#clojure – 2015-08-22

2015-08-22

01:22	mcktrtl	how do I share preconditions from two different functions?
01:25	domokato_	is there a function that given a collection returns a new empty collection of the same type?
01:30	domokato_	nevermind
01:41	amalloy	mcktrtl: how would you usually share code in general, between two different functions?
01:41	mcktrtl	put the shared code in a third function
01:42	amalloy	so, why can't you do that here?
01:43	amalloy	write a function that your precondition calls
01:43	mcktrtl	i'm not sure, i think i'm confused with how the {:pre [] :post []} maps work
02:56	dagda1_	I have this binary tree https://gist.github.com/dagda1/499772c530244dcd935f that I'm using to solve this problem https://www.hackerrank.com/challenges/swap-nodes
02:56	dagda1_	I need to add the ability to swap nodes does anyone have any high level advice on how I might achieve this?
04:06	hiredman	/win 17
04:06	jeaye	invalid window number: 17
05:33	thealpine	Hello!
07:09	expez	Bronsa: Do you have some ballpark idea (this year?) when you'll bring t.a.js up to date? We want to use it to add cljs support to clj-refactor.
07:33	pepijndevos	If I want to split a multimethod and its implementation, which files should include which?
07:34	pepijndevos	The implementation needs the definition, but the user also needs to load the implementations.
07:34	justin_smith	pepijndevos: a multimethod definition should be in a file with as few deps as possible
07:35	justin_smith	that ns should be required by both the code using the methods, and the code implementing them
07:35	justin_smith	the latter two namespaces should have nothing to do with one another, other than both referring to the multimethod def
07:37	justin_smith	(and the fact that your app code would require both of course)
07:44	pepijndevos	ok, thanks
07:44	clojurebot	Cool story bro.
07:45	justin_smith	pepijndevos: and of course it is totally legit to put the multimethod definition and impl in completely different libraries
07:45	justin_smith	(if the design calls for it of course)
07:46	pepijndevos	justin_smith but if I put the def in one, the impl in another, {requiring the def), and the usage in yet another (requiring the def), nothing requires the impl, so I think the usage should require that too?
07:47	justin_smith	pepijndevos: oh, yeah, of course
07:47	justin_smith	the whole structure is like a diamond - app at top, def at bottom, impl on one side
07:47	justin_smith	triangle, something
07:47	pepijndevos	right
07:47	justin_smith	I think you get the idea
07:48	justin_smith	but the more fleshed out version is like a diamond
07:48	justin_smith	def at bottom
07:48	justin_smith	some lib that uses an impl on one side
07:48	justin_smith	some concrete impl on the other side
07:48	justin_smith	no connection between those two
07:48	pepijndevos	Mine is probably more like a hairball. haha
07:48	justin_smith	app at the top bringing the two together
07:50	justin_smith	pepijndevos: concrete example - ring itself doesn't have any need to know http-kit's impl or composure. http-kit and composure are also fully independent, though each builds on a different side of ring. finally your app requires compojure and http-kit and ring and brings it all together
07:50	justin_smith	pepijndevos: that's protocols not multimethods, but it's the same design shape
07:50	pepijndevos	right
08:20	lokien_	Hey, why can't I just (map (+) [1 2 3]) and have to use reduce instead? Is map different from haskell one?
08:24	wink	lokien_: sounds like an arity problem to me
08:24	justin_smith	lokien_: (+) does not return a function
08:24	justin_smith	,(+)
08:24	clojurebot	0
08:24	justin_smith	,(map + [1 2 3])
08:24	clojurebot	(1 2 3)
08:25	lokien_	wink: I see there are unnecessary parens here, but map version returns [1 2 3] instead of 6
08:25	lokien_	Yes, this
08:25	justin_smith	lokien_: map is not different from haskell's map, but () is different from haskell's ()
08:25	wink	lokien_: my bad for phrasing it. but you could map a "+ 1" function, so to say.
08:25	justin_smith	lokien_: not unnecessary, but probably unwanted (and definitely error causing)
08:25	wink	what justin_smith said :)
08:26	lokien_	Wait a minute, I'll try it
08:27	wink	I still think map'ing a + doesnt# make sense. or I am too much into clojure and not other functional languages
08:27	lokien_	,(map #(+ % 1) [1 2 3])
08:27	clojurebot	(2 3 4)
08:27	lokien_	So I guess I have to do it that way
08:28	justin_smith	wink: it's weird, but it's possible
08:28	justin_smith	,(map + [1 2 3] [4 5 6]) ; wink
08:28	clojurebot	(5 7 9)
08:28	wink	lokien_: well, did you actually want to calculate 1 + 2 + 3 ?
