IRCBrowse

2022/01/07

2022-01-07 00:01:01 +0100 <dmj`> Inst: a@(x:xs) will never match on the empty list, so null a will never be called, it will pattern match failure instead
2022-01-07 00:01:13 +0100 <Inst> thanks
2022-01-07 00:02:31 +0100xb0o2(~xb0o2@user/xb0o2)
2022-01-07 00:03:52 +0100deadmarshal(~deadmarsh@95.38.112.110)
2022-01-07 00:03:54 +0100tromp(~textual@dhcp-077-249-230-040.chello.nl) (Quit: My iMac has gone to sleep. ZZZzzz…)
2022-01-07 00:04:25 +0100johnw(~johnw@2607:f6f0:3004:1:c8b4:50ff:fef8:6bf0)
2022-01-07 00:04:53 +0100tromp(~textual@dhcp-077-249-230-040.chello.nl)
2022-01-07 00:05:51 +0100 <Inst> monochrom: more about flexing
2022-01-07 00:06:00 +0100 <dmj`> geekosaur: fclabels didn't need existentials :)
2022-01-07 00:07:14 +0100 <monochrom> What did fclabels need?
2022-01-07 00:07:35 +0100 <Inst> gah, maybe i'll try again later
2022-01-07 00:07:36 +0100 <Inst> too tired
2022-01-07 00:08:14 +0100 <dmj`> monochrom: nothing basically, but chooses to use TypeOperators
2022-01-07 00:14:12 +0100 <[itchyjunk]> myMap :: (a -> b) -> [a] -> [b], does this type signature look okay?
2022-01-07 00:14:31 +0100 <monochrom> Yes.
2022-01-07 00:14:42 +0100 <[itchyjunk]> I don't understand the error I am getting : https://bpa.st/Z42Q
2022-01-07 00:15:24 +0100 <monochrom> Cannot reproduce.
2022-01-07 00:15:38 +0100sonny(~sonny@bras-base-london1483w-grc-32-70-52-175-166.dsl.bell.ca)
2022-01-07 00:16:56 +0100 <geekosaur> I feel like you used parentheses where you weren't supposed to. Show how you're invoking it?
2022-01-07 00:17:15 +0100 <[itchyjunk]> *Main> myMap +1 [1..5]
2022-01-07 00:17:21 +0100 <[itchyjunk]> :x
2022-01-07 00:17:25 +0100 <monochrom> myMap (+ 1) [1..5]
2022-01-07 00:17:26 +0100Vajb(~Vajb@2001:999:50:e6be:1e98:9376:d93e:4506) (Remote host closed the connection)
2022-01-07 00:17:28 +0100 <sonny> section requires parens right?
2022-01-07 00:17:38 +0100 <[itchyjunk]> what's section?
2022-01-07 00:17:42 +0100 <[itchyjunk]> hmm was that the only issue?
2022-01-07 00:17:43 +0100Vajb(~Vajb@2001:999:50:e6be:1e98:9376:d93e:4506)
2022-01-07 00:17:44 +0100 <sonny> +1
2022-01-07 00:17:47 +0100 <monochrom> (+ 1) and (1 +)
2022-01-07 00:17:59 +0100machinedgod(~machinedg@24.105.81.50) (Ping timeout: 256 seconds)
2022-01-07 00:18:01 +0100 <sonny> not sure how to describe it
2022-01-07 00:18:01 +0100 <[itchyjunk]> wow, so the code was right and i used it wrong :<
2022-01-07 00:18:02 +0100 <monochrom> > map (+ 1) [1..5]
2022-01-07 00:18:04 +0100 <lambdabot> [2,3,4,5,6]
2022-01-07 00:18:21 +0100 <sonny> haskell does give you that confident feeling ;)
2022-01-07 00:18:27 +0100chele(~chele@user/chele) (Remote host closed the connection)
2022-01-07 00:18:39 +0100max22-(~maxime@2a01cb0883359800b8731b08b5ca29d9.ipv6.abo.wanadoo.fr) (Quit: Leaving)
2022-01-07 00:18:39 +0100 <geekosaur> a section is a partially applied operator. It requires parentheses to distinguish it from a normal application
2022-01-07 00:18:49 +0100 <geekosaur> so `map + 1` looks like adding 1 to the function map
2022-01-07 00:19:07 +0100 <geekosaur> but `map (+1)` is mapping a partially applied addition operator
2022-01-07 00:20:19 +0100 <geekosaur> (spaces are not relevant here)
2022-01-07 00:20:31 +0100 <geekosaur> :t map +1
2022-01-07 00:20:32 +0100 <lambdabot> Num ((a -> b) -> [a] -> [b]) => (a -> b) -> [a] -> [b]
2022-01-07 00:20:53 +0100 <geekosaur> not the weird constraint
2022-01-07 00:20:56 +0100 <geekosaur> *note
2022-01-07 00:21:11 +0100Morrow(~user@bzq-110-168-31-106.red.bezeqint.net)
2022-01-07 00:21:19 +0100 <[itchyjunk]> ah
2022-01-07 00:22:05 +0100 <sonny> [itchyjunk] what's =>
2022-01-07 00:23:14 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com)
2022-01-07 00:23:14 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com) (Changing host)
2022-01-07 00:23:14 +0100wroathe(~wroathe@user/wroathe)
2022-01-07 00:24:13 +0100deadmarshal(~deadmarsh@95.38.112.110) (Ping timeout: 256 seconds)
2022-01-07 00:24:53 +0100 <[itchyjunk]> in the type signatuer? i haven't learned the constraint stuff yet xD
2022-01-07 00:25:14 +0100 <[itchyjunk]> you can apply constraints to the function with it
2022-01-07 00:25:19 +0100 <[itchyjunk]> i think
2022-01-07 00:25:46 +0100 <geekosaur> in this case it would be asserting that the type of `map` must have a Num instance (which it doesn't, being a function)
2022-01-07 00:25:47 +0100 <Heffalump[m]> A simpler example of something with a constraint is
2022-01-07 00:25:47 +0100 <Heffalump[m]> (+) :: Num a => a -> a -> a
2022-01-07 00:26:14 +0100 <Heffalump[m]> which just says "+" works on any type that happens to be an instance of the Num class.
2022-01-07 00:26:18 +0100 <geekosaur> Haskell will happily let you do that right up until you try to use it and it discovers there is no Num instance for that type
2022-01-07 00:26:38 +0100 <[itchyjunk]> ah
2022-01-07 00:27:11 +0100 <geekosaur> anyway, Num is what lets us treat Int, Integer, Float, and Double (and some others) the same way instead of having to have separate addition and multiplication operators for each
2022-01-07 00:27:13 +0100 <sonny> ok, so Num is the typeclass?
2022-01-07 00:27:32 +0100polyphem_(~rod@2a02:810d:640:776c:e450:3ca3:b389:687a)
2022-01-07 00:27:40 +0100 <geekosaur> SML used to require a different addition operator for floats and doubles, which was pretty icky
2022-01-07 00:27:53 +0100 <sonny> yeah, that's really strict
2022-01-07 00:27:55 +0100Morrow(~user@bzq-110-168-31-106.red.bezeqint.net) (Quit: leaving)
2022-01-07 00:27:59 +0100 <geekosaur> `1 + 2`, but `1.0 +. 2.0`
2022-01-07 00:28:44 +0100polyphem(~rod@2a02:810d:640:776c:e450:3ca3:b389:687a) (Ping timeout: 252 seconds)
2022-01-07 00:29:12 +0100merijn(~merijn@83-160-49-249.ip.xs4all.nl)
2022-01-07 00:29:15 +0100 <[itchyjunk]> Num is an interface iirc
2022-01-07 00:29:38 +0100 <geekosaur> not quite, but somewhat close
2022-01-07 00:30:03 +0100 <[itchyjunk]> I am still stuck with keeping a counter through recursion
2022-01-07 00:30:08 +0100gehmehgeh(~user@user/gehmehgeh) (Quit: Leaving)
2022-01-07 00:30:15 +0100 <monochrom> Don't keep a counter.
2022-01-07 00:30:27 +0100 <[itchyjunk]> i wany a myTupels :: [a] -> [(Int,a)] where the int represents the position of each element
2022-01-07 00:30:54 +0100 <Heffalump[m]> this is a standard idiom: zip [1..] xs
2022-01-07 00:30:55 +0100 <geekosaur> think about it differently
2022-01-07 00:30:57 +0100 <sonny> monochrom it's the accumulator
2022-01-07 00:30:59 +0100 <monochrom> Oh OK, keep a counter.
2022-01-07 00:31:18 +0100 <[itchyjunk]> hmm i'll try thinking about it differently
2022-01-07 00:31:48 +0100 <[itchyjunk]> i was thinking : myTuples (x:xs) = (count,x) : myTuples xs might work if i could keep track of count but i'd have to pass that around which isn't ideal
2022-01-07 00:31:53 +0100Midjak(~Midjak@may53-1-78-226-116-92.fbx.proxad.net) (Quit: This computer has gone to sleep)
2022-01-07 00:32:34 +0100 <monochrom> If you know how to achieve "f n = [n, n+1, n+2, ...]", it is the same idea.
2022-01-07 00:32:55 +0100 <[itchyjunk]> hmm, idk if i do. guess i'll do that first
2022-01-07 00:33:04 +0100 <[itchyjunk]> oh wait
2022-01-07 00:33:06 +0100 <monochrom> You will have to "pass that around".
2022-01-07 00:34:03 +0100 <geekosaur> there's an idiom for that too. foo xs = go 0 xs where go cnt [] = ...; go cnt (x:xs) = ...
2022-01-07 00:34:34 +0100 <geekosaur> and on recursion you add 1 to the cnt you pass to the recursive call
2022-01-07 00:34:59 +0100werneta(~werneta@70-142-214-115.lightspeed.irvnca.sbcglobal.net) (Ping timeout: 256 seconds)
2022-01-07 00:35:35 +0100Morrow(~user@bzq-110-168-31-106.red.bezeqint.net)
2022-01-07 00:35:39 +0100 <[itchyjunk]> hmm f :: Int -> [Int]
2022-01-07 00:35:40 +0100Morrow(~user@bzq-110-168-31-106.red.bezeqint.net) (Client Quit)
2022-01-07 00:35:50 +0100 <[itchyjunk]> f x = x : f (x+1), i thought this might work.
2022-01-07 00:35:57 +0100Morrow(~user@bzq-110-168-31-106.red.bezeqint.net)
2022-01-07 00:36:15 +0100 <geekosaur> it might, depending on what you intend "work" to be
2022-01-07 00:36:34 +0100 <[itchyjunk]> <interactive>:16:1: error: Variable not in scope: f :: Integer -> t
2022-01-07 00:36:36 +0100 <geekosaur> > let f x = x : f (x+1) in take 5 (f 4)
2022-01-07 00:36:37 +0100 <lambdabot> [4,5,6,7,8]
2022-01-07 00:36:44 +0100epolanski(uid312403@id-312403.helmsley.irccloud.com) (Quit: Connection closed for inactivity)
2022-01-07 00:36:50 +0100werneta(~werneta@70-142-214-115.lightspeed.irvnca.sbcglobal.net)
2022-01-07 00:37:31 +0100 <geekosaur> show what you actually did to get that error
2022-01-07 00:37:59 +0100bitdex(~bitdex@gateway/tor-sasl/bitdex)
2022-01-07 00:38:20 +0100 <[itchyjunk]> https://bpa.st/WPWQ
2022-01-07 00:38:47 +0100 <geekosaur> you're being bitten by ghci
2022-01-07 00:38:54 +0100 <[itchyjunk]> hmm
2022-01-07 00:39:01 +0100 <geekosaur> you need to enter the type signature and the function on the same line, with a semicolon between them
2022-01-07 00:39:15 +0100 <geekosaur> ghci can't tell you're going to enter the actual function next
2022-01-07 00:39:25 +0100 <[itchyjunk]> ah let me do it in a file as always
2022-01-07 00:39:34 +0100 <Axman6> or you can use :{ to start a multi line definition and :} to close it
2022-01-07 00:39:41 +0100 <[itchyjunk]> argh infinite list, it works
2022-01-07 00:39:47 +0100 <Axman6> :{
2022-01-07 00:39:53 +0100 <Axman6> f :: Int -> [Int]
2022-01-07 00:40:01 +0100 <monochrom> Ugh no, "f :: Int -> [Int]" leads to an error message that says "Int" not "Integer" nor "t".
2022-01-07 00:40:03 +0100 <Axman6> f x = x : f (x+1)
2022-01-07 00:40:05 +0100 <Axman6> :}
2022-01-07 00:40:25 +0100 <monochrom> "f x = x : f (x+1)" does not lead to any error message.
2022-01-07 00:40:37 +0100 <monochrom> "f 0" under that does not lead to any error message either.
2022-01-07 00:40:43 +0100 <monochrom> So, again, cannot reproduce.
2022-01-07 00:40:49 +0100 <[itchyjunk]> Yes it's fixed now
2022-01-07 00:41:51 +0100 <[itchyjunk]> so back to :: [a] ->[(Int,a)] problem. for the f :: Int -> [Int] , i passed an int to the function which it was incrimenting
2022-01-07 00:42:19 +0100 <monochrom> So make a helper function that has the extra Int parameter.
2022-01-07 00:42:21 +0100 <[itchyjunk]> but for mine, i am only passing it some list, it would have to start with some var and add 1 to it each time or somesuc
2022-01-07 00:42:37 +0100 <geekosaur> I showed an example of how we do that earlier
2022-01-07 00:42:47 +0100 <geekosaur> [06 23:34:03] <geekosaur> there's an idiom for that too. foo xs = go 0 xs where go cnt [] = ...; go cnt (x:xs) = ...
2022-01-07 00:42:54 +0100bitdex(~bitdex@gateway/tor-sasl/bitdex) (Ping timeout: 276 seconds)
2022-01-07 00:43:42 +0100 <[itchyjunk]> hmmmm
2022-01-07 00:43:57 +0100 <geekosaur> `go` is a helper function, as monochrom said
2022-01-07 00:44:16 +0100 <geekosaur> since it's defined in a where clause, there's no particular reason to give it a fancy name
2022-01-07 00:44:57 +0100shapr(~user@2601:7c0:c202:5190:e39f:2980:57ec:6939) (Ping timeout: 240 seconds)
2022-01-07 00:45:26 +0100 <Axman6> what as this function supposed to do [itchyjunk]?
2022-01-07 00:46:02 +0100 <Axman6> given [1,1,1,2,2,3], what should I get back?
2022-01-07 00:46:21 +0100 <Axman6> are we doing run length encoding? just ziping indices?
2022-01-07 00:46:41 +0100 <[itchyjunk]> [(0,1), (1,1), (2,1), (3,2), (4,2), (5,3)]
2022-01-07 00:47:17 +0100 <[itchyjunk]> I am trying to work my way up to problem 2 here :
2022-01-07 00:47:18 +0100 <[itchyjunk]> http://www.cas.mcmaster.ca/~dalvescb/LH_Week05_Exercises.pdf
2022-01-07 00:47:28 +0100 <Axman6> ok, then the suggestion of writing a worker (go) and a wrapper is a good idea
2022-01-07 00:47:48 +0100 <[itchyjunk]> I am trying to understand the helper go function :x
2022-01-07 00:47:56 +0100_xor(~xor@dsl-50-5-233-169.fuse.net) (Quit: bbiab)
2022-01-07 00:48:23 +0100 <monochrom> go 4 [x,y,z] = [(x,4), (y,5), (z,6)]
2022-01-07 00:48:32 +0100 <[itchyjunk]> ah
2022-01-07 00:48:51 +0100 <[itchyjunk]> i think i get it
2022-01-07 00:48:54 +0100[itchyjunk]tries stuff
2022-01-07 00:49:03 +0100 <Axman6> (or [(4,x),(5,y),(6,z)] with the above type)
2022-01-07 00:49:17 +0100 <monochrom> This is why I grew out of using either words or precise formulas to explain to beginners.
2022-01-07 00:49:40 +0100 <monochrom> The most effective communication is semi-concrete semi-symbolic examples.
2022-01-07 00:49:51 +0100 <monochrom> Such as "map f [x,y,z] = [f x, f y, f z]"
2022-01-07 00:50:06 +0100dsrt^(~dsrt@207.5.21.20) (Read error: Connection reset by peer)
2022-01-07 00:50:19 +0100 <monochrom> As opposed to "it applies f to every element" or writing out the code.
2022-01-07 00:50:24 +0100xb0o2(~xb0o2@user/xb0o2) (Quit: Client closed)
2022-01-07 00:52:05 +0100vicfred(~vicfred@user/vicfred)
2022-01-07 00:52:12 +0100 <monochrom> Well, in the case of "map f", the wording is short enough to be probably understandable by beginners. But you will run into larger cases where the wording is so lengthy, the beginner simply stops reading.
2022-01-07 00:52:19 +0100machinedgod(~machinedg@24.105.81.50)
2022-01-07 00:52:36 +0100 <Axman6> that opne of the reasons I usually ask "what output do you expect for <this> input?"
2022-01-07 00:52:58 +0100 <Axman6> that's one*
2022-01-07 00:52:59 +0100 <[itchyjunk]> This is what my helper ended up looking like
2022-01-07 00:52:59 +0100 <[itchyjunk]> https://bpa.st/CF6Q
2022-01-07 00:53:01 +0100 <[itchyjunk]> seems to work
2022-01-07 00:53:42 +0100 <monochrom> Yeah, like that.
2022-01-07 00:53:46 +0100 <Axman6> Looks pretty good to me
2022-01-07 00:54:50 +0100 <[itchyjunk]> https://bpa.st/HPNA
2022-01-07 00:55:00 +0100 <Axman6> there are other (actually infinite) ways to write that, but this is one of the most clear. There are different ways that Haskellers might prefer to use though, we tend to avoid explicit recursion unless it's necessary
2022-01-07 00:55:02 +0100 <[itchyjunk]> this works /o\. think i am ready to tackle that problem 2 now
2022-01-07 00:55:25 +0100 <[itchyjunk]> hmm what's explicit vs implicit recursion?
