Logs on 2022-05-08 (liberachat/#haskell)

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05:27:05	<Guest61>	@help
05:27:05	<lambdabot>	help <command>. Ask for help for <command>. Try 'list' for all commands
05:27:11	<Guest61>	list
05:27:15	<Guest61>	@list
05:27:16	<lambdabot>	What module? Try @listmodules for some ideas.
05:27:20	<Guest61>	@listmodules
05:27:20	<lambdabot>	activity base bf check compose dice dict djinn dummy elite eval filter free fresh haddock help hoogle instances irc karma localtime metar more oeis offlineRC pl pointful poll pretty quote search
05:27:20	<lambdabot>	seen slap source spell system tell ticker todo topic type undo unlambda unmtl version where
05:27:41	<Guest61>	@pl \xs n -> take n xs ==> flip take
05:27:42	<lambdabot>	flip flip (flip take) . ((==>) .) . flip take
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05:29:16	<Guest61>	@pl \fn1 fn2 a1 a2 -> fn1 (fn2 a1) (fn2 a2)
05:29:16	<lambdabot>	join . ((flip . ((.) .)) .) . (.)
05:29:53	<Guest61>	@pl \fn2 a1 a2 -> (fn2 a1) (fn2 a2)
05:29:53	<lambdabot>	flip =<< ((.) .)
05:30:30	<elmyr>	@src (.)
05:30:30	<lambdabot>	(f . g) x = f (g x)
05:30:49	<elmyr>	Day 1 of checking if lambdabot is back to Caleskell.
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05:51:31	<Guest27>	hello
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06:17:06	<ski>	elmyr : you should be checking `type' rather than `src', for that
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07:03:46	<tomsmeding>	What was the deal with (.) earlier then
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07:46:30	<c_wraith>	:t (\f g -> pure f =<< g) `asTypeOf` (.) -- tomsmeding
07:46:31	<lambdabot>	(a -> b) -> (a -> a) -> a -> b
07:47:05	<tomsmeding>	c_wraith: so, fmap?
07:47:10	<c_wraith>	I commented that `pure f =<< g' is a very long walk to reimplement (.)
07:47:30	<tomsmeding>	Ah, now I remember people saying that lambdabot had (.) = fmap at some point :)
07:47:47	<c_wraith>	yep. that was the "caleskell" being referred to
07:47:53	<tomsmeding>	Right
07:50:01	<tomsmeding>	So fmap and (<<<) both generalise (.), I wonder if those are incompatible
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07:50:37	<c_wraith>	:t (>>>) `asTypeOf` fmap
07:50:38	<lambdabot>	(a -> a) -> (a -> a) -> a -> a
07:50:44	<c_wraith>	err
07:50:48	<c_wraith>	:t (<<<) `asTypeOf` fmap
07:50:50	<lambdabot>	(b -> c) -> (a -> b) -> a -> c
07:51:10	<c_wraith>	between the two of them, every polytypic variable in the other is monomorphized
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07:51:18	<tomsmeding>	You'd need an fmap' that takes a 'cat a b' as the function argument
07:51:24	<tomsmeding>	But that makes no sense for some functors
07:51:48	<tomsmeding>	So they are indeed incompatible generalisations
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07:53:45	<tomsmeding>	Hm, `class Category cat => CFunctor cat f where fmap :: cat a b -> cat (f a) (f b)` maybe, with `type Functor = CFunctor (->)`
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07:56:35	<tomsmeding>	Hm, then you'd want `instance CFunctor cat (cat c)` but not sure whether that can work in general
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09:02:34	<mikoto-chan>	how do I install libmpd with cabal?
09:02:38	<mikoto-chan>	I get a weird error
09:02:47	<mikoto-chan>	Cannot build the executables in the package libmpd because it does not
09:02:50	<mikoto-chan>	contain any executables
09:06:31	<maerwald[m]>	mikoto-chan: the library?
09:10:34	<mikoto-chan>	maerwald[m]: --lib :\|
09:12:04	<mikoto-chan>	can I ask questions about xmobar here?
09:12:26	<mikoto-chan>	the mpd plugin isn't exactly working
09:12:33	<mikoto-chan>	do I need to use the system-wide daemon?
09:13:14	<mikoto-chan>	yes seems like it
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09:30:28	<AndreasK>	I have a possible stupid question. Is `cabal install cabal-install` supposed to work?
09:31:06	<AndreasK>	And if the answer is yes, which ghc versions are supposed to build the latest version that way?
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09:33:30	<AndreasK>	I guess it just doesn'T support building with 9.2 yet
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09:58:23	<AndreasK>	Or 9.0
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10:35:25	<maerwald>	AndreasK: it works sometimes
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10:37:00	<AndreasK>	As far as I can tell it should work with 8.10 but on this box my oldest GHC is 9.0.1
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10:50:59	<maerwald>	AndreasK: can you install 8.10?
10:52:19	<AndreasK>	Yes. But I think I will just download a 3.6 binary instead.
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11:40:07	<dminuoso>	I have a bunch of `IO T` where T has Monoid, is some shorter version of `fmap mconcat <$> sequence [a, b, c]`?
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11:46:23	<[exa]>	dminuoso: `fold` with Ap? https://hackage.haskell.org/package/base-4.16.1.0/docs/Data-Monoid.html#g:6
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11:49:40	<dminuoso>	[exa]: Mmm ah yes, I think thats what I was looking for. Not convinced this is better.
11:50:42	<[exa]>	:t getAp . fold . fmap Ap
11:50:44	<lambdabot>	forall k (t :: * -> ) (f :: k -> ) (a :: k). (Foldable t, Monoid (Ap f a), Functor t) => t (f a) -> f a
11:51:20	<[exa]>	would get competitive if there'd be some kind of `foldVia Ap` :D
11:51:33	<dminuoso>	Well that'
11:51:37	<dminuoso>	Well that's `ala` territory.
11:51:53	<dminuoso>	:t ala
11:51:54	<lambdabot>	(Functor f, Rewrapped s t, Rewrapped t s) => (Unwrapped s -> s) -> ((Unwrapped t -> t) -> f s) -> f (Unwrapped s)
11:51:57	<[exa]>	true
11:52:22	<[exa]>	is there a rewrapper?
11:52:39	<dminuoso>	rewrapper?
11:53:28	<dminuoso>	:t overF
11:53:29	<lambdabot>	error:
11:53:30	<lambdabot>	• Variable not in scope: overF
11:53:30	<lambdabot>	• Perhaps you meant one of these:
11:55:39	<[exa]>	:t al Ap foldMap
11:55:40	<lambdabot>	error:
11:55:40	<lambdabot>	• Variable not in scope:
11:55:40	<lambdabot>	al :: (f0 a0 -> Ap f0 a0) -> ((a1 -> m0) -> t0 a1 -> m0) -> t
11:55:45	<[exa]>	too much `a`
11:55:59	<[exa]>	:t ala Ap foldMap
11:56:01	<lambdabot>	forall k1 (t :: * -> ) (g :: k1 -> ) (b :: k1). (Foldable t, Monoid (Ap g b)) => t (g b) -> g b
11:56:27	<[exa]>	still I like the sequence one better :]
11:56:31	<dminuoso>	> ala Ap foldMap [pure [1,2] :: IO [Int], pure [3,4]]
11:56:33	<lambdabot>	<IO [Int]>
11:56:47	<dminuoso>	You use this if you have your coworkers.
11:56:50	<dminuoso>	s/have/hate/
11:57:07	<dminuoso>	And ideally you use not `newtypes` but `lens` for it.
11:57:22	<dminuoso>	(definitely not coercible-utils)
11:58:01	<[exa]>	:]
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12:01:23	<[Leary]>	dminuoso: Isn't it just "fold"? We have Monoid a => Monoid (IO a).
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12:12:48	<[exa]>	[Leary]: something needs to tell it how to fold the applicatives
12:13:22	<[exa]>	ah for IO that could work, yes
12:13:35	<[exa]>	cool.
