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2020-11-26 01:02:32 <ski> (and i wonder how to best represent stuff like "maximal munch". to a large extent, i think i'd prefer it, if `p' parses `s' and `q' parses `t' implies that `p * q' parses `s ++ t')
2020-11-26 01:02:33 × erisco quits (~erisco@d192-186-117-226.static.comm.cgocable.net) (Ping timeout: 256 seconds)
2020-11-26 01:03:37 <monochrom> Nondeterminism comes into the equation because it is a very good way of understanding any implementation strategy.
2020-11-26 01:03:43 <sarahzrf> i like the earley library
2020-11-26 01:04:28 <monochrom> CFG tools are mostly unsupportive of negative specification because set subtraction of two CFLs seldom give you a CFL.
2020-11-26 01:04:55 <monochrom> Whereas RLs are closed under set subtraction, so regex tools are much happier with it.
2020-11-26 01:05:43 <monochrom> and intersection too. CFLs not closed under intersection, RLs closed under intersection.
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2020-11-26 01:07:16 <monochrom> How to discover two CFLs that don't intersect to a CFL:
2020-11-26 01:07:43 <monochrom> Always remember that the poster child non-CFL example is { a^n b^n c^n | n natural }
2020-11-26 01:08:01 hackage network 3.1.2.1 - Low-level networking interface https://hackage.haskell.org/package/network-3.1.2.1 (KazuYamamoto)
2020-11-26 01:08:05 <monochrom> So simply come up with two CFLs that intersect to that. This is within your reach. :)
2020-11-26 01:10:50 <koz_> monochrom: Ah yes, that wonderful example that came up on my ToC assignment.
2020-11-26 01:11:28 <ski> { aᵐ⋅bᵐ⋅cⁿ | m,n : ℕ } ∩ { aᵐ⋅bⁿ⋅cⁿ | m,n : ℕ }
2020-11-26 01:11:29 <ski> ?
2020-11-26 01:11:35 <monochrom> Yeah!
2020-11-26 01:11:42 <ski> cool :)
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2020-11-26 01:12:13 <monochrom> Generally, if a language has to synchronize three things, you can bet it has a problem.
2020-11-26 01:12:34 <koz_> And that's even before we get to the fact that nondeterminism actually adds power to CFGs (but not RLs).
2020-11-26 01:12:43 <monochrom> Synchronizing just two things, we know how to CFG it, it's just another "matching parentheses".
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2020-11-26 01:15:07 <koz_> sarahzrf: Earley parsers are quite cool, because their asymptotics are tied directly to matrix multiplication.
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2020-11-26 01:15:30 <shachaf> Hmm, is there some sort of dual-context-free that has intersection but not union?
2020-11-26 01:15:57 <shachaf> Like there are NFAs and dual NFAs that make unions and intersections respectively easy.
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2020-11-26 01:16:39 <koz_> shachaf: You lose intersection closure _very_ quickly with most recognizers.
2020-11-26 01:16:57 <koz_> (like, whichever way you increase expressive power tends to kill you)
2020-11-26 01:17:27 <shachaf> Hmm, but maybe concatenation isn't supported either.
2020-11-26 01:17:36 <shachaf> But I'm curious what this is like.
2020-11-26 01:17:40 <koz_> So I doubt such a thing exists, or at least in any meaningful sense as a 'dual' to CFGs.
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2020-11-26 01:29:14 ski . o O ( <https://en.wikipedia.org/wiki/Categorial_grammar>,<https://en.wikipedia.org/wiki/Montague_grammar>,<https://en.wikipedia.org/wiki/Pregroup_gramm> )
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2020-11-26 01:31:39 <shachaf> Instead of "dual NFA" I should say "existential NFA" for the normal kind and "universal NFA" for the weird dual kind.
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2020-11-26 01:34:09 <ski> are there any adjunctions present, involving them ?
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2020-11-26 02:11:17 <koz_> shachaf: Do you have a formal definition of these NFAs?
2020-11-26 02:15:13 <koz_> Suppose I wanted to write a package that adds http://hackage.haskell.org/package/optics-core-0.3.0.1/docs/Optics-At-Core.html#t:Ixed definitions for, say, massiv arrays. However, the only way I can see to provide these instances is orphans, or asking massiv to cart around optics as a dep by integrating optics. Am I missing some third way?
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2020-11-26 02:16:46 <monochrom> asking optics to card around massiv :)
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2020-11-26 02:16:57 <koz_> monochrom: _Fourth_ way, you pedant. :P
2020-11-26 02:17:12 <monochrom> My view is that this is one of those times orphaning is desirable.
2020-11-26 02:17:44 <koz_> monochrom: Yeah, I can't think of a way to do this without orphaning or newtypes.
2020-11-26 02:17:51 <koz_> And newtypes would kinda defeat the whole exercise.
2020-11-26 02:17:55 ocamler joins (3263cbdb@50.99.203.219)
2020-11-26 02:18:55 <ocamler> hello friends! I have a probably simple question, I have a function which is wraps the state monad: `solve :: [(Int, Int)] -> ST s [Int]` which is called from `main :: IO ()`, how can I get these types to match?
2020-11-26 02:20:23 <koz_> ST s [Int] would need to be runST'd to get out the [Int].
2020-11-26 02:20:46 <koz_> (and state monad /= ST)
2020-11-26 02:21:10 <ocamler> oh oops right, wow I never knew there is a runST, is that still considered pure?
2020-11-26 02:21:18 <monochrom> yes
2020-11-26 02:21:36 <koz_> ocamler: It's the effect describing (locally) mutable state.

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