2022-01-07 00:55:30 +0100 <[itchyjunk]> Don't think I know the difference
2022-01-07 00:55:30 +0100 <Axman6> usually we would define that `go` function in a where clause of `myTuples`
2022-01-07 00:55:40 +0100 <[itchyjunk]> ah
2022-01-07 00:55:56 +0100 <Axman6> unless it's also useful for other things too
2022-01-07 00:56:28 +0100 <geekosaur> explicit recursion is what you have been writing. implicit recursion is using a function that does the recursion internally, like map or foldr
2022-01-07 00:56:43 +0100 <Axman6> I think for now you can ignore that there are other ways to do what you've done, it's pretty likely you'll start to see some patterns and think "Can I write that pattern once and reuse it?"
2022-01-07 00:59:59 +0100bitdex(~bitdex@gateway/tor-sasl/bitdex)
2022-01-07 01:03:27 +0100merijn(~merijn@83-160-49-249.ip.xs4all.nl) (Ping timeout: 256 seconds)
2022-01-07 01:07:43 +0100tromp(~textual@dhcp-077-249-230-040.chello.nl) (Quit: My iMac has gone to sleep. ZZZzzz…)
2022-01-07 01:07:57 +0100kupi(uid212005@id-212005.hampstead.irccloud.com) (Quit: Connection closed for inactivity)
2022-01-07 01:08:08 +0100 <[itchyjunk]> https://bpa.st/2WEA
2022-01-07 01:08:26 +0100 <[itchyjunk]> Here, i want to apply f to the resulting list after applying myTuples
2022-01-07 01:08:51 +0100 <[itchyjunk]> So apply myTuples to x, take the first element of this list and apply f to it, is how i am thinking
2022-01-07 01:09:19 +0100 <[itchyjunk]> oh wait i see an issue already
2022-01-07 01:09:55 +0100 <Axman6> I have two questions for you: what is the type of `x`? what is the type of `ys`?
2022-01-07 01:10:03 +0100 <[itchyjunk]> Ah, nm. i thought of a different approach
2022-01-07 01:10:16 +0100doyougnu(~doyougnu@c-73-25-202-122.hsd1.or.comcast.net) (Ping timeout: 256 seconds)
2022-01-07 01:10:33 +0100 <[itchyjunk]> x is a list [a], ys is a [(Int,a)] looking list
2022-01-07 01:10:43 +0100 <[itchyjunk]> i think i have an idea though
2022-01-07 01:11:06 +0100 <[itchyjunk]> wait, not i don't xD
2022-01-07 01:11:39 +0100 <Axman6> so you have mapWithIndex f x = f y : mapWithIndex f ys, and based on what you said above, x and ys have different types, yes?
2022-01-07 01:12:35 +0100 <Axman6> have you ever seen a function with the type (a -> b) -> [a] -> [b]?
2022-01-07 01:12:40 +0100 <[itchyjunk]> yes in my code, the ys is giving me the problem
2022-01-07 01:12:51 +0100 <[itchyjunk]> i would need to pass the [a] type instead of ys type there
2022-01-07 01:12:57 +0100pretty_dumm_guy(trottel@gateway/vpn/protonvpn/prettydummguy/x-88029655) (Quit: WeeChat 3.4)
2022-01-07 01:13:04 +0100 <[itchyjunk]> yes i have seem map
2022-01-07 01:13:13 +0100 <[itchyjunk]> i also implementd a myMap with that type earlier
2022-01-07 01:13:31 +0100 <Axman6> do you think you could use it here?
2022-01-07 01:13:45 +0100 <[itchyjunk]> Use map itself?
2022-01-07 01:13:45 +0100 <Axman6> you have a way to turn [a] -> [(Int,a)]
2022-01-07 01:14:03 +0100 <[itchyjunk]> i thought of using map but not sure if that's cheating or not
2022-01-07 01:14:05 +0100 <Axman6> and you have myMap :: (a -> b) -> [a] -> [b] right?
2022-01-07 01:14:17 +0100 <[itchyjunk]> i can map f myTuples(x)
2022-01-07 01:14:18 +0100 <Axman6> if you wrote the code, it's definitely not cheating
2022-01-07 01:14:25 +0100 <Axman6> can you?
2022-01-07 01:14:35 +0100 <[itchyjunk]> hmm
2022-01-07 01:14:58 +0100 <Axman6> also, it's worth pointing out now that we don't call functions like that in HAskell, myTuples(x) means myTuples (x) which is myTuples x
2022-01-07 01:15:10 +0100 <Axman6> to pass x to my tuples, you just use a space
2022-01-07 01:15:44 +0100 <[itchyjunk]> map f (myTuples x)
2022-01-07 01:15:46 +0100 <Axman6> if you need to ensure that is understood as a single expression, you can use (myTuples x)
2022-01-07 01:15:52 +0100 <Axman6> does it work?
2022-01-07 01:16:00 +0100 <[itchyjunk]> i haven't tried, let me try it now
2022-01-07 01:17:27 +0100 <[itchyjunk]> it compiles but idk how to test it @_@
2022-01-07 01:17:39 +0100 <[itchyjunk]> mapWithIndex ? [1..10]
2022-01-07 01:17:53 +0100 <ProfSimm> Actually... why not have mutable local variables/
2022-01-07 01:17:54 +0100 <Axman6> (\(i,x) -> x*i)
2022-01-07 01:18:13 +0100 <Axman6> ProfSimm: what does local mean?
2022-01-07 01:18:46 +0100 <[itchyjunk]> https://bpa.st/YEWA
2022-01-07 01:18:48 +0100 <jackdk> Axman6: inside of a `runST`? `0:-)`
2022-01-07 01:18:53 +0100 <ProfSimm> Axman6: that's a good question
2022-01-07 01:18:54 +0100 <[itchyjunk]> I don't think i understand the problem statement very well :(
2022-01-07 01:19:00 +0100 <Axman6> ssshhh, we're getting there :P
2022-01-07 01:19:08 +0100 <[itchyjunk]> i think i have a solution but idk how to test it
2022-01-07 01:19:23 +0100 <Axman6> [itchyjunk]: I gave you a function above to use for ?
2022-01-07 01:19:36 +0100 <[itchyjunk]> oh
2022-01-07 01:19:50 +0100 <jackdk> [itchyjunk]: use ghci? Also the equation at line 18 is redundant, as `myMap` handles empty lists
2022-01-07 01:20:04 +0100 <Axman6> what result do you expect to get for mapWithIndex (\(i,x) -> x*i) [1..10]?
2022-01-07 01:20:51 +0100 <[itchyjunk]> [0,2,6,..]
2022-01-07 01:20:58 +0100wyrd(~wyrd@gateway/tor-sasl/wyrd) (Quit: Lost terminal)
2022-01-07 01:21:03 +0100 <[itchyjunk]> 90 as the last element
2022-01-07 01:21:57 +0100 <[itchyjunk]> ah, right i guess the [] handeling is redundent
2022-01-07 01:22:05 +0100 <[itchyjunk]> Axman6, i get what i expect
2022-01-07 01:22:13 +0100 <[itchyjunk]> [0,2,6,12,20,30,42,56,72,90]
2022-01-07 01:22:17 +0100 <Square> I had a File.hs with instances a,b,c of verbose instances over data types. I found i could generate "a" and "b" of these instances with TH. So i add a $(buildMyInstances ..) to same file. But now i got dependency issues as "a" and "b" depends on "c" and "c" depends on "a".
2022-01-07 01:22:49 +0100 <Square> I had a File.hs with verbose instances a,b,c. *
2022-01-07 01:23:26 +0100 <[itchyjunk]> guess my solution works \o/
2022-01-07 01:23:41 +0100 <Square> is there some trick to enjoy some 2-pass compilation even with TH generation?
2022-01-07 01:24:43 +0100 <Axman6> ProfSimm: it turns out that you can do what you're asking for, but it's not a straight forward as you might expect. laziness makes this particularly difficult
2022-01-07 01:24:49 +0100wyrd(~wyrd@gateway/tor-sasl/wyrd)
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2022-01-07 01:26:34 +0100 <Axman6> Square: with TH, the order of definitions matters - that looks like it might not be possible if there's a cyclic dep though. can you do all the definitions in TH in the same spot?
2022-01-07 01:27:22 +0100 <Square> Axman6, im afraid not. I guess i need to change plan
2022-01-07 01:31:00 +0100 <jackdk> It may be possible to mix TH and .hs-boot files, but that's for a braver soul than I
2022-01-07 01:33:37 +0100merijn(~merijn@83-160-49-249.ip.xs4all.nl)
2022-01-07 01:34:36 +0100deadmarshal(~deadmarsh@95.38.112.110)
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2022-01-07 01:45:21 +0100 <dmj`> monochrom: can't a free monad library be written w/o existentials though
2022-01-07 01:46:07 +0100 <Axman6> or without an existential crisis?
2022-01-07 01:46:13 +0100 <Axman6> Seems hard
2022-01-07 01:46:48 +0100sonny(~sonny@bras-base-london1483w-grc-32-70-52-175-166.dsl.bell.ca) ()
2022-01-07 01:47:18 +0100TonyStone(~TonyStone@cpe-74-76-51-197.nycap.res.rr.com) (Remote host closed the connection)
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2022-01-07 01:52:51 +0100 <ProfSimm> Axman6: I was thinking what if we could reuse names by basically internally appending counts to them (so if I declare X three times internally it's X1, X2, X3)
2022-01-07 01:53:04 +0100 <ProfSimm> Axman6: but it becomes weird in some cases
2022-01-07 01:55:35 +0100TonyStone(~TonyStone@2603-7080-8607-c36a-9cdb-69bc-753b-1e50.res6.spectrum.com)
2022-01-07 01:57:36 +0100ProfSimm(~ProfSimm@87.227.196.109) (Remote host closed the connection)
2022-01-07 01:57:46 +0100 <Axman6> you might want to look a the ST monad, it gives you genuine mutatable variables in a way that guarantees that things are pure from the outside
2022-01-07 01:58:13 +0100 <geekosaur> they just quit
2022-01-07 01:59:13 +0100ouestbillie(~gallup@192-222-138-215.qc.cable.ebox.net) (Remote host closed the connection)
2022-01-07 01:59:49 +0100 <EvanR> does the word concatenate imply joining two things with discrete pieces, like a string or list
2022-01-07 02:00:24 +0100 <EvanR> or does it work for solids, shapes
2022-01-07 02:01:08 +0100 <geekosaur> I think for those you need to say how you;re combining them
2022-01-07 02:04:12 +0100mvk(~mvk@2607:fea8:5cdd:f000::45db)
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2022-01-07 02:22:33 +0100 <sonny> [itchyjunk] how is this function used?
2022-01-07 02:23:37 +0100cosimone(~user@2001:b07:ae5:db26:c24a:d20:4d91:1e20)
2022-01-07 02:24:03 +0100 <sonny> seems like it's just to transform a single element in the list
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2022-01-07 02:30:44 +0100wyrd_(~wyrd@gateway/tor-sasl/wyrd)
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2022-01-07 02:34:55 +0100 <sonny> can you list a lambda function parameters in a definition?
2022-01-07 02:35:17 +0100wyrd(~wyrd@gateway/tor-sasl/wyrd)
2022-01-07 02:37:28 +0100 <dmj`> sonny: what would that look like
2022-01-07 02:38:24 +0100 <sonny> mapWithIndex \((idx, elem)) lst = ...
2022-01-07 02:38:48 +0100 <EvanR> what on earth
2022-01-07 02:39:29 +0100 <[itchyjunk]> sonny, idk how it's used
2022-01-07 02:39:38 +0100 <[itchyjunk]> sonny, the one gives to me here to test was
2022-01-07 02:39:44 +0100 <sonny> not sure how else to interpret "mapWithIndex is just like map, however it takes a function that takes a tuple with the corresponding index of the element in list"
2022-01-07 02:40:02 +0100 <[itchyjunk]> <Axman6> what result do you expect to get for mapWithIndex (\(i,x) -> x*i) [1..10]?
2022-01-07 02:40:59 +0100 <sonny> [1..i..10] -> [1..i*x..10]
2022-01-07 02:41:18 +0100 <[itchyjunk]> hmm?
2022-01-07 02:41:45 +0100 <[itchyjunk]> [0,2,6,12,20,30,42,56,72,90]
2022-01-07 02:41:47 +0100 <sonny> I think it just gives you a new list with the element at position i updated
2022-01-07 02:41:48 +0100 <[itchyjunk]> this is the result
2022-01-07 02:42:07 +0100 <[itchyjunk]> did you end up writing the function in problem 2?
2022-01-07 02:42:14 +0100 <sonny> that's just map ...
2022-01-07 02:42:22 +0100 <sonny> I am trying to understand problem 2 now
2022-01-07 02:42:46 +0100 <dmj`> sonny: what is the type of elem
2022-01-07 02:42:51 +0100 <[itchyjunk]> how is it map? map :: (a->b)-> [a] -> [b]
2022-01-07 02:43:07 +0100 <[itchyjunk]> this one is ((Int,a) -> b) -> [a] -> [b]
2022-01-07 02:43:17 +0100Inst(~delicacie@c-98-208-218-119.hsd1.fl.comcast.net) (Ping timeout: 240 seconds)
2022-01-07 02:43:17 +0100 <[itchyjunk]> so not quite map
2022-01-07 02:43:18 +0100 <sonny> dmj`: `((Int,a) -> b) -> [a] -> [b]`
2022-01-07 02:44:37 +0100 <sonny> oh ok
2022-01-07 02:44:38 +0100 <EvanR> mapWithIndex devolves into map if you choose not to use the Int
2022-01-07 02:44:57 +0100 <sonny> I think I sorta get what it's asking
2022-01-07 02:45:40 +0100vysn(~vysn@user/vysn)
2022-01-07 02:45:54 +0100jakalx(~jakalx@base.jakalx.net) (Error from remote client)
2022-01-07 02:46:18 +0100 <sonny> nvm, I'm super confused
2022-01-07 02:46:22 +0100 <[itchyjunk]> sonny, did you mean this is a higher order function?
2022-01-07 02:46:26 +0100jakalx(~jakalx@base.jakalx.net)
2022-01-07 02:46:36 +0100 <[itchyjunk]> sonny, i used map as a solution in mine. i wrote my own map and used it
2022-01-07 02:46:46 +0100 <[itchyjunk]> i helped me understand things better
2022-01-07 02:47:02 +0100 <sonny> higher order function?
2022-01-07 02:47:40 +0100 <[itchyjunk]> isn't that what it's called? map take in function as an input so we call it higher order function right?
2022-01-07 02:47:49 +0100 <sonny> nah
2022-01-07 02:47:51 +0100 <[itchyjunk]> not sure if i am remembering things properly anymore xD
2022-01-07 02:47:54 +0100 <sonny> it's just a function
2022-01-07 02:48:08 +0100 <sonny> unless there is some math terminology
2022-01-07 02:48:18 +0100 <[itchyjunk]> think i was learning map because it was higher order function
2022-01-07 02:48:23 +0100 <[itchyjunk]> math calls it functionals i think
2022-01-07 02:48:30 +0100 <[itchyjunk]> programming calls it higher order functions?
2022-01-07 02:48:37 +0100 <[itchyjunk]> like (\x.xx) (\x.xx)
2022-01-07 02:48:40 +0100 <sonny> no?
2022-01-07 02:49:20 +0100 <[itchyjunk]> https://en.wikipedia.org/wiki/Higher-order_function
2022-01-07 02:49:25 +0100 <sonny> well, I'm probably not the one to ask
2022-01-07 02:49:26 +0100Gurkenglas(~Gurkengla@dslb-002-203-144-204.002.203.pools.vodafone-ip.de) (Ping timeout: 256 seconds)
2022-01-07 02:49:45 +0100 <sonny> but yeah I don't get what mapWithIndex is supposed to do
2022-01-07 02:49:56 +0100 <[itchyjunk]> it takes 2 parameter
2022-01-07 02:49:59 +0100 <[itchyjunk]> a function and a list
2022-01-07 02:50:01 +0100 <[itchyjunk]> and returns a list
2022-01-07 02:50:07 +0100 <[itchyjunk]> its a higher order function
2022-01-07 02:50:16 +0100 <[itchyjunk]> similar to map
2022-01-07 02:50:21 +0100 <sonny> ok
2022-01-07 02:50:35 +0100 <[itchyjunk]> thats why i reimplremented map
2022-01-07 02:50:48 +0100 <[itchyjunk]> to understand a function that can take a function as parameter
2022-01-07 02:50:52 +0100 <sonny> yeah I don't get what's different
2022-01-07 02:51:20 +0100 <[itchyjunk]> (a -> b) -> [a] -> [b], (a->b) is a function
2022-01-07 02:51:38 +0100 <sonny> yes
2022-01-07 02:51:54 +0100 <EvanR> [itchyjunk], yes, in the old days higher order functions would be this awesome thing
2022-01-07 02:52:04 +0100 <EvanR> by I mean, javascript can do it, not that special
2022-01-07 02:52:07 +0100 <EvanR> but*
2022-01-07 02:52:22 +0100 <EvanR> I mean, C kind of does it
2022-01-07 02:52:30 +0100 <EvanR> pointer to function
2022-01-07 02:52:33 +0100 <[itchyjunk]> i saw it in table of contents of a haskell book so i figured its one of those things that you have to learn
2022-01-07 02:52:42 +0100 <sonny> {(a->b) -> [a]} -> [b]
2022-01-07 02:52:48 +0100 <[itchyjunk]> i don't have the attention to read a book so making due with table of contents xD
2022-01-07 02:53:01 +0100 <[itchyjunk]> sonny, idk what that is
2022-01-07 02:53:01 +0100 <EvanR> map :: (a -> b) -> ([a] -> [b])
2022-01-07 02:53:10 +0100 <sonny> that nomenclature might be subject to debate
2022-01-07 02:53:37 +0100 <EvanR> sonny, mapWithIndex just passes the current index along with the value
2022-01-07 02:53:50 +0100 <sonny> [itchyjunk] I was trying to show the order
2022-01-07 02:54:11 +0100 <EvanR> {(a -> b) -> [a]} -> [b] doesn't look right at all
2022-01-07 02:54:15 +0100 <[itchyjunk]> its right associative so it would be (a -> b) -> ([a] -> [b]) i think
2022-01-07 02:54:21 +0100 <sonny> oh
2022-01-07 02:54:24 +0100 <[itchyjunk]> you're doing left associativity for some reason?
