#clojure – 2008-07-28

2008-07-28

01:47	mebaran151	if I have a function in the form of (fn [x] (+ x 1)) or something, is it possible to get its quoted form back
01:50	hoeck	mebaran151: please explain, do you mean its backquoted form or the functions source code?
01:51	mebaran151	I meant the src of function
01:51	mebaran151	what does the backquote do?
01:51	mebaran151	(I'm still learning Lisp)
01:52	shoover	a single quote could give you the code as a list: '(fn [x] (+ x 1))
01:52	hoeck	backquote and un-backquote are basically abbrevations for list and for eval
01:52	shoover	and if you put that into a variable with let, you could later eval it
01:53	hoeck	you could, but thats considered bad style
01:55	shoover	ok. I was thinking if you did need the code as a list and you also needed it to evaluate, that would be one way. Is there another way you're thinking of?
01:55	hoeck	mebaran151: instead of writing (list 'a b c 'd) you can write `(a ~b ~c d)
01:56	mebaran151	I just want to be able to get at the underlying src of a compiled of function just in case
01:56	mebaran151	I'm writing a little object persistence layer in clojure I've named Oscar, and this might come in handy
01:58	mebaran151	(Oscar searches creates and removes) or (Object store: creation and retrieval)
01:58	hoeck	shoover: i guess if you write something like a repl, this is okay
01:59	mebaran151	I'd basically like to quote an already eval'ed function, but maybe clojure throws away such minor points
01:59	hoeck	mebaran151: cool, i had the same idea, storing a functions source code (as string) in its metadata
02:00	mebaran151	the metadata is coming in very handy
02:00	shoover	Clojure emits the source as debugging information during compilation, but I'm not sure how you could access that.
02:00	mebaran151	it's where I keep all of oscars internal state
02:01	hoeck	then it would be nice to browse the source like in delphi or slime
02:01	mebaran151	yeah that could be nice
02:01	mebaran151	I thought lisp was all about that whole getting the syntax tree back
02:01	mebaran151	but I guess the tree has to be cut down at some point
02:02	shoover	The tree is available to you in macros, but once those are resolved to function calls, Clojure compiles everything down to Java classes.
02:03	mebaran151	I see
02:04	shoover	http://clojure.org/lisp goes into it a little bit
02:05	shoover	... at least the part about how macros get to see the tree and transform it
02:06	mebaran151	I sort of get macros
02:06	shoover	That sort of makes 2 of us :)
02:08	mebaran151	so here's my idea for an object persistence store in lisp and I'm wondering if you guys have any feedback on the general idea of the design
02:09	mebaran151	my basic unit is the hash: I derive a database template from it, recursing to define nested templates under it
02:09	mebaran151	these templates define how I later run the insert statements and do joins and what not
02:10	mebaran151	I'm trying to make up for the fact I don't have classes to play with, so the next time I try to save an object, it looks in a central ref'ed var and attempts to match the hash given by its keys
02:14	shoover	What would one of these templates look like?
02:15	shoover	Also, are you talking about clojure HashMaps or computing a hash using some hash function?
02:17	hoeck	and what kind of objects do you store, clojure data-structures or any kind of (clojure) object?
02:19	mebaran151	I'm starting just with hashes
02:19	mebaran151	the templates are pretty simple
02:20	shoover	mebaran151: This sounds interesting, but I gotta run. I will be glad to check the log later to see the answers to these questions
02:20	mebaran151	just a list of mappings of functions to keys to attributes and relationships
02:20	mebaran151	where I'm stuck is modeling intra db relationships
02:21	mebaran151	(serializing and retrieving single use hashes is easy)
02:24	hoeck	mebaran151: what do you mean with 'hashes'?