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13:40:29	<Simon98>	Hello there! Is there a list of adjustments that I can make with :set in GHCI?
13:41:12	<Simon98>	Also im looking for a :set action that was called something with ...morpho... or so and I think it would specify the :t outputs and not always just say "Num". Do you know how it is called?
13:41:12	<geekosaur>	https://downloads.haskell.org/ghc/9.0.2/docs/html/users_guide/ghci.html#the-set-and-seti-commands
13:41:37	<Simon98>	Ahh I think it was XNoMonomorphismRestriction
13:41:42	<Simon98>	Thanks geekosaur
13:42:08	<geekosaur>	you may be thinking of :set -XMonomorphismRestriction, but it won't affect :t directly like that
13:42:26	<geekosaur>	types donb't get defaulted until applied
13:42:59	<Simon98>	what do you mean by that last line?
13:43:16	<geekosaur>	you need a fully applied expression for monomorphization to happen
13:43:36	<Simon98>	And also the link: There are indeed some things that work with :set, but it doesn't look like a complete list or so. Or is there simply no complete list since there can be new :set specifications added or so?
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13:44:24	<geekosaur>	:set also allows any ghc option at https://downloads.haskell.org/ghc/9.0.2/docs/html/users_guide/flags.html that is marked Dynamic
13:45:08	<geekosaur>	and any extension selectable with -X, of which I don't think there's a single compact list
13:45:10	<Simon98>	what does marked Dynamic mean?
13:45:29	<Simon98>	I see, no -X list
13:45:42	<geekosaur>	the link I gave you is a table of options, whether an option is dynamic or not is listed in the third column of the table
13:46:47	<geekosaur>	you can get a full list of -X options with `ghc --supported-extensions`
13:47:05	<geekosaur>	(sadly, with no documentation. but you can then search the manual)
13:47:33	<Simon98>	Wow, there are a lot
13:47:45	<Simon98>	I wonder what all of them do haha
13:47:57	<Simon98>	Another question:
13:50:24	<Simon98>	I'm new to Haskell and there just seem to be some huge differences to other, more common languages like Java or JavaScript. Not just regarding the programming paradigma but also with things like this :set and so on.
13:50:25	<Simon98>	Do you know if there are big software branches or industries out there where Haskell is used a lot or where it might even be the standard or are most of the problems that occur in the major branches just solved more easily with other languages?
13:51:00	<Lycurgus>	yes
13:51:15	<Simon98>	Ok, great that you know it! What would it be?
13:52:23	<Lycurgus>	it?
13:52:48	<Lycurgus>	TIOBE might be what ur lookin for
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13:53:44	<Simon98>	Yeah so Haskell is pretty low there. But still, are there branches where it is de facto standard? Due to whatever reason?
13:54:16	<Lycurgus>	No
13:54:22	<maerwald[m]>	Most of industry doesn't solve problems, but needs just another iteration of the same thing
13:54:35	<maerwald[m]>	Languages don't matter to them, but engineers do
13:54:49	<Lycurgus>	although it's cachet in academe was very high, but peaked in the last decade imo
13:54:56	<Simon98>	What do you mean by your first line mearwald?
13:55:09	<maerwald[m]>	And engineers think everything is about programming languages
13:55:29	<Lycurgus>	this channel for example has about half its population of a decade ago
13:56:01	<Simon98>	Why would you say is it popular in academia? (at least at my uni)
13:56:01	<hpc>	that's not a very good measure, that entire population loss is explained by the freenode debacle
13:56:22	<Lycurgus>	what maerwald[m] is referring to is a character of modern IT that is different from it's youth
13:56:44	<Lycurgus>	which is that IT became competent but dull
13:56:53	<Lycurgus>	real innovation dried up
13:56:56	<Simon98>	But why another iteration of the same thing?
13:57:15	<maerwald[m]>	To me, engineering would spend 60% of the time on specifications, then come up with the most constrained language (or DSL) possible that can be checked against the spec and doesn't require overly smart programmers.
13:58:02	<Lycurgus>	mostly because IT became a multi trillion dollar industry
13:58:02	<Simon98>	This is how you would like it to be or how you think it currently is?
13:58:56	<Lycurgus>	Simon98, you should address individuals as such when using first person
13:58:56	<Simon98>	Isn't IT one of the biggest innovators currently? Yet alone due to its size as Lycurgus says
13:59:13	<maerwald[m]>	But currently everyone likes turing complete general purpose languages and is interested in more expressivity, not less.
13:59:14	<Lycurgus>	i just said it wasn't
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14:00:31	<Simon98>	Yeah, you're right. Maybe I'm surprised that it's not
14:00:40	<ProofTechnique>	Is there an established name for `f :: Functor f => f (a -> b, c -> d) -> f (a -> c -> (b, d)) = fmap (curry . uncurry bimap)`?
14:02:39	<ProofTechnique>	IT is incredibly stagnant. It's just "here are all the business problems of decades ago, but now do it on someone else's infrastructure and bigger". All the "new" work is in crypto and that's literally worse than nothing.
14:03:07	<Simon98>	Interesting, now I get it
14:03:16	<Simon98>	But why is crypto a problem in your opinion?
14:03:30	<darkling>	Yeah, I'm fed up of different ways to do RPC.
14:03:58	<maerwald[m]>	Crypto is (technically) one of the biggest challenges. But no one knows what business problems it sovles
14:04:08	<ProofTechnique>	Environmental impact, governance, lack of utility.
14:04:26	<maerwald[m]>	ProofTechnique: environmental impact?
14:04:34	<ProofTechnique>	It's just a very fancy way to create private currency, which has always been bad
14:05:00	<maerwald[m]>	You're aware that proof of stake has basically no significant environmental impact?
14:05:22	<ProofTechnique>	Cool, let me know when _anyone_ that matters is using PoS
14:05:29	<maerwald[m]>	Cardano
14:05:31	<ProofTechnique>	I'm sure ETH will do it any day now
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14:05:51	<tochicool>	any way to get GHC to deduce the right constraint without pattern matching on the constructor? https://paste.tomsmeding.com/hxyLAkke
14:06:01	<maerwald[m]>	The biggest blockchain written in Haskell
14:06:08	<Simon98>	Cardano?
14:06:09	<ProofTechnique>	It's a fancy way to make private money, which is actively corrosive to democratic control of society
14:06:10	<maerwald[m]>	Seems you're not informed
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14:06:40	<ProofTechnique>	I'm incredibly aware of Cardano
14:06:43	<maerwald[m]>	I think that's as much BS as anything else about money and banks
14:07:02	<ProofTechnique>	I'm so excited to see how the neocolonialism in Africa pans out
14:07:10	<ski>	tochicool : i think, no
14:07:25	<tochicool>	:( why not?
14:08:05	<maerwald[m]>	ProofTechnique: I'm not into crypto, I just think most of the criticism is hypocritical
14:08:29	<ski>	i don't think there's any "you've exhausted all other cases, so it must correspond to the remaining case", while not matching on a GADT data constructor
14:08:38	<ProofTechnique>	Crypto does not solve any problem except how to part fools from their money and how to make the already exploitative relations of capitalism _even less regulated_
14:09:42	<ProofTechnique>	To be clear, I'm also against banks, but my preferred solution is to dismantle banks, not create dozens of hyper-exploitative bank-fiefs
14:11:02	<Simon98>	ProofTechnique Can you think of at least one major usecase for crypto?
14:11:05	<maerwald[m]>	Seems all very shallow critique to me, but you have some sympathies with https://github.com/sdiehl/popping-the-crypto-bubble
14:11:07	<ProofTechnique>	There are none
14:11:37	<tochicool>	ski: i see, thanks. i hoped it might be possible as ghc can do smarter things than that. would be really helpful if you had a lot of constructors with the same index.
