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2020-10-07 07:58:22 → bor0 joins (~boro@unaffiliated/boro/x-000000001)
2020-10-07 07:58:43 <dminuoso> So, for all GHC knows, `map Foo` could change the length of a list for example.
2020-10-07 07:59:35 <dminuoso> In some trivial cases GHC can figure this out for sure. But once you get into recursive definitions, I think it starts to get slippery.
2020-10-07 08:00:08 <dminuoso> So perhaps `fmap Foo` might be a no-op for Identity
2020-10-07 08:00:27 <dminuoso> (Again, if the definition of fmap is inlined at all)
2020-10-07 08:00:48 → jonatanb joins (~jonatanb@79.184.190.239.ipv4.supernova.orange.pl)
2020-10-07 08:00:52 <tomsmeding> > `map Foo` could change the length for example | indeed, this is quite an involved optimisation that would have to inspect the definition of 'map'
2020-10-07 08:00:55 <lambdabot> <hint>:1:1: error: <hint>:1:1: error: parse error on input ‘`’
2020-10-07 08:00:59 → CheRRy2fly21 joins (~CheRRy@129.205.112.30)
2020-10-07 08:00:59 <tomsmeding> that's a fair point
2020-10-07 08:01:40 <tomsmeding> for the trivial program: newtype Foo a = Foo a deriving (Show) ; main = getContents >>= print . map Foo . lines
2020-10-07 08:01:49 <tomsmeding> ghc -ddump-simpl does seem to introduce a `cast`
2020-10-07 08:02:10 → chaosmasttter joins (~chaosmast@p200300c4a70b400140e8baf6489c3871.dip0.t-ipconnect.de)
2020-10-07 08:02:40 frot-lab is now known as hungrydonkey
2020-10-07 08:02:48 <tomsmeding> https://paste.tomsmeding.com/fzcokv87
2020-10-07 08:03:36 <tomsmeding> (that's the only definition in the -ddump-simpl output that contains a call to 'lines', to sort-of justify exclusion of all the rest)
2020-10-07 08:04:12 <dminuoso> Well you cant trust GHC to do this in all the places. So if you really need this to be free, just coerce.
2020-10-07 08:04:28 <dminuoso> I'd be interested in how GHC knows that cast is appropriate here.
2020-10-07 08:04:28 × GyroW quits (~GyroW@unaffiliated/gyrow) (Quit: Someone ate my pie)
2020-10-07 08:04:34 <dminuoso> Perhaps it's special cased for map?
2020-10-07 08:04:48 → GyroW joins (~GyroW@ptr-48ujrfd1ztq5fjywfw3.18120a2.ip6.access.telenet.be)
2020-10-07 08:04:49 × GyroW quits (~GyroW@ptr-48ujrfd1ztq5fjywfw3.18120a2.ip6.access.telenet.be) (Changing host)
2020-10-07 08:04:49 → GyroW joins (~GyroW@unaffiliated/gyrow)
2020-10-07 08:05:00 <dminuoso> Since GHC can know that map at least satisfies functor laws.
2020-10-07 08:05:14 <tomsmeding> perhaps
2020-10-07 08:05:21 <dminuoso> What happens if you use fmap instead of map?
2020-10-07 08:05:33 <dminuoso> Oh well, that might not be helpfujl
2020-10-07 08:05:48 <dminuoso> https://hackage.haskell.org/package/base-4.14.0.0/docs/src/GHC.Base.html#line-1115
2020-10-07 08:05:54 <dminuoso> Yeah no that wont help, it'll just get inlined
2020-10-07 08:06:13 <tomsmeding> same output :p
2020-10-07 08:06:28 <dminuoso> What if you had `IO [Something]` and `fmap . fmap` with that?
2020-10-07 08:06:32 → yoneda joins (~mike@193.206.102.122)
2020-10-07 08:07:48 <tomsmeding> I re-implemented map as map2 and called that instead, and now I _think_ the cast is gone?
2020-10-07 08:07:56 <tomsmeding> like, there still is a cast, but it also explicitly calls map2
2020-10-07 08:08:05 × todda7 quits (~torstein@ppp141255053143.access.hol.gr) (Ping timeout: 240 seconds)
2020-10-07 08:08:21 <tomsmeding> https://paste.tomsmeding.com/gdJrKr2U
2020-10-07 08:09:30 <tomsmeding> dminuoso: for 'main = fmap (fmap Foo) (fmap lines getContents) >>= print', same output as the original case, so map is elided
2020-10-07 08:09:55 × falafel quits (~falafel@2605:e000:1527:d491:1ccf:5c8d:7928:e9cc) (Ping timeout: 240 seconds)
2020-10-07 08:10:10 → cpressey joins (~cpressey@88.144.95.3)
2020-10-07 08:11:32 × Sgeo quits (~Sgeo@ool-18b982ad.dyn.optonline.net) (Read error: Connection reset by peer)
2020-10-07 08:12:52 <dminuoso> Well, it's good to know that for the `IO [A]` case it gets optimized away. That's nice to hear, since getting a coerce in can create some additional undesirable noise.
2020-10-07 08:13:29 <dminuoso> I frequently have that problem when working with postgresql-simple, say for some (query ...) :: IO [Only Int]
2020-10-07 08:13:44 <dminuoso> Never bothered to analyze core because it was just an annoyance, not a performance issue.