2022-01-07 02:54:30 +0100 <sonny> yeah lol
2022-01-07 02:54:36 +0100 <sonny> mistake
2022-01-07 02:54:51 +0100 <EvanR> map has 2 args, if you pass just 1, you are left with [a] -> [b], 1 arg to go
2022-01-07 02:55:24 +0100 <[itchyjunk]> sonny, i make like 6 mini problems and solved it to solve that problem 2
2022-01-07 02:55:26 +0100 <[itchyjunk]> https://bpa.st/YEWA
2022-01-07 02:55:43 +0100 <[itchyjunk]> each of the function i wrote there, i thought of a mini problem to solve
2022-01-07 02:56:31 +0100 <sonny> EvanR ok, so I just need to make sure that I have the current index?
2022-01-07 02:56:39 +0100 <sonny> otherwise it's the same?
2022-01-07 02:56:48 +0100 <EvanR> I don't know what the actual question is, sorry
2022-01-07 02:56:56 +0100 <sonny> one sec
2022-01-07 02:57:04 +0100 <[itchyjunk]> http://www.cas.mcmaster.ca/~dalvescb/LH_Week05_Exercises.pdf
2022-01-07 02:57:07 +0100 <[itchyjunk]> problem 2) there
2022-01-07 02:57:30 +0100 <EvanR> implement mapWithIndex
2022-01-07 02:57:51 +0100 <EvanR> we've all be repeating the requirements for this function, we're all in agreement, so great xD
2022-01-07 02:58:02 +0100 <EvanR> been*
2022-01-07 02:58:58 +0100sonnyscratches head
2022-01-07 02:59:25 +0100 <[itchyjunk]> :D
2022-01-07 02:59:28 +0100 <EvanR> 1. understand the question 3. write down the solution
2022-01-07 02:59:31 +0100 <EvanR> step 2 is overrated
2022-01-07 02:59:45 +0100 <[itchyjunk]> step 1 is really hard
2022-01-07 02:59:48 +0100 <EvanR> ^
2022-01-07 03:03:37 +0100Morrow(~user@bzq-110-168-31-106.red.bezeqint.net) (Remote host closed the connection)
2022-01-07 03:07:12 +0100Morrow(~user@bzq-110-168-31-106.red.bezeqint.net)
2022-01-07 03:10:00 +0100 <EvanR> >write a quickCheck property to test both simultaneously (i.e check one in terms of the other)
2022-01-07 03:10:15 +0100 <EvanR> does that really succeed in testing both simultaneously
2022-01-07 03:11:01 +0100n8chan(~nate@108-233-125-227.lightspeed.sntcca.sbcglobal.net) (Ping timeout: 240 seconds)
2022-01-07 03:11:27 +0100spdr(~bc8147f2@cerf.good1.com)
2022-01-07 03:12:24 +0100ubert1(~Thunderbi@p200300ecdf09947d3ce845fd45b74154.dip0.t-ipconnect.de)
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2022-01-07 03:13:39 +0100n8chan(~nate@108-233-125-227.lightspeed.sntcca.sbcglobal.net)
2022-01-07 03:14:10 +0100 <jackdk> it's a test that exercises both at once
2022-01-07 03:14:10 +0100 <[itchyjunk]> is that like unit tests?
2022-01-07 03:14:37 +0100Morrow(~user@bzq-110-168-31-106.red.bezeqint.net) (Ping timeout: 240 seconds)
2022-01-07 03:14:45 +0100 <EvanR> yeah... though both could be wrong in such a way that cancels out... two wrongs make a right xD
2022-01-07 03:15:12 +0100 <EvanR> oh now I see where they are going with it
2022-01-07 03:15:33 +0100 <EvanR> "who cares as long as *the property* is satisfied"
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2022-01-07 04:33:39 +0100EvanR(~EvanR@user/evanr) (Quit: Leaving)
2022-01-07 04:34:31 +0100EvanR(~EvanR@user/evanr)
2022-01-07 04:34:58 +0100arjun(~arjun@user/arjun)
2022-01-07 04:36:19 +0100Guest32(~Guest32@115.98.235.146)
2022-01-07 04:37:47 +0100 <Guest32> hi.. I need to sum all digits of a number till I arrive at a single digit eg 29 = 2+9 =11 =1+1 =2
2022-01-07 04:37:56 +0100 <Guest32> how to I do it?
2022-01-07 04:38:41 +0100 <Guest32> I have created a function which splits the numbers into a list
2022-01-07 04:38:44 +0100 <Guest32> toDigits x
2022-01-07 04:38:44 +0100 <Guest32>   | x < 1 = []
2022-01-07 04:38:45 +0100 <Guest32>   | otherwise = toDigits (div x 10) ++ [mod x 10]
2022-01-07 04:38:59 +0100 <EvanR> nice, see also divMod
2022-01-07 04:39:13 +0100Maxdamantus(~Maxdamant@user/maxdamantus) (Ping timeout: 256 seconds)
2022-01-07 04:39:15 +0100 <EvanR> > divMod 25 7
2022-01-07 04:39:16 +0100 <lambdabot> (3,4)
2022-01-07 04:39:46 +0100 <int-e> > divmod (3^2 + 4^2) (3 + 4)
2022-01-07 04:39:47 +0100 <lambdabot> error:
2022-01-07 04:39:47 +0100 <lambdabot> • Variable not in scope: divmod :: t0 -> t1 -> t
2022-01-07 04:39:47 +0100 <lambdabot> • Perhaps you meant one of these:
2022-01-07 04:39:55 +0100 <int-e> > divMod (3^2 + 4^2) (3 + 4)
2022-01-07 04:39:56 +0100 <lambdabot> (3,4)
2022-01-07 04:40:12 +0100Inst(~delicacie@c-98-208-218-119.hsd1.fl.comcast.net)
2022-01-07 04:41:14 +0100 <Guest32> divMod 23
2022-01-07 04:41:22 +0100 <Guest32> >divMod 23
2022-01-07 04:41:23 +0100 <EvanR> :t divMod 23
2022-01-07 04:41:24 +0100 <lambdabot> Integral a => a -> (a, a)
2022-01-07 04:41:40 +0100 <Guest32> :t divMod 23
2022-01-07 04:41:41 +0100 <lambdabot> Integral a => a -> (a, a)
2022-01-07 04:44:15 +0100 <EvanR> > echo
2022-01-07 04:44:16 +0100 <lambdabot> echo
2022-01-07 04:44:27 +0100 <Guest32> @Evanr how do I get to a single digit?
2022-01-07 04:44:27 +0100 <lambdabot> Unknown command, try @list
2022-01-07 04:45:12 +0100 <EvanR> you want to just sum all the digits?
2022-01-07 04:45:18 +0100 <EvanR> or all but the last digit
2022-01-07 04:45:34 +0100 <EvanR> or just take the last digit
2022-01-07 04:45:51 +0100shapr(~user@2601:7c0:c202:5190:f139:f199:c0b7:ebd5) (Remote host closed the connection)
2022-01-07 04:46:06 +0100 <Guest32> all digits
2022-01-07 04:46:14 +0100 <Guest32> till the total gets to one digit
2022-01-07 04:46:19 +0100 <EvanR> > sum [1,2,3,4,5]
2022-01-07 04:46:21 +0100 <lambdabot> 15
2022-01-07 04:46:36 +0100 <EvanR> > sum (init [1,2,3,4])
2022-01-07 04:46:37 +0100 <lambdabot> 6
2022-01-07 04:46:44 +0100 <EvanR> > last [1,2,3,4,5]
2022-01-07 04:46:45 +0100 <lambdabot> 5
2022-01-07 04:47:09 +0100td_(~td@94.134.91.33) (Ping timeout: 256 seconds)
2022-01-07 04:47:52 +0100Maxdamantus(~Maxdamant@user/maxdamantus)
2022-01-07 04:47:52 +0100 <Guest32> > sum divMod 29
2022-01-07 04:47:54 +0100 <lambdabot> error:
2022-01-07 04:47:54 +0100 <lambdabot> • No instance for (Foldable ((->) Integer))
2022-01-07 04:47:54 +0100 <lambdabot> arising from a use of ‘e_129’
2022-01-07 04:48:08 +0100 <Guest32> divMod 29
2022-01-07 04:48:21 +0100 <EvanR> divMod takes a divisor and a dividend, two arguments
2022-01-07 04:48:21 +0100 <Guest32> > divMod 29
2022-01-07 04:48:23 +0100 <lambdabot> <Integer -> (Integer,Integer)>
2022-01-07 04:48:39 +0100 <EvanR> er, dividend, and divisor
2022-01-07 04:48:44 +0100 <jackdk> whoa, functions with a show instance?
2022-01-07 04:48:47 +0100td_(~td@94.134.91.64)
2022-01-07 04:49:04 +0100 <Guest32> ok
2022-01-07 04:49:14 +0100 <Guest32> > divMod 29 10
2022-01-07 04:49:16 +0100 <lambdabot> (2,9)
2022-01-07 04:49:30 +0100 <Guest32> > sum divMod 29 10
2022-01-07 04:49:32 +0100 <lambdabot> error:
2022-01-07 04:49:32 +0100 <lambdabot> • Couldn't match type ‘(t0, t0)’ with ‘t1 -> t’
2022-01-07 04:49:32 +0100 <lambdabot> Expected type: t0 -> t0 -> t1 -> t
2022-01-07 04:49:41 +0100 <Guest32> > sum (divMod 29 10)
2022-01-07 04:49:43 +0100 <lambdabot> 9
2022-01-07 04:50:07 +0100 <EvanR> \o/
2022-01-07 04:50:19 +0100 <Guest32> shouldn't this be giving 11?
2022-01-07 04:50:35 +0100 <EvanR> divMod doesn't give digits
2022-01-07 04:51:09 +0100 <EvanR> but it does the two things you did to get digits
2022-01-07 04:52:29 +0100 <Guest32> ok
2022-01-07 04:57:39 +0100sirlensalot(~sirlensal@ool-44c5f8c9.dyn.optonline.net) (Quit: sirlensalot)
2022-01-07 04:58:37 +0100waleee(~waleee@2001:9b0:21d:fc00:398f:b003:b90d:acf4) (Ping timeout: 240 seconds)
2022-01-07 05:00:01 +0100haasn(~nand@haasn.dev) (Quit: ZNC 1.7.5+deb4 - https://znc.in)
2022-01-07 05:01:22 +0100haasn(~nand@haasn.dev)
2022-01-07 05:02:15 +0100Guest32(~Guest32@115.98.235.146) (Quit: Client closed)
2022-01-07 05:04:43 +0100shapr(~user@2601:7c0:c202:5190:ca94:a895:80bc:42cf)
2022-01-07 05:11:11 +0100abarbu(~user@c-66-31-23-28.hsd1.ma.comcast.net)
2022-01-07 05:19:29 +0100[_](~itchyjunk@user/itchyjunk/x-7353470)
2022-01-07 05:20:05 +0100[itchyjunk]Guest2700
2022-01-07 05:26:39 +0100mbuf(~Shakthi@122.178.240.232)
2022-01-07 05:27:57 +0100 <abarbu> How can I avoid type variables leaking out of this code?
2022-01-07 05:27:58 +0100 <abarbu> I want a phantom that is True if any two other variables are True.
2022-01-07 05:27:58 +0100 <abarbu> type family Or (a :: Bool) (b :: Bool) :: Bool where
2022-01-07 05:28:01 +0100 <abarbu> Or True a = True
2022-01-07 05:28:04 +0100 <abarbu> Or a True = True
2022-01-07 05:28:07 +0100 <abarbu> Or False False = False
2022-01-07 05:28:09 +0100 <abarbu> one :: Proxy a
2022-01-07 05:28:12 +0100 <abarbu> one = undefined
2022-01-07 05:28:15 +0100 <abarbu> combine :: Proxy a -> Proxy b -> Proxy (Or a b)
2022-01-07 05:28:18 +0100 <abarbu> combine _ _ = undefined
2022-01-07 05:28:22 +0100 <abarbu> fn = combine one one
2022-01-07 05:28:28 +0100 <abarbu> The type of fn comes out to be fn :: D (GOr a b)
2022-01-07 05:28:31 +0100 <abarbu> Everything works, but the more you use this code, the more it leaks out strangely-named type variables in trees of Or whose structure depends on the internals of the code. Seems like a very poor API. How can I avoid this leakage?
2022-01-07 05:28:34 +0100 <abarbu> Is there some other way to approach this problem?
2022-01-07 05:31:04 +0100deadmarshal(~deadmarsh@95.38.112.110)
2022-01-07 05:37:25 +0100arjun(~arjun@user/arjun) (Quit: Leaving)
2022-01-07 05:41:33 +0100wroathe(~wroathe@user/wroathe) (Ping timeout: 256 seconds)
2022-01-07 05:42:07 +0100bontaq(~user@ool-45779fe5.dyn.optonline.net) (Ping timeout: 256 seconds)
2022-01-07 05:48:32 +0100cyphase(~cyphase@user/cyphase) (Ping timeout: 240 seconds)
2022-01-07 05:56:58 +0100 <Axman6> @where paste
2022-01-07 05:56:58 +0100 <lambdabot> Help us help you: please paste full code, input and/or output at e.g. https://paste.tomsmeding.com
2022-01-07 05:57:53 +0100sonny(~sonny@bras-base-london1483w-grc-32-70-52-175-166.dsl.bell.ca) (Closing Window)
2022-01-07 06:00:03 +0100tromp(~textual@dhcp-077-249-230-040.chello.nl)
2022-01-07 06:01:46 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com)
2022-01-07 06:01:46 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com) (Changing host)
2022-01-07 06:01:46 +0100wroathe(~wroathe@user/wroathe)
2022-01-07 06:04:58 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 06:07:03 +0100wroathe(~wroathe@user/wroathe) (Ping timeout: 256 seconds)
2022-01-07 06:13:46 +0100tromp(~textual@dhcp-077-249-230-040.chello.nl) (Quit: My iMac has gone to sleep. ZZZzzz…)
2022-01-07 06:16:05 +0100jiribenes(~jiribenes@rosa.jiribenes.com) (Remote host closed the connection)
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2022-01-07 06:32:50 +0100Jing(~hedgehog@2604:a840:3::103c)
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2022-01-07 06:33:20 +0100phma(phma@2001:5b0:211b:f778:91c:a71f:b4a2:a400) (Read error: Connection reset by peer)
2022-01-07 06:35:00 +0100phma(phma@2001:5b0:211c:3a48:e7cb:c702:2cb6:39c)
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2022-01-07 06:43:25 +0100shapr(~user@2601:7c0:c202:5190:d7e6:1445:a66d:b9b1)
2022-01-07 06:46:38 +0100cods(~fred@82-65-232-44.subs.proxad.net) (Ping timeout: 268 seconds)
2022-01-07 06:54:19 +0100takuan(~takuan@178-116-218-225.access.telenet.be)
2022-01-07 06:59:24 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Remote host closed the connection)
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2022-01-07 07:00:08 +0100nhatanh02(~satori@123.24.172.30)
2022-01-07 07:05:24 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 07:05:42 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 07:06:43 +0100johnw(~johnw@2607:f6f0:3004:1:c8b4:50ff:fef8:6bf0) (Quit: ZNC - http://znc.in)
2022-01-07 07:16:37 +0100nhatanh02(~satori@123.24.172.30) (Ping timeout: 240 seconds)
2022-01-07 07:28:46 +0100FinnElija(~finn_elij@user/finn-elija/x-0085643) (Remote host closed the connection)
2022-01-07 07:29:06 +0100FinnElija(~finn_elij@user/finn-elija/x-0085643)
2022-01-07 07:39:33 +0100 <hyiltiz> Happy New Years and hope a safe new year to all!
2022-01-07 07:42:38 +0100nhatanh02(~satori@123.24.172.30)
2022-01-07 07:44:06 +0100bitdex(~bitdex@gateway/tor-sasl/bitdex) (Ping timeout: 276 seconds)
2022-01-07 07:44:49 +0100bitdex(~bitdex@gateway/tor-sasl/bitdex)
2022-01-07 07:47:29 +0100 <hyiltiz> When did the channel topic started with a r/haskell link?