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14:12:18	<maerwald[m]>	People also thought the radio or TV is going to end the world as we know it
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14:12:46	<ProofTechnique>	Radio didn't use the entire electrical output of the Netherlands
14:13:35	<tochicool>	it's harder to see the benefits of bitcoin from the first world
14:13:37	<maerwald[m]>	Neither does proof of stake
14:13:47	<maerwald[m]>	You're being deliberately imprecise
14:15:03	<ski>	tochicool : a somewhat similar example to this would be `Right x >>= k = k x; e >>= _ = e', where we'd like `e' to bound to have type `forall a. Either e a' (where `k :: a -> Either e b'), so that it can be used at type `Either e b'
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14:16:10	<ski>	@src Either (>>=)
14:16:10	<lambdabot>	Left l >>= _ = Left l
14:16:10	<lambdabot>	Right r >>= k = k r
14:16:25	<ski>	(note the annoying code repetition)
14:16:58	<ProofTechnique>	Then make an actual point instead of just complaining that I'm not sufficiently deferential to the claims of known con artists
14:17:24	hpc	. o O ( are lisp programmers... cons artists? )
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14:17:55	<ProofTechnique>	More of a used `car` salesperson
14:18:28	<hpc>	never bring a lisp programmer to a party, they'll defun it
14:19:41	<tochicool>	ski : yes that is annoying. are there any planned extensions the type system to help with this or is there some fundamental reason why this isn't supported?
14:20:49	<ski>	neither, afai aware
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14:22:49	<ski>	(i think the problem i sketched, at least, could probably be speced and implemented without too much trouble (although it might turn out to be more involved than expected, of course) .. but, in any case, it would be a complication, and so people would be asking whether it's worth it, compared to how much/often people would benefit from it)
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14:23:40	<ski>	(for the GADT one, it's not as clear to me how one'd want this to behave, systematically. but then i've not pondered this before, either)
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14:28:45	<Simon98>	If I have a function like: allSame a b c = (a==b && a==c) && (c==b) with allSame :: Eq a => a -> a -> a -> Bool
14:28:45	<Simon98>	Can someone explain to me what each arrow exactly stands for?
14:29:03	<Simon98>	Ahhh
14:29:27	<Simon98>	No
14:29:33	<Simon98>	But the a stands for Bool
14:29:51	<ski>	no
14:30:01	<Simon98>	Crap
14:30:03	<Simon98>	Right
14:30:33	<Simon98>	A stands for the type that my a b c have. But if they have different types?
14:30:39	<Simon98>	a*
14:31:44	<hpc>	if they have different types, you can't use (==) with them
14:31:48	<geekosaur>	they can't
14:31:49	<ski>	allSame :: Eq a => a -> a -> a -> Bool
14:31:51	<ski>	-- params&result ^ a ^ b ^ c ^ result
14:31:59	<hpc>	> "five" == 5 -- not valid
14:32:00	<lambdabot>	error:
14:32:00	<lambdabot>	• No instance for (Num [Char]) arising from the literal ‘5’
14:32:00	<lambdabot>	• In the second argument of ‘(==)’, namely ‘5’
14:32:32	<ski>	also, `(==)' ought to be symmetric and transitive, so you should be able to remove one of the equality checks
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14:33:20	<ski>	`a' is the type of the three values that are being compared for equality. the `->'s come after each parameter/argument type. the result type comes last
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14:34:40	<Simon98>	So e. g. allSame 1 2 3
14:34:41	<Simon98>	is basically
14:34:41	<Simon98>	Eq a => 1 -> 2 -> 3 -> false
14:34:42	<Simon98>	?
14:34:52	<ski>	the `=>' arrow separates the constraint context (to the left) from the usual (parameter and result types) signature. `Eq a' is a constraint that says that you can only use this operation (`allSame'), in case the argument type `a' is an instance of the type class `Eq', which is the case if it supports equality (checking) (`(==)' and `(/=)')
14:34:57	<ski>	no
14:35:15	<ski>	if `1',`2',`3' there have type `Integer', then, for this call to `allSame', `a' becomes `Integer'
14:35:18	<ski>	iow
14:35:20	<Simon98>	What do i use for the first a? And where does the "Eq" come from? Is it like "Eq a => a -> a -> a -> Bool" is the description for each "==" comparison?
14:35:21	<ski>	allSame :: Eq a => a -> a -> a -> Bool
14:35:22	<ski>	becomes
14:35:33	<ski>	allSame :: Eq Integer => Integer -> Integer -> Integer -> Bool
14:35:47	<ski>	but since `Eq Integer' holds, it's a known fact, this simplifies to just
14:35:52	<ski>	allSame :: Integer -> Integer -> Integer -> Bool
14:36:21	<ski>	(which then gives the actual type used for this call to `allSame')
14:36:52	<ski>	the `Eq a' constraint comes because you're calling `(==)', which has type `Eq a => a -> a -> Bool'
14:37:24	<ski>	you can only do equality checking on values of a type that supports equality checking (a type that is an instance of `Eq')
14:38:03	<Simon98>	very interesting
14:38:10	<Simon98>	but wait
14:38:10	<tomsmeding>	Read `Eq a => a -> a -> Bool` like "if `Eq a` holds, then this has type `a -> a -> Bool`"
14:38:31	<tomsmeding>	Or, well, that's one way to read it, at least
14:38:47	<ski>	so, for that to work, either (a) you need to use some particular type (that is known to be an instance of `Eq'), like `Integer', or `[(String,Bool)]' or something; or (b) you can delegate the responsibility for ensuring that `a' is in `Eq', which is what your current `allSame' does (because it has `Eq a' as a constraint in its type signature)
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14:39:13	<Simon98>	But what do you mean with "if `Eq a` holds"? Holds what?
14:39:26	<geekosaur>	different usage of "holds"
14:39:37	<geekosaur>	try "if a is a type that has an Eq instance"
14:39:44	<ski>	"`Eq a' holds" is a brief way to say "`a' is an instance of `Eq'" or "there is an `Eq a' instance"
14:40:23	<ski>	`Eq Integer' holds, because, somewhere in the base library, there is a declaration
14:40:29	<ski>	instance Eq Integer
14:40:29	<ski>	where
14:40:36	<ski>	... == ... = ...
14:40:39	<ski>	... /= ... = ...
14:40:39	<geekosaur>	importantly, only types are typeclass instances, not values
14:40:52	<Simon98>	Instead of "is an instance of" could also be said: "a is an object of something that inherits from the class Eq" or so?
14:41:15	<ski>	that declaration gives the actual implementation (the code) that will be run, when calling `(==)' and `(/=)' on `Integer's
14:41:22	<geekosaur>	typeclasses are not OOP
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14:41:31	<Simon98>	Ah right
14:41:38	<ski>	Simon98 : no, `a' is not an object (objects are values). `a' is a type
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14:41:50	<ski>	`a' doesn't exist at run-time
14:42:02	<ski>	(instances do, though)
14:42:56	<Simon98>	Ohhh, but ´a` (lets say, it's Integer in our example) is not just in instance of Eq but also of many other classes (?) like Num, right?
14:43:03	<Simon98>	or maybe not "many" but still
14:43:05	<[exa]>	Simon98: the intuition from OOP "traits" is kinda useful, but there are significant differences from the common OOP use. Most notably, typeclasses aren't objects but actual predicates, a bit more like c++ concepts
14:43:08	<tomsmeding>	Simon98: don't get confused by the _type_ `a` being called the same as the first _argument_ to the function, also called `a`
14:43:15	<tomsmeding>	They're completely different things
14:43:21	<ski>	Simon98 : sure, yes
14:44:11	<ski>	(it might be helpful to rename the parameters to say `x',`y',`z', to avoid confusing them with the type variables in the type signature)
14:44:43	<Simon98>	tomsmeding Ohhh, right
14:45:01	<Simon98>	ski Ohh, I'll try that
14:45:08	<Simon98>	So helpful all of you guys, thanks a lot !