08:28	wink	justin_smith: not what I meant.
08:28	lokien_	wink: kinda
08:28	wink	yeah, I'd file that into reduce and it surprises me to do that via map at all. in any language
08:29	wink	but I could be very wrong :)
08:29	lokien_	It's just that prefix notation of lisps
08:29	lokien_	Gets me confused every time
08:29	justin_smith	lokien_: also haskell doesn't do multiple arities, and we do it extensively
08:29	justin_smith	,(> 3 2 1 -21)
08:29	clojurebot	true
08:30	lokien_	justin_smith: that's why I'm cheating on her with clojure
08:30	justin_smith	haha
08:31	lokien_	justin_smith: I can't do anything if any other language has small breasts or something, here I can just create a macro for it
08:31	justin_smith	lokien_: clojure is the fun, easygoing, though maybe at times unreliable one
08:32	justin_smith	haskell is marriage material, but sometimes a pain in the ass
08:32	lokien_	justin_smith: unreliable, you mean?
08:32	justin_smith	lokien_: no type checking
08:32	justin_smith	lokien_: functions that just pass your junk data to some other function, with no attempt to check for validity
08:33	lokien_	justin_smith: can I check this somehow?
08:33	justin_smith	stack traces that go 30 frames deep because finally someone found nil that was introduced at the top
08:33	justin_smith	lokien_: you can, but clojure's internals don't usually
08:33	justin_smith	lokien_: it's a joke, I love clojure, but it definitely doesn't do much to anticipate errors or validate data
08:34	lokien_	justin_smith: static languages are a pain in the ass when you want to add new stuff to them, or modify them
08:34	justin_smith	lokien_: right, this is the tradeoff I was trying to joke about
08:35	lokien_	Like random function in haskell would produce IO.Integer or some other stuff and I have to exploit it every time I want to use it
08:35	justin_smith	lokien_: clojure lets you get away with a lot more - but sometimes you pay the price that it will let you do something very stupid
08:35	lokien_	God damn it, it's just an integer
08:35	justin_smith	right
08:35	justin_smith	haha
08:35	lokien_	Thanks for help, have an awesome day
08:35	justin_smith	you too
09:13	bodie_	I'm trying to figure out the syntax for this. I have a fn f of two items and a vector of vectors of two items v. how do I map f over v such that f will be called with the contents of each vector, resulting in a vector of the results?
09:16	bodie_	`map` isn't what I need, since it applies to the first element of each vector, then the second element, etc. what I want is basically the opposite of that.
09:17	bodie_	I guess I'm asking a dumb question or something, but I can't seem to figure out how to hunt down the answer to this.
09:18	justin_smith	,(map #(apply + %) [[1 2] [3 4]]) ; bodie_ - something like this?
09:18	clojurebot	(3 7)
09:18	bodie_	yes
09:18	bodie_	thanks justin_smith :)
09:18	justin_smith	,(map + (map list [[1 2] [3 4]])) ; alternately
09:18	clojurebot	#<ClassCastException java.lang.ClassCastException: Cannot cast clojure.lang.PersistentList to java.lang.Number>
09:18	justin_smith	err
09:19	bodie_	hmm, weird. I was using map with apply, but I wasn't getting what I expected
09:19	justin_smith	,(apply map + (map list [[1 2] [3 4]])) ; alternately
09:19	clojurebot	#<ClassCastException java.lang.ClassCastException: clojure.lang.PersistentVector cannot be cast to java.lang.Number>
09:19	justin_smith	something like thus
09:20	justin_smith	haha, the original is the right way, anyway, the other way is silly even if I get it right
09:24	Wild_Cat	what kind of text generation/formatting do you guys use? I'm playing around with Clojure code that generated C++ and doing everything with (str ...) calls sort of feels inelegant.
