevents the evaluation of the thing; in other words, the result of 'thing is thing for whatever the thing might be. see:
14:59	TMA	,(+ 1 2)
14:59	clojurebot	3
14:59	TMA	,'(+ 1 2)
14:59	clojurebot	(+ 1 2)
15:01	backnforth	,:(+ 1 2)
15:01	clojurebot	#<RuntimeException java.lang.RuntimeException: Invalid token: :>
15:01	backnforth	,(= 'a 'a)
15:01	clojurebot	true
15:01	backnforth	Then why used :thing?
15:08	TMA	,(:foo {:foo 1})
15:08	clojurebot	1
15:08	TMA	,('foo {'foo 1})
15:08	clojurebot	1
15:10	TMA	backnforth: no idea, :foo is a keyword, 'foo is a symbol; there might be some reason I do not know why they are separate
15:10	TMA	backnforth: maybe there is something with namespaces that make :foo better in some contexts than 'foo
15:41	justin_smith	TMA: 'foo is usually used in those cases where you eventually want to look up foo (eg. it's a var to resolve / eval later), while :foo doesn't have that implication
15:42	justin_smith	TMA: of course we could just use 'foo instead of :foo, but that adds a little bit of ambiguity about what kind of lookup / meaning we expect with that symbol
15:42	TimMc	That's a good way of putting it.
15:42	justin_smith	I mean, really, we could use strings for all of these things anyway, the rest is nuance
15:42	justin_smith	TimMc: thanks
15:50	TimMc	I usually put it as "symbols usually refer to code, keywords are usually used in data structures" but of course code is data so... :-P
16:16	matt______	a little bit confused about an error i'm getting using deftype and implementing an interface. stripped-down example is here: http://pastebin.com/AVupasmR
16:16	amalloy	keywords are faster too
16:17	amalloy	interface methods are interop calls. they're not functions
16:18	matt______	nailed it, amalloy. thanks.
16:25	sdegutis	Can (for [x xs, y ys] (get-in y [...])) be simplified/combined somehow?
16:27	amalloy	i don't think so
16:34	sdegutis	Thanks.
16:45	justin_smith	amalloy ♥'s for
17:16	randomcharhere	why does this not work (apply inc '(1 2 3 4)) but this does (apply + '(1 2 3 4)) ?
17:18	yellow13	inc is a function of only one argument
17:18	yellow13	+ receives 1..n argr
17:19	TEttinger	0..n
17:19	TEttinger	,(+)
17:19	randomcharhere	my assumption was that apply would iterate of the arg?
17:19	clojurebot	0
17:23	yellow13	actually apply take the args from [1 2 3 ...] and then call (fn arg1 arg2 arg3 ...)
17:23	macrolicious	I'm loving testing db calls from within my code via nREPL but I'm still unclear what it is in functional languages that make this possible and why it's not in other types of languages... can someone explain?
17:26	randomcharhere	evidently map was design to iterate over args
17:28	randomcharhere	Db calls can be made from within other languages nothing to do with funtioanl languages its just more imediate with repl shrug
18:26	rhg135	there's an assembly repl out there. not functional at all
18:26	rhg135	it's mostly the power of repls and recognizing their utility
18:44	TimMc	macrolicious: Being able to define functions outside of classes makes it easier to define functions. :-)
18:45	TimMc	You could imagine a Java REPL that allows you to add static methods to a ReplFunctions class.
18:45	TimMc	and then fix up references to make it work
18:46	tjd	I'm calling a function with keyword args, (foo :a 1 :b 2), if I have a map {:a 1 :b 2}, how can I effectively execute (foo {:a 1 :b 2})?
18:48	TEttinger	apply, I'd say, but I am not sure I understand tjd
18:48	TEttinger	ohhh
18:48	TEttinger	nvm
18:49	tjd	The keyword-args map is passed in to me, and I'm just sending it along the way. Really don't want to break it apart, because what
18:49	tjd	Because the content is implementation detais that my function doesn't care about
18:49	TEttinger	,(defn foo [{a :a b :b}] (+ a b))
18:49	clojurebot	#'sandbox/foo
18:49	TEttinger	,(foo :a 1 :b 2)
18:49	clojurebot	#error {\n :cause "Wrong number of args (4) passed to: sandbox/foo"\n :via\n [{:type clojure.lang.ArityException\n :message "Wrong number of args (4) passed to: sandbox/foo"\n :at [clojure.lang.AFn throwArity "AFn.java" 429]}]\n :trace\n [[clojure.lang.AFn throwArity "AFn.java" 429]\n [clojure.lang.AFn invoke "AFn.java" 44]\n [sandbox$eval50 invokeStatic "NO_SOURCE_FILE" 0]\n [sandbox$eval5...