02:24	mebaran151	I mean hashmaps
02:24	mebaran151	I started with ruby where they're called hashes
02:24	hoeck	ahh, okay
02:24	mebaran151	I'd like to eventually do any clojure object
02:25	mebaran151	the goal would be that I provide sane templates to get you started but a user could smack it around if they wanted via customizing the archetype I slyly stored in the metadata, which I have to admit, was an inspired invention
02:27	mebaran151	I always hated how rigid activerecord felt, but I Hibernate never had any dynamicness, and besides, neither project has as great a name as Oscar
02:29	hoeck	:) i've never used any (object) persistence system, so can you explain to me what are the templates for and how such a persistence system works??
02:31	hoeck	i was always pretty satisfied with lisps loading their own code and data (at least in a small scale)
02:32	mebaran151	well I'm expecting a lot of objects on this scale
02:32	mebaran151	in this app
02:34	mebaran151	I basically am planning to allow designers to specify a template against which their objects will be persisted: within the template you would provide either symbols or functions which I would run over the hash and their results would be inputted properly in the database
02:35	mebaran151	(hash in this case meaning hashmap)
02:38	mebaran151	it would record which keys were of interest and whether to serialize them to the filesystem or to sql
02:40	hoeck	i see, have you any simple use-case for explanation to me?
02:40	mebaran151	well you have a lot of users
02:40	mebaran151	each has a profile per se
02:41	mebaran151	and can have a profile picture
02:41	mebaran151	you wouldn't want to put the profile picture in the database
02:41	mebaran151	so that's a simiple nested requirement
02:42	mebaran151	you should have a table for the flat information about users like his name and hashed password, andprobably have a separate table for profile data while keeping his jpg in a hash somewhere on the file system
02:43	hoeck	ahh, cool, i got it!
02:43	mebaran151	*jpg in a file somewhere on the file system
02:43	mebaran151	now let's get a bit more complex
02:44	mebaran151	users have profiles in whcih they can customize the fields, like add favorite soups or something
02:44	mebaran151	building a new column for that would be sort of silly, esp if only one user ever declared himself to have a favorite soup
02:44	mebaran151	so that part of the hash is probably best serialized to the file system
02:46	mebaran151	that's why I think a hybrid approach is best for a dynamic language like lisp where some objects might not look exactly like the rest
02:48	mebaran151	this profile might also be modeled as sequence of sections or something
02:48	hoeck	what is the non-hybrid approach?
02:48	mebaran151	just using SQL for everything
02:50	jykrd	hi
02:50	mebaran151	I'll be back in a moment
02:50	hoeck	jykrd: hi
02:52	jykrd	So I'm using (take n (repeatedly (fn [] (. (new BufferedReader (new InputStreamReader (. param getInputStream))) readLine))) to pull in lines
02:52	jykrd	but I don't want to use take n
02:53	jykrd	I want it to keep on taking values until it his a nil, and then stop
02:53	hoeck	then use (take-while identity ..)
02:54	jykrd	what does the identity part mean?
02:54	hoeck	identity is a function
02:54	hoeck	(identity 1) -> 1
02:54	hoeck	(identity nil) -> nil
02:54	jykrd	right, so basically take-while (not-returning-nill)
02:54	hoeck	and serves in take-while as a predicate
02:54	hoeck	exactly
02:55	jykrd	oh, so actually write identity
02:56	hoeck	you could also write it more verbose (take-while (fn [element] (not (= nil element))) ...)
02:57	jykrd	right
02:57	jykrd	identity sounds easier
02:58	jykrd	I'm getting strange results here now
02:59	jykrd	i do this to make processes:
02:59	jykrd	(import '(java.io BufferedReader IOException InputStreamReader))
02:59	jykrd	(defn $ [p] (.. Runtime getRuntime (exec (str p))))
02:59	jykrd	then this to get input on it:
02:59	jykrd	(defn $in [n obj]
02:59	jykrd	(dorun (map println (take-while identity
02:59	jykrd	(repeatedly (fn [] (.
02:59	jykrd	(new BufferedReader (new InputStreamReader (.
