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2021-08-11 01:51:27 <euouae> But sequence takes a monad
2021-08-11 01:51:30 <euouae> Not an applicative
2021-08-11 01:52:10 <Axman6> it days that, but almost always it's only using the Applicative instance, since all Monads are Applicatives
2021-08-11 01:52:25 <Axman6> and the type is mostly a historical artefact
2021-08-11 01:52:31 <euouae> It may be, but why is that important?
2021-08-11 01:52:44 <euouae> Why are you protesting about my mention of `>>`?
2021-08-11 01:52:44 <dsal> :t sequenceA
2021-08-11 01:52:45 <lambdabot> (Traversable t, Applicative f) => t (f a) -> f (t a)
2021-08-11 01:52:51 <Axman6> you tell me, I still don't know what your point is
2021-08-11 01:53:04 <dsal> I don't understand what >> has to do with traverse. They seem unrelated.
2021-08-11 01:53:15 <euouae> Ok look, a while ago you admitted sequence can have many implementations
2021-08-11 01:53:24 <Axman6> because you will almost certainly never see any use of >> in any implementation of Traversable
2021-08-11 01:53:24 <euouae> I'm saying that the one implementation the sequence has is not well-documented to distinguish it from all others
2021-08-11 01:53:49 <dsal> @src sequenceA
2021-08-11 01:53:49 <lambdabot> Source not found. :(
2021-08-11 01:53:51 <dsal> @src sequence
2021-08-11 01:53:51 <lambdabot> sequence [] = return []
2021-08-11 01:53:51 <lambdabot> sequence (x:xs) = do v <- x; vs <- sequence xs; return (v:vs)
2021-08-11 01:53:51 <lambdabot> --OR
2021-08-11 01:53:51 <lambdabot> sequence xs = foldr (liftM2 (:)) (return []) xs
2021-08-11 01:54:13 <euouae> There you go, it uses `do` which uses `>>` right?
2021-08-11 01:54:18 × geekosaur quits (~geekosaur@xmonad/geekosaur) (Ping timeout: 258 seconds)
2021-08-11 01:54:24 <dsal> @undo do v <- x; vs <- sequence xs; return (v:vs)
2021-08-11 01:54:24 <lambdabot> x >>= \ v -> sequence xs >>= \ vs -> return (v : vs)
2021-08-11 01:54:27 → geekosaur joins (~geekosaur@xmonad/geekosaur)
2021-08-11 01:54:34 <Axman6> I don't think there are many law abiding implementations of sequence which don't do what we've talked about
2021-08-11 01:55:07 <euouae> To be law abiding you need laws written down
2021-08-11 01:55:14 <Axman6> like, traverse pure = pure ensures the structure is kept intact and the order of elements can't change
2021-08-11 01:55:15 <euouae> Where's the laws for sequence documented?
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2021-08-11 01:55:30 <dsal> https://en.wikibooks.org/wiki/Haskell/Traversable#The_Traversable_laws
2021-08-11 01:55:54 <euouae> but can't sequence have many different implementations?
2021-08-11 01:56:02 <davean> also https://hackage.haskell.org/package/base-4.15.0.0/docs/Data-Traversable.html#g:10
2021-08-11 01:56:12 <euouae> couldn't you throw away the result of the action of v <- x; and just collect v instead?
2021-08-11 01:56:16 <davean> euouae: all that follow those laws
2021-08-11 01:56:43 <dsal> You could try, but if you're implementing Traversable, you should run your implementation against checkers and see if you've made any mistakes.
2021-08-11 01:57:07 <euouae> so you're saying that the above example of `evalState (sequence $ repeat $ do { n <- get; put (n*2); return n }) 1`
2021-08-11 01:57:17 <euouae> is forced to produce [1,2,4,8,...] because of Traversable?
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2021-08-11 01:57:28 <euouae> Could it not had been [1,1,1,...] ?
2021-08-11 01:57:57 <Axman6> yes
2021-08-11 01:58:06 <euouae> got it
2021-08-11 01:58:45 euouae needs to think about this more
2021-08-11 02:01:23 <dsal> One easy way to think about it is to try to make the thing that you think is bad and then verify it's lawful.
2021-08-11 02:01:55 <euouae> unlawful?
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2021-08-11 02:03:25 <dsal> Well, if you make a lawful type that does something you think is bad, then it's a concrete discussion point.
2021-08-11 02:03:48 <euouae> Ok
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2021-08-11 02:17:17 <Axman6> hat's the type whose Applicative instance is something like (Foo mf) <*> (Foo ma) = Foo ((\x f -> f a) <$> ma <*> mf)?
2021-08-11 02:18:06 <Axman6> What's*
2021-08-11 02:18:59 <pavonia> Is that supposed to be (\a f -> f a)?
2021-08-11 02:19:11 <Axman6> uh yes
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2021-08-11 02:19:50 <Axman6> the Applicative with the order of effects reversed basically
2021-08-11 02:20:16 <pavonia> Hhm, no idea
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2021-08-11 02:21:51 <geekosaur> https://downloads.haskell.org/ghc/latest/docs/html/libraries/transformers-0.5.6.2/Control-Applicative-Backwards.html
2021-08-11 02:22:06 <Axman6> <3
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2021-08-11 02:32:23 <dibblego> @type flip (<**>)
2021-08-11 02:32:24 <lambdabot> Applicative f => f (a -> b) -> f a -> f b
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