09:25	justin_smith	Wild_Cat: there's format of course, and clojure.pprint/cl-format
09:32	Wild_Cat	justin_smith: oh, that one looks powerful
09:36	justin_smith	Wild_Cat: yeah, cl-format can do amazing things
09:36	Wild_Cat	now to handle indentation... :p
09:39	Wild_Cat	...or maybe I should just defer code formatting until a later phase. I'll sleep on it.
09:39	justin_smith	there's always the "shell call to emacs" method
09:40	justin_smith	or one of the single-purpose C auto-formatters
09:40	justin_smith	I assume they have ones that can do C++
09:41	Wild_Cat	could be. C++ is a pain in the ass to autoformat, what with both the preprocessor and the templates being Turing-complete
09:41	Wild_Cat	but since I'm just emitting a subset of C++ (one that unfortunately uses templates, though) maybe I could get away with it.
09:41	justin_smith	C++ templates are the weirdest macro system ever I swear
09:42	Wild_Cat	the entire language is terribly inelegant, really. The solution to everything is text substitution.
09:46	justin_smith	Wild_Cat: I imagine as a lisper using macro systems and higher order programming in other languages, I know what it must be like to be an Italian visiting the American midwest and someone taking you to like little ceasars for pizza.
09:47	justin_smith	"I mean I guess I understand on an abstract level that these things are in the same category, but this version makes me very sad"
09:51	Wild_Cat	justin_smith: in all fairness I'm a Clojure noob.
09:51	Wild_Cat	my weapon of choice has been Python for quite a long time
09:52	Wild_Cat	but Clojure's focus on immutability, smart datastructures and powerful parallelism/concurrency facilities are convincing me to switch
10:19	hyPiRion	is there any edn test suite anywhere?
11:33	lvh	oh hello willb
11:33	lvh	Oh, Wild_Cat is gone already.
12:24	Bronsa	expez: I'm sorry, I can't promise anything. cljs had big changes in the last year so getting t.a.js up to date with that won't be a small task and I don't know when I'll have the time to do that
13:33	sobel	does anyone know of nginx-clojure in production somewhere? http://nginx-clojure.github.io/index.html
15:47	expez	how can I catch and adorn an exceptioninfo with more data?
15:49	expez	What I'm doing now is catching it, grabbing ex-data, then calling ex-info passing .getMessage and associng new stuff onto data
15:49	expez	this seems like more work than what's intended
15:53	justin_smith	,(try (throw (ex-info "OK" {})) (catch clojure.lang.ExceptionInfo e (throw (ex-info (.getMessage e) (assoc (.getData e) :also "WAT")))))
15:53	clojurebot	justin_smith: excusez-moi
15:53	justin_smith	:P
15:54	justin_smith	expez: you could also make a new ex-info and throw the new one you caught into the ex-data
15:54	justin_smith	and let the top level decide whether to pull out the insides
15:55	justin_smith	expez: it seems like a "add to ex-info and re-throw" would be an easy function to write though
15:55	expez	justin_smith: yeah I ended up doing exactly what you proposed
16:12	dagda1_	I've got this code https://gist.github.com/dagda1/499772c530244dcd935f that creates a tree, I need the nodes of a tree in order to solve this puzzle https://www.hackerrank.com/challenges/swap-nodes
16:12	dagda1_	I'm not entirely sure how I go about swapping the nodes at a given depth
16:17	RasHasGul	can redefine a function in Clojure without restarting the application?
16:17	RasHasGul	+you
16:17	justin_smith	RasHasGul: yes
16:18	RasHasGul	justin_smith: I don't know clojure, but do you know where can I read about this?
16:19	justin_smith	RasHasGul: you redefine a function the same way you define it
16:19	justin_smith	so, usually using defn (or indirectly by requiring some file that calls defn)
16:19	RasHasGul	justin_smith: and how will the application will use this modified definition without restarting it?
16:20	justin_smith	RasHasGul: because the functions are not usually inlined
16:20	justin_smith	the next time you call the function, the newer definition is found
16:22	justin_smith	RasHasGul: are you a java programmer?
16:22	RasHasGul	justin_smith: so in the clojure repl I just change the body of a function and the application will start using the new definition?
16:22	RasHasGul	justin_smith: no
16:22	RasHasGul	justin_smith: but I'm familiar with it
16:23	justin_smith	RasHasGul: right, you can call defn again, and the new definition will be used
16:23	justin_smith	RasHasGul: the reason I ask is that unlike java where you compile some class, and that class is loaded and you call a method on that class...