02:59	jykrd	obj getInputStream))) readLine)))))))
02:59	jykrd	(sorry 'bout the flood)
03:00	jykrd	and when I do a ($in 10 ($ "ps -ef")) I get strange results
03:00	jykrd	doing it repeatedly returns different sections of the results
03:00	hoeck	you can use lisppaste for bigger code chunks
03:00	jykrd	rather than all of it, but perhaps the output has escape characters?
03:01	hoeck	i guess its because you create a new BufferedReader each time you request a line
03:02	jykrd	hmm
03:02	jykrd	ok, so I could chop it into smaller functions
03:04	hoeck	or put the reader creation into a let
03:08	hoeck	(let [r (new BufferedReader (new InputStreamReader ..))] (take-while identity (repeatedly #(.readline r))))
03:09	jykrd	yup
03:10	jykrd	that works
03:10	jykrd	good eye
03:11	jykrd	so #() is short for (fn [] ())
03:12	hoeck	yes
03:12	jykrd	all this new syntax
03:12	hoeck	yes, kind of
03:13	jykrd	and .method
03:13	jykrd	thats new to me
03:13	jykrd	I remember it was talked about
03:13	hoeck	are you using svn or a release from the clojure site?
03:13	jykrd	site
03:14	jykrd	but that all works
03:14	hoeck	in svn there is also (Object. ..) instead of (new Object ..)
03:14	hoeck	i think its in the release too
03:18	jykrd	yea, that works here
03:19	jykrd	so I've got it to do system commands.. so I might be able to do some system scripting clojure once I figure it out :)
03:23	jykrd	what to make though.. maybe yet another backup tool
03:26	hoeck	jykrd: fetching clojure sources would be cool :)
03:27	hoeck	jykrd: but on shell-level, it wouldn't be too portable
03:32	jykrd	hoeck: yea, I guess that's why there isn't much system scripting done with java or it's derivitives
03:34	hoeck	i'm going to work, bye
03:34	jykrd	later, thanks for the help
03:35	hoeck	np
03:38	jykrd	lisppaste*
03:38	jykrd	lisppaste8
08:05	rhickey	jykrd: you might want to check out line-seq
08:17	jykrd	rhickey: ok
08:47	jykrd	Yea, that's smoother
08:48	rhickey	find-doc is your friend - e.g. (find-doc "line")
08:50	jykrd	Why is is that, if i wrap the line-seq with a (map println(...)), then it puts a nil on the front of each line?
08:51	Chouser	jykrd: println returns nil, which the repl prints
08:51	rhickey	map is functional and lazy and println is a side effect. To get side-effects to happen you need some form of 'do' - (dorun (map ...
08:51	jykrd	oh
08:52	jykrd	ohhoh
08:53	jykrd	I never knew. That's been getting me for a while. That should go somewhere in the wiki.
08:53	rhickey	map returns a sequence of the values of the function you call, which as Chouser said, is nil in this case. You really don't care about those values, only about the side effects
10:05	cemerick	Chouser: I'm suddenly feeling very uneasy about the underscore name mangling
10:05	Chouser	really? why's that?
10:08	cemerick	It's a totally workable approach technically, but putting myself in the shoes of someone who doesn't necessarily know what gen-class is or how it works, it looks like a serious wart.
10:09	Chouser	hm. I have actually drifted the other direction. When actually looking at the example namespace I cobbled together, I thought the underscores looked quite nice.
10:09	cemerick	You'd like to be able to point someone at a namespace, and say, "here's the implementation of the same-named class", period. With this, the most common FAQ will be, "What's with all of the underscores?" "Oh, don't worry about that."
10:09	rhickey	When thinking about the namespace relationships last night, I thought perhaps ClassName-methodname might be best
10:09	Chouser	...with the possible exception of underscores when calling the functions directly.
10:09	cemerick	rhickey: you mean a namespace per method?