2022-01-07 07:48:27 +0100cyphase(~cyphase@user/cyphase)
2022-01-07 07:48:56 +0100cods(~fred@82-65-232-44.subs.proxad.net)
2022-01-07 08:02:33 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com)
2022-01-07 08:02:33 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com) (Changing host)
2022-01-07 08:02:33 +0100wroathe(~wroathe@user/wroathe)
2022-01-07 08:04:07 +0100deadmarshal(~deadmarsh@95.38.112.110)
2022-01-07 08:07:45 +0100wroathe(~wroathe@user/wroathe) (Ping timeout: 256 seconds)
2022-01-07 08:11:35 +0100spdr(~bc8147f2@cerf.good1.com) (Quit: CGI:IRC (Session timeout))
2022-01-07 08:11:59 +0100kaph_(~kaph@net-2-38-107-19.cust.vodafonedsl.it)
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2022-01-07 08:18:54 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 08:19:18 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 08:19:37 +0100zmt01(~zmt00@user/zmt00) (Ping timeout: 240 seconds)
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2022-01-07 08:30:15 +0100coolnickname(uid531864@user/coolnickname)
2022-01-07 08:31:27 +0100mc47(~mc47@xmonad/TheMC47)
2022-01-07 08:32:15 +0100[itchyjunk](~itchyjunk@user/itchyjunk/x-7353470) (Read error: Connection reset by peer)
2022-01-07 08:35:16 +0100Codaraxis_(~Codaraxis@user/codaraxis)
2022-01-07 08:38:37 +0100Codaraxis(~Codaraxis@user/codaraxis) (Ping timeout: 240 seconds)
2022-01-07 08:54:46 +0100simendsjo(~user@84.211.91.241)
2022-01-07 08:59:57 +0100tromp(~textual@dhcp-077-249-230-040.chello.nl)
2022-01-07 09:00:24 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 09:00:47 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 09:07:42 +0100jumper149(~jumper149@base.felixspringer.xyz)
2022-01-07 09:14:46 +0100puke(~puke@user/puke)
2022-01-07 09:18:31 +0100shriekingnoise(~shrieking@186.137.144.80) (Quit: Quit)
2022-01-07 09:21:33 +0100jespada_(~jespada@87.74.32.18) (Quit: My MacBook has gone to sleep. ZZZzzz…)
2022-01-07 09:24:36 +0100Sgeo_(~Sgeo@user/sgeo) (Read error: Connection reset by peer)
2022-01-07 09:33:19 +0100simendsjo(~user@84.211.91.241) (Ping timeout: 256 seconds)
2022-01-07 09:33:37 +0100shapr(~user@2601:7c0:c202:5190:d7e6:1445:a66d:b9b1) (Ping timeout: 240 seconds)
2022-01-07 09:33:38 +0100econo(uid147250@user/econo) (Quit: Connection closed for inactivity)
2022-01-07 09:35:19 +0100zaquest(~notzaques@5.130.79.72) (Remote host closed the connection)
2022-01-07 09:37:50 +0100zaquest(~notzaques@5.130.79.72)
2022-01-07 09:43:46 +0100mc47(~mc47@xmonad/TheMC47) (Remote host closed the connection)
2022-01-07 09:43:59 +0100Brumaire(~quassel@37.166.249.26)
2022-01-07 09:45:53 +0100vpan(~0@212.117.1.172)
2022-01-07 09:47:34 +0100gehmehgeh(~user@user/gehmehgeh)
2022-01-07 09:51:01 +0100machinedgod(~machinedg@24.105.81.50)
2022-01-07 09:53:04 +0100mc47(~mc47@xmonad/TheMC47)
2022-01-07 09:53:20 +0100Gurkenglas(~Gurkengla@dslb-002-203-144-204.002.203.pools.vodafone-ip.de)
2022-01-07 09:53:55 +0100cemguresci(~cemguresc@2001:a61:11ff:a001:2dad:6df8:999e:4708)
2022-01-07 09:56:12 +0100chele(~chele@user/chele)
2022-01-07 10:00:08 +0100inkbottle[m](~inkbottle@2001:470:69fc:105::2ff5) (Quit: You have been kicked for being idle)
2022-01-07 10:00:21 +0100acode(~acode@dslb-188-100-024-238.188.100.pools.vodafone-ip.de)
2022-01-07 10:03:23 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com)
2022-01-07 10:03:23 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com) (Changing host)
2022-01-07 10:03:23 +0100wroathe(~wroathe@user/wroathe)
2022-01-07 10:04:30 +0100coot(~coot@89-64-85-93.dynamic.chello.pl)
2022-01-07 10:05:12 +0100mmhat(~mmh@55d459b4.access.ecotel.net)
2022-01-07 10:05:58 +0100 <juhp> Missing file: /usr/lib64/ghc-8.10.7/lib/settings
2022-01-07 10:06:00 +0100 <juhp> hmm
2022-01-07 10:06:13 +0100tzh(~tzh@c-24-21-73-154.hsd1.or.comcast.net) (Quit: zzz)
2022-01-07 10:06:51 +0100 <juhp> I am getting this from stack after replacing ~/.stack/programs/x86_64-linux/ghc-tinfo6-8.10.7
2022-01-07 10:08:02 +0100 <juhp> The problem being that the file exists...
2022-01-07 10:08:36 +0100wroathe(~wroathe@user/wroathe) (Ping timeout: 256 seconds)
2022-01-07 10:08:40 +0100 <juhp> Oops no it doesn't ughhh
2022-01-07 10:09:37 +0100Tuplanolla(~Tuplanoll@91-159-68-11.elisa-laajakaista.fi)
2022-01-07 10:09:56 +0100 <juhp> Ok I need to work a bit harder on this hack, sorry
2022-01-07 10:16:55 +0100geekosaur(~geekosaur@xmonad/geekosaur) (Read error: Connection reset by peer)
2022-01-07 10:17:46 +0100geekosaur(~geekosaur@xmonad/geekosaur)
2022-01-07 10:18:58 +0100acode(~acode@dslb-188-100-024-238.188.100.pools.vodafone-ip.de) (Quit: Client closed)
2022-01-07 10:22:20 +0100 <maerwald[m]> Aha
2022-01-07 10:23:42 +0100puke(~puke@user/puke) (Remote host closed the connection)
2022-01-07 10:23:58 +0100puke(~puke@user/puke)
2022-01-07 10:24:52 +0100ubert(~Thunderbi@p200300ecdf09947d3ce845fd45b74154.dip0.t-ipconnect.de) (Remote host closed the connection)
2022-01-07 10:25:12 +0100 <cemguresci> Hi guys, I am trying to learn data types and I am having some trouble. I run this code in ghci. https://paste.tomsmeding.com/aK5GQ3vV
2022-01-07 10:25:55 +0100 <cemguresci> I wrote the error message in paste as well :D
2022-01-07 10:26:44 +0100_ht(~quassel@82-169-194-8.biz.kpn.net)
2022-01-07 10:26:51 +0100 <[exa]> cemguresci: why do you use `data` for TimeStamp when it's an alias?
2022-01-07 10:26:54 +0100 <cemguresci> My first intention was actually have an object with timestamp automatically but I couldn't figure it out as well
2022-01-07 10:26:58 +0100 <[exa]> (or looks like you use it as alias to me)
2022-01-07 10:27:07 +0100 <[exa]> you probably want:
2022-01-07 10:27:20 +0100 <[exa]> `data TimeStamp = TimeStamp UTCTime deriving Show`
2022-01-07 10:27:27 +0100 <[exa]> or
2022-01-07 10:27:40 +0100 <[exa]> `type TimeStamp = UTCTime` (no way to do `deriving` here tho)
2022-01-07 10:28:05 +0100 <[exa]> the 2nd variant should work with the rest of the code
2022-01-07 10:28:54 +0100 <[exa]> with the 1st variant you're defining a struct, so you'd need to add a constructor to the use, such as: `test = Test "haskell" (TimeStamp ct)`
2022-01-07 10:29:16 +0100eggplantade(~Eggplanta@108-201-191-115.lightspeed.sntcca.sbcglobal.net) (Remote host closed the connection)
2022-01-07 10:30:21 +0100off^(~off@207.5.21.20)
2022-01-07 10:32:34 +0100 <cemguresci> exa: whats the difference between `data TimeStamp = TimeStamp UTCTime deriving Show and `data TimeStamp = UTCTime deriving Show ?
2022-01-07 10:33:04 +0100 <[exa]> the second defines that "UTCTime" is a constructor for your empty structure
2022-01-07 10:33:19 +0100 <[exa]> which is probably not what you want
2022-01-07 10:33:44 +0100 <[exa]> the syntax for `data` is: `data TypeName = ConstructorName Content1 Content2 | Constructor2Name Content1 Content2 Content3 | ..."
2022-01-07 10:34:20 +0100Codaraxis__(~Codaraxis@user/codaraxis)
2022-01-07 10:34:24 +0100 <[exa]> it defines the TypeName (as the name for the whole thing) and all ConstructorNames (as kinda "functions" that create the type)
2022-01-07 10:35:04 +0100 <[exa]> in your case, the "UTCTime" becomes a constructor for a variant of the TypeName type that has no contents
2022-01-07 10:35:15 +0100Brumaire(~quassel@37.166.249.26) (Quit: ran away)
2022-01-07 10:35:36 +0100Brumaire(~quassel@37.166.249.26)
2022-01-07 10:35:53 +0100 <[exa]> it is a bit confusing for newcomers because in so many other languages the constructor names and type names are forcibly same
2022-01-07 10:36:55 +0100 <cemguresci> yes, I am really confused :D
2022-01-07 10:37:08 +0100 <[exa]> Simpler example: `data Bool = False | True`
2022-01-07 10:37:27 +0100 <[exa]> this gives 2 constructors of the type, `False :: Bool` and `True :: Bool`
2022-01-07 10:37:38 +0100 <[exa]> and both variants contain nothing
2022-01-07 10:37:55 +0100 <cemguresci> what do you mean by containing nothing?
2022-01-07 10:38:03 +0100 <[exa]> there are no data fields in there
2022-01-07 10:38:04 +0100Codaraxis_(~Codaraxis@user/codaraxis) (Ping timeout: 256 seconds)
2022-01-07 10:38:19 +0100 <[exa]> what's your previous language?
2022-01-07 10:38:25 +0100 <cemguresci> python
2022-01-07 10:39:20 +0100 <[exa]> ah okay I'm not good in Python but you can imagine this e.g. as 2 empty classes True and False that share a common "parent", so they can be used interchangeably
2022-01-07 10:40:09 +0100 <cemguresci> okay, I see
2022-01-07 10:40:52 +0100 <[exa]> a more useful example: `data MaybeNumber = ActualNumber Int | NoNumber`
2022-01-07 10:41:27 +0100 <[exa]> defines 1 structure that contains an integer, 1 structure that doesn't contain anything, and both are of the type MaybeNumber
2022-01-07 10:41:51 +0100 <[exa]> (a more generic parametrized version of this is the standard Maybe, `data Maybe a = Nothing | Just a`
2022-01-07 10:41:59 +0100puke(~puke@user/puke) (Quit: puke)
2022-01-07 10:42:37 +0100 <[exa]> anyway, in your case the `data TimeStamp = UTCTime` translates to basically `class UTCTime: pass`
2022-01-07 10:42:40 +0100 <cemguresci> awesome, now I understand.
2022-01-07 10:42:54 +0100 <cemguresci> another question. can we use getCurrentTime function in data definition. I want to have timestamp when its defined
2022-01-07 10:43:13 +0100 <[exa]> getCurrentTime has type (IO UTCTime) right?
2022-01-07 10:43:18 +0100 <cemguresci> yes
2022-01-07 10:43:45 +0100 <[exa]> so it's not a "value", but a description of an IO action that you need to explicitly run at a certain point
2022-01-07 10:43:53 +0100Codaraxis_(~Codaraxis@user/codaraxis)
2022-01-07 10:44:10 +0100 <[exa]> one way is what you did, `<-` in `do` notation is something that "runs" these actions and gets their results as actual values
2022-01-07 10:45:00 +0100 <[exa]> but there are tools to do that less verbosely, e.g. you can write `Test "haskell" <$> getCurrentTime`, which nicely combines the action with the struct creation
2022-01-07 10:45:22 +0100 <[exa]> (and you get a thing of type `IO Test`, which is the action that creates your whole structure right away)
2022-01-07 10:45:29 +0100max22-(~maxime@2a01cb088335980037d8471a1d5e7a78.ipv6.abo.wanadoo.fr)
2022-01-07 10:46:11 +0100 <[exa]> (`<$>` is like `$`, but "through some kind of <box>", which is the IO action here)
2022-01-07 10:46:51 +0100 <cemguresci> hmm thats interesting
2022-01-07 10:47:12 +0100 <[exa]> this is one interesting thing about purity in haskell, it forces you to organize the stuff precisely (e.g., no reliance on argument evaluation order as in C's and pythons)
2022-01-07 10:47:42 +0100Codaraxis__(~Codaraxis@user/codaraxis) (Ping timeout: 256 seconds)
2022-01-07 10:47:49 +0100 <[exa]> which gets really inconvenient "by default", but there's a lot of the helpers like <$> that magically make it more convenient and safer than in the languages where the action order is kinda implicit
2022-01-07 10:48:47 +0100neurocyte091(~neurocyte@user/neurocyte) (Quit: The Lounge - https://thelounge.chat)
2022-01-07 10:49:11 +0100Midjak(~Midjak@may53-1-78-226-116-92.fbx.proxad.net)
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2022-01-07 10:49:59 +0100neurocyte0917(~neurocyte@IP-046243081042.dynamic.medianet-world.de)
2022-01-07 10:49:59 +0100neurocyte0917(~neurocyte@IP-046243081042.dynamic.medianet-world.de) (Changing host)
2022-01-07 10:49:59 +0100neurocyte0917(~neurocyte@user/neurocyte)
2022-01-07 10:50:57 +0100 <cemguresci> exa: thank you so much teaching some information in this short time. I will do more research
2022-01-07 10:51:25 +0100 <[exa]> the main takeaway is that instead of "running commands" here you compose the "program descriptions" (with types such as `IO xxx`) to make larger program descriptions, and haskell runtime takes the program description in `main` and runs it for you
2022-01-07 10:52:20 +0100 <cemguresci> yes, excatly thats what I feel :D
2022-01-07 10:52:48 +0100Erutuon(~Erutuon@user/erutuon) (Ping timeout: 256 seconds)
2022-01-07 10:53:19 +0100 <[exa]> btw the `do` notation does just this, most commands are connected with >> (basically a semicolon in imperative languages) or >>= (a semicolon that carries the result)
2022-01-07 10:53:26 +0100 <[exa]> :t putStrLn "a"
2022-01-07 10:53:27 +0100 <lambdabot> IO ()
2022-01-07 10:53:31 +0100polyphem(~rod@2a02:810d:640:776c:e450:3ca3:b389:687a)
2022-01-07 10:53:47 +0100 <[exa]> (IO action that returns "empty type", ie nothing)
2022-01-07 10:53:57 +0100 <[exa]> :t putStrLn "a" >> putStrLn "b"
2022-01-07 10:53:58 +0100 <lambdabot> IO ()
2022-01-07 10:54:09 +0100 <[exa]> (2 IO actions combined into one)
2022-01-07 10:54:22 +0100ubert(~Thunderbi@2a02:8109:9880:303c:de3b:67d7:83e8:947e)
2022-01-07 10:55:16 +0100 <[exa]> :t readLn >>= (\x -> print $ 2*x)
2022-01-07 10:55:17 +0100 <lambdabot> IO ()
2022-01-07 10:55:56 +0100user0(~aj@154.0.137.32)
2022-01-07 10:56:00 +0100spaceseller(~spacesell@31.147.205.13)
2022-01-07 10:56:03 +0100 <[exa]> (2 actions combined into one with carrying the result, this is what `do x<-readLn; print (2*x);` looks like without the fancy syntax )
2022-01-07 10:56:37 +0100user0(~aj@154.0.137.32) ()
2022-01-07 10:57:08 +0100 <cemguresci> cool stuff :D
2022-01-07 10:58:22 +0100 <[exa]> and well, eventually someone will tell you that all stuff that can be combined in such way belongs to a wider, infamously named category of composable computations :D
2022-01-07 10:58:23 +0100 <juhp> okay I made this to create stack program symlinks to Fedora ghc's: https://gist.github.com/juhp/a9c49281a8e478eb9af30a78a87ab0d7
2022-01-07 10:59:27 +0100nhatanh02(~satori@123.24.172.30) (Ping timeout: 256 seconds)
2022-01-07 10:59:43 +0100 <cemguresci> exa: more theory of everything :D
2022-01-07 10:59:58 +0100 <cemguresci> abstracting the abstraction :D
2022-01-07 11:02:05 +0100spaceseller(~spacesell@31.147.205.13) (Quit: Leaving)
2022-01-07 11:02:09 +0100Everything(~Everythin@37.115.210.35)
2022-01-07 11:10:31 +0100 <maerwald[m]> juhp: why
2022-01-07 11:11:17 +0100 <juhp> maerwald[m]: because I prefer to use the Fedora built ghc on Fedora
2022-01-07 11:11:34 +0100 <maerwald[m]> juhp: https://docs.haskellstack.org/en/stable/yaml_configuration/#system-ghc
2022-01-07 11:12:24 +0100 <juhp> maerwald[m]: yes I know but I have multiple Fedora ghc's (ghc8.10, ghc9.0, ghc9.2)
2022-01-07 11:13:15 +0100 <juhp> Having an extra copy under ~/.stack is just a waste of diskspace :)
2022-01-07 11:13:24 +0100 <juhp> copies
2022-01-07 11:13:30 +0100 <maerwald[m]> juhp: then use a patched stack: https://github.com/commercialhaskell/stack/pull/5585
2022-01-07 11:14:36 +0100 <maerwald[m]> Here are prebuilt binaries https://downloads.haskell.org/~ghcup/unofficial-bindists/stack/2.7.3.1/
2022-01-07 11:14:37 +0100n3rdy1(~n3rdy1@2600:1700:4570:3480:1b88:50f:dae0:9293) (Ping timeout: 240 seconds)
2022-01-07 11:15:37 +0100 <juhp> maerwald[m]: cool
2022-01-07 11:15:47 +0100 <juhp> We have stack packaged in fedora too
2022-01-07 11:16:05 +0100 <maerwald[m]> And?