16:23	justin_smith	in clojure we have a special class - clojure.lang.Var, and most clojure code will try to find the Var instance that holds the thing you want
16:24	justin_smith	when you use def or defn, you are changing the contents of (and potentially creating anew) some var
16:26	RasHasGul	ok cool, so this is done live, clojure compiles the modified defn to bytecode on fly and injects it on to the app right?
16:29	justin_smith	RasHasGul: exactly
16:29	justin_smith	RasHasGul: in fact doing this at runtime in an app, defining things at load, and defining things in a repl all work exactly the same way
16:29	justin_smith	which is very helpful for interactive development
16:32	RasHasGul	yeah very nice, is real live in the literal sense, you don't have to throw away your data or restart your app when modifying a procedure
16:32	justin_smith	exactly
16:32	justin_smith	RasHasGul: sometimes we need to use tricks when it comes to scope closure
16:32	RasHasGul	Racket is not like this :/
16:32	justin_smith	where a function isn't using a var by name, but it is instead defined based on some anonymous argument
16:33	RasHasGul	emacs is though :)
16:33	justin_smith	clojure isn't quite as free and easy with redefinitions as emacs
16:33	justin_smith	but comes close
16:34	RasHasGul	justin_smith: ah, so its not all smooth sailing, what tricks you talk about?
16:35	justin_smith	RasHasGul: for example when starting the ring web server, you are expected to pass a function as the argument
16:35	justin_smith	just because the function is redefined, doesn't mean ring is using the new version, so you can hack it by passing in the var holding the function instead
16:36	justin_smith	when you call a var as if it were a function, it automatically looks up its contents and tries calling it
16:36	justin_smith	,(= #'+ +)
16:36	clojurebot	false
16:36	justin_smith	,(type #'+)
16:36	clojurebot	clojure.lang.Var
16:36	justin_smith	,(#'+ 2 3)
16:36	clojurebot	5
16:37	RasHasGul	justin_smith: so you mean that instead of passing an anonymous function to ring web server you pass it a named function instead? to be able to redefine it
16:38	justin_smith	RasHasGul: not quite - one moment, I wrote a stack overflow answer that shows how this works
16:40	justin_smith	RasHasGul: this SO answer shows how it works http://stackoverflow.com/questions/28904260/dynamic-handler-update-in-clojure-ring-compojure-repl/28905078#28905078
16:48	justin_smith	tl;dr it's not just that the arg needs to be named - when capturing something to call later, you need to capture the var and not the function the var points to in order to see updates
16:51	RasHasGul	justin_smith: I see, so is just that existing code won't use the modified defnitions until you do the trick you showed in SO
16:55	rhg135	when you pass the plain function, it's just it's current definition. if you pass a var it's a refernce to it essentially
16:56	rhg135	an endowed one, but 'tis mutable
17:00	RasHasGul	oh I get it, didn't understand the #'foo part in the SO example
17:01	justin_smith	,'#'foo
17:01	clojurebot	(var foo)
17:01	justin_smith	it's just a reader macro
17:38	justin_smith	google isn't helping me much - I wonder if anyone is making anything like mirage that clojure could use - maybe porting the jvm to a rump kernel
17:39	justin_smith	I ask because it would be awesome to run clojure this way http://www.skjegstad.com/blog/2015/08/17/jitsu-v02/
17:52	rhg135	openjdk zero shouldn't be too hard to build for rump
17:53	justin_smith	rhg135: instant spin-up on-demand clojure apps would be awesome
17:53	rhg135	they would be
17:56	justin_smith	rhg135: ooooh looks like OSv might be close to this http://events.linuxfoundation.org/sites/events/files/slides/OSv_ACEU14.pdf
17:59	rhg135	some processors can run java bytecode, I would have expected that to be chaper
18:04	futuro	I'm looking for a semi-robust way to deal with xml schemas -- specifically it is Wikimedia dumps -- and I'm curious how people handle data type translation from xml files
18:05	futuro	That is, if there's a schema defining the types inside an xml file, do folks normally enter/define this by hand in their code, or is there a clean way to read xsd files to generate this for you?
18:05	futuro	I'm currently searching the web, but I thought I'd ask here as well
18:05	mcktrtl	might anyone be able to suggest a project where metadata is used in an interesting way?