10:11	rhickey	if you are gen-ing org.myns.Foo, under the Java rules the package is org.myns, and thus the Clojure namespace should be org.myns too. This would make it easy to gen and implement several fns in a single file
10:12	Chouser	hm!
10:13	Chouser	several classes in a single file?
10:13	cemerick	rhickey: That's actually something like what I was thinking of over the weekend, except instead of ClassName-methodname, have a map of method names and fn's def-ed to each ClassName,
10:13	rhickey	so make a org/myns/myns.clj with Foo-doThis, Foo-doThat fns. org.myns.Bar could be defined in the same file, or have org/myns/myns load Foo.clj and Bar.clj is you want them separate
10:14	rhickey	cemerick: using a map requires a special defing form
10:15	Chouser	Foo-doThis is still probably more terse than "public static final doThis"
10:16	cemerick	rhickey: Not sure I follow; wouldn't it be simply (def ClassFoo {:toString (fn [this] "blah")}), etc?
10:18	rhickey	cemerick: if you do that then redefining/testing single functions becomes ungainly, and you lose dynamic per-thread rebinding of methods
10:19	rhickey	one of the cool things about gen-class is that Java classes inherit Clojure goodness, like that rebinding capability, or transactionality if state is a Ref
10:21	cemerick	I'd say that rebinding probably isn't a very common use-case in connection with gen-class impls -- and, if someone wanted to support that, it'd be a piece of cake to have the real impl of a function in a val (which can be rebound) that is invoked from within the class impl map.
10:22	rhickey	Java methods can also be multimethods
10:23	rhickey	cemerick: true, it's hard to know what the use-cases are yet. Per-context logging is particularly useful
10:24	cemerick	sure, and the class impl map could dispatch to a multimethod elsewhere, too. My only point is that, right now, getting the simplest stuff done via gen-class requires just as much work/mental overhead/understanding of gen-class as the the most ambitious stuff.
10:25	rhickey	if these uses become common you'll have to write 2 functions, the second of which will have ad-hoc names
10:25	rhickey	speaking of names, the anonymous fns in the map won't have useful ones during debugging
10:27	rhickey	I guess it seems to me like you could have a (defimplementation ClassFoo .. that looks like what you want but generates real named fns
10:27	cemerick	via the ClassFoo-methodfoo naming pattern, you mean?
10:27	rhickey	right
10:29	rhickey	all I see the map saving you is repeating the ClassFoo- prefix, at the cost of making the class definition atomic, and thus not very Clojure-like
10:29	cemerick	Yeah, that seems like it'd be OK.
10:30	cemerick	Well, in the nexus of Java and Clojure (gen-class), I'm happy to sacrifice a little bit of clojure-ness in order to minimize the appearance of magic. Perhaps we can have our cake and eat it too, though.
10:32	cemerick	Yeah, I'll +1 the ClassFoo-methodname notion, with the defimpl macro.
10:34	lisppaste8	rhickey pasted "method def options" at http://paste.lisp.org/display/64357
10:37	lisppaste8	rhickey annotated #64357 with "defimpl" at http://paste.lisp.org/display/64357#1
10:40	rhickey	a nice thing about the defimpl macro is you needn't put everything in there, if you have a couple of multimethod methods you can define just them a la carte
10:40	hoeck	i would prefer the (defn Foo-doThis [] ..) form
10:40	rhickey	hoeck: me too, defimpl is optional
10:41	rhickey	but I can understand its appeal
10:44	hoeck	maybe it is because of my long exposition to emacs-lisp, where usually function-names have a common beginning
10:58	Chouser	Could defimpl could be rolled into genclass?
10:59	rhickey	Chouser: I think it's important to remember the dual static/dynamic nature of genclass.
10:59	Chouser	I guess it would then have to do namespace magic as well, but you'd get something that feels more like a "normal" class definition.