2022-01-07 11:17:31 +0100 <juhp> maerwald[m]: happy to use stack hooks once it is merged upstream :)
2022-01-07 11:17:49 +0100mastarija(~mastarija@2a05:4f46:e0e:5000:e9aa:f35a:429e:f1b8)
2022-01-07 11:18:18 +0100 <maerwald[m]> juhp: it will never be
2022-01-07 11:19:07 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com)
2022-01-07 11:19:07 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com) (Changing host)
2022-01-07 11:19:07 +0100wroathe(~wroathe@user/wroathe)
2022-01-07 11:19:18 +0100 <juhp> Well maybe I can apply your patch to Fedora stack then - would be nice indeed to automatically prefer or even install the Fedora build
2022-01-07 11:20:25 +0100 <juhp> (Fedora ghcX.Y build)
2022-01-07 11:20:29 +0100 <maerwald[m]> Since stack has stagnated, it should be easy to maintain the patch downstream
2022-01-07 11:20:41 +0100 <juhp> Ya I suppose
2022-01-07 11:20:51 +0100acidjnk(~acidjnk@p200300d0c7271e249cd77df40fde183d.dip0.t-ipconnect.de)
2022-01-07 11:20:51 +0100acidjnk_new3(~acidjnk@p200300d0c7271e249cd77df40fde183d.dip0.t-ipconnect.de)
2022-01-07 11:24:23 +0100wroathe(~wroathe@user/wroathe) (Ping timeout: 256 seconds)
2022-01-07 11:28:45 +0100 <juhp> maerwald[m]: alright I parked your patch in my Fedora stack package directory - I may consider it for Fedora 36, thanks
2022-01-07 11:29:46 +0100eggplantade(~Eggplanta@108-201-191-115.lightspeed.sntcca.sbcglobal.net)
2022-01-07 11:33:25 +0100 <juhp> Btw for those using Stackage Nightly: the next snapshot should be based on ghc-9.0.2 hopefully (thanks to Adam Bergmark)
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2022-01-07 11:51:17 +0100 <[exa]> cemguresci: actually these things are pretty concrete requirements, "do stuff in order based on some defined ordering logic" and "use results from earlier steps"
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2022-01-07 12:46:02 +0100nhatanh02(~satori@123.24.172.30)
2022-01-07 12:48:43 +0100 <cemguresci> exa: right that makes sense
2022-01-07 12:49:22 +0100 <cemguresci> exa: when I define these, `data Recipient = Recipient String | Nothing deriving Show` `data Amount = Amount Double | Nothing deriving Show` , I get this error "Multiple declarations of `Nothing'" Why it happens?
2022-01-07 12:49:53 +0100 <c_wraith> constructors must be unique (per module)
2022-01-07 12:50:10 +0100Hanicef(~gustaf@81-229-9-108-no92.tbcn.telia.com)
2022-01-07 12:50:14 +0100 <c_wraith> But the fact that you're using the name Nothing suggests a misunderstanding
2022-01-07 12:50:39 +0100 <c_wraith> Those aren't the same Nothing as is defined in the Maybe type
2022-01-07 12:50:52 +0100 <c_wraith> those are your own value named Nothing
2022-01-07 12:50:57 +0100 <cemguresci> I am combining these with other data types and I want to construct the latest data type with nullable of this data types
2022-01-07 12:51:32 +0100 <c_wraith> When you declare a data type, you declare constructors *for that type*
2022-01-07 12:51:43 +0100 <sub0> your Nothing construct will conflict with Nothing from Maybe
2022-01-07 12:51:48 +0100 <sub0> constructor*
2022-01-07 12:52:16 +0100 <sshine> cemguresci, maybe you want: 'type Recipient = String; type Amount = Double' and then in your functions you can write 'Maybe Recipient' and 'Maybe Amount' types to signify values like 'Just "Bob" :: Maybe Recipient' and 'Nothing :: Maybe Recipient' and 'Just 42.0 :: Maybe Amount' and 'Nothing :: Maybe Amount'?
2022-01-07 12:52:23 +0100 <c_wraith> sub0: not actually true. Maybe is defined in a different module. that error is coming from defining Nothing twice in the same module. There would be an ambiguity error using it, though
2022-01-07 12:53:02 +0100 <cemguresci> c_wraith: you are right. it is not the same Nothing in Maybe :D
2022-01-07 12:53:03 +0100 <sshine> cemguresci, it's not that creating your own nullable data type is necessarily bad. but maybe you want to consider using the existing Maybe type to describe whether or not there's a recipient/amount?
2022-01-07 12:53:31 +0100 <sub0> c_wraith, Nothing is in Prelude. it will conflict with his name unless he took measures to prevent it
2022-01-07 12:53:41 +0100 <c_wraith> sub0: but that's not what that error was reporting.
2022-01-07 12:53:49 +0100 <sub0> I didn't comment on the error
2022-01-07 12:54:11 +0100 <c_wraith> cemguresci: it is a requirement of Haskell's type inference that constructors always are unique to types.
2022-01-07 12:54:47 +0100 <c_wraith> cemguresci: the fully-qualified names thereof, at least.
2022-01-07 12:55:15 +0100 <cemguresci> I see, I confused how to use Nothing actually to make it nullable :D
2022-01-07 12:55:18 +0100ubert(~Thunderbi@2a02:8109:9880:303c:de3b:67d7:83e8:947e) (Remote host closed the connection)
2022-01-07 12:55:31 +0100ubert(~Thunderbi@2a02:8109:9880:303c:6bbe:db4a:c5b0:8e19)
2022-01-07 12:56:29 +0100 <cemguresci> This is actually what I want, data Test = Test {
2022-01-07 12:56:29 +0100 <cemguresci> amount :: Maybe Amount,
2022-01-07 12:56:29 +0100 <cemguresci> recipient :: Maybe Recipient
2022-01-07 12:56:29 +0100 <cemguresci> } deriving (Eq, Show, Generic)
2022-01-07 12:56:29 +0100 <[exa]> cemguresci: better name it unambiguously as `NoRecipient`
2022-01-07 12:56:56 +0100 <[exa]> I'd say that there you may go for `Maybe String` right away
2022-01-07 12:57:07 +0100 <[exa]> or `Maybe Name`
2022-01-07 12:57:28 +0100 <[exa]> naming the whole thing as Recipient sounds kinda like you also store the whole person there, with all organs etc :D
2022-01-07 12:57:39 +0100 <cemguresci> haha :D
2022-01-07 12:57:46 +0100 <[exa]> (hard-learned OOP lesson :D )
2022-01-07 12:57:56 +0100 <sshine> yea, Recipient does sound like a nested data type :) RecipientName or Name. but meh.
2022-01-07 12:58:14 +0100 <cemguresci> you are right
2022-01-07 12:58:16 +0100 <[exa]> `type Name=String` is a pretty common sight in packages
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2022-01-07 12:58:27 +0100 <[exa]> and yeah, meh. :D
2022-01-07 12:58:42 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
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2022-01-07 13:40:53 +0100 <joel135> I just found the word Haskalah. Sounds like haskell :P
2022-01-07 13:46:52 +0100Rum(~bourbon@user/rum)
2022-01-07 13:48:05 +0100 <Hecate> Haskallah Al-Rahman Al-Raheem? :P
2022-01-07 13:49:09 +0100benin(~benin@183.82.176.241)
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2022-01-07 14:06:41 +0100 <absence> can cabal use a "resolver" from stack/stackage to decide which package versions to use?
2022-01-07 14:09:29 +0100 <geekosaur> not yet
2022-01-07 14:10:17 +0100 <absence> yet? is it planned or being worked on?
2022-01-07 14:10:27 +0100 <geekosaur> yes
2022-01-07 14:11:28 +0100 <absence> cool, is there somewhere i can read about it and/or follow the progress?
2022-01-07 14:11:57 +0100cosimone(~user@2001:b07:ae5:db26:c24a:d20:4d91:1e20) (Remote host closed the connection)
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2022-01-07 14:14:16 +0100 <geekosaur> lemme see if I can find the ticket again
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2022-01-07 14:18:00 +0100 <geekosaur> https://github.com/haskell/cabal/issues/7556
2022-01-07 14:19:35 +0100mmhat(~mmh@55d45069.access.ecotel.net)
2022-01-07 14:20:56 +0100 <absence> looks promising, thanks!
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2022-01-07 14:44:06 +0100geekosaurwonders how close one could get to this by translating a resolver into an incomplete freeze file
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2022-01-07 14:45:57 +0100 <fendor[m]> iirc, the issue describes how far you can get with freeze files and what the limitations are
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2022-01-07 16:15:21 +0100 <sclv> absence, geekosaur stackage already provides those freeze files: https://www.stackage.org/lts-18.5/cabal.config
2022-01-07 16:15:45 +0100 <geekosaur> so I saw when I read the ticket
2022-01-07 16:15:58 +0100 <sclv> there's no link anywhere from the stackage page itself (its an "easter egg feature") because they decided they didn't like promoting it, ostensibly because those don't handle revisions
2022-01-07 16:16:51 +0100 <sclv> the feature i've been working on would let you add a line "import https://foo/cabal.config" directly to a project file
2022-01-07 16:17:06 +0100jkaye(~jkaye@2601:281:8300:7530:960c:6e00:5eeb:eb5a)
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2022-01-07 16:17:35 +0100 <sclv> and the main issue is merge constraint semantics are not useful right now
2022-01-07 16:17:46 +0100 <sclv> it just picks up all constraints and applies them all.
2022-01-07 16:17:55 +0100 <sclv> so you can't ever "override" a resolver
2022-01-07 16:18:49 +0100Sgeo(~Sgeo@user/sgeo)
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2022-01-07 17:45:14 +0100 <cemguresci> Hi guys, why this function errors stack overfow, i dont understand. ppow abc a = xx
2022-01-07 17:45:14 +0100 <cemguresci> where fd = read (take 4 . reverse $ show(hashWithSalt a abc)) :: Integer
2022-01-07 17:45:14 +0100 <cemguresci> xx = if fd < 5999
2022-01-07 17:45:14 +0100 <cemguresci> then a
2022-01-07 17:45:14 +0100 <cemguresci> else (ppow abc a+1)
2022-01-07 17:45:20 +0100slowButPresent(~slowButPr@user/slowbutpresent)
2022-01-07 17:45:23 +0100 <EvanR> @where paste
2022-01-07 17:45:23 +0100 <lambdabot> Help us help you: please paste full code, input and/or output at e.g. https://paste.tomsmeding.com
2022-01-07 17:45:27 +0100 <EvanR> dang that's handy
2022-01-07 17:46:21 +0100 <cemguresci> all right. https://paste.tomsmeding.com/xrs11gGJ
2022-01-07 17:46:40 +0100 <cemguresci> this works, *Main Data.Hashable Data.Hashable.Time Data.Int> ppow z 33
2022-01-07 17:46:40 +0100 <cemguresci> 33
2022-01-07 17:46:50 +0100 <EvanR> did you want to do (ppow abc (a + 1)) at the end
2022-01-07 17:47:12 +0100Akiva(~Akiva@user/Akiva)
2022-01-07 17:47:12 +0100 <EvanR> or (ppow abc a) + 1
2022-01-07 17:47:15 +0100 <cemguresci> *Main Data.Hashable Data.Hashable.Time Data.Int> ppow z 32
2022-01-07 17:47:15 +0100 <cemguresci> *** Exception: stack overflow
2022-01-07 17:47:15 +0100 <cemguresci> this doesnt
2022-01-07 17:48:09 +0100 <EvanR> note how the second understanding leads to an infinite loop
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2022-01-07 17:48:28 +0100 <cemguresci> now it owkrs :D
2022-01-07 17:48:35 +0100 <cemguresci> works :D
2022-01-07 17:48:46 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 17:49:34 +0100 <EvanR> rather if fd starts < 5999 it remains so forever because the same question gets repeated infinitely
2022-01-07 17:50:21 +0100 <cemguresci> i thought making a+1 will act like (a + 1), never assume that, right
2022-01-07 17:50:45 +0100Inst(~delicacie@c-98-208-218-119.hsd1.fl.comcast.net)
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2022-01-07 17:50:55 +0100 <EvanR> + just has lower parsing precedence than the space in 'f x'
2022-01-07 17:51:10 +0100 <EvanR> function application binds tighter
2022-01-07 17:51:43 +0100 <EvanR> similar to 'times' in algebra xy + ab
2022-01-07 17:52:10 +0100 <EvanR> but it also binds tighter than *
2022-01-07 17:52:45 +0100nhatanh02(~satori@123.24.172.30)
2022-01-07 17:53:29 +0100stefan-_(~cri@42dots.de) (Ping timeout: 250 seconds)
2022-01-07 17:56:39 +0100 <Hecate> Hello, I'm doing user research regarding a feature I'm hoping to get into Cabal, that would allow people to seamlessly integrate native compiled languages (read: rust/zig/C) in their Cabal project
2022-01-07 17:56:46 +0100 <Hecate> Based on the ideas in https://gist.github.com/Kleidukos/729fd6a091307e0929f7519126b4a6c8
2022-01-07 17:56:57 +0100mbuf(~Shakthi@122.178.240.232) (Quit: Leaving)
2022-01-07 17:57:17 +0100stefan-_(~cri@42dots.de)
2022-01-07 17:58:28 +0100 <Hecate> long story short I'm gathering your testimonials in order to know how I can best serve you
2022-01-07 17:58:38 +0100 <sclv> Hecate: i don't understand your reference to hackage builders there at all
2022-01-07 17:58:39 +0100 <Hecate> the idea is to provide an alternative to custom Setup.hs
2022-01-07 17:58:58 +0100 <cemguresci> thanks EvanR
2022-01-07 17:59:00 +0100nunggu(~q@gateway/tor-sasl/nunggu)
2022-01-07 17:59:04 +0100 <Hecate> sclv: When you upload a library to Hackage, isn't it impossible to specify a custom command to have them run?
2022-01-07 17:59:12 +0100cemgurescicemg
2022-01-07 17:59:17 +0100 <sclv> no hackage uses a standard cabal build
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2022-01-07 17:59:42 +0100 <sclv> but standard cabal builds can use custom setup.hs
2022-01-07 18:00:01 +0100waleee(~waleee@2001:9b0:21d:fc00:398f:b003:b90d:acf4) (Ping timeout: 268 seconds)
2022-01-07 18:00:09 +0100 <Hecate> yes but we're actively trying to get rid of those ;)
2022-01-07 18:00:14 +0100eggplantade(~Eggplanta@108-201-191-115.lightspeed.sntcca.sbcglobal.net)
2022-01-07 18:00:23 +0100 <sclv> right but the reference to hackage makes no sense
2022-01-07 18:00:27 +0100 <EvanR> cemguresci, worth understanding precedence in haskell because 1. it's relevant to stuff like a -> b -> c, which is understood as a -> (b -> c), 2. people sprinkle $ everywhere, often gratuitously, to adjust precedence and 3. you can define the precedence of custom operators
2022-01-07 18:00:30 +0100 <sclv> its just one of many systems that uses cabal build
2022-01-07 18:00:31 +0100 <Hecate> wait wait let me finish
2022-01-07 18:00:34 +0100 <sclv> there's nothing special about it
2022-01-07 18:01:04 +0100 <Hecate> one of the critics I've received is: Why don't you use $other_tool or just run commands in the right order?
2022-01-07 18:01:16 +0100 <Hecate> and my answer was "there are systems that only run standard cabal builds"
2022-01-07 18:01:19 +0100 <Hecate> like Hackage runners
2022-01-07 18:01:28 +0100 <sclv> you can make that argument more generally
2022-01-07 18:01:30 +0100 <Hecate> where you can't specify a custom command to run
2022-01-07 18:01:40 +0100 <Hecate> yup' but I thought an example would be more speaking?
2022-01-07 18:01:44 +0100 <sclv> any time package X wants to depend on package Y then cabal will build package Y with a standard cabal build
2022-01-07 18:01:49 +0100 <Hecate> but yes it's more general than just Hackage
2022-01-07 18:01:56 +0100 <Hecate> great, thank you :)
2022-01-07 18:02:26 +0100 <sclv> that said, I think you can do 95% of this with build-tool-depends and not needing any changes to cabal grammar
2022-01-07 18:03:19 +0100 <sclv> you _might_ not be able to do it with custom stanzas per tool in the cabal grammar (not sure about nested syntax of x-fields) but you could just put that config in a distinct file
2022-01-07 18:03:43 +0100 <sclv> so i really would encourage you to try build-tool-depends for this, and document what if any limitations that has
2022-01-07 18:03:50 +0100 <sclv> and maybe that could just be mildly fixed or extended
2022-01-07 18:04:41 +0100 <Hecate> sclv: I have a hard time understanding the operational semantics of build-tool-depends, does it run anything? Does it add anything to the pipeline?
2022-01-07 18:05:02 +0100vysn(~vysn@user/vysn) (Ping timeout: 240 seconds)
2022-01-07 18:05:40 +0100 <Hecate> I'm understanding that it provides executables in the scope (PATH?) during the duration of the component
2022-01-07 18:06:56 +0100 <Hecate> sclv: you're right in that I can declare the necssity of having the cargo-driver (for instance) in the $PATH, this does the majority of the job I think
2022-01-07 18:07:14 +0100 <sclv> fair point it doesn't actually run it
2022-01-07 18:07:22 +0100 <Hecate> but then I'd have to register the driver to run before the component is built
2022-01-07 18:07:46 +0100 <Hecate> sclv: that being said the code behind build-tool-depends can absolutely be reused! :)
2022-01-07 18:08:12 +0100 <sclv> actually wait, i have an open pr that almost does this: https://github.com/haskell/cabal/pull/7688
2022-01-07 18:08:18 +0100 <sclv> its just limited to test suites only now
2022-01-07 18:08:48 +0100 <sclv> i think i didn't want it in main stanzas because it can generate new hs modules and we want the cabal file to have a manifest of all exposed cabal modules
2022-01-07 18:08:58 +0100tzh(~tzh@c-24-21-73-154.hsd1.wa.comcast.net)
2022-01-07 18:08:58 +0100 <sclv> so i don't think we want that
2022-01-07 18:08:59 +0100Akiva(~Akiva@user/Akiva) (Ping timeout: 256 seconds)
2022-01-07 18:09:39 +0100 <sclv> but arguably i'd just want one new field, "build-tools-pipeline" that runs a list of executables in order
2022-01-07 18:09:47 +0100 <sclv> (with build-tools-depends used to bring them into scope)
2022-01-07 18:10:36 +0100 <sclv> which is almost exactly your build-drivers field, but i'm leaning against having the x- fields in the cabal file get passed in
2022-01-07 18:10:39 +0100 <Hecate> sclv: don't we have autogen-modules for those?
