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Logs: liberachat/#haskell

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2021-07-12 22:00:27 <geekosaur> think of it as type level undefined, maybe?
2021-07-12 22:00:40 <boxscape> it is bad if you want to have a consistent type theory
2021-07-12 22:01:05 <boxscape> (haskell's type system isn't consistent in more than one way)
2021-07-12 22:01:20 <monochrom> Haskell is not for arguing.
2021-07-12 22:01:21 <boxscape> s/isn't consistent/is inconsistent
2021-07-12 22:01:50 <monochrom> Unpopular opinion: It is the stance "use Haskell for proofs" that is inconsistent.
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2021-07-12 22:02:48 <maralorn> monochrom: +1
2021-07-12 22:03:35 <chisui> Well I tried to create a category implementation `data Phantom k (a :: k) (b :: k) = Phantom` and `type Empty = Phantom Void`
2021-07-12 22:03:54 <maralorn> I have been confused and slightly insecure about the Haskell typesystem for years because people kept saying it is inconsistent.
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2021-07-12 22:04:37 <monochrom> The Haskell term system, type system, and kind system are very much consistent.
2021-07-12 22:05:02 <monochrom> You do lose a few axioms you would expect from other logics, yes.
2021-07-12 22:05:03 <chisui> monochrom: if you allow bottom?
2021-07-12 22:05:21 <Hecate> 👀
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2021-07-12 22:07:44 <monochrom> You should still feel insecure that you can still make a mistake of non-termination in Haskell, yes.
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2021-07-12 22:08:47 <monochrom> But looking at how C programmers don't really feel insecure with even less safety nets, I would say "take it easy".
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2021-07-12 22:10:36 <chisui> Well I like type systems where you can't write `unsafeCoerce`
2021-07-12 22:10:40 <monochrom> My opinion on ensuring termination and doing so ergonomically is still with: don't do it with types, do it with an extra static analysis tool.
2021-07-12 22:11:37 <monochrom> I can change my opinion when I see an ergonomic dependently typed language. I don't think Agda etc have achieved it.
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2021-07-12 22:18:21 <chisui> monochrom: You are completely right. Nevertheless I was stumped by this. I mean GHC even warned my that this would be an issue.
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2021-07-12 22:25:23 <maralorn> chisui: I am not convinced that unsafeCoerce is even a property of the typesystem.
2021-07-12 22:27:13 <geekosaur> I see it as a property of the language to evade the typesystem
2021-07-12 22:29:46 <boxscape> Well, if your typesystem is logically inconsistent (like haskell's), that means it allows you to construct a function of type `forall a b . a -> b`, at least. Though whether it allows you to construct a function that behaves like unsafeCoerce is a different matter
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2021-07-12 22:46:05 <monochrom> @quote monochrom unsafeCoerce
2021-07-12 22:46:05 <lambdabot> monochrom says: isTrue = (unsafeCoerce :: Either a b -> Bool) . (unsafeCoerce :: Maybe c -> Either a b) . (unsafeCoerce :: Bool -> Maybe c)
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2021-07-12 22:52:39 <Guest25> how efficient is Foreign.Storable.peek? like say I have a Ptr Int and need the value multiple times, should I call (peek ptr) each time or store the value as a Haskell Int on the first call?
2021-07-12 22:52:56 <Guest25> (doing some FFI stuff or I wouldn't be dealing with Ptrs manually)
2021-07-12 22:54:18 <geekosaur> reasonably efficient but it'll still do the peek each time instead of optimizing it down via CSE. then again if this matters to performance you're arguably making a mistake somewhere else
2021-07-12 22:55:47 <Guest25> cool thanks!
2021-07-12 22:55:52 <Guest25> and yeah, it probably won't matter
2021-07-12 22:56:58 <hololeap> with optparse-applicative, I want to use a specific configuration if no options are passed to the command line. how can I do this?
2021-07-12 22:58:27 <monochrom> I think I specified default values for every option.
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2021-07-12 22:59:27 <hpc> it's also Alternative, so maybe you can have options <|> defaultOptions
2021-07-12 23:01:23 <hololeap> hpc, that's what I was thinking but I haven't used the library enough to have an intuition for how it works
2021-07-12 23:03:04 <hpc> it's pretty much like any other parser's Alternative, but you don't have to worry about using try to not consume input
2021-07-12 23:04:39 <monochrom> https://github.com/treblacy/random-read/blob/eb89d291e687b72269c30d2a2903cd26cf8f6f73/random-read.hs is how I did it with every option having "<> value mydefaultforthis"
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2021-07-12 23:04:57 <hololeap> so, when does it fail (in the Alternative sense)? when options are given out-of-order? when they are not given?
2021-07-12 23:05:48 <hpc> whenever the parser would error out normally
2021-07-12 23:05:57 <hpc> if the program would bail out with help text, instead try this other parser
2021-07-12 23:06:18 <hololeap> hm, it sounds like I'll just have to play around with it until I build an intuition for it
2021-07-12 23:07:23 <geekosaur> sounds to me like it would work best if there's otherwise at least one required option
2021-07-12 23:08:34 <hpc> yeah, but if the program would do the right thing in that case problem solved :D
2021-07-12 23:08:50 <hpc> who even needs the alternate parser at that point
2021-07-12 23:09:43 <hpc> hololeap: if it helps, normally the Alternative instance is so you can do things like "foo --create --name=foo" vs "foo --delete --id=12345"
2021-07-12 23:10:57 <hpc> data FooAction = Create String | Delete Int | Version | Help | etc etc
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2021-07-12 23:43:08 <Raugh> I'm trying to use Database.PostgreSQL.Simple with queries read from a file but I can't figure out how to go from [Char] to Query. The docs say to use overloaded strings and construct the Queries in place but I'm reading them from a file
2021-07-12 23:48:23 <geekosaur> https://hackage.haskell.org/package/postgresql-simple-0.6.4/docs/src/Database.PostgreSQL.Simple.Types.html#line-90
2021-07-12 23:48:30 <geekosaur> evil hack, but.
2021-07-12 23:48:45 <Axman6> @hoodle IsString
2021-07-12 23:48:45 <lambdabot> Data.String class IsString a
2021-07-12 23:48:45 <lambdabot> GHC.Exts class IsString a
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