10:59	rhickey	or do you mean put the macro into genclass.clj?
10:59	Chouser	no, you understood me.
10:59	rhickey	Chouser: normal class definitions suck, as they are static
11:00	Chouser	I understand, but it would actually be normal, just give the illusion. If that's something you're specifically trying to avoid, then so be it.
11:00	Chouser	s/would actually/wouldn't actually/
11:01	rhickey	I think it would be a shame if you had to rebuild your Java when you changed your Clojure implementation code
11:01	rhickey	maybe others disagree
11:02	rhickey	I like generating a servlet stub once and forgetting about Java
11:02	Chouser	yes, I agree. Well, that is I'm entirely willing to agree. I'm not arguing against that, as you could still use the (def Foo-doThis) form for rebinding.
11:02	Chouser	ah, nevermind, I see what you're saying.
11:03	Chouser	there's a usage style difference here between gen-and-save-class and gen-and-load-class.
11:04	Chouser	For the -load- case, I wouldn't at all mind having the definitions optionally embedded in the gen-class statement.
11:04	rhickey	gen-and-load-class has such marginal utility, IMO
11:05	Chouser	In fact it's be nice to not have to switch around namespaces and such. Dynamic re-binding would still be supported, but having the "canonical" version of your implementation in your gen-class statement wouldn't hurt anything.
11:05	rhickey	most of the time you genclass it's because some Java code needs to know the names
11:06	Chouser	with gen-and-save-class it makes a lot of sense to have it in a separate -gen.clj file that you very much leave alone, and would want any implementation inside.
11:06	cemerick	we use gen-and-load-class specifically to make it possible to at least co-locate the gen-class definition near the impl
11:07	cemerick	(see the save-gen-class macro in my genbean post from Friday)
11:07	rhickey	what I foresaw, which may not have come to pass, was that gen-class wouldn't normally be enumerating the members, given that they come from superclasses or interfaces
11:08	rhickey	(gen-and-save-class FooServlet :extends HttpServlet)
11:08	Chouser	when a gen-interface exists, that may become more true.
11:08	rhickey	why would I want to stick method defs in that?
11:09	Chouser	hm, it looks like my one real-world use of gen-class is a gen-and-load-class that could probably now be replaced with proxy, since super-calls are now supported there.
11:10	Chouser	Maybe my experiences are much help in this conversation. :-)
11:10	Chouser	aren't
11:10	Chouser	sheesh
11:10	cemerick	rhickey: well, you'd certainly want to add methods to class definition -- not in a HttpServlet context, but elsewhere, that's very desirable
11:10	cemerick	whether the impl defs are inline with the gen-class is another story
11:12	rhickey	cemerick: I understand that when they are not inline, you have to repeat the method names, like in c++ headers/source
11:12	cemerick	rhickey: very tangentially to this conversation, I'd urge you to not over-focus on the web development use-cases. I don't think you have to date, but how to hook into a servlet container is a very narrow context.
11:13	rhickey	cemerick: I'm not, enclojure is the biggest consumer of genclass from my perspective - many of the features, including adding members, came from their use cases
11:15	cemerick	Name repetition sucks, but dislocation of source code sucks more. That's why we have save-gen-class, and that's also why I'm sure I'll be writing something similar so one form can utilize defimpl and spin off a gen-and-save-class class at build time.
11:15	rhickey	OTOH, having done C++/Java/C# for 20 years, I often miss headers when in C#/Java, especially from a build dependency standpoint. Thus I'd emphasize interfaces whenever adding member so you get decoupling from implementation changes
11:16	rhickey	cemerick: agreed, but they are 2 different things. save-gen-class doesn't need the impls inline
11:17	cemerick	rhickey: true, but that's only the case because of how gen-class works. All of our gen-class usages at the moment are 100% static, so I'd be perfectly happy dropping impls into it.