14:45:17	<Simon98>	So:
14:45:23	<ski>	(eventually, you get used to the distinction, and then the name-punning can be useful)
14:45:59	ski	still doesn't like punning a type constructor with a data constructor, though
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14:46:19	<ski>	(i guess, partially, because the scope of those are not local)
14:47:21	<Simon98>	If I understand correctly now, "allSame :: Eq a => a -> a -> a -> Bool" is not an description of what the function "allSame" actually does (you could just guess that it does comparation) but it is just an description (or a guideline?) of the Types used and part of that function?
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14:49:34	<Simon98>	ski Hmm, the renaming didn't work as expected: Prelude> allSame x y z = (x==y && y==z)
14:49:35	<Simon98>	allSame :: Eq a => a -> a -> a -> Bool
14:50:14	<[exa]>	Simon98: yes, a "description of the admissible types" would work. If you know C++, in C++ it would be something like `template<typename a> bool allSame(a, a, a);`
14:51:33	<[exa]>	Simon98: btw try removing the `&& y==z` part from the comparison and see what happens with the type.
14:52:13	<ski>	Simon98 : why didn't you expect that ?
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14:52:29	<ski>	(it looks like the result you got would be what i would expect ..)
14:52:47	<ski>	the parameter (values) are `x',`y',`z'. their common type is `a'
14:52:59	<[exa]>	Simon98: for comparison again, c++ version for your unexpected result is: `template<typename a> allSame(a x, a y, a z) {...}`
14:53:20	ski	idly wonders whether Simon98 even has seen C++
14:53:33	<[exa]>	ah.
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14:54:25	<ski>	(asking, not insinuating)
14:55:05	<[exa]>	as usual, I didn't really read much of scrollback. :]
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14:59:41	ski	. o O (: hindsight, what's that ? :)
14:59:42	<Simon98>	[exa] I'm not familiar with C++ but your notation reminds me of Java Generics
15:00:20	<ski>	yea, in Java, it'd be `<a> allSame(a x,a y,a z) { ... }', iirc
15:00:21	<Simon98>	Why is there sometimes a * before your name ski and your Name is not before the time?
15:00:23	<Simon98>	in the chat
15:00:31	<Simon98>	Ohhhhhhhhhhhhh
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15:00:36	ski	glances around nervously
15:00:41	<ski>	it's called an ACTION
15:00:44	<Simon98>	So it can somehow be compared to Java Generics?
15:00:47	<ski>	try entering the following :
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15:00:57	<ski>	/me nods and smiles
15:01:39	<Simon98>	ski it confused me because of what you said here "(it might be helpful to rename the parameters to say `x',`y',`z', to avoid confusing them with the type variables in the type signature)", but now I get it (was thinking in a wrong way
15:01:43	<Simon98>	)
15:01:53	Simon98	nods and smiles
15:01:56	<Simon98>	hahahaha
15:02:05	Simon98	finds that nice
15:02:13	<ski>	it's typically used to describe something you're doing, or else describe some property of yourself (in third person, mind !) .. i also often use it for various associations i get and things i'm reminded of
15:03:42	<Simon98>	[exa] I tried it and look what happened: allSameX :: Eq a => a -> a -> p -> Bool
15:03:43	<Simon98>	So p can be z different type then x and y? But doesn't that disagree with the Eq restriction of only comparing same types?
15:04:11	<ski>	anyway, using type variables (begins with lower case (or `_')) in a type signature, indicates parametric polymorphism (which is called "generics", in e.g. Java). the initial `<typename a>' / `<a>' part can (usually) be elided in Haskell, but you can also spell it out explicitly as `forall a. '
15:04:21	<ski>	allSame :: forall a. Eq a => a -> a -> a -> Bool
15:05:56	<ski>	(you'll need to enable at least `ExplicitForAll' to be able to do that. there are a couple of more extensions that actually let you do more with `forall' than merely being explicit, rather than eliding a `forall' (letting the implementation implicitly insert it at the start, right after the `::'))
15:07:22	<ski>	Simon98 : yes, the type of `x' is `a' and the type of `y' is also `a', in that signature. but the type of `z' is `p', which is a distinct type variable, because `z' is not compared (for equality) with `x' nor `y', and so there's no need to assume it needs to have the same type, and so the implementation inferred a distinct type variable as its type (and for some reason happened to call that `p')
15:07:58	<ski>	"So p can be z different type then x and y?" -- right. "But doesn't that disagree with the Eq restriction of only comparing same types?" -- no, because you removed the comparision of `z' with one of `x' and `y'
15:08:22	<ski>	(specifically `y', i see above)
15:09:36	<Simon98>	I see, thank you!
15:09:46	<Simon98>	Why do you think the letter "p" was used?
15:09:51	<ski>	@type (==)
15:09:53	<lambdabot>	Eq a => a -> a -> Bool
15:09:57	<ski>	hm
15:10:03	<ski>	dunno
15:10:40	<geekosaur>	that has to do with the guts of the typechecker, which generally aren't introspectable
15:11:01	<geekosaur>	it tends to pick "t" or "p" in recent versions
15:11:20	<ski>	(sometimes it picks up a type variable name from a particular type variable name in an explicit type signature of an operation that is used, involving the type variable with it)
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15:14:49	<[exa]>	Simon98: a _p_arameter type, perhaps. The names of the variables don't really matter.
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15:15:20	<Simon98>	And another thing: Let's stay with " allSameX :: Eq a => a -> a -> p -> Bool"
15:15:20	<Simon98>	Are the arrows also actually meaning "flow" or something? Because that would not make sense.
15:15:21	<Simon98>	With the "allSame :: Eq a(0) => a(1) -> a(2) -> a(3) -> Bool" [I added the numbers] I could have imagined that we do one comparison and then the a(1) yet again will be type a(2) and with the next comparison it will stlil be a(3).
15:15:21	<Simon98>	But actually not even that makes sense since after one comparison they would already be Booleans instead of Integers
15:15:51	<Simon98>	[exa] how do you do the underlining?
15:16:09	<[exa]>	put underscores around, many clients will render it right
15:16:14	<[exa]>	(mine does not tbh... :D )
15:16:16	<Simon98>	I don't know why the name linking does not work sometimes. I typed "[e" then pressed tab and then enter or so
15:16:31	<Simon98>	_p_
15:16:43	<[exa]>	also the [ in my nick is not very popular with client software. I should get rid of it. :D
15:17:02	<Simon98>	Ahh. In my case it looks like doubleUnderline then p underlined then another double underline
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15:17:20	<[exa]>	anyway, regarding the "flow" -- (->) is the actual type of a haskell function, and we technically only have 1-parameter functions
15:17:40	<[exa]>	so if you'd really print the allSame type as-is, you'd get something like:
15:17:59	<[exa]>	`a -> (a -> (a -> Bool))`
15:18:10	<[exa]>	(I omitted the Eq)
15:18:15	<yushyin>	with decent clients you can write ex<tab> and it will become [exa]
15:19:11	<[exa]>	Simon98: the logic behind the parenthesization is that basically you feed the function parameters, and it becomes to something simpler and simpler, until it eventually becomes the Bool (which is not a function type, so you can't feed it parameters)
15:19:34	<Simon98>	So in practice it could be `Integer -> (Integer -> (Integer -> Bool))`
15:19:37	<[exa]>	yes
15:19:47	<Simon98>	waaaaaaait
15:20:01	<Simon98>	could you please also formulate it as math functions? with f(a) ?
15:20:01	<[exa]>	Illustration:
15:20:30	<hpc>	in that notation it'd be like saying f(a)(b)(c)
15:20:39	<[exa]>	ah yes, in the usual prefix notation, you'd write a single-parameter function not as `a->b` but as `(->) a b`
15:21:08	<[exa]>	(compare with `1+2` vs `(+) 1 2` vs `plus(1,2)` from other languages)
15:21:20	<hpc>	and in fact it's that exact notation in a lot of other languages where you can attempt such things
15:21:52	<hpc>	although then it's really tedious, you have to write stuff like f = function(a){return function(b){return function(c){...}}}
15:22:53	<hpc>	^ is javascript, if you want to pop into an f12 console and try it out
15:22:54	<[exa]>	:t let allSame a b c = a==b && b==c in (allSame, allSame 1, allSame 1 2, allSame 1 2 3)
15:22:56	<lambdabot>	(Eq a1, Eq a2, Eq a3, Num a2, Num a3) => (a1 -> a1 -> a1 -> Bool, a2 -> a2 -> Bool, a3 -> Bool, Bool)
15:23:36	<Simon98>	what is the prefix notation again in "allSame a b c = a==b && b==c"?