18:11	futuro	mcktrtl: what do you mean by "interesting"?
18:13	mcktrtl	anything past private/public, docstrings, and how the project "dire" works... im just curious to look at any other applications
19:47	amalloy	most interesting usages of metadata are "clever", not good
19:48	mcktrtl	interesting things in general usually are :)
20:40	rhg135	"interesting" hardly ever means good
20:41	rhg135	not in code at least :(
21:22	RasAsGhul	justin_smith: ping
21:22	android1	hi
22:38	WickedShell	I'm having trouble importing java classes (specifically anything from the java.awt.geom package other things from java.awt work but (:import java.awt.geom.Rectangle2D.Float) fails to find the class every time. Any way to figure out why this is happening? (Before I restarted the REPL with the changes saved to disk (:import 'java.awt.geom.Rectangle2D.Float) worked without a problem in the REPL
22:39	justin_smith	,(:import 'it.doesnt.Matter.what.you.put.here.but.it.doesnt.do.what.you.Think)
22:39	clojurebot	nil
22:40	WickedShell	ahhh well that explains that bit :P
22:40	justin_smith	outside the ns special form you want import not :import
22:40	WickedShell	yeah was thinking that as I typed it in here actually
22:40	justin_smith	,(import java.util.HashMap)
22:40	clojurebot	java.util.HashMap
22:41	justin_smith	also you don't want the '
22:41	WickedShell	I thought the ' was needed in the REPL?
22:41	justin_smith	namespaces need it because they are not bound to anything when you call require
22:41	justin_smith	when you call import, the name of the class resolves to tell it what class to import
22:42	justin_smith	import is not a pre-requisite to using a class - they are automatically resolved and loaded - it's a convenience though
22:43	WickedShell	If I don't import first (in the past) things fail to compile with lein (at least that was the error I recall getting and importing solved it)
22:43	justin_smith	WickedShell: if you don't use import, you need to fully type out the package every time
22:43	justin_smith	that's the only difference
22:44	WickedShell	oh.. yeah that makes sense lol
22:44	justin_smith	the real magic happens in setting up your classpath, which lein does
22:44	justin_smith	then symbols are looked up in the classpath
22:46	WickedShell	Is there a way to see in the REPL if it can resolve an object? I can't figure out why I can't find java.awt.geom.RoundRectangle2D.Float when I have a straight java program that is finding it without any problem
22:47	justin_smith	WickedShell: you can just type in the class name
22:47	justin_smith	,java.util.HashMap
22:47	clojurebot	java.util.HashMap
22:47	justin_smith	,java.util.ThisDoesNotExist
22:47	clojurebot	#error {\n :cause "java.util.ThisDoesNotExist"\n :via\n [{:type clojure.lang.Compiler$CompilerException\n :message "java.lang.ClassNotFoundException: java.util.ThisDoesNotExist, compiling:(NO_SOURCE_PATH:0:0)"\n :at [clojure.lang.Compiler analyze "Compiler.java" 6704]}\n {:type java.lang.ClassNotFoundException\n :message "java.util.ThisDoesNotExist"\n :at [java.net.URLClassLoader$1 run "U...
22:47	WickedShell	,java.awt.geom.RoundRectangle2D.Float
22:47	clojurebot	#error {\n :cause "java.awt.geom.RoundRectangle2D.Float"\n :via\n [{:type clojure.lang.Compiler$CompilerException\n :message "java.lang.ClassNotFoundException: java.awt.geom.RoundRectangle2D.Float, compiling:(NO_SOURCE_PATH:0:0)"\n :at [clojure.lang.Compiler analyze "Compiler.java" 6704]}\n {:type java.lang.ClassNotFoundException\n :message "java.awt.geom.RoundRectangle2D.Float"\n :at [ja...
22:48	WickedShell	,java.awt.geom.RoundRectangle2D
22:48	clojurebot	java.awt.geom.RoundRectangle2D
22:48	WickedShell	ooohhh I think I tripped over the java side of it...
22:48	justin_smith	,java.awt.geom.RoundRectangle2D$Float ; maybe it is an inner class
22:48	clojurebot	java.awt.geom.RoundRectangle2D$Float
22:48	justin_smith	it is!
22:48	justin_smith	there's your answer
22:50	WickedShell	justin_smith, yup tripped over that... Thanks for your help!