11:17	cemerick	I'd emphasize "at the moment" :-)
11:18	rhickey	ok, let me think about it
11:18	cemerick	FWIW, that's very, very low on my personal wish list. Nailing down the namespace/lib/gen-class-naming issues within the current architecture is far more important, IMO.
11:22	rhickey	cemerick: I think the org.myns.Foo -> org/myns/myns.clj with Foo-doThis, Foo-doThat conforms to the new system, and Steve seems to be moving along with lib
11:23	rhickey	just need to do the genclass changes
11:24	cemerick	rhickey: Sounds good, thanks. I've not kept up with Steve's progress in svn, though; been distracted elsewhere.
11:25	cemerick	we're still holding at r937 until that's stabilized
11:25	Chouser	genclass's arguments would remain unchanged, right? Just the namespace name and function names would change?
11:28	rhickey	Chouser: right. I'm thinking now the file name should still org/myns/Foo.clj, but the code in it will be in org.myns. This way you can still get per-class load-on-demand
11:29	rhickey	Chouser: I think you can just change your patch from _ to ClassName-
11:29	Chouser	you want to do the changes this time, or do you want to wait again for me to fumble my way through?
11:29	Chouser	ah. I'll try it.
11:30	cemerick	rhickey: would it be bad for the load-on-demand to load /org/myns/myns.clj and /org/myns/Foo.clj? Having both options work automatically would be a plus, I think.
11:30	rhickey	I'm finishing up multimethod dispatch-value preferences
11:31	rhickey	cemerick: what happens when you genclass multiple classes in the same ns, independently?
11:32	rhickey	would load myns.clj more than once
11:32	cemerick	rhickey: ah, I'm presuming that lib is available
11:33	rhickey	cemerick: yes, lib will be rolled into Clojure soon, then genclass will use it
11:34	cemerick	nifty
11:50	Chouser	huh. The class doesn't exist yet, so I can't ask it for its simpleName. I guess I'll just chop off everything thru the last "."
11:50	rhickey	Chouser: right
12:02	Chouser	rhickey: as a general rule, do you prefer diff/patch files, or whole replacement files?
12:04	rhickey	Chouser: diff files as attachments are best
12:04	Chouser	ok
12:05	cemerick	(def a (new java.util.ArrayList<String>)) => error; is there a different incantation for referring to parameterized classes, or is this not yet supported?
12:05	Chouser	no need to provide the param class
12:05	Chouser	(java.util.ArrayList.)
12:06	cemerick	right, no reification
12:07	cemerick	I've been targeting 1.4 forever; I need to adjust my expectations :-P
12:18	Chouser	http://n01se.net/paste/cIN?pretty=no -- genclass-classname.patch
12:23	Chouser	example usage: http://n01se.net/paste/9g3J
12:59	rhickey	Chouser: cool, thanks! I don't understand:
12:59	rhickey	; the follow would fail because when we have a namespace and class
12:59	rhickey	; named the same, the "/" syntax is ambiguous?
12:59	rhickey	;(prn (net.n01se.TestObj/makeone 9))
12:59	Chouser	oh, those are left over from the last patch. I haven't tested them with this one.
13:00	Chouser	indeed, that works now.
13:01	rhickey	could you please post patch to group, with diff as attachment? (can't take contribs from pastes) - thanks
13:01	Chouser	sure, just a sec.
13:12	Chouser	sent
13:15	Chouser	It's interesting that this removes the class/method vs. namespace/function ambiguity.
13:15	rhickey	yes
13:15	Chouser	since now its package/simpleclass-function for the latter case.
13:29	rhickey	Chouser: patch applied, thanks
13:30	Chouser	of course just as you said that I was realizing I failed to update the doc string.
13:31	rhickey	ah
13:37	Chouser	would you prefer to have your existing test code in (comment) at the end? or mine, or nothing?
13:38	rhickey	something that works would be good :) mine doesn't
13:47	Chouser	well, I posted a patch to be applied on top of the old one. Of course feel free to edit to your preference.