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15:23:52	<Simon98>	and hpc
15:24:18	<Simon98>	and hpc why would you put a type class (=a) in a function and not the actual value? (f(a)(b)(c))
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15:26:23	<[exa]>	Simon98: where's the typeclass?
15:26:24	<geekosaur>	> let allSame a b c = a == b && b == c in allSame "foo" "foo" "foo" -- works for any type with an Eq instance, not just Integer
15:26:25	<lambdabot>	True
15:26:44	<hpc>	those were the values
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15:26:49	<hpc>	pretend i wrote f(x)(y)(z) :P
15:27:34	<Simon98>	can this _function_ in _function applications_ be paraphrased to use _function_ with _function applications_ for me to better understand it?
15:30:11	<Simon98>	I get the latter parenthesis (good example!) but why are there 5 elements in the first parenthesis?
15:30:12	<Simon98>	(Eq a1, Eq a2, Eq a3, Num a2, Num a3) => (a1 -> a1 -> a1 -> Bool, a2 -> a2 -> Bool, a3 -> Bool, Bool)
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15:30:54	<[exa]>	Simon98: it actually needs to describe a lot of constraints in the returned types, so there they are:
15:30:54	<geekosaur>	because each call is considered separately
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15:32:00	<[exa]>	in order, `Eq a1` ensures that the types of the parameters of the first `allSame` are comparable, similarly for `Eq a2` and `Eq a3`. Fully applied `allSame 1 2 3` doesn't need any constraint because it just returns Bool, no matter what.
15:32:10	<Simon98>	hpc but what should " f(x)(y)(z) " mean?
15:32:11	<Simon98>	Like f(x,y,z) or h(g(f(x))) with f(x) = y and g(y) = z would make sense for me but your notation not
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15:32:54	<[exa]>	Then `Num a2` is there because I already put `1` into `allSame 1`, and `1` can stand as any numeric type. So it tells you an extra information that you must put in other arguments as numeric too -- for example you couldn't do `allSame 1 "whatevs"`
15:33:06	<[exa]>	(similar for Num a3)
15:33:36	<Simon98>	ahh, thanks [exa]
15:33:52	<Simon98>	and how would you paraphrase the "=>" here?
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15:34:08	<[exa]>	haha, tricky
15:35:14	<Simon98>	:)
15:35:38	<haskell_apprenti>	question: I'm going through Haskell programming from first principles, in the book they say a function with the signature blahFunc :: b -> String totally throws away its first argument and is effectively a constant value of type String. Can't we define a toString method that works for every type? I find it hard to reason about saying a function has
15:35:39	<haskell_apprenti>	to be a particular function due to its type signature
15:35:44	<[exa]>	it's an actual implication, given you have an `a` that satisfies the `Eq`, you can assume that your type is a->a->...
15:36:34	<geekosaur>	haskell_apprenti, what would toString be for a function?
15:36:42	<Simon98>	wow
15:36:58	<Simon98>	Is the "=>" in Haskell syntax always an actual implication?
15:37:00	<geekosaur>	remember, Haskell is compiled, it does not have the source code available, especially for a typeclass method like (+)
15:37:01	<[exa]>	haskell_apprenti: "for every type" is hard. Do you know what custom-defined type am I going to send you in 5 minutes from now?
15:37:47	<haskell_apprenti>	doesn't all data need some kind of text representation to be viewed on a screen though?
15:38:15	<[exa]>	haskell_apprenti: that implies that you already know something about the type. That would be `blahFunc :: HasBitRepresentation b => b->String`
15:39:04	<haskell_apprenti>	don't all types need a data declaration though? so theoretically you can print that, since that's common to all types. just for the sake of argument
15:39:20	<Simon98>	And is one implication here sufficient ((Eq a1, Eq a2, Eq a3, Num a2, Num a3) => (a1 -> a1 -> a1 -> Bool, a2 -> a2 -> Bool, a3 -> Bool, Bool)) because you put the function applications all in one parenthesis ((allSame, allSame 1, allSame 1 2, allSame 1 2 3)) and therefore to make it work everything has to meet the requirements at a time?
15:39:42	<[exa]>	haskell_apprenti: yes, there's actually a typeclass for that too (Generic). But still if you use it, you have to declare it.
15:40:24	<[exa]>	Simon98: yes, it's 1 big type with 1 big sets of "conditions", so only a single => is required in between
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15:40:40	ski	. o O ( no underscores )
15:41:01	<ski>	haskell_apprenti : types that are primitive doesn't need `data' or `newtype' declarations
15:41:20	<[exa]>	Simon98: you can definitely try for isolated (partial) calls of allSame in your ghci, with different argument types. It should become quite intuitive once you play with it for some time
15:41:58	<ski>	e.g. `(->)' .. or, an implementation could have `Char',`Int',`Integer',`Float',`Double',`Array',`IO',`IORef' all be primitive, as well
15:43:55	<ski>	@type let foo x = (typeOf x,cast x :: Maybe String) in foo
15:43:57	<lambdabot>	Typeable a => a -> (TypeRep, Maybe String)
15:43:59	<ski>	> let foo x = (typeOf x,cast x :: Maybe String) in foo False
15:44:01	<lambdabot>	(Bool,Nothing)
15:44:06	<ski>	> let foo x = (typeOf x,cast x :: Maybe String) in foo "True"
15:44:08	<lambdabot>	([Char],Just "True")
15:44:51	<haskell_apprenti>	[exa] geekosaur I think I understand thinking about it more, thanks
15:45:24	<geekosaur>	now, we do have a typeclass for what you've been talking about: Show
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15:45:31	<geekosaur>	and your toString is show
15:45:51	<[exa]>	haskell_apprenti: btw the "some kind of representation exists" doesn't really hold in haskell programs. Stuff may be easily erased before it reaches runtime, and there are actual definition-less types (`data Void`)
15:45:53	<geekosaur>	but again you must declare that you're using it
15:46:42	<ski>	haskell_apprenti : you can use `Typeable', if you want to do type casting stuff. `Generic' to actually do introspect stuff on how the type was declared
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15:47:34	<ski>	(well, i'd rather say that `Void' has a collection of data constructors .. it just happens to be the empty collection)
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15:49:35	<ski>	haskell_apprenti : anyway .. what you might see as an annoyance here is actually a boon, in the sense that it allows one to reason about, infer stronger properties (things an operation definitely can't do), solely by inspecting its type signature. this is called "parametricity". parametric polymorphism in Haskell enjoys this. parametric polymorphism (called "generics") in e.g. Jave doesn't, because of
15:49:41	<ski>	`instanceof' and up-casting (and methods on `Object')
15:51:00	<haskell_apprenti>	I don't find it annoying, I'm just interested in the theory of why its definitely true that a particular type signature must have a certain type implentation
15:51:26	<haskell_apprenti>	like id be interested if there are proofs about it written somewhere if anyone could point me to that
15:51:36	<ski>	e.g. if you see `foo :: (a -> Maybe b) -> [a] -> [b]', you know that `foo' can't itself inspect the `a' elements of the list, but can only pass them on to the callback, which is also the only place where the `b' elements in the output could possibly come from (apart from using `undefined' & `error' & `Control.Exception.throw', or infinite loops)
15:51:45	<haskell_apprenti>	sorry not type implementation, concrete function implemenetation
15:52:18	<ski>	@free bar :: Int -> [a] -> [a]
15:52:18	<lambdabot>	$map f . bar x = bar x . $map f
15:52:54	<ski>	this is a "free theorem", that says that it doesn't matter if you map some function `f' to the elements of the list, before or after you call `bar', since `bar' definitely won't look at, or change, the elements
15:53:20	<ski>	(and this relies on parametricity)
15:53:31	<ski>	@help free
15:53:31	<lambdabot>	free <ident>. Generate theorems for free
15:54:01	<ski>	@free transpose
15:54:03	<lambdabot>	$map ($map f) . transpose = transpose . $map ($map f)
15:54:11	<ski>	@free concat :: [[a]] -> [a]
15:54:12	<lambdabot>	$map f . concat = concat . $map ($map f)
15:55:49	<haskell_apprenti>	ski don't understand the @ free thing
15:56:30	<ski>	@free reverse
15:56:31	<lambdabot>	$map f . reverse = reverse . $map f
15:56:34	<haskell_apprenti>	I feel like what you're saying though is since its parametrically polymorphic, the only thing we could do that will work with all types is pass it through eg identity
15:56:54	<haskell_apprenti>	and the extension of that eg with list of types, pass through list of types
15:57:14	<ski>	it says `$map' instead of `map', since it's assuming a generic mapping. but they should be the same. so read that as claiming
15:57:23	<ski>	map f . reverse = reverse . map f
15:57:39	<ski>	is a true law/equality/equation (for every function `f')
15:57:57	<ski>	or, expanding (putting in an explicit argument), this says that
15:58:05	<ski>	(map f . reverse) xs = (reverse . map f) xs
15:58:11	<ski>	(for every `f' and every list `xs')
15:58:28	<ski>	which is the same (by the definition of function composition, `(.)')