2022-01-07 18:10:44 +0100 <sclv> i think it confuses the grammar to make that extensible
2022-01-07 18:11:14 +0100 <Hecate> sclv: when you say "get passed in" I'm not sure to fully understand
2022-01-07 18:11:57 +0100 <sclv> well i'm given to understand if you say build-driver: cargo-driver then the x-cargo-driver stanza somehow gets passed to cargo-driver
2022-01-07 18:12:14 +0100 <sclv> i'd rather you just call "cargo-driver" and it finds its settings like in some other file or something
2022-01-07 18:12:38 +0100 <Hecate> sclv: oh no it doesn't get passed-in to the driver
2022-01-07 18:12:45 +0100 <sclv> ok then what does it do
2022-01-07 18:12:47 +0100 <Hecate> I'd have the cargo-driver parse the Cabal file
2022-01-07 18:12:51 +0100 <Hecate> get its stanza
2022-01-07 18:12:57 +0100 <Hecate> this is low-tech enough
2022-01-07 18:13:10 +0100 <sclv> as i said idk if we can have x-stanzas or just x-fields
2022-01-07 18:13:22 +0100 <Hecate> aaaah ok I understand now
2022-01-07 18:13:39 +0100notzmv(~zmv@user/notzmv)
2022-01-07 18:14:06 +0100 <sclv> the minimal proposal i'd support would be just build-drivers (but i'd prefer it called build-tools-pipeline or the like for uniformity, though that's totally something people can argue about on a ticket, etc)
2022-01-07 18:15:06 +0100 <Hecate> > Notice that you can create custom stanzas in your foo.cabal. I have provided the code to support a stanza something like:
2022-01-07 18:15:07 +0100 <lambdabot> <hint>:1:43: error: parse error on input ‘in’
2022-01-07 18:15:09 +0100 <Hecate> https://webcache.googleusercontent.com/search?q=cache:ug9swepTVJoJ:https://www.py4u.net/discuss/19…
2022-01-07 18:16:19 +0100 <sclv> not sure that's accurate let me check
2022-01-07 18:17:06 +0100 <geekosaur> iirc it at least used to be possible
2022-01-07 18:17:50 +0100 <sclv> yeah, it works as is
2022-01-07 18:18:06 +0100 <Hecate> hurray :D
2022-01-07 18:18:19 +0100 <Hecate> this saves the x-$driver stanza
2022-01-07 18:18:22 +0100 <sclv> ok, so drivers can read custom stanzas or other files or whatever its up to them :-)
2022-01-07 18:18:29 +0100 <Hecate> sclv: :D yes!
2022-01-07 18:18:47 +0100 <Hecate> ah man this makes me so happy
2022-01-07 18:18:48 +0100 <sclv> again this means the minimal proposal is just a single new field that adds executables to a preprocessor pipeline
2022-01-07 18:19:18 +0100 <sclv> there might be some prior tickets on this lying around, but imho it makes a lot of sense
2022-01-07 18:19:19 +0100 <Hecate> yup', as advertised in the FAQ I want this to be minimally invasive for Cabal
2022-01-07 18:19:50 +0100 <Hecate> And this is a step forward getting rid of a legitimate usage of Setup.hs
2022-01-07 18:19:52 +0100 <sclv> it might be worth trying to figure out how many current uses of custom Setup.hs can be obviated by this
2022-01-07 18:19:53 +0100 <sclv> yep
2022-01-07 18:20:23 +0100 <Hecate> sclv: speaking of which, I've been contacted with someone that has quite a horrific situation: https://twitter.com/marunarh/status/1479496482063589376
2022-01-07 18:20:46 +0100 <Hecate> you said that generated .hs modules in Setup.hs are Not Good™, would it be better if they were registered in autogen-modules?
2022-01-07 18:20:46 +0100Jing(~hedgehog@2604:a840:3::103c) (Quit: My MacBook has gone to sleep. ZZZzzz…)
2022-01-07 18:20:49 +0100CiaoSen(~Jura@p200300c957347b002a3a4dfffe84dbd5.dip0.t-ipconnect.de)
2022-01-07 18:21:37 +0100 <sclv> right, we really want the cabal file to statically list all modules a package can provide
2022-01-07 18:21:42 +0100waleee(~waleee@2001:9b0:21d:fc00:398f:b003:b90d:acf4)
2022-01-07 18:22:19 +0100 <Hecate> perfect, so I can tell people to do this then
2022-01-07 18:22:23 +0100 <Hecate> 👍*
2022-01-07 18:27:04 +0100econo(uid147250@user/econo)
2022-01-07 18:28:50 +0100 <[itchyjunk]> When it says "define your own list type", am i supposed to create a new datastructure somehow?
2022-01-07 18:29:16 +0100 <[itchyjunk]> "define your own list type and then implement your own version of the following functions : " it says
2022-01-07 18:30:03 +0100 <geekosaur> yes
2022-01-07 18:30:14 +0100 <geekosaur> it's not even particularly difficult
2022-01-07 18:30:24 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 18:30:41 +0100 <[itchyjunk]> hmmmmm
2022-01-07 18:31:00 +0100Hafydd(~Hafydd@user/hafydd)
2022-01-07 18:31:10 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 18:33:37 +0100 <geekosaur> the one thing you can't readily do is use [x,y,z] syntax with it
2022-01-07 18:34:07 +0100 <geekosaur> (there's a way around that but I'm pretty sure they don't want you to do that now)
2022-01-07 18:35:24 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 18:35:41 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 18:42:59 +0100doyougnu(~doyougnu@c-73-25-202-122.hsd1.or.comcast.net) (Ping timeout: 256 seconds)
2022-01-07 18:44:53 +0100cemg(~cemguresc@2001:a61:11ff:a001:2dad:6df8:999e:4708) (Ping timeout: 252 seconds)
2022-01-07 18:48:06 +0100 <[itchyjunk]> hmm
2022-01-07 18:48:13 +0100lavaman(~lavaman@98.38.249.169)
2022-01-07 18:48:35 +0100 <EvanR> remind me why it would be a bad idea to have a default instance of some class that select types "reimplement" OOP style
2022-01-07 18:48:56 +0100 <EvanR> it breaks separate compilation or
2022-01-07 18:49:30 +0100 <geekosaur> separate compilation has to be able to find instances by fixed names
2022-01-07 18:49:45 +0100 <geekosaur> which then become global across the entire program
2022-01-07 18:49:57 +0100 <[itchyjunk]> I want a `data List a = someConstructorHere variable | someOtherCons moreVariables
2022-01-07 18:49:58 +0100 <[itchyjunk]> `
2022-01-07 18:50:27 +0100 <geekosaur> that said, you can do this with default implementations in the class head, depending on what you really need
2022-01-07 18:50:48 +0100 <EvanR> just curious, don't need it!
2022-01-07 18:52:35 +0100 <[itchyjunk]> I suppose i want my type to be deriving Num
2022-01-07 18:52:37 +0100lavaman(~lavaman@98.38.249.169) (Ping timeout: 256 seconds)
2022-01-07 18:52:56 +0100 <geekosaur> [itchyjunk], not if you're reimplementing a list, no
2022-01-07 18:52:58 +0100 <EvanR> [itchyjunk], are you throwing spaghetti at a wall now
2022-01-07 18:53:22 +0100 <[itchyjunk]> Always have been!
2022-01-07 18:53:26 +0100Erutuon(~Erutuon@user/erutuon)
2022-01-07 18:53:54 +0100 <[itchyjunk]> yeah i am trying to implement list where i can define a mySum and sum all the elements of the list
2022-01-07 18:54:24 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Read error: Connection reset by peer)
2022-01-07 18:54:29 +0100 <EvanR> that requires Num support on elements and not the list
2022-01-07 18:54:42 +0100 <[itchyjunk]> hmm right
2022-01-07 18:55:33 +0100jonathanx(~jonathan@h-178-174-176-109.a357.priv.bahnhof.se)
2022-01-07 18:55:46 +0100 <[itchyjunk]> define a list containing a, where a is constrained to the Num interface like thingy
2022-01-07 18:55:59 +0100 <[itchyjunk]> `data List a = ?`
2022-01-07 18:56:48 +0100coot(~coot@89-64-85-93.dynamic.chello.pl) (Quit: coot)
2022-01-07 18:56:57 +0100 <[itchyjunk]> not the `a` either, apparently
2022-01-07 18:57:02 +0100 <c_wraith> GHC has disabled the functionality that used to allow that, because.. it turned out to not be useful.
2022-01-07 18:57:18 +0100 <c_wraith> Just put constraints on the places that need them. the data constructor does not need them
2022-01-07 18:58:09 +0100 <geekosaur> is there anything else you're supposed to define?
2022-01-07 18:58:22 +0100Hayek(~xxx@rrcs-173-196-3-254.west.biz.rr.com)
2022-01-07 18:58:27 +0100 <geekosaur> :t sum -- note we put the constraint on the function, not the list
2022-01-07 18:58:27 +0100 <lambdabot> (Foldable t, Num a) => t a -> a
2022-01-07 18:58:34 +0100 <geekosaur> meh
2022-01-07 18:58:42 +0100 <geekosaur> % :t sum @[]
2022-01-07 18:58:42 +0100 <yahb> geekosaur: Num a => [a] -> a
2022-01-07 18:58:43 +0100 <Hayek> src sum
2022-01-07 18:58:47 +0100 <[itchyjunk]> the full problem is here :http://www.cas.mcmaster.ca/~dalvescb/LH_Week05_Exercises.pdf
2022-01-07 18:58:58 +0100 <Hayek> % :t sum
2022-01-07 18:58:58 +0100 <yahb> Hayek: (Foldable t, Num a) => t a -> a
2022-01-07 18:59:00 +0100 <[itchyjunk]> problem 3), mySum, ++, myReverse
2022-01-07 18:59:20 +0100 <geekosaur> right, I'd put the Num part on mySum because the others don't need it
2022-01-07 18:59:55 +0100 <geekosaur> and myReverse would be pretty limited if it only worked on lists of numbers
2022-01-07 19:00:12 +0100nurupo(~nurupo.ga@user/nurupo) (Quit: nurupo.ga)
2022-01-07 19:00:25 +0100nurupo(~nurupo.ga@user/nurupo)
2022-01-07 19:00:28 +0100 <[itchyjunk]> i see what you mean. i only want it to be numbers when i need to add then, not always.
2022-01-07 19:01:04 +0100 <c_wraith> The problem even gives you types for each - only one of which has a constraint
2022-01-07 19:01:32 +0100 <[itchyjunk]> Right :x
2022-01-07 19:01:41 +0100waleee(~waleee@2001:9b0:21d:fc00:398f:b003:b90d:acf4) (Ping timeout: 268 seconds)
2022-01-07 19:01:57 +0100 <[itchyjunk]> I don't grasp the purpose of type constructors
2022-01-07 19:02:01 +0100eggplantade(~Eggplanta@108-201-191-115.lightspeed.sntcca.sbcglobal.net) (Remote host closed the connection)
2022-01-07 19:02:23 +0100 <[itchyjunk]> here they say data FightMove = Punch | Kick | Block
2022-01-07 19:02:24 +0100 <[itchyjunk]> https://mmhaskell.com/blog/2016/12/17/making-your-own-data-types-in-haskell
2022-01-07 19:02:31 +0100 <[itchyjunk]> So it's the things that type can do
2022-01-07 19:02:51 +0100 <monochrom> But you need a parametrized type now.
2022-01-07 19:02:53 +0100 <[itchyjunk]> so for my list, would the constructors be the type of things the list can do like produce of sum of elements?
2022-01-07 19:02:56 +0100 <geekosaur> those are data constructors, not type constructors
2022-01-07 19:02:57 +0100 <[itchyjunk]> hmm
2022-01-07 19:03:05 +0100 <geekosaur> consider data Bool = False | True
2022-01-07 19:03:05 +0100[itchyjunk]scrolls down to parametrized types to read
2022-01-07 19:03:16 +0100 <glguy> [itchyjunk]: In your data FightMove ... , FightMove was the type constructor
2022-01-07 19:03:19 +0100 <[itchyjunk]> ah
2022-01-07 19:03:27 +0100 <geekosaur> Bool is the type constructor, False and True are the data constructors
2022-01-07 19:03:28 +0100waleee(~waleee@h-98-128-229-110.na.cust.bahnhof.se)
2022-01-07 19:03:40 +0100 <geekosaur> they are values just like 1 or "foo"
2022-01-07 19:07:32 +0100 <geekosaur> in data Maybe a = Nothing | Just a, Maybe is a type constructor which takes a type parameter; Nothing is a value, Just is a data constructor which takes a value of the type you specified with the type constructor
2022-01-07 19:07:36 +0100eggplantade(~Eggplanta@108-201-191-115.lightspeed.sntcca.sbcglobal.net)
2022-01-07 19:07:51 +0100 <geekosaur> so Just 'a' is a value whose type is Maybe Char
2022-01-07 19:08:36 +0100 <glguy> [itchyjunk]: the cool thing about data constructors is that you can case on them. When you see capitalized identifiers in patterns you know they only match values created with that constructor
2022-01-07 19:08:44 +0100cheater(~Username@user/cheater)
2022-01-07 19:09:22 +0100 <[itchyjunk]> I get the Maybe being a type constructor but why isn't Just a type constructor but a data constructor?
2022-01-07 19:09:33 +0100 <[itchyjunk]> because of its appearence in RHS there?
2022-01-07 19:09:41 +0100 <geekosaur> because it constructs data instead of constructing types
2022-01-07 19:10:12 +0100 <glguy> [itchyjunk]: there are two distinct levels. Type-level and value-level.
2022-01-07 19:10:20 +0100 <[itchyjunk]> so `Just a` is a value whose type is `Maybe` ?
2022-01-07 19:10:25 +0100 <[itchyjunk]> Why is it `Maybe Char` ?
2022-01-07 19:10:34 +0100 <geekosaur> because I applied Just to a Char
2022-01-07 19:10:42 +0100 <geekosaur> :t 'a'
2022-01-07 19:10:43 +0100 <lambdabot> Char
2022-01-07 19:10:43 +0100 <[itchyjunk]> ahh Just 'a' right
2022-01-07 19:11:25 +0100 <[itchyjunk]> Why is it `Nothing` and not `Nothing a` ?
2022-01-07 19:11:47 +0100 <monochrom> Because "Nothing 5" makes no sense.
2022-01-07 19:11:49 +0100 <Michal[m]> the type is 'Maybe a' not Maybe
2022-01-07 19:11:50 +0100 <[itchyjunk]> Nothing represents when the parameter is left empty right?
2022-01-07 19:11:59 +0100 <geekosaur> because it doesn't take a parameter
2022-01-07 19:12:00 +0100 <[itchyjunk]> Michal[m], oh
2022-01-07 19:12:03 +0100 <geekosaur> :t Just
2022-01-07 19:12:03 +0100 <lambdabot> a -> Maybe a
2022-01-07 19:12:12 +0100 <geekosaur> :t Nothing
2022-01-07 19:12:13 +0100 <lambdabot> Maybe a
2022-01-07 19:12:25 +0100 <geekosaur> this is like the empty list, which can be of any list type
2022-01-07 19:12:27 +0100 <geekosaur> :t []
2022-01-07 19:12:28 +0100 <lambdabot> [a]
2022-01-07 19:12:44 +0100 <geekosaur> but a list ['c'] is necessarily a list of Char
2022-01-07 19:12:51 +0100 <[itchyjunk]> `data List a = Nothing | ?` so here, i have accounted for my type `List a` to be empty ?
2022-01-07 19:13:12 +0100 <geekosaur> you can't reuse Nothing, unfortunately, it's already associated with Maybe
2022-01-07 19:13:20 +0100 <[itchyjunk]> ah
2022-01-07 19:13:42 +0100 <geekosaur> for historical reasons we often call that Nil
2022-01-07 19:13:46 +0100 <[itchyjunk]> `data List a = EmptyList | ? `
2022-01-07 19:13:55 +0100 <[itchyjunk]> oh i see `data List a = Nil | ? `
2022-01-07 19:14:25 +0100 <geekosaur> now think about how a list works. not the [x,y,z] form but the other one which you'll mostly have seen as (x:xs)
2022-01-07 19:14:40 +0100DNH(~DNH@2a02:8108:1100:16d8:ad26:5398:3e1f:d97d) (Quit: My MacBook has gone to sleep. ZZZzzz…)
2022-01-07 19:15:26 +0100 <[itchyjunk]> a : data List xs 'ish
2022-01-07 19:15:32 +0100 <[itchyjunk]> oops
2022-01-07 19:15:39 +0100 <[itchyjunk]> x : data List xs, maybe?