18:50	TEttinger	can't remember how this is done
18:51	TEttinger	something like the first example here, https://stuartsierra.com/2010/01/15/keyword-arguments-in-clojure ?
18:51	tjd	This works: (apply foo (flatten (into [] {:a 1 :b 2})))
18:51	tjd	Not proud of that, though.
18:51	TEttinger	ohhh, :keys
18:52	TEttinger	,(defn foo [& {:keys [a b]}] (+ a b))
18:52	clojurebot	#'sandbox/foo
18:52	TEttinger	,(foo :a 1 :b 2)
18:52	clojurebot	3
18:53	matt______	TEttinger: i think you're solving a different problem than tjd. :)
18:53	TEttinger	,(foo (apply into [] {:a 1 :b 2}))
18:53	clojurebot	#error {\n :cause "Key must be integer"\n :via\n [{:type java.lang.IllegalArgumentException\n :message "Key must be integer"\n :at [clojure.lang.APersistentVector invoke "APersistentVector.java" 292]}]\n :trace\n [[clojure.lang.APersistentVector invoke "APersistentVector.java" 292]\n [clojure.core$transduce invokeStatic "core.clj" 6598]\n [clojure.core$into invokeStatic "core.clj" 6614]\n [...
18:53	TEttinger	,(apply foo (apply into [] {:a 1 :b 2}))
18:53	clojurebot	#error {\n :cause "Key must be integer"\n :via\n [{:type java.lang.IllegalArgumentException\n :message "Key must be integer"\n :at [clojure.lang.APersistentVector invoke "APersistentVector.java" 292]}]\n :trace\n [[clojure.lang.APersistentVector invoke "APersistentVector.java" 292]\n [clojure.core$transduce invokeStatic "core.clj" 6598]\n [clojure.core$into invokeStatic "core.clj" 6614]\n [...
18:53	TEttinger	yeah, I'm still figuring out kwargs, matt______
18:54	tjd	,(defn x [& {:keys [a b]}] (println a b))
18:54	clojurebot	#'sandbox/x
18:54	matt______	well, he wants all the keys and all the values passed to a function in order, it seems.
18:54	tjd	,(apply x (flatten (into [] {:a 1 :b 2})))
18:54	clojurebot	1 2\n
18:55	tjd	Although I can't help but think I should insist that my caller pass in a function instead of arguments to a sub-function.
18:55	TEttinger	,(apply foo (apply concat {:a 1 :b 2}))
18:55	clojurebot	3
18:55	TEttinger	,(apply x (apply concat {:a 1 :b 2}))
18:55	clojurebot	1 2\n
18:55	tjd	oh my
18:55	TEttinger	it doesn't order them though
18:56	TEttinger	,(apply x (apply concat {:a 1 :b [1 2 3]}))
18:56	clojurebot	1 [1 2 3]\n
18:56	TEttinger	which flatten would break
18:56	tjd	boo
18:56	TEttinger	apply concat only does one level of "flattening"
18:57	TEttinger	hash-maps are never ordered
18:57	TEttinger	so if you pass a hash-map there's no guarantee of order
18:57	matt______	i meant as k1 v1 k2 v2, etc.
18:58	TEttinger	that's a kwarg thing
18:58	TEttinger	,(defn foo [& {:keys [b a]}] (+ a b))
18:58	clojurebot	#'sandbox/foo
18:58	TEttinger	,(apply foo (apply concat {:a 1 :b 2}))
18:58	clojurebot	3
18:59	matt______	i don't think so. he said he doesn't care about the keys or values and is just acting as proxy.
18:59	amalloy	~mapply
18:59	clojurebot	You have to do something like (defn mapply [f & args] (apply f (apply concat (butlast args) (last args)))), which just goes to show why unrolled keyword args are a bad idea
18:59	matt______	i mean, he also said he has a solution. in (apply foo (flatten (into [] {:a 1 :b 2})))
19:00	TEttinger	dothat isn't a solution, matt______
19:00	TEttinger	flatten kills any nesting
19:00	amalloy	~flatten
19:00	clojurebot	flatten is rarely the right answer. Suppose you need to use a list as your "base type", for example. Usually you only want to flatten a single level, and in that case you're better off with concat. Or, better still, use mapcat to produce a sequence that's shaped right to begin with.