15:58:40	<ski>	map f (reverse xs) = reverse (map f xs)
15:58:49	<[exa]>	haskell_apprenti: that's true, the only non-crashing function with type `a->a` is id. The only other thing you can do in haskell is to crash it with `undefined`.
15:58:57	<haskell_apprenti>	ski think i need the ELI5 version
15:59:21	<ski>	and now this is explicitly saying that if you reverse `xs', and then `map' `f' on every element of the reversed list, then that's the same as first mapping `f' on `xs', and then reversing the mapped list
15:59:27	<haskell_apprenti>	[exa] is that proven formally somewhere
15:59:53	<[exa]>	yes
16:00:10	<ski>	haskell_apprenti : do you understand the last version of the equation, above ?
16:00:21	<ski>	(with my attempted elucidation of it)
16:00:45	<ski>	btw, you could perhaps try checking "Theorems for free!" by Philip Wadler in 1989-09 at <https://homepages.inf.ed.ac.uk/wadler/topics/parametricity.html#free>
16:01:23	<haskell_apprenti>	[exa] can you point me to where that is proven
16:01:35	<haskell_apprenti>	ski yes I think I understand that last version thanks
16:01:41	<[exa]>	yes, trying to find it written somewhere
16:02:01	<[exa]>	(likely the Wadler's paper above will contain the intuition too)
16:02:02	<haskell_apprenti>	ski I understand the statement of the theorem, but how do we know its true
16:02:28	<ski>	the previous versions are merely fancy (so-called, "pointless") ways to express the same thing (using composition / function pipeline, instead)
16:03:50	<haskell_apprenti>	ahh ok that wadler "theorems for free" looks like what I want to look at
16:03:54	<haskell_apprenti>	looks dense thuogh
16:03:59	<haskell_apprenti>	thanks for the help!
16:06:33	<ski>	haskell_apprenti : we know it holds for an idealized calculus (second-order polymorphic lambda calculus (F2), in the papers mentioning Reynolds in the abstract, at the link i gave you), because of the abstraction theorem. the "theorems for free" is about deriving an immediate result/law, from a `forall'-type (a universal type), using that theorem
16:08:39	<ski>	i'm not sure if someone has attempted to prove the corresponding thing, for a system that looks more like Haskell (including various stuff like partiality, nontermination, and possibly a bunch of fancy type system features making it more powerful than F2) .. but we're basically treating it like it behaves similarly
16:08:57	<[exa]>	haskell_apprenti: btw it's useful to read about curry-howard correspondence; by dragging in logic it paints a much cleaner image of stuff that can't be done. E.g. here: https://en.wikibooks.org/wiki/Haskell/The_Curry%E2%80%93Howard_isomorphism#Intuitionistic_vs_classical_logic
16:09:20	<ski>	(don't worry, the "full abstraction" stuff by Reynolds is denser)
16:11:05	<ski>	for Curry-Howard, it can also be neat if one knows a little about basic set theory (cardinality, cartesian product, disjoint union, exponential set (function set))
16:13:18	<ski>	haskell_apprenti : "but how do we know its true" -- from an appeal to intuition standpoint, there is no way that `reverse' could inspect or interact with the elements (apart from forcing them, and the worst that may do is give nontermination or partiality). .. so, the only thing it can do is return some of the input elements, as output elements (possibly reordering, and possibly duplicating (and dropping
16:13:24	<ski>	others))
16:13:49	<ski>	but its behaviour can't depend on the innards of the elements, it can only depend on the length of the input list
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16:14:26	<Simon91>	Hello again
16:14:52	<ski>	(the only way to depend on the innards would be to either pass off an element to a callback (but there's no such, in this case), or to use a typeclass-overloaded operation on them (but there's no class constraints in the type signature, so that's not going to happen, either))
16:15:34	<Simon91>	GHCI coming up with "funktionB :: Integral a => [a] -> [a]" for "funktionB x = [ if (y `mod` 2 /= 0) then (2 * y) else y \| y <- x]" is due to GHCI being smart and knowing that you need Integers for the operations in brackets?
16:16:33	<c_wraith>	It's inference from the way the elements are used.
16:16:34	<ski>	if you do `foo :: Eq a => Int -> [a] -> [a]', then `foo' can pass off elements to `(==)' and `(/=)' (and other operations with an `Eq' constraint, like e.g. `allDistinct :: Eq a => [a] -> Bool')
16:16:52	<c_wraith>	You're using (/=), (*), and mod.
16:17:03	<ski>	@type mod
16:17:04	<lambdabot>	Integral a => a -> a -> a
16:17:14	<ski>	@type (*)
16:17:17	<lambdabot>	Num a => a -> a -> a
16:17:19	<ski>	@type (/=)
16:17:20	<lambdabot>	Eq a => a -> a -> Bool
16:17:28	<ski>	`Num' and `Eq' are superclasses of `Integral'
16:17:31	<c_wraith>	from that, it derives Eq, Num, and Integral - but it turns out Integral requires Eq and Num, so it reduces the display set
16:18:02	<ski>	Simon91 : also, your (round) brackets there are redundant
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16:20:28	<c_wraith>	Oh, there's one other thing contributing to inference there - the 0 literal. It also implies a Num constraint. It's redundant in this case, but worth knowing
16:20:46	<c_wraith>	Err. the 0 and 2 literals.
16:20:49	<Simon91>	c_wraith and it chooses Integral because it always chooses the most sub subclass from all classes involved?
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16:21:13	<c_wraith>	Simon91: no, doesn't show Eq or Num because they're implied by Integral
16:21:36	<ski>	haskell_apprenti : so, anyway. the only way to do type introspection stuff, and being able to look "inside" an input whose type is a type variable (apart from passing it off to a callback that accepts it, but then the callback comes from the caller, not the callee/implementor of the operation) is to explicitly opt-in to it, by using a `Typable' or `Generic' constraint, or so, on the type variable
16:21:58	<ski>	(well, there's also GADTs ..)
16:22:05	<Simon91>	ski yeah I thought so, but it felt weird and error-prone not putting them (even though it's probably the other way round)
16:22:06	<c_wraith>	Simon91: that may sound like the same thing, but classes aren't all in a single hierarchy
16:22:44	<c_wraith>	Simon91: so there's no guarantee there is such a thing as a single most-sub subclass.
