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2020-10-23 19:26:09 <dminuoso> % :set -XDataKinds
2020-10-23 19:26:09 <yahb> dminuoso:
2020-10-23 19:26:13 <dminuoso> % data Foo = Foo Foo
2020-10-23 19:26:14 <yahb> dminuoso:
2020-10-23 19:26:18 → conal joins (~conal@64.71.133.70)
2020-10-23 19:26:18 <dminuoso> % data Foo = Foo 'Foo
2020-10-23 19:26:19 <yahb> dminuoso: ; <interactive>:140:16: error:; * Data constructor `Foo' cannot be used here (it is defined and used in the same recursive group); * In the type 'Foo; In the definition of data constructor `Foo'; In the data declaration for `Foo'
2020-10-23 19:26:34 <blip> Yeah, that's understandable, the compiler would loop
2020-10-23 19:26:36 <davean> I mean you can't generate an infinite type either
2020-10-23 19:27:01 <dminuoso> blip: Hold on, in the above, is the B supposed to have a tick or not?
2020-10-23 19:27:03 <blip> But if I promote another constructor it's not infinite
2020-10-23 19:27:07 <blip> yep
2020-10-23 19:27:12 <blip> they are omittable
2020-10-23 19:27:14 <dminuoso> blip: But that's the same example.
2020-10-23 19:27:25 <dminuoso> Im just aksing because it could be ambgiuous without more context
2020-10-23 19:27:35 <dminuoso> Oh, my example was poor
2020-10-23 19:27:46 <dminuoso> % data Foo = F 'F
2020-10-23 19:27:46 <yahb> dminuoso: ; <interactive>:141:14: error:; * Data constructor `F' cannot be used here (it is defined and used in the same recursive group); * In the type 'F; In the definition of data constructor `F'; In the data declaration for `Foo'
2020-10-23 19:28:09 <blip> data Foo = F | X (Proxy F')
2020-10-23 19:28:12 <blip> darn
2020-10-23 19:28:16 <dminuoso> Note the choice of the word "group"
2020-10-23 19:28:21 <blip> data Foo = F | X (Proxy 'F)
2020-10-23 19:28:44 <blip> yes, I know that it doesn't work. The question is why.
2020-10-23 19:29:10 <dminuoso> blip: Ask Richard Eisenberg? :p
2020-10-23 19:29:12 → christo joins (~chris@81.96.113.213)
2020-10-23 19:29:49 <dminuoso> Almost confident it's an GHC engineering problem
2020-10-23 19:30:35 <blip> I'm solving that in a very ugly and unsafe way with Symbols
2020-10-23 19:30:38 <dminuoso> blip: See note [Recursion and promoting data constructors]
2020-10-23 19:30:50 <dminuoso> in compiler/GHC/Tc/TyCl.hs
2020-10-23 19:30:58 → dcoutts_ joins (~duncan@33.14.75.194.dyn.plus.net)
2020-10-23 19:31:23 → aarvar joins (~foewfoiew@50.35.43.33)
2020-10-23 19:31:43 <dminuoso> Mmm that note doesnt actually contain something useful
2020-10-23 19:32:14 <dminuoso> But perhaps this would loop the kind checker when the data declaration is checked?
2020-10-23 19:32:26 → N3RGY joins (~N3RGY@65.141.87.122)
2020-10-23 19:33:08 × ubert quits (~Thunderbi@p200300ecdf10db38e6b318fffe838f33.dip0.t-ipconnect.de) (Remote host closed the connection)
2020-10-23 19:33:12 <blip> I think it would loop if you would reference the same Constructor
2020-10-23 19:33:28 <blip> data A = B (Proxy 'B)
2020-10-23 19:33:56 <blip> Or mutal recursion: data A = B (Proxy 'C) | C (Proxy 'B)
2020-10-23 19:34:23 <dminuoso> blip: again, this is probably better asked in #ghc, the ghc dev mailing list or the issue tracker. :)
2020-10-23 19:34:27 × conal quits (~conal@64.71.133.70) (Quit: Computer has gone to sleep.)
