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2021-04-05 18:28:28 justsomeguy joins (~justsomeg@unaffiliated/--/x-3805311)
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2021-04-05 18:35:17 <wroathe> Would someone mind explaining why GHC can't deduce (Show (t (Bar a))) in the second example here: https://gist.github.com/JustinChristensen/cdc37922ecb6eb7d385acab527fd367c?
2021-04-05 18:35:57 × Feuermagier quits (~Feuermagi@213.178.26.41) (Ping timeout: 268 seconds)
2021-04-05 18:37:10 <monochrom> t (Bar a) ≠ Bar a, t (Bar a) ≠ t a
2021-04-05 18:38:00 <wroathe> Hmm, isn't a Bar a a kind of a though?
2021-04-05 18:38:33 <glguy> no, in that case the 'a' has already been picked by the user
2021-04-05 18:38:40 <glguy> it some specific type that you don't get to know
2021-04-05 18:38:50 <monochrom> "for all a" vs "the particular a of 'Foo t a'"
2021-04-05 18:39:24 <wroathe> Right. So what would be the best way to do this then? Is manually defining a Show instance the way to go?
2021-04-05 18:39:42 <wroathe> I essentially just want the default Show behavior
2021-04-05 18:39:59 <monochrom> I think Show1 is involved again.
2021-04-05 18:40:02 raehik joins (~raehik@cpc95906-rdng25-2-0-cust156.15-3.cable.virginm.net)
2021-04-05 18:40:14 <Tuplanolla> It's definitely a job for `Show1`.
2021-04-05 18:40:37 <wroathe> Ok. I'll look into that more. Thanks all!
2021-04-05 18:40:54 _bin joins (~bin@2600:1700:10a1:38d0:590a:8b89:3c71:b467)
2021-04-05 18:40:57 <glguy> to do it with a derived instance you need UndecidableInstances and : deriving instance (Show (t (Bar a)), Show a) => Show (Foo t a)
2021-04-05 18:41:26 <wroathe> glguy: Yeah, I did try that and saw the message about UndecidableInstances. I've always heard that UD instances were to be avoided though...
2021-04-05 18:41:26 × hugo quits (znc@verdigris.lysator.liu.se) (Quit: ZNC 1.7.5 - https://znc.in)
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2021-04-05 18:41:52 <monochrom> Yes some people fearmonger against that.
2021-04-05 18:42:09 <glguy> wroathe: the risk is you could use the instance wrong and cause compilation not to terminate
2021-04-05 18:42:14 <wroathe> But it sounds like Show1 would be preferable here regardless
2021-04-05 18:42:21 <glguy> but for the normal cases that instance would work fine
2021-04-05 18:42:56 <Tuplanolla> There are Template Haskell support libraries to generate `Show1` instances.
2021-04-05 18:44:41 <wroathe> Do you guys have any good resources that explain GHC's instance resolution algorithm in detail?
2021-04-05 18:45:03 <Tuplanolla> Does the user guide?
2021-04-05 18:45:09 doraemon joins (~doraemon@117.222.66.254)
2021-04-05 18:46:42 <wroathe> I think it does have some sections on it, but I sometimes find the user guide to be a little terse, and so I figured some supplementary material would be good to review also.
2021-04-05 18:47:14 <monochrom> The Haskell Report is a start for the standard one. "typing haskell in haskell" https://web.cecs.pdx.edu/~mpj/thih/ formalizes it further.
2021-04-05 18:47:39 <monochrom> That's for the extensionless one. For each extension, GHC user's guide.
2021-04-05 18:48:01 <wroathe> monochrom: Thanks! :)
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2021-04-05 19:29:47 <tomsmeding> shapr | geekosaur: fair enough, I just want "last active"
2021-04-05 19:29:48 × Tario quits (~Tario@201.192.165.173) (Read error: Connection reset by peer)
2021-04-05 19:30:00 <tomsmeding> shapr: I guess ircbrowse has the information to answer such a query
2021-04-05 19:30:13 <geekosaur> for the 2 channels it's in
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2021-04-05 19:30:36 <tomsmeding> heh lol true
2021-04-05 19:33:38 <tomsmeding> the information shouldn't take all that much memory though; the sum of the lengths of all nicks seen in #haskell and #xmonad in the past couple months is 3.3 million
2021-04-05 19:33:51 <shapr> int-e: have you seen the recent GRIN optimizer work?
2021-04-05 19:33:52 <tomsmeding> at 8507 distinct nicks
2021-04-05 19:34:18 <shapr> int-e: specifically https://grin-compiler.github.io/
2021-04-05 19:34:34 <shapr> I read Urban Boquist's thesis and really enjoyed it, but he never responded to email questions :-(
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2021-04-05 19:36:34 <monochrom> But don't forget that GHC multiplies memory footprint by 10 to 100. >:)
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