16:22:45	<Simon91>	c_wraith I see. Very interesting.
16:22:54	<ski>	Simon91 : pointing out redundant brackets (when it's likely they weren't put in consciously for an explicit reason), is a pet peeve of mine ;)
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16:23:19	<Simon91>	hahah
16:23:42	<c_wraith>	ski: parse error, unmatched closing ')' at end of input
16:24:22	<ski>	example of a consciously inserted pair of brackets :
16:24:28	<ski>	map :: ( a -> b )
16:24:31	<ski>	-> ([a] -> [b])
16:24:37	<ski>	(the second pair of round brackets)
16:24:51	<ski>	@type map . map . map
16:24:53	<lambdabot>	(a -> b) -> [[[a]]] -> [[[b]]]
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16:25:11	<ski>	@type zipWith . zipWith
16:25:14	<lambdabot>	(a -> b -> c) -> [[a]] -> [[b]] -> [[c]]
16:25:59	<c_wraith>	that doesn't look useful! :P
16:26:32	<c_wraith>	(I'm sure it's come up once or twice in history)
16:27:06	<ski>	@let foldL :: (s -> a -> s) -> (s -> [a] -> s); foldL = foldl
16:27:07	<lambdabot>	Defined.
16:27:13	<ski>	@type foldL . foldL
16:27:14	<lambdabot>	(s -> a -> s) -> s -> [[a]] -> s
16:28:54	<ski>	(the types of the fold right function in OCaml also allows this. but, alas, the signature of the Haskell one prevents this, without interleaving a `flip')
16:29:45	<ski>	Simon91 : anyway, you'll get used to it (hopefully)
16:31:24	<ski>	(for some reason, it seems that many people who've been using Haskell for years still don't know that the brackets in `(Foo ...) == ... = ...' and in `case ... of (x:xs) -> ...; ...' or `... where (x:xs) = ...' are redundant ..)
16:32:05	<ski>	(hm, and there's also `foo :: (Eq a) => ..a..')
16:34:13	<geekosaur>	I know it but I generally go for consistency
16:34:51	<ski>	yea, i figure some do (and several don't know)
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16:44:07	<haskell_apprenti>	ski will check out the wiki books thing you sent
16:45:01	<haskell_apprenti>	also nice intuition thanks
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16:46:48	<elmyr>	@type (.)
16:46:49	<lambdabot>	(b -> c) -> (a -> b) -> a -> c
16:47:02	<elmyr>	ski: doesn't look like Caleskell there either
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16:55:49	<dminuoso>	[Leary]: Oh wow, thanks. Yes!
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17:00:24	ski	nods to elmyr
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18:43:06	<maerwald>	does haskell CPP on windows need anything special? I'm getting massive errors that I don't get on unix
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18:47:18	<hpc>	probably something to do with how it picks what cpp command to run?
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19:30:00	<dminuoso>	Okay so Im writing a hardware library, that exposes a bunch of `init/finalize` or `open/close` functions. Im debating whether to provide `with` CPS helpers - and the reason Im debating this is because I dont want to make a choice for `bracket`.
19:30:07	<dminuoso>	i.e. do I use base or safe-exceptions bracket
19:30:49	<dminuoso>	My thinking is: just expose the manual functions, defer writing a bracket'ed helper to the user who can then chose whatever library they want
19:30:52	<dminuoso>	Is this a sane choice?
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19:33:43	<hpc>	presumably you aren't already depending on safe-exceptions
19:33:47	<monochrom>	base itself takes the approach of providing both, with the latter hardwired to IO.
19:33:49	<hpc>	but you're certainly already depending on base
19:34:03	<hpc>	so provide the base functions and a with-function for base bracket
19:34:15	<hpc>	the user can write a safe-exceptions with-function
19:34:19	<dminuoso>	monochrom: both
19:34:21	<dminuoso>	?
19:34:31	<dminuoso>	hpc: Mmm, I guess I can do that.
19:34:44	<monochrom>	base has both openFile+hClose and withFile.
19:34:50	<dminuoso>	Ahh, I see
19:36:36	<monochrom>	But everyone knows how to use bracket. If you don't provide a "with", it's OK.
19:37:31	<monochrom>	I haven't needed safe-exceptions.
19:38:06	<dminuoso>	"needed" is a bit strong, in case of bracket its rather about a rare edge case that is really hard to trigger
19:39:01	<dminuoso>	I sincerely believe that defaulting to `mask` instead of `uninterruptibleMask` inside the implementation is a dangerous mistake that leads to false assumptions.
19:39:15	<dminuoso>	And it goes into "everyone thinks they know how to use bracket" rather than "everyone knows"
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19:46:46	<mxs>	would this be a candidate for base? elemIndex :: (Traversable t, Eq a, Num b) => a -> t a -> Maybe b
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19:47:56	<dminuoso>	The Num polymorphism is a bit weird
19:48:22	<mxs>	can be Int. I just like the generic* functions
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19:49:08	<mxs>	it's about the Traversable elemIndex, I find myself using it a lot
19:49:48	<dminuoso>	Traversable is way too strong
19:49:51	<dminuoso>	You only need Foldable
19:51:12	<mxs>	mhm yeah I suppose, even better. I wrote it with mapAccum for efficiency that's why
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19:52:20	<dminuoso>	Not sure how mapAccum would help make it more efficient
19:52:40	<mxs>	how would you write it?
19:52:42	<dminuoso>	elemIndex' e = elemIndex e . toList
19:53:59	<dminuoso>	Im not sure this combinator would cross the Fairbairn threshold
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19:54:25	<dminuoso>	If you find yourself needing this a lot, it might be an indicator of working with the wrong data types
19:54:53	<Bulby[m]>	it's always traverse!
19:55:04	<Bulby[m]>	what is Fairbairn
19:55:11	<dminuoso>	I guess the thing is, in a Foldable this is generally not useful since you have no guarantee to do random access on that
19:55:38	<dminuoso>	Finding the index of an arbitrary foldable structure seems like an awkward information if you cant say manipulate the structure on that index
19:56:36	<dminuoso>	On lists at least this has clear meaning, but what does "index in a tree" mean exactly?
19:56:55	<dminuoso>	Bulby[m]: https://wiki.haskell.org/Fairbairn_threshold
19:57:49	<mxs>	elemIndex a = msum . snd . mapAccumL fn 0 where fn s x = (s+1, guard(a == x) >> Just s)
19:58:06	<mxs>	without toList, but I'm not sure how much that saves on second thought
19:58:15	<dminuoso>	Im confident `elemIndex' e = elemIndex e . toList` is going to be cheaper.
19:58:39	<dminuoso>	Recall that in non-strict semantics the list is being generated lazily
19:58:57	<dminuoso>	But really, all this boils down to the same problem:
19:59:12	<dminuoso>	Your code does semantically the same: turn it into a list in sequencing order, and find the index inside that list.
19:59:19	<dminuoso>	Is this a generally useful operation on arbitrary foldable structures?
20:00:59	<dminuoso>	mxs: btw, the above is going to use findIndices internally , which has some carefully crafted code to trigger deforestation
20:01:17	<dminuoso>	https://hackage.haskell.org/package/base-4.16.1.0/docs/src/Data-OldList.html#findIndices
20:02:03	<dminuoso>	So depending on how the structure is made, this can be quite efficient
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20:04:39	<kaol>	Today I learned that it pays to sometimes think a bit and not just hammer at the types until they match.
20:05:11	<monochrom>	Intelligent Design > Evolution
20:05:12	<kaol>	join . listToMaybe was too easy, I needed getFirst . mconcat . fmap First instead.
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20:08:34	<tomsmeding>	kaol: isn't that `catMaybes`
20:11:18	<kaol>	listToMaybe . catMaybes actually.
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20:11:30	<tomsmeding>	Ah right
20:12:10	<tomsmeding>	kaol: hmm, so isn't it `asum`
20:12:32	<tomsmeding>	The Alternative instance for Maybe picks the leftmost Just
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20:14:47	<kaol>	Well I'll be. I think I have reached par on this golf journey.