2020-10-23 19:34:31 × N3RGY quits (~N3RGY@65.141.87.122) (Client Quit)
2020-10-23 19:34:52 <blip> dminuoso: ok, thanks. I'll ponder it a bit and ask tomorrow in #ghc
2020-10-23 19:35:16 <dminuoso> The mailing list is likely a better candidate
2020-10-23 19:35:39 → conal joins (~conal@64.71.133.70)
2020-10-23 19:35:45 <blip> ok
2020-10-23 19:37:10 × conal quits (~conal@64.71.133.70) (Client Quit)
2020-10-23 19:40:16 × isovector1 quits (~isovector@172.103.216.166) (Quit: Leaving)
2020-10-23 19:42:05 × erolm_a quits (~erolm_a@62.18.213.68) (Ping timeout: 240 seconds)
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2020-10-23 19:47:04 → conal joins (~conal@64.71.133.70)
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2020-10-23 19:48:48 × elliott_ quits (~elliott_@pool-108-51-141-12.washdc.fios.verizon.net) (Read error: Connection reset by peer)
2020-10-23 19:50:45 → elliott_ joins (~elliott_@pool-108-51-141-12.washdc.fios.verizon.net)
2020-10-23 19:51:39 <blip> dminuoso: another question, is there a function Foo with following properties: `data A = B; Foo 'B = "B" :: Symbol`
2020-10-23 19:52:02 <blip> like ShowType from the type error messages, but which returns a Symbol and not a Text
2020-10-23 19:53:25 → invaser joins (~Thunderbi@31.148.23.125)
2020-10-23 19:53:47 → wroathe joins (~wroathe@c-68-54-25-135.hsd1.mn.comcast.net)
2020-10-23 19:54:10 × conal quits (~conal@64.71.133.70) (Quit: Computer has gone to sleep.)
2020-10-23 19:55:43 <dminuoso> blip: There's only the bits for type errors
2020-10-23 19:55:46 × notnatebtw quits (~nate@110.138.18.157) (Quit: WeeChat 2.9)
2020-10-23 19:56:32 × heatsink quits (~heatsink@107-136-5-69.lightspeed.sntcca.sbcglobal.net) (Remote host closed the connection)
2020-10-23 19:56:57 <blip> hm, i'll try to unsafeCoerce, perhaps it's under the hood the same
2020-10-23 19:56:59 × Quarl quits (~Quarl@94.191.136.110.mobile.tre.se) (Read error: Connection reset by peer)
2020-10-23 19:57:30 <dminuoso> unsafeCoerce on the type level?
2020-10-23 19:57:34 <dminuoso> We have that?
2020-10-23 19:57:37 × thir quits (~thir@p200300f27f19de001ce90606181a98e7.dip0.t-ipconnect.de) (Ping timeout: 260 seconds)
2020-10-23 19:58:05 × wroathe quits (~wroathe@c-68-54-25-135.hsd1.mn.comcast.net) (Ping timeout: 240 seconds)
2020-10-23 19:58:14 <blip> with proxies
2020-10-23 19:59:06 <blip> unsafeCoerce :: KnownSymbol a => Proxy ErrorMessage -> Proxy a
2020-10-23 19:59:07 <blip> ?
2020-10-23 19:59:45 × alp quits (~alp@2a01:e0a:58b:4920:552d:a100:fe9e:8159) (Ping timeout: 272 seconds)
2020-10-23 20:01:26 <dminuoso> blip: What's your intention here?
2020-10-23 20:02:02 <blip> I want to get the name of a promoted constructor as a Symbol
2020-10-23 20:02:44 → conal joins (~conal@64.71.133.70)
2020-10-23 20:03:00 → asheshambasta joins (~user@ptr-e1lysawl9rr13i61o92.18120a2.ip6.access.telenet.be)
2020-10-23 20:04:01 × gxt quits (~gxt@gateway/tor-sasl/gxt) (Remote host closed the connection)
2020-10-23 20:04:08 <ghoulguy> To get constructors as symbols I'd expect you to have to write some TH to actually generate the code
2020-10-23 20:04:45 → gxt joins (~gxt@gateway/tor-sasl/gxt)
2020-10-23 20:04:48 <ghoulguy> Like a: type family AsSymbol (a :: k) :: Symbol -- and then a bunch of generated instances
2020-10-23 20:05:36 <blip> If they aren't promoted it would work via generics
2020-10-23 20:06:52 × asheshambasta quits (~user@ptr-e1lysawl9rr13i61o92.18120a2.ip6.access.telenet.be) (Remote host closed the connection)
2020-10-23 20:06:57 <ghoulguy> yeah, looks like it
2020-10-23 20:06:59 <blip> Yeah, I'd love to avoid TH
2020-10-23 20:07:04 → notnatebtw joins (~nate@110.138.18.157)
2020-10-23 20:08:15 <ghoulguy> >>> data T = C deriving (Generic)
2020-10-23 20:08:15 <ghoulguy> >>> :kind! Rep T ()
2020-10-23 20:08:15 <ghoulguy> Rep T () :: * = D1 ('MetaData "T" "Ghci3" "interactive" 'False) (C1 ('MetaCons "C" 'PrefixI 'False) U1) ()
2020-10-23 20:08:45 <ghoulguy> "T" is a Symbol there
2020-10-23 20:08:57 <blip> Yes, and "C" as well.
2020-10-23 20:10:47 → mirrorbird joins (~psutcliff@2a00:801:42b:7891:16b1:e53f:55b2:15e1)
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2020-10-23 20:14:13 × ggole quits (~ggole@2001:8003:8119:7200:553e:28c1:9eff:faae) (Quit: Leaving)
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