19:00	matt______	well, maybe that matters.
19:00	matt______	tjd: does nesting matter for your use case?
19:01	tjd	nesting does not matter
19:01	TEttinger	flatten's fine but still terrible then
19:01	tjd	:-)
19:01	amalloy	people who think nesting doesn't matter are (a) usually wrong, and (b) working with data simple enough that mapcat or concat is easy
19:01	clojurebot	Ik begrijp
19:01	amalloy	nice
19:02	TEttinger	~people who think nesting doesn't matter
19:02	clojurebot	Titim gan éirí ort.
19:02	TEttinger	~people
19:02	clojurebot	you mean BugFactorySingletons
19:02	TEttinger	haha
19:02	amalloy	~people who think nesting doesn't matter are (a) usually wrong, and (b) working with data simple enough that mapcat or concat
19:02	clojurebot	people who think nesting doesn't matter are (a) usually wrong, and (b) working with data simple enough that mapcat or concat is easy
19:02	TEttinger	mm
19:09	matt______	fair enough
19:09	matt______	tjd: unflattened: (apply foo (apply concat (into [] {:a 1 :b 2})))
19:10	TEttinger	don't need the into []
19:10	matt______	good call.
19:11	TEttinger	but yeah, this does seem a bit odd to have the unrolled kwargs mixed up with maps of those args
19:11	TEttinger	amalloy's mapply example is a good point
19:31	X-warrior	hey guys I'm new to clojure and I'm doing a project to learn it, I'm thinking if my code is on the right way of doing things on clojure and if it is readable. Could anyone take a look at it? https://bitbucket.org/matheusbrat/clojure
19:40	maya__	Hi, I have some bug with clojure interop with java, when I write the same (I think) code in the two languages, I got two diferent results. I don't have any idea why
19:40	maya__	(println (.contains (.getAllowedValues (PropertyInteger/create "propertyBottomPosition" 0 4)) 0)) // false System.out.println(PropertyInteger.create("propertyBottomPosition", 0, 4).getAllowedValues().contains(0)); // true
19:41	maya__	Do you have any idea about what can be wrong here ?
19:43	amalloy	unrelatedly to your problem, it will certainly be easier to read if you write it like (println (-> "propertyBottomPosition") (PropertyInteger/create 0 4) (.getAllowedValues) (.contains 0)))
19:45	maya__	amalloy: you'r right, juste didn't have the reflex yet
19:46	amalloy	those two snippets look equivalent to me, though. i'd say confirm that that's the exact code you're running, and if you still get different results then start seeing if there's something about the context you run them in in the respective languages
19:47	hiredman	well
19:48	hiredman	the difference would be, in java that 0 is an int, in clojure it is a long
19:48	amalloy	oh dang
19:48	hiredman	so it depends on what the behavior of .contains is given that
19:48	amalloy	yeah that is almost certainly the answer. nice spot
19:50	maya__	getAllowedValue return a com.google.common.collect.RegularImmutableSet
19:51	hiredman	yeah, you want something like (Integer/valueOf 0) for contains
19:51	amalloy	hiredman: just (int 0) should do it, right? i think it doesn't re-box for interop calls
19:51	amalloy	right, hiredman's point is that your clojure code translates to (...).contains(0L)
19:52	maya__	amalloy, hiredman : ok thx, I will try to fix that
19:52	amalloy	or well, obviously it does re-box, but it knows that it has an int so it boxes to an int rather than a long. unless you're on specifically clojure 1.3 or whatever version that was
19:53	hiredman	I dunno, it seems like the most explicit code is best here. it really needs to be an Integer
19:54	hiredman	the fact that there can be some uncertainty and some wiggle room around 'int', well maybe it isn't the best choice
19:54	amalloy	fair
20:09	maya__	Ok, that was the probleme, thx. Is that a way to specify to the reader the type (to Integer) of my literal ? other than (int 0)
20:12	justin_smith	no
20:25	Guest58040	What is the best way to determine if something is a collection or a single symbol? (complement coll?) ?
20:33	TimMc	Guest58040: Do you know it's always a symbol if it's not a collection?
20:33	TimMc	If so, you can use symbol? to check instead.