13:53	rhickey	Chouser: that's up, thanks again
13:53	Chouser	sure, sorry for the stutter. :-)
13:53	rhickey	:)
13:55	Chouser	sounds like a good life
13:57	rhickey	actually, the multimethod enhancements are huge, once people figure out what they can do with them
13:59	Chouser	I believe you. It's fascinating to me how many things are (apparently) lumped into the OO class and hierarchy model that I had never conciously separated.
13:59	Chouser	Clojure seems to be aggressively deconstructing OO.
13:59	rhickey	:)
14:00	rhickey	CL's generic functions were an eye opener for me, after so many years of the C++ system
14:00	Chouser	why should the namespace be a class? why should the class of the first argument be the only dispatch criteria? Why should the heirarchy control inheritence?
14:02	Chouser	I worked for a couple year in a C++ codebase that had custom-built a sort of runtime-resolved two-argument multi-method system. The implementation was unimpressive, but the idea fascinated me.
14:02	Chouser	So when I read onlisp, I was ready for CLOS. I still haven't used it (or Clojure multimethods) yet.
14:03	rhickey	Now I think objects are a trivialization that is holding us back, and many new languages are content to stick with the same-old worldview
14:04	Chouser	But anyway, this is a good system. If having folks writing two-line patches to genclass or architecting lib.clj frees you up to keep thinking through the tricky stuff, then we all win.
14:04	rhickey	Greenspun's 10th is true, once the systems get large you need the flexibility of Lisp, and end up implementing it ad-hoc
14:05	Chouser	I don't know how it'll help you feed your family though. I hope they all like ice cream.
14:06	rhickey	Chouser: thanks
14:08	Chouser	Qt is sort of an attempt to fix some of the problems metnioned in that paper.
14:09	rhickey	Yes, RougueWave, boost et al all moved the idea forward in subsequent years
14:10	Chouser	But it's amazing the amount of work they've done to implement signals/slots in C++. A somewhat naive implementation in a dynamic language like JavaScript took only a couple dozen lines.
14:11	rhickey	Chouser: exactly
14:59	kotarak	is it possible to assign doc strings to multimethods?
15:04	Chouser	(defmulti #^{:doc "foo does foo stuff"} foo identity)
15:05	kotarak	But what, when the docs actually depend on the defmethod part?
15:05	Chouser	ah. hm.
15:06	Chouser	How would you look up the doc on a defmethod?
15:06	rhickey	kotarak: there should be a generic way to describe what a multimethod does. A multimethod is an open set, so it better represent an abstraction of some sort. Individual methods should all be implementations of that abstraction.
15:07	rhickey	i.e. the same way you can read the docs for an interface and use it
15:07	kotarak	I thought about something like: (defmulti foo) (defmethod foo :a "bla" ...) (defmethod foo :b "blub" ...) (doc foo) -> ":a:\n bla\n:b:\n blub"...
15:09	kotarak	rhickey: the problem comes from my monad adventures. There you have a bind function, which takes a monad and a function which does something to the monad returning another monad. But how this is actually established depends on the actual monad.
15:10	kotarak	But maybe I should do it differently.
15:10	kotarak	Just because this is done like that in Haskell, it's not necessarily a good idea to do it like that in Clojure.
15:11	rhickey	a user of a multimethod needs for there to be a single logical abstraction behind it - they shouldn't need to know or care what the methods are
15:14	ericthorsen	chouser: Sorry to have to ask...but where are the archives of this chat room?
15:15	Chouser	not a problem: http://clojure-log.n01se.net/
15:17	rhickey	That should probably go in the login banner on the IRC - logged at: ...
15:17	ericthorsen	thx
18:51	shoover	Along the lines of lisp features and thinking differently than mainstream languages, I'm curious if there's any interest in a CL-like condition/restart system to allow error handling directives to be established at a higher level without unwinding the stack.