2020-10-07 08:13:45 × bahamas quits (~lucian@unaffiliated/bahamas) (Ping timeout: 240 seconds)
2020-10-07 08:17:54 × Clough quits (~Cain@27-33-147-252.static.tpgi.com.au) (Read error: Connection reset by peer)
2020-10-07 08:19:19 → mmohammadi981266 joins (~mmohammad@5.115.44.157)
2020-10-07 08:19:23 × GyroW quits (~GyroW@unaffiliated/gyrow) (Quit: Someone ate my pie)
2020-10-07 08:19:33 → GyroW joins (~GyroW@d54C03E98.access.telenet.be)
2020-10-07 08:19:33 × GyroW quits (~GyroW@d54C03E98.access.telenet.be) (Changing host)
2020-10-07 08:19:33 → GyroW joins (~GyroW@unaffiliated/gyrow)
2020-10-07 08:20:53 × mmohammadi98126 quits (~mmohammad@5.238.172.236) (Ping timeout: 260 seconds)
2020-10-07 08:21:09 <dminuoso> maerwald: https://gist.github.com/dminuoso/daa633ce513a71b5df3bfef0c0b41e5c
2020-10-07 08:21:18 <dminuoso> I feel being lied to.
2020-10-07 08:21:43 → bahamas joins (~lucian@188.24.181.166)
2020-10-07 08:21:43 × bahamas quits (~lucian@188.24.181.166) (Changing host)
2020-10-07 08:21:43 → bahamas joins (~lucian@unaffiliated/bahamas)
2020-10-07 08:21:58 <maerwald> dminuoso: ghcup set ghc 8.6.5
2020-10-07 08:22:17 <dminuoso> Ah. :>
2020-10-07 08:22:20 <maerwald> both commands shouldn't even parse
2020-10-07 08:22:25 <dminuoso> They do!
2020-10-07 08:22:28 × sw1nn quits (~sw1nn@2a00:23c6:2385:3a00:f5c5:6984:9c64:d791) (Quit: WeeChat 2.9)
2020-10-07 08:22:32 <dminuoso> The install even worked that wa
2020-10-07 08:22:38 <maerwald> that's because the version parser is too lax
2020-10-07 08:22:41 <dminuoso> heh
2020-10-07 08:22:51 <dminuoso> [ Error ] NotInstalled GHC "8.6.5"
2020-10-07 08:22:59 × xerox_ quits (~xerox@unaffiliated/xerox) (Ping timeout: 240 seconds)
2020-10-07 08:23:02 <dminuoso> The diagnostic suggested that `ghc set ghc-8.6.5` was parsed properly
2020-10-07 08:23:15 <maerwald> read the second line of the output :)
2020-10-07 08:23:23 <dminuoso> Sure, but that reads more like a deprecation notice
2020-10-07 08:23:45 <dminuoso> But anyhow, cheers.
2020-10-07 08:23:50 → sw1nn joins (~sw1nn@host86-173-104-87.range86-173.btcentralplus.com)
2020-10-07 08:24:09 <maerwald> I'm not even sure why the first one succeeds
2020-10-07 08:25:32 → xerox_ joins (~xerox@unaffiliated/xerox)
2020-10-07 08:26:07 × mmohammadi981266 quits (~mmohammad@5.115.44.157) (Ping timeout: 258 seconds)
2020-10-07 08:26:21 × CheRRy2fly21 quits (~CheRRy@129.205.112.30) (Ping timeout: 260 seconds)
2020-10-07 08:28:15 × hungrydonkey quits (3b47f017@gateway/web/cgi-irc/kiwiirc.com/ip.59.71.240.23) (Quit: Connection closed)
2020-10-07 08:28:38 × justsomeguy quits (~justsomeg@unaffiliated/--/x-3805311) ()
2020-10-07 08:28:57 <maerwald> dminuoso: I think you just made ghcup believe that is a cross-compiler :)
2020-10-07 08:29:52 <maerwald> ghcup install bar-8.6.3 # works as well
2020-10-07 08:30:40 <maerwald> the pre-version part is assumed to be a triple like armv7-unknown-linux-gnueabihf
2020-10-07 08:30:41 → frot-lab joins (3b47f017@gateway/web/cgi-irc/kiwiirc.com/ip.59.71.240.23)
2020-10-07 08:30:56 → mmohammadi981266 joins (~mmohammad@5.238.172.236)
2020-10-07 08:33:18 <dminuoso> GHC is a pretty obscure architecture
2020-10-07 08:33:29 <dminuoso> :P
2020-10-07 08:33:44 <dminuoso> Btw, that triple has 4 parts to it!
2020-10-07 08:33:47 × darjeeling_ quits (~darjeelin@112.16.171.8) (Ping timeout: 240 seconds)
2020-10-07 08:36:27 × Mlpearc quits (~Mlpearc@178.239.168.171) (Remote host closed the connection)
2020-10-07 08:37:19 → GyroW_ joins (~GyroW@d54C03E98.access.telenet.be)
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2020-10-07 08:42:39 × shatriff quits (~vitaliish@217.27.153.240) (Remote host closed the connection)
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2020-10-07 08:44:27 → GyroW joins (~GyroW@d54C03E98.access.telenet.be)
2020-10-07 08:44:27 × GyroW quits (~GyroW@d54C03E98.access.telenet.be) (Changing host)
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2020-10-07 08:44:45 → heatsink joins (~heatsink@107-136-5-69.lightspeed.sntcca.sbcglobal.net)
2020-10-07 08:45:15 → thc202 joins (~thc202@unaffiliated/thc202)
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