2022-01-07 19:15:52 +0100 <[itchyjunk]> Wait no, idk what i am saying
2022-01-07 19:16:09 +0100 <Michal[m]> you can construct a list by taking an existing list and adding an element to it
2022-01-07 19:16:19 +0100mikko(~mikko@2a02:7b40:d418:6a61::1) (Quit: WeeChat 2.7.1)
2022-01-07 19:16:20 +0100 <geekosaur> you can't reuse : for the same reason you can't reuse Nothing
2022-01-07 19:16:28 +0100 <Michal[m]> this should give you the second constructor, beside Nil
2022-01-07 19:16:29 +0100 <[itchyjunk]> Oh :<
2022-01-07 19:16:34 +0100 <int-e> @src []
2022-01-07 19:16:34 +0100 <lambdabot> data [] a = [] | a : [a]
2022-01-07 19:17:00 +0100 <geekosaur> I was hoping not to give them the answer right out :)
2022-01-07 19:17:34 +0100 <int-e> (this is a lie, you can't actually write that in Haskell (except that's literally how GHC.Types does it))
2022-01-07 19:17:36 +0100 <geekosaur> should be able to figure that out from how theyve been recursing on the RHS of a list
2022-01-07 19:18:33 +0100 <int-e> we seemed to be a little too far off the correct syntax though :-/
2022-01-07 19:18:54 +0100 <geekosaur> they're supposed to be building their own list type and defining some functions on it
2022-01-07 19:19:19 +0100 <int-e> (And we still have to figure out what that looks like with different type and constructor names)
2022-01-07 19:19:28 +0100 <[itchyjunk]> hmm
2022-01-07 19:19:36 +0100gehmehgeh(~user@user/gehmehgeh) (Ping timeout: 276 seconds)
2022-01-07 19:20:00 +0100ProfSimm(~ProfSimm@87.227.196.109) (Remote host closed the connection)
2022-01-07 19:21:40 +0100 <[itchyjunk]> i need to recursively define it as first element plus rest of List xs and it does down all the way to Nil condition.. i think that is the idea?
2022-01-07 19:22:08 +0100dyeplexer(~dyeplexer@user/dyeplexer)
2022-01-07 19:22:26 +0100 <geekosaur> yes
2022-01-07 19:22:41 +0100 <geekosaur> the same way you've been recursing on real lists
2022-01-07 19:23:54 +0100jonathanx(~jonathan@h-178-174-176-109.a357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 19:24:12 +0100ProfSimm(~ProfSimm@87.227.196.109)
2022-01-07 19:24:17 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 19:24:59 +0100 <geekosaur> I was hoping I could coach you through using how you had been recursing on real lists to realize how they must be defined, and thereby how you would need to define your own
2022-01-07 19:25:18 +0100 <geekosaur> since understanding this is key to understanding how lists work
2022-01-07 19:25:28 +0100 <[itchyjunk]> `data List a = Nil | List a` ish ..
2022-01-07 19:25:44 +0100 <geekosaur> not quite. remember (x:xs)
2022-01-07 19:25:53 +0100 <geekosaur> you only have xs there
2022-01-07 19:26:28 +0100 <[itchyjunk]> `data List a = Nil | a along with List a`
2022-01-07 19:26:40 +0100 <geekosaur> well, actually as written you have x with a data constructor name List
2022-01-07 19:27:03 +0100 <geekosaur> right, now you need to work out how to write that "along with"
2022-01-07 19:27:08 +0100 <monochrom> I happen to think that this is a poor exercise. Be it unpopular opinion.
2022-01-07 19:27:23 +0100gehmehgeh(~user@user/gehmehgeh)
2022-01-07 19:27:31 +0100 <monochrom> Case 1. If you have taught the [] type properly, then this exercise is too trivial.
2022-01-07 19:27:47 +0100 <geekosaur> you have a better idea for an introduction to recursive data types?
2022-01-07 19:28:06 +0100 <monochrom> Case 2. If you have taught the [] type improperly, then this exercise punishes the good students and rewards the bad students. Here is why:
2022-01-07 19:28:12 +0100jrm(~jrm@156.34.249.199) (Read error: Connection reset by peer)
2022-01-07 19:28:32 +0100jrm(~jrm@156.34.249.199)
2022-01-07 19:29:12 +0100 <monochrom> For student who want to understand: Since you taught [] improperly, they don't know where to start for understanding, hell, you probably taught them wrong ideas to start. There is nothing to chew on.
2022-01-07 19:29:55 +0100 <monochrom> For student who want to cargo-cult: They can just look at "data [a] = [] | a : [a]" and change syntax. This still does not need understanding.
2022-01-07 19:30:05 +0100 <[itchyjunk]> How does the : look like without sugar syntax?
2022-01-07 19:30:25 +0100 <geekosaur> it's not sugar, it's just an operator-style data constructor
2022-01-07 19:30:45 +0100 <geekosaur> these all start with : which is arbitrarily considered an "uppercase" symbol character
2022-01-07 19:31:02 +0100enikarsuggest renamed : as cons
2022-01-07 19:31:15 +0100 <c_wraith> the [] case is sugar though. That one is a totally special case.
2022-01-07 19:31:49 +0100 <c_wraith> monochrom: I think there's value in showing people they can reimplement what [] does - the only magical things are the names.
2022-01-07 19:31:58 +0100lavaman(~lavaman@98.38.249.169)
2022-01-07 19:32:01 +0100 <geekosaur> we also have data NonEmpty a = a :| [a]
2022-01-07 19:32:02 +0100 <[itchyjunk]> `data List (x:xs) = Nil| x : List xs` conceptually but i don't get to use : because it's already used ?
2022-01-07 19:32:22 +0100 <geekosaur> where :| is the constructor
2022-01-07 19:32:30 +0100 <monochrom> Yes, therefore I don't pose it as an exercise, I give it as an example.
2022-01-07 19:32:57 +0100raehik(~raehik@cpc95906-rdng25-2-0-cust156.15-3.cable.virginm.net) (Ping timeout: 240 seconds)
2022-01-07 19:33:03 +0100 <[itchyjunk]> hmm
2022-01-07 19:33:21 +0100 <monochrom> A good exercise is not to ask students to reinvent list but to design variations.
2022-01-07 19:33:40 +0100zer0bitz(~zer0bitz@196.244.192.57)
2022-01-07 19:36:13 +0100 <EvanR> reinventing the let wheel = "roll... " : wheel in wheel
2022-01-07 19:39:00 +0100jgeerds(~jgeerds@55d4bbed.access.ecotel.net)
2022-01-07 19:40:24 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 19:42:30 +0100 <[itchyjunk]> I don't think i've managed to reinvent this wheel yet though. hopefully this clicks soon..
2022-01-07 19:42:37 +0100dyeplexer(~dyeplexer@user/dyeplexer) (Remote host closed the connection)
2022-01-07 19:44:17 +0100jrm(~jrm@156.34.249.199) (Ping timeout: 240 seconds)
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2022-01-07 19:51:38 +0100 <geekosaur> all you need to do is pick some other operator name that starts with a colon. :| and :+ are taken, and comma is reserved so :, won't work
2022-01-07 19:51:58 +0100 <geekosaur> or you can define it with a prefix name instead of an infix operator
2022-01-07 19:52:58 +0100 <c_wraith> oh, huh. It never occurred to me that , is too reserved to use in an operator. I guess [ and ] are, too.
2022-01-07 19:53:23 +0100 <geekosaur> I thought it might work until I considered (:,)
2022-01-07 19:56:27 +0100DNH(~DNH@2a02:8108:1100:16d8:ad26:5398:3e1f:d97d)
2022-01-07 19:56:38 +0100 <geekosaur> it does raise an interesting parse error if you attempt it
2022-01-07 19:59:09 +0100 <[itchyjunk]> Right, i think i solved the mystery. When you said pick an operator, that was a strong hint that i wasn't internalizing
2022-01-07 19:59:19 +0100 <[itchyjunk]> data constructor is an actual operator
2022-01-07 19:59:35 +0100 <[itchyjunk]> `data List a = Nil | Cons a (List a)`
2022-01-07 20:00:59 +0100 <geekosaur> there you go
2022-01-07 20:01:19 +0100 <geekosaur> you could also choose an operator like ::: although it'd be a PITA
2022-01-07 20:01:25 +0100 <EvanR> data I'mCool a = Shade :~!#$? Shade
2022-01-07 20:01:29 +0100 <geekosaur> (:: is taken)
2022-01-07 20:02:14 +0100eggplantade(~Eggplanta@108-201-191-115.lightspeed.sntcca.sbcglobal.net)
2022-01-07 20:02:17 +0100eastbillie(~gallup@192-222-138-215.qc.cable.ebox.net)
2022-01-07 20:02:18 +0100abarbu(~user@c-66-31-23-28.hsd1.ma.comcast.net) (Read error: Connection reset by peer)
2022-01-07 20:02:23 +0100eastbillie(~gallup@192-222-138-215.qc.cable.ebox.net) (Client Quit)
2022-01-07 20:02:51 +0100 <c_wraith> I'd probably pretend I don't know Cofree exists and just use :<
2022-01-07 20:02:52 +0100ouestbillie(~gallup@192-222-138-215.qc.cable.ebox.net)
2022-01-07 20:03:09 +0100 <monochrom> I use :>
2022-01-07 20:03:16 +0100 <[itchyjunk]> so `I'mCool` is a type constructor and `a` is a parameter. this only has one data constructor called `Shade` that takes 2 parameter `:~!#$?` and `Shade` ?
2022-01-07 20:03:28 +0100 <geekosaur> nope
2022-01-07 20:03:32 +0100 <EvanR> no :~!#$? is the constructor
2022-01-07 20:03:33 +0100 <[itchyjunk]> :(
2022-01-07 20:03:44 +0100 <EvanR> just like in []
2022-01-07 20:03:47 +0100 <geekosaur> remember iniitial : is an operator-style constructor
2022-01-07 20:03:49 +0100 <EvanR> starts with a colon
2022-01-07 20:04:23 +0100 <EvanR> haskell is cool for having this but now I'm questioning if it's quite counterintuitive xD
2022-01-07 20:04:25 +0100 <geekosaur> so you have a constructor :-!#$? with two Shade parameters
2022-01-07 20:04:31 +0100 <c_wraith> and since no one else has called it out, I will. you can be cool if you have a pair of shades
2022-01-07 20:04:51 +0100simendsjo(~user@84.211.91.241)
2022-01-07 20:05:34 +0100 <monochrom> BTW if you have "data List a = Nil | a `Cons` List a deriving Show" or "data I'mCool a = (:~!#$?) Shade Shade deriving Show", the derived Show instances will actually respect your non-default choice of fixity.
2022-01-07 20:06:04 +0100 <EvanR> did not know that
2022-01-07 20:06:19 +0100qwertyasda(~Qwerty@wsip-174-71-193-82.lv.lv.cox.net)
2022-01-07 20:07:00 +0100justsomeguy(~justsomeg@user/justsomeguy)
2022-01-07 20:07:19 +0100 <EvanR> @let data Int2 = Int `I2` Int
2022-01-07 20:07:20 +0100 <lambdabot> Defined.
2022-01-07 20:07:26 +0100 <EvanR> > I2 1 2
2022-01-07 20:07:28 +0100 <lambdabot> error:
2022-01-07 20:07:28 +0100 <lambdabot> • No instance for (Show Int2)
2022-01-07 20:07:28 +0100 <lambdabot> arising from a use of ‘show_M59481879713528625638’
2022-01-07 20:07:33 +0100 <EvanR> @undefined
2022-01-07 20:07:33 +0100 <lambdabot> Undefined.
2022-01-07 20:07:36 +0100 <EvanR> @let data Int2 = Int `I2` Int deriving Show
2022-01-07 20:07:37 +0100 <lambdabot> Defined.
2022-01-07 20:07:38 +0100 <EvanR> > I2 1 2
2022-01-07 20:07:40 +0100 <lambdabot> 1 `I2` 2
2022-01-07 20:07:41 +0100qwertyasda(~Qwerty@wsip-174-71-193-82.lv.lv.cox.net) (Quit: Leaving)
2022-01-07 20:08:32 +0100 <EvanR> next time I'm at a loss at a party I'll bring that up
2022-01-07 20:09:46 +0100 <c_wraith> I seem to recall derived show not respecting fixity declarations on punctuation operator constructors, though
2022-01-07 20:11:06 +0100 <geekosaur> I recall thatr being raised as a bug several years ago but don't know if it's been fixed
2022-01-07 20:11:49 +0100jgeerds(~jgeerds@55d4bbed.access.ecotel.net) (Ping timeout: 240 seconds)
2022-01-07 20:16:45 +0100 <glguy> @let data Example = Int :* Example | End deriving Show; infixr 5 :*
2022-01-07 20:16:46 +0100 <lambdabot> Defined.
2022-01-07 20:16:46 +0100 <glguy> 1 :* 2 :* 3 :* End
2022-01-07 20:16:51 +0100 <glguy> > 1 :* 2 :* 3 :* End
2022-01-07 20:16:52 +0100 <lambdabot> 1 :* (2 :* (3 :* End))
2022-01-07 20:17:29 +0100 <geekosaur> mm, the one I recall is where it omits necessary parens, such that the result isn't parsable
2022-01-07 20:17:45 +0100 <geekosaur> that one's just a little unfortunate but still works
2022-01-07 20:18:06 +0100 <glguy> > Just (1 :* 2 :* 3 :* End)
2022-01-07 20:18:07 +0100 <lambdabot> Just (1 :* (2 :* (3 :* End)))
2022-01-07 20:18:33 +0100 <glguy> I don't know about the unparsable issue
2022-01-07 20:19:04 +0100 <geekosaur> I didn't find it on a quick search so that one may have been fixed already
2022-01-07 20:24:40 +0100justsomeguy(~justsomeg@user/justsomeguy) (Quit: WeeChat 3.3)
2022-01-07 20:31:24 +0100burnsidesLlama(~burnsides@dhcp168-021.wadham.ox.ac.uk) (Remote host closed the connection)
2022-01-07 20:33:57 +0100lavaman(~lavaman@98.38.249.169) (Ping timeout: 240 seconds)
2022-01-07 20:35:56 +0100 <c_wraith> what's odd is that showsPrec is so mechanical to implement respecting fixity, it seems like it would be feasible to have the deriving mechanism do it.
2022-01-07 20:36:42 +0100 <glguy> I think the trouble is that showsPrec doesn't know about fixity, only precedence, so it has to make a worst case assumption
2022-01-07 20:37:55 +0100coot(~coot@89-64-85-93.dynamic.chello.pl)
2022-01-07 20:44:23 +0100johnw(~johnw@2607:f6f0:3004:1:c8b4:50ff:fef8:6bf0)
2022-01-07 20:48:52 +0100cosimone(~user@2001:b07:ae5:db26:c24a:d20:4d91:1e20) (Remote host closed the connection)
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2022-01-07 20:53:17 +0100jgeerds(~jgeerds@55d4bbed.access.ecotel.net)
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2022-01-07 20:54:28 +0100tromp(~textual@dhcp-077-249-230-040.chello.nl)
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2022-01-07 21:04:35 +0100cheater(~Username@user/cheater)
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2022-01-07 21:09:15 +0100burnsidesLlama(~burnsides@dhcp168-021.wadham.ox.ac.uk)
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2022-01-07 21:16:19 +0100coolnickname(uid531864@user/coolnickname)
2022-01-07 21:36:28 +0100motherfsck(~motherfsc@user/motherfsck) (Remote host closed the connection)
2022-01-07 21:37:33 +0100tromp(~textual@dhcp-077-249-230-040.chello.nl) (Quit: My iMac has gone to sleep. ZZZzzz…)
2022-01-07 21:38:39 +0100Hayek(~xxx@rrcs-173-196-3-254.west.biz.rr.com) (Ping timeout: 256 seconds)
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2022-01-07 21:46:59 +0100 <dmj`> almost started funding the wrong haskell foundation https://www.haskellfoundation.org/donate/
2022-01-07 21:47:21 +0100vysn(~vysn@user/vysn)
2022-01-07 21:49:36 +0100tromp(~textual@dhcp-077-249-230-040.chello.nl)
2022-01-07 21:49:56 +0100 <Hecate> hahahahahaha
2022-01-07 21:51:21 +0100burnsidesLlama(~burnsides@dhcp168-021.wadham.ox.ac.uk)
2022-01-07 21:51:50 +0100 <dmj`> saw "tribal affiliation" and was like "Is this related to the burning bridges proposal?"
2022-01-07 21:53:02 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 21:55:12 +0100Shiranai(~Shiranai@190.237.13.79)
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2022-01-07 21:55:57 +0100pavonia(~user@user/siracusa)
2022-01-07 22:01:13 +0100Inst(~delicacie@c-98-208-218-119.hsd1.fl.comcast.net)
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2022-01-07 22:02:44 +0100 <Shiranai> Hello, I'm writing a function with signature `(Int, Bool) -> Command -> Just (Int, Bool)` for use in a foldM. I want Bool to be used as a flag for shortcircuiting the loop, I tried `myFunc (val, True)=Just (val, True)` but does not seem to shortcircuit as I expected
2022-01-07 22:03:26 +0100cosimone(~user@2001:b07:ae5:db26:c24a:d20:4d91:1e20) (Ping timeout: 252 seconds)
2022-01-07 22:03:31 +0100 <Shiranai> I meant `myFunc (val, True) _ = Just (val, True)`
2022-01-07 22:03:38 +0100takuan(~takuan@178-116-218-225.access.telenet.be) (Remote host closed the connection)
2022-01-07 22:04:07 +0100 <xerox> @src foldM
2022-01-07 22:04:07 +0100 <lambdabot> foldM _ a [] = return a
2022-01-07 22:04:07 +0100 <lambdabot> foldM f a (x:xs) = f a x >>= \fax -> foldM f fax xs
2022-01-07 22:04:07 +0100 <Shiranai> how do shortcircuit correctly?