20:40	Guest58040	Heh, my terminology might be bad. I did end up using coll? for my problem.
20:40	Guest58040	So, what would you call the first element of this list? (1 2 3)
20:41	Guest58040	vs the first element of this list ([1] 2 3)
20:41	Guest58040	Is 1 a symbol?
20:41	Guest58040	Okay, it's not... what can I call it?
20:42	amalloy	it's a number
20:42	Guest58040	I guess I'm looking for an equivalent term to "atom" from Scheme lingo...
20:43	amalloy	we don't have that, because clojure code is built of more than two primitive types
20:43	Guest58040	A primitive, then?
20:43	amalloy	there's no atom/pair dichotomy
20:44	amalloy	no, primitive means something else. are you sure you want to make this distinction, even?
20:45	justin_smith	I guess we have "self evaluating objects that are not data structures" and "everything else", but given that java.lang.Long is an object I don't know how many things really belong in the former category if any...
20:45	Guest58040	Hmm. Perhaps I will stick with number for now - I don't seem to have the vocabulary to express myself well.
20:45	Guest58040	I see that the JVM complicates what I should call things.
20:45	turbofail	i mean... collection vs. non-collection seems to be pretty much what you're looking for
20:45	justin_smith	Guest58040: clojure chooses not to mask or manipulate the representations of its vm
20:46	justin_smith	turbofail: but Long is a class, its instances have fields, it has methods
20:46	amalloy	not data structures? that's not really a good description imo
20:46	amalloy	since eg Symbol is a pair of strings
20:46	justin_smith	indeed
20:46	turbofail	justin_smith: yeah but you can't reduce over a Long
20:47	Guest58040	Have you ever gotten excellent instruction by doing something incorrectly in front of a room full of skilled folks?
20:49	justin_smith	Guest58040: oh man I was arrogant enough to audit a graduate seminar, before I had even enrolled in college, when I was 19. I feel sorry for the other people in that room, but I learned a lot.
20:50	amalloy	Guest58040: https://meta.wikimedia.org/wiki/Cunningham%27s_Law
20:51	Guest58040	And now I even have a term for it. Thanks!
21:23	csd_	why is ring telling me that i have an invalid csrf token when i havent enabled the anti-csrf middleware (at least, to the best of my knowledge)
21:24	csd_	i'm using ring-defaults but didn't enable the feature
21:25	csd_	oh wait, ugh i take that back :-/
21:40	amalloy	(filter (comp seq identity) xs)
22:34	renl	hi may i ask why drop would check a vector into a list?
22:34	renl	ack * check = change
22:34	justin_smith	renl: I think you want seq
22:34	justin_smith	,(seq [1 2 3])
22:34	clojurebot	(1 2 3)
22:34	justin_smith	renl: why do you need a list though?
22:35	justin_smith	most things that work with lists work with vectors without needing any explicit conversion
22:35	renl	i didnt want a list, but i did a drop on a vector, then i did a conj on that but it added the new stuff at the front which i didnt want
22:35	justin_smith	then you didn't have a vector
22:35	justin_smith	drop returns a list, not a vector
22:35	justin_smith	,(drop 3 [1 2 3 4])
22:35	clojurebot	(4)
22:36	justin_smith	(doc subseq)
22:36	clojurebot	"([sc test key] [sc start-test start-key end-test end-key]); sc must be a sorted collection, test(s) one of <, <=, > or >=. Returns a seq of those entries with keys ek for which (test (.. sc comparator (compare ek key)) 0) is true"
22:36	justin_smith	err
22:36	justin_smith	(doc subvec)
22:36	clojurebot	"([v start] [v start end]); Returns a persistent vector of the items in vector from start (inclusive) to end (exclusive). If end is not supplied, defaults to (count vector). This operation is O(1) and very fast, as the resulting vector shares structure with the original and no trimming is done."
22:37	justin_smith	,(subvec [1 2 3 4] 3) ; you can use subvec instead of drop if you need the return value to be a vector
22:37	clojurebot	[4]
22:37	renl	k thanks just felt that it would cause bugs for newbies when i put a vector into a function and the outcome gave me a list :(
22:37	renl	ok thanks :D
22:37	justin_smith	renl: nope, pretty much every list function silently turns vectors into lists, by design
22:38	renl	nod
22:38	justin_smith	well that's wrong, sorry, they don't turn anything into anything - for a vector arg they return things that are seq not vector
22:39	renl	k