18:51	shoover	I know at times my C# methods get bloated in order to wrap all the error situations (or I have to pass additional arguments down the stack). Is it too complicated, too slow, does anyone need it?
18:52	slava	shoover: restarts are very handy and lead to a whole new way of thinking about error handling
18:57	shoover	slava: It definitely seems that way. On the other hand, with CL's handler-case, handler-bind, restart-case, invoke-restart, and unwind-protect, there's more to get the mind around than good old try/catch. I'm wondering if those who have used restarts find them that useful in practice.
18:57	slava	I do
18:57	slava	I wouldn't want to do serious programming in a language without them.
18:58	shoover	Wow, that's a strong statement. You must not use a lot of languages for serious programming!
19:05	rhickey	The recommended pattern for Clojure is to dynamically bind a handler fn at a higher level - the lower level code can call it in order to get alternative values etc, the handler can possibly handle, or throw if no alternative
19:06	rhickey	one way to look at the CL condition system is as a special purpose set of dynamic functions in a language that otherwise doesn't have them
19:07	rhickey	dynamic functions + exceptions let you build whatever you want
19:07	slava	the real benefit of having conditions comes when they're actually used pervasively by the standard library
19:09	rhickey	maybe, I don't know that there is enough evidence to support that, and that conditions are needed to supply those benefits
19:10	rhickey	any high/low level coordination has to be pretty carefully orchestrated, I think it is more likely to work when you own both levels
19:20	shoover	rhickey: Interesting, thanks. I'll chew on this. All else aside, binding a dynamic function is easier to remember how to use.
19:40	shoover	Of course, now that you mention it it comes flooding back that dynamic vars were made for this context. If someone wanted the handler-bind, invoke-restart terminology I think it could be built on binding and find-var
19:43	rhickey	shoover: right, and defns end up in vars already, so no find needed. A fn need only say: if I get stuck I'm going to call handle-unparseable-input if it is bound, and use its return if not nil, and ignore if nil.
19:45	Chouser	gen-interface would really be gen-and-save-interface and gen-and-load-interface?
19:45	Chouser	or "would also have" I guess.
19:47	rhickey	Chouser: I'm trying to imagine a scenario for gen-and-load, who could be the consumer of such an interface?
19:47	rhickey	but generally, yes, a code generator and then helpers that use the code, like gen-class
19:48	Chouser	gen-and-load still creates the named class, just not the class file. So any combination of proxy and gen-and-load-class could use it.
19:49	rhickey	Chouser: I guess more generally, if you proxied/loaded an interface you just made up, who could use it?
19:50	rhickey	the logic for gen-and-load-class was that other Clojure code could new instances by name
19:50	rhickey	interfaces are contracts between independent pieces of code
20:33	Chouser	does gen-interface need to supported nested types?
20:33	Chouser	I assume it should at least support constants.
20:52	rhickey	Chouser: no, interface constants are not something I want to support, nor nested
21:53	hashendgame	I'm trying to write a def- macro that is identical to def, but adds :private true to the metadata (similar, I think, to defn- vs defn). My best attempt is at http://pastebin.ca/1085831 , but (def- woot 3) gives me a "second arg to def must be a Symbol" error.
21:56	Chouser	I think you want the with-meta to happen when your macro is called, rather than being put into the expansion.
21:56	Chouser	did you look at how defn- is defined in boot.clj?
22:00	hashendgame	I am now. Looks like the with-meta gets evaluated at call time.
22:04	hashendgame	http://pastebin.ca/1085839 has a working version, for those interested.
22:05	hashendgame	thanks Chouser
22:05	Chouser	sure, glad you got it working.
22:35	Chouser	using real classes and getInternalName for :extends means all your interface classes must be loaded before you can gen your derived class?
22:39	rhickey	It seems so
23:21	Chouser	but by using a real classes you can take advantage of imported class names.