2022-01-07 22:04:21 +0100 <xerox> looks like f can't decide to shortcut
2022-01-07 22:04:22 +0100raehik(~raehik@cpc95906-rdng25-2-0-cust156.15-3.cable.virginm.net)
2022-01-07 22:05:01 +0100 <xerox> >>= is happening no matter what f uses of its arguments
2022-01-07 22:05:24 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 22:05:44 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 22:05:51 +0100 <Shiranai> hmmm thanks, any idea how to shortcut through other means?
2022-01-07 22:06:16 +0100 <xerox> @src foldr
2022-01-07 22:06:16 +0100 <lambdabot> foldr f z [] = z
2022-01-07 22:06:16 +0100 <lambdabot> foldr f z (x:xs) = f x (foldr f z xs)
2022-01-07 22:06:27 +0100 <xerox> this one can because f can ignore the rest of the fold, it's second argument
2022-01-07 22:06:43 +0100eggplantade(~Eggplanta@108-201-191-115.lightspeed.sntcca.sbcglobal.net)
2022-01-07 22:07:06 +0100 <Shiranai> is there a monadic version though? I need to use Maybe
2022-01-07 22:08:02 +0100 <sshine> use Maybe where?
2022-01-07 22:09:28 +0100 <dmj`> why use Bool to short circuit when Maybe automatically short circuits
2022-01-07 22:09:29 +0100 <Shiranai> I'm parsing a list of commands so I need to use something like foldM and Maybe
2022-01-07 22:10:18 +0100 <Shiranai> because I want to rescue the other value in the pair (Int, Maybe)
2022-01-07 22:10:19 +0100 <EvanR> you can also use direct recursion to short circuit
2022-01-07 22:11:18 +0100 <Shiranai> (Int, Bool)* I meant
2022-01-07 22:11:19 +0100 <EvanR> I suspect there is a more elegant way for you to write it without the Bool flag in a pair
2022-01-07 22:11:27 +0100 <Shiranai> agree
2022-01-07 22:11:31 +0100 <xerox> what does the fold do?
2022-01-07 22:11:48 +0100 <Shiranai> I have no idea what it may be though
2022-01-07 22:12:14 +0100 <EvanR> what is the Just for
2022-01-07 22:12:20 +0100 <EvanR> I mean, Maybe
2022-01-07 22:12:37 +0100 <EvanR> that also can short circuit
2022-01-07 22:13:16 +0100 <c_wraith> You probably want Either instead of Maybe, in this case
2022-01-07 22:13:35 +0100 <c_wraith> Either Int Int short-circuits and actually returns the result. :)
2022-01-07 22:14:02 +0100 <xerox> ah nice the left interrupts >>= !
2022-01-07 22:14:13 +0100 <c_wraith> yes it does!
2022-01-07 22:15:04 +0100 <Shiranai> the fold parses a list of comments, most of the commands change the value of an Int, but the return command implies that there is no need for keep reading the rest of the commands, so that's why I thought of using (Int, Bool) as the accumulator
2022-01-07 22:15:06 +0100 <EvanR> then there's the awkward use of Either ErrorMsg () which is like reversed use of Maybe
2022-01-07 22:17:11 +0100simendsjo(~user@84.211.91.241) (Ping timeout: 256 seconds)
2022-01-07 22:17:49 +0100 <dmj`> Shiranai: can you paste your code?
2022-01-07 22:17:52 +0100 <EvanR> when it comes to "complicated" monadic loops, I often write the loop logic as a new combinator and use that
2022-01-07 22:18:07 +0100 <EvanR> instead of trying to use a premade loop (from a package) or foldM
2022-01-07 22:18:17 +0100nhatanh02(~satori@123.24.172.30) (Ping timeout: 240 seconds)
2022-01-07 22:18:28 +0100 <EvanR> Control.Monad.Loops has like 30 loops and often none of them fit
2022-01-07 22:18:48 +0100 <Shiranai> dmj` I probably shouldn't since it's some kind of assignment, that's why I'm being vague, sorry about that
2022-01-07 22:19:17 +0100raehik(~raehik@cpc95906-rdng25-2-0-cust156.15-3.cable.virginm.net) (Ping timeout: 240 seconds)
2022-01-07 22:19:40 +0100 <Shiranai> yeah I think doing a custom loop is the way to go without refactoring a lot of a code, thanks!
2022-01-07 22:20:21 +0100 <EvanR> but c_wraith idea sounded likely
2022-01-07 22:21:09 +0100_ht(~quassel@82-169-194-8.biz.kpn.net) (Remote host closed the connection)
2022-01-07 22:21:42 +0100Franciman(~Franciman@mx1.fracta.dev)
2022-01-07 22:21:54 +0100Franciman(~Franciman@mx1.fracta.dev) (haskell is cringe)
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2022-01-07 22:25:46 +0100Franciman(~Franciman@mx1.fracta.dev)
2022-01-07 22:25:49 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 22:25:57 +0100 <Franciman> hello, what's the difference between the native code generator of haskell
2022-01-07 22:26:01 +0100 <Franciman> and the llvm based one?
2022-01-07 22:26:10 +0100 <Franciman> and why is the llvm based one known to be better even if slower?
2022-01-07 22:26:17 +0100 <Franciman> what's the use of a native code generator of haskell?
2022-01-07 22:26:22 +0100 <Franciman> why would i need it?
2022-01-07 22:26:23 +0100f-a(f2a@f2a.jujube.ircnow.org)
2022-01-07 22:26:35 +0100 <Franciman> is it to have a sort of autarchy?
2022-01-07 22:26:39 +0100 <Franciman> having a self contained system?
2022-01-07 22:26:49 +0100 <geekosaur> llvm is slower because we can't pass it information it needs to optimize and they have no interest in adding ghc-specific support that would be needed
2022-01-07 22:27:24 +0100 <geekosaur> you can get significantly better code natively
2022-01-07 22:27:36 +0100 <Franciman> yet i seem to understand it produce at least as good code as the native code generator
2022-01-07 22:27:40 +0100 <Franciman> that's what the docs report
2022-01-07 22:27:51 +0100 <Franciman> i suppose
2022-01-07 22:28:33 +0100 <geekosaur> ghc itself does, but llvm's optimizer defaults to doing as little as possible of its own optimization because it doesn't really understand the IR ghc generates
2022-01-07 22:29:00 +0100 <geekosaur> and never will because it's all CPSed and llvm won't add support for ghc's CPS transforms
2022-01-07 22:29:23 +0100 <Franciman> makes total sense to me
2022-01-07 22:29:58 +0100 <geekosaur> and ghc needs all the optimization help it can get because graph reduction is inherently less performant than direct code
2022-01-07 22:30:34 +0100 <Franciman> makes sense i see. Do you think LLVM backend can help soothe this problem, tho? https://gitlab.haskell.org/ghc/ghc/-/issues/20445
2022-01-07 22:31:01 +0100n3rdy1(~n3rdy1@2600:1700:4570:3480::41)
2022-01-07 22:31:03 +0100 <Franciman> that's why i was asking what's the need of a native backend when it's bugged
2022-01-07 22:31:09 +0100 <Franciman> but the fact that it supports special needs
2022-01-07 22:31:13 +0100 <Franciman> is more than better answer
2022-01-07 22:31:15 +0100 <Franciman> thanks geekosaur
2022-01-07 22:31:43 +0100 <geekosaur> 9.0.2 should hopefully fix that one
2022-01-07 22:32:03 +0100 <geekosaur> it's not unusual that .1 point releases are buggy, that's why there are later releases
2022-01-07 22:32:36 +0100 <geekosaur> we actually went through the same thing with m1 llvm support, but the ".1" release was 8.10.5
2022-01-07 22:32:44 +0100 <geekosaur> wasn't stable until 8.10.7
2022-01-07 22:32:54 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 22:33:06 +0100 <geekosaur> so it's not like llvm is always better codegen-wise
2022-01-07 22:33:15 +0100jonathanx(~jonathan@h-178-174-176-109.a357.priv.bahnhof.se)
2022-01-07 22:34:50 +0100 <Franciman> i just quoted the docs
2022-01-07 22:35:16 +0100 <dmj`> If GHC went from STG to LLVM directly it'd probably be faster than the current approach of Cmm to LLVM.
2022-01-07 22:36:29 +0100 <Franciman> dmj`: faster but maybe produce worse code
2022-01-07 22:36:56 +0100 <EvanR> clarification please, the LLVM backend is slower... meaning it takes longer to produce code, or the resulting code is slower
2022-01-07 22:37:17 +0100 <Franciman> takes longer to produce code
2022-01-07 22:38:01 +0100 <EvanR> and resulting code is about the same performance?
2022-01-07 22:39:06 +0100 <dmj`> Franciman: it actually took longer to produce ARM code before we got the native ARM backend, since LLVM was just being used as an additional translation layer to get to ARM by way of Cmm.
2022-01-07 22:39:07 +0100burnsidesLlama(~burnsides@dhcp168-021.wadham.ox.ac.uk)
2022-01-07 22:42:43 +0100 <geekosaur> the code is also generally less performant although this depends on the exact code
2022-01-07 22:42:57 +0100 <geekosaur> numeric operations are often as fast or faster
2022-01-07 22:43:24 +0100burnsidesLlama(~burnsides@dhcp168-021.wadham.ox.ac.uk) (Ping timeout: 256 seconds)
2022-01-07 22:48:00 +0100 <dmj`> geekosaur: do we have any benchmarks to compare STG -> LLVM vs. Cmm -> LLVM? I think that would be super interesting.
2022-01-07 22:48:27 +0100Shiranai(~Shiranai@190.237.13.79) (Quit: Connection closed)
2022-01-07 22:50:03 +0100 <geekosaur> no, there is currently no way for ghc to go directly stg -> llvm
2022-01-07 22:50:29 +0100 <geekosaur> and little interest in doing so since the llvm folks aren't interested either
2022-01-07 22:51:08 +0100mc47(~mc47@xmonad/TheMC47) (Remote host closed the connection)
2022-01-07 22:51:19 +0100 <geekosaur> you might wan tto talk to the folks in #ghc about it but this is my understanding of the situation
2022-01-07 22:51:33 +0100 <geekosaur> (I think you want moritz angermann)
2022-01-07 22:51:54 +0100jonathanx(~jonathan@h-178-174-176-109.a357.priv.bahnhof.se) (Remote host closed the connection)
2022-01-07 22:52:06 +0100Franciman(~Franciman@mx1.fracta.dev) (long live telescope)
2022-01-07 22:52:12 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
2022-01-07 22:53:11 +0100 <geekosaur> llvm is currently something of a bastard child because doing anything significant over what ghc already does requires teaching llvm about ghc's cps-ed code
2022-01-07 22:53:57 +0100 <geekosaur> so almost all effort has gone into the native backends, with the exception of m1 support because it required such radical changes
2022-01-07 22:55:41 +0100 <geekosaur> (basically, apple decided to get rid of C-style type promotion, everything is its native size. which had to be reflected everywhere, so for example in 9.2.x Char# is 32 bits and Word8# is 8 bits)
2022-01-07 22:56:05 +0100OscarZ_(~oscarz@95.175.104.170)
2022-01-07 22:57:46 +0100 <dmj`> geekosaur: Interesting, I know compiling HOFs isn't feasible, which I imagine a CPS pass would create a lot of. GRIN can handle those (HOFs) through a defunctionalization pass. This could also be done in Core before you even get to STG / Cmm. I've wondered why GHC doesn't completely monomorphize up front, then CPS transform, defunctionalize, optimize, then codegen to LLVM. MLTon does this more or less.
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2022-01-07 22:58:23 +0100 <geekosaur> you'd have to ask them
2022-01-07 22:58:25 +0100 <dmj`> well, you'd have to lambda lift and closure convert before defunctionalizing too
2022-01-07 22:58:52 +0100 <dmj`> geekosaur: I think its because you can't encode existentials when you monomorphize, but maybe I'm wrong
2022-01-07 22:59:26 +0100f-a(f2a@f2a.jujube.ircnow.org) ()
2022-01-07 22:59:27 +0100 <geekosaur> afaik existentials as such cease to exist as distinct entities past the typechecker
2022-01-07 23:00:05 +0100DNH(~DNH@2a02:8108:1100:16d8:ad26:5398:3e1f:d97d) (Quit: My MacBook has gone to sleep. ZZZzzz…)
2022-01-07 23:00:25 +0100 <monochrom> My understanding is that STG moves support for HOFs to the RTS and it is a very direct form of support, i.e., without encoding it by defunctionalization.
2022-01-07 23:02:42 +0100 <monochrom> For example if you look at generated Cmm code you can see it calling functions with names like "ap1_fast", which are functions provided by the RTS.
2022-01-07 23:03:15 +0100sub0(~bc8147f2@cerf.good1.com)
2022-01-07 23:03:17 +0100Pickchea(~private@user/pickchea)
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2022-01-07 23:04:14 +0100 <dmj`> monochrom: interesting, I know defunctionalization requires a whole program pass, so maybe GHC being incremental makes it a non-starter.
2022-01-07 23:04:20 +0100jonathanx(~jonathan@h-178-174-176-109.a357.priv.bahnhof.se)
2022-01-07 23:04:49 +0100 <monochrom> I would describe STG as thunk-passing style instead of continuation-passing style. :)
2022-01-07 23:04:51 +0100 <geekosaur> that was one of the changes grin had to make to ghc, yeh
2022-01-07 23:05:03 +0100 <monochrom> Or s/thunk/closure/ if you will.
2022-01-07 23:05:10 +0100glguy(x@libera/staff/glguy) (Quit: Quit)
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2022-01-07 23:05:43 +0100jonathanx(~jonathan@h-178-174-176-109.A357.priv.bahnhof.se)
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2022-01-07 23:06:14 +0100 <dmj`> geekosaur: hmm, yea the modpak files got merged iirc. I wonder if a ghc-plugin would have been more appropriate, or if that is even possible with the plugin architecture.
2022-01-07 23:08:03 +0100 <dmj`> monochrom: One of the arguments I've heard against GHC going whole program optimizing is that cross module inlining is good enough. I wonder how well this holds up in practice, because I'm pretty sure GHC will generate code that does a blind JMP to some function pointer address for all unknown calls, which are probably a lot I imagine.
2022-01-07 23:09:20 +0100 <geekosaur> I find myself wondering of there are some other barriers to it
2022-01-07 23:09:30 +0100 <int-e> memory usage?
2022-01-07 23:10:03 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com)
2022-01-07 23:10:03 +0100wroathe(~wroathe@206-55-188-8.fttp.usinternet.com) (Changing host)
2022-01-07 23:10:03 +0100wroathe(~wroathe@user/wroathe)
2022-01-07 23:10:15 +0100 <geekosaur> like, the inlinePerformIO hullabaloo suggests to me that ghc relies on *not* doing inlining in some cases to prevent lifting things that shouldn't be lifted
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2022-01-07 23:11:02 +0100 <geekosaur> and of WPC exposes IO definitions for inlining then that barrier might be hard to maintain
2022-01-07 23:11:18 +0100 <geekosaur> *if WPC
2022-01-07 23:12:07 +0100jackhillKM4MBG
2022-01-07 23:12:35 +0100KM4MBGjackhill
2022-01-07 23:16:31 +0100 <dmj`> seems like Lennart has done it and thinks its ok https://twitter.com/Augustsson/status/1104924762499768320
2022-01-07 23:16:46 +0100coot(~coot@89-64-85-93.dynamic.chello.pl) ()
2022-01-07 23:17:11 +0100coot(~coot@2a02:a310:e03f:8500:5cc8:47c:8ec0:b827)
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2022-01-07 23:18:22 +0100 <EvanR> monochrom, you just changed from thunk to closure. I'm not sure which one is more vague (outside context of GHC guts)
2022-01-07 23:18:28 +0100 <geekosaur> the question I have there, as above, is whether *ghc* can do this or if it'd require significant rearchitecting to the point of writing a whole new compiler as lennart did
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2022-01-07 23:21:58 +0100acidjnk_new3(~acidjnk@p200300d0c7271e73e4c690103e77be5f.dip0.t-ipconnect.de)
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2022-01-07 23:22:08 +0100 <monochrom> EvanR, the good news and bad news is that STG finds that it can use closures for thunks (and a lot of other things) so "everything is a closure". In this context, "closure" is not vague.
2022-01-07 23:22:32 +0100 <EvanR> everything is a closure, great
2022-01-07 23:22:35 +0100 <EvanR> so it's like a box
2022-01-07 23:22:43 +0100xff0x(~xff0x@2001:1a81:525f:5800:6161:847e:32a5:3ca7)
2022-01-07 23:24:32 +0100 <dmj`> geekosaur: that's a good question, I don't know. Not many optimizations happen in STG (afaik), GRIN is its supposed successor, yet it performs all the optimizations. So if GRIN is to be included in GHC why do the optimizations in Core at all? Unless there is a way to combine GRIN and Core. GRIN being first-order makes me lean no.
2022-01-07 23:25:19 +0100 <dmj`> If you keep the compiler frontend is it considered a rewrite ? :)
2022-01-07 23:25:45 +0100 <geekosaur> you might ask the grin folks that question :)
2022-01-07 23:26:09 +0100 <geekosaur> I'd also be interested in finding out as above if they had any issues with IO escaping its boundaries
2022-01-07 23:26:38 +0100 <geekosaur> although I guess that part lives in the frontend, so probably no unless they didn;t do due diligence with the WPC part
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2022-01-07 23:39:30 +0100 <dmj`> geekosaur: sure, will see what I can find out about IO escaping boundaries
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2022-01-07 23:54:33 +0100 <geekosaur> I'm not absolutely certain that it's a problem, but like I said the inlinePerformIO thing seems strongly suggestive
2022-01-07 23:54:36 +0100vysn(~vysn@user/vysn) (Ping timeout: 268 seconds)
2022-01-07 23:55:03 +0100 <geekosaur> just inlining unsafePerformIO wouldn't be expected to have that severe an effect on how ghc treats IO-using code
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