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20:15:53	<mxs>	dminuoso: thanks for the insight, you're probably right - I avoided toList but now that I think about it, there's no reason
20:16:33	<tomsmeding>	kaol: knowing the variety of utility functions that happen to do useful things on Maybe is more learning/experience than art :p
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20:33:35	<dminuoso>	mxs: https://gist.github.com/dminuoso/e285f19e9dac2de2300a52e74ca82279
20:34:43	<dminuoso>	What is interesting is that fusion did not trigger, and even despite that its still a lot less code.
20:35:35	<dminuoso>	Part of that is because findIndices then ends up being a simple fold, but mapAccumL is a traverse over simplified State transformer
20:36:50	<dminuoso>	Ah, turns out that according to #15426 the fusion is broken currently for findIndex
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20:44:19	<energizer>	can i use hoogle or something to find a bunch of interesting examples of Monoid?
20:46:08	<dsal>	energizer: You can find a bunch just by looking at haddock.
20:46:15	<geekosaur>	@instances Monoid
20:46:17	<lambdabot>	(), (a -> b), (a, b), All, Any, Dual a, IO a, Maybe a, Ordering, Product a, ST s a, Sum a
20:46:33	<dsal>	https://hackage.haskell.org/package/base-4.16.1.0/docs/Data-Monoid.html#t:Monoid
20:46:36	<geekosaur>	and those are just the ones in Prelude iirc
20:46:48	<geekosaur>	@instances-importing Data.Monoid Monoid
20:46:50	<lambdabot>	(), (a -> b), (a, b), All, Any, Dual a, IO a, Maybe a, Ordering, Product a, ST s a, Sum a
20:47:25	<dsal>	(a->b) and Ordering are pretty interesting ones together.
20:48:44	<dsal>	I use the tuple ones sometimes, but for that type of thing, often just make a new product type.
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22:56:45	<ski>	> sortBy (compare <> comparing length) (words "The quick brown fox jumps over the lazy dog")
22:56:47	<lambdabot>	["The","brown","dog","fox","jumps","lazy","over","quick","the"]
22:56:53	<ski>	@where monoids
22:56:54	<lambdabot>	comment on "Monoids? In my programming language?" by Cale in 2008 (or 2009 ?) at <http://www.reddit.com/r/programming/comments/7cf4r/monoids_in_my_programming_language/c06adnx> about a use of `
22:56:54	<lambdabot>	instance Monoid a => Monoid (rho -> a)'
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22:57:49	<ski>	well, sorry, actually
22:57:56	<ski>	> sortBy (comparing length <> compare) (words "The quick brown fox jumps over the lazy dog")
22:57:58	<lambdabot>	["The","dog","fox","the","lazy","over","brown","jumps","quick"]
22:58:32	<ski>	energizer : ^ that's what dsal was alluding to. sorting primarily by length, and secondarily by the ordinary lexicographic ordering (among words that have the same length)
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23:07:29	<energizer>	✓
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23:11:43	<dminuoso>	Mmm, is there any ligtweight json library around that doesnt pull what feels like half of hackage along with it?
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23:16:55	<energizer>	in some language there is a memory buffer where i can store `xs = [1,2,3]` and then reuse that buffer for the value of `ys = map double xs` if i'm not going to reuse `xs`. is there a way to specify that i want to reuse the storage area of xs in haskell?
23:17:44	<dminuoso>	energizer: You have to do memory access yourself.
23:17:50	<dminuoso>	Sadly we dont have this built into Haskell.
23:18:00	<energizer>	are there idioms for it?
23:18:09	<dminuoso>	Clean has this, they do automatic mutation in such cases.
23:18:29	<dminuoso>	(And from what I hear, that alone makes them competive over the well attended GHC in a select few benchmarcks)
23:18:56	<dminuoso>	energizer: it depends a lot on what your access pattern is
23:19:11	<dminuoso>	But you can start looking at Data.Vector.Mutable
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23:27:36	<melas>	Forgive me, as I'm brand new to all this, but would you consider it relatively easy to create a standalone windows program that can do basic network tests like ping / traceroute, etc. and save the to a log file? I guess my question is are the classes for this type of this typically up to date in Haskell ecosystem?
23:27:50	<dminuoso>	Regarding json, I think I have something https://hackage.haskell.org/package/JSONb
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23:28:16	<melas>	Just trying to come up with a first program to code once I learn all the basics
23:28:17	<dminuoso>	It's not been maintained for a while, but its very minimalistic and doesnt pull in 80 packages behind it.
23:37:27	<geekosaur>	melas, that might be difficult in any language. ICMP typically requires privileged access because you're working with raw IP packets
23:37:48	<geekosaur>	traceroute, at least for IPv4, is simpler though
23:40:37	<geekosaur>	(you can do bad things to a network by sending control packets on it, which is the primary purpose of ICMP)
23:41:05	<sclv>	dminuoso: if you don't mind the performance, https://hackage.haskell.org/package/json
23:42:46	<melas>	@diminuoso why would privileged access make it difficult?
23:42:46	<lambdabot>	Unknown command, try @list
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23:44:43	<dminuoso>	sclv: Ah, how did I not find this. Yes, this would work nicely. A bit sad this uses String instead of Text for JSString, but oh well.
23:44:51	<dminuoso>	Thanks, I think I will use this.
23:44:59	<hpc>	huh? icmp doesn't require privileges
23:45:19	<hpc>	traceroute only requires root for tcp/udp because there's not otherwise a way to set the ttl
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23:45:38	<sclv>	dminuoso: its the old galois library. i believe it actually _predates text_ by one year!
23:46:26	<hpc>	oh, on windows
23:47:06	<geekosaur>	maybe they changed things. in the bad old days you needed a raw IP socket
23:47:16	<dminuoso>	hpc, geekosaur: /run/wrappers/bin/ping cap_setpcap,cap_net_raw=p
23:47:29	<geekosaur>	right, that's privileged
23:47:44	<hpc>	melas: if you want networkish stuff to try, something like a web server or client would be better
23:48:00	<hpc>	s/web/whatever protocol fits your fancy/
23:49:36	<geekosaur>	oh, and even if you have some way to limit to ICMP ECHO {REQUEST,REPLY} you can typically take out a network by sending >100/s
23:49:56	<dminuoso>	melas: I dont see a reason why you couldn't. Things like permission problems affect all other languages, and in case of ICMP echo requests its easily addressed by setting CAP_NET_RAW and cap_setpcap
23:50:10	<geekosaur>	this is windows so the perms probably differ
23:50:27	<geekosaur>	windows has a more expressive permissions system though
23:50:48	dminuoso	is not sure how you would take out a network this way
23:50:56	<geekosaur>	(also hopefully they don't use raw IP sockets, they're a pain)
23:51:18	<geekosaur>	send them through a router. it prioritizes ICMP usually so it won't pass anything else
23:51:45	<melas>	Hmm. Ok cool, thanks. I'm a long way from that anyway. Really just feeling things out. My end goal actually is to mess with stuff like Euterpea and/or tidalcycles
23:51:47	<dminuoso>	Sure, cheap plastic home routers might be taken down like this.
23:51:50	<geekosaur>	you could still use the network locally but you will have isolated it
23:53:41	<dminuoso>	But a hundred ICMP per second will not take down a local network. Typical home routers can usually route upwards of a million pps, full line rate routing with 1.5mpps is not unheard of for plastic routers
23:54:28	<dminuoso>	I think a more meaningful impact is that of local control plane
23:54:40	<dminuoso>	Specifically on the target
23:55:02	<dminuoso>	Depending on how the networking stack works, ICMP flood can quickly cause a lot of kernel time to occur
23:56:20	<dminuoso>	Im really not sure about linux or windows, but all our routers at work have pretty aggressive policers
23:56:46	<dminuoso>	Which is mostly a thing to dampen potential DDoS situations
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All times are in UTC on 2022-05-08.