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2020-10-05 17:42:37 → klardotsh joins (~klardotsh@c-71-231-242-112.hsd1.wa.comcast.net)
2020-10-05 17:42:48 <ski> at top of your source file :
2020-10-05 17:42:50 <ski> {-# LANGUAGE InstanceSigs #-}
2020-10-05 17:42:53 <ski> later :
2020-10-05 17:42:58 <ski> data MyEither dog cat = MyLeft dog
2020-10-05 17:43:02 <ski> | MyRight cat
2020-10-05 17:43:06 <ski> deriving Show
2020-10-05 17:43:12 <ski>
2020-10-05 17:43:15 <ski> instance Functor (MyEither doodad)
2020-10-05 17:43:16 <zoom84> sorry ski, missed that. it's hard to follow multiple threads of help at once. i'll at it
2020-10-05 17:43:23 <ski> where
2020-10-05 17:43:28 <ski> fmap :: (a -> b) -> (MyEither doodad foobar -> MyEither a b)
2020-10-05 17:43:32 <ski> fmap f (MyLeft x) = MyLeft x
2020-10-05 17:43:36 <ski> fmap f (MyRight y) = MyRight (f y)
2020-10-05 17:43:45 <ski> zoom84 : like that ^
2020-10-05 17:44:21 <ski> zoom84 : "fmap is in a library source file. you're saying i should put it there?" -- yes, there is a general type signature of `fmap' in the type class declaration of `Functor', it looks like
2020-10-05 17:44:25 <ski> class Functor f
2020-10-05 17:44:27 <ski> where
2020-10-05 17:44:33 <ski> fmap :: (a -> b) -> (f a -> f b)
2020-10-05 17:45:22 <ski> however, when making an `instance' declaration, you can actually (if you enable the `InstanceSigs' language extension, as above) put the specific type signatures, for your instance, on the type class methods
2020-10-05 17:45:35 × tessier quits (~treed@kernel-panic/copilotco) (Ping timeout: 260 seconds)
2020-10-05 17:46:03 × ym555 quits (~ym@41.42.210.219) (Ping timeout: 260 seconds)
2020-10-05 17:46:26 <ski> geekosaur : pretty sure they have relevant indentation in their source code :)
2020-10-05 17:46:55 × snakemasterflex quits (~snakemast@213.100.206.23) (Ping timeout: 240 seconds)
2020-10-05 17:46:58 <geekosaur> I'm not, because you get that error instead of "turn on InstanceSigs" if you didn't indent it.
2020-10-05 17:47:31 <geekosaur> and you don't get other errors you might think you would, it'd just be a local redeclaration which is legal
2020-10-05 17:47:52 <ski> ah, i missed that. perhaps they dedented, then, since from earlier discussion, it seemed the issue wasn't some error, but understanding the code in question
2020-10-05 17:47:57 <geekosaur> until you go to use it and it complains it's declared twice in the same scope, one in Prelude
2020-10-05 17:48:24 × vicfred quits (~vicfred@unaffiliated/vicfred) (Quit: Leaving)
2020-10-05 17:48:31 <ski> zoom84 : yes, make sure the definition (and type signature) of `fmap' is actually indented more than the `instance Functor ..' line
2020-10-05 17:48:47 <zoom84> indent was ok. here's what I get:
2020-10-05 17:49:03 <zoom84> instance Functor (MyEither doodad) where
2020-10-05 17:49:09 <zoom84> fmap :: (a -> b) -> MyEither doodad foobar -> MyEither a b
2020-10-05 17:49:29 <zoom84> fmap f (MyRight x) = MyRight (f x)
2020-10-05 17:49:42 <zoom84> fmap f (MyLeft x) = MyLeft x
2020-10-05 17:49:43 → mirrorbird joins (~psutcliff@2a00:801:2d5:9d73:ff00:6553:d451:a276)
2020-10-05 17:49:50 <zoom84> • Couldn't match type ‘a’ with ‘doodad’ ‘a’ is a rigid type variable bound by the type signature for: fmap :: forall a b foobar. (a -> b) -> MyEither doodad foobar -> MyEither a b
2020-10-05 17:50:09 <zoom84> that error is for the fmap f (MyLeft x) = MyLeft x line
2020-10-05 17:50:10 <ski> zoom84 : is there actually some (more) spaces in front of those last three lines you showed, in your source code ?
2020-10-05 17:50:24 <zoom84> spaces. don't know how to retain intent pasting into this web irc client
2020-10-05 17:50:30 <ski> zoom84 : yes, you get that error because your type signature is wrong (as mentioned before)
2020-10-05 17:50:44 <ski> it's ok, as long as they're there, in your code
2020-10-05 17:50:55 × albert_99 quits (~Albert@p200300e5ff0b5b425d211d042df94ce7.dip0.t-ipconnect.de) (Ping timeout: 240 seconds)
2020-10-05 17:51:04 → thir joins (~thir@p200300f27f0fc60038c1b16891cbfa03.dip0.t-ipconnect.de)
2020-10-05 17:51:06 <zoom84> missed the correction in the cross-talk. what's the correct sig
2020-10-05 17:51:16 × Guest_57 quits (590fec7f@x590fec7f.dyn.telefonica.de) (Remote host closed the connection)
2020-10-05 17:51:26 <ski> the point, i thought, was that you wanted to figure out the correct signature yourself ?
2020-10-05 17:51:40 → conal joins (~conal@64.71.133.70)
2020-10-05 17:51:56 <zoom84> i do
2020-10-05 17:52:04 <zoom84> why is the sig I wrote incorret
2020-10-05 17:52:23 <zoom84> ie, what's the correct sig
2020-10-05 17:52:29 → nievlo joins (bd801243@189.128.18.67)
2020-10-05 17:52:38 → tessier joins (~treed@kernel-panic/copilotco)
2020-10-05 17:52:48 × geekosaur quits (42d52102@66.213.33.2) (Remote host closed the connection)
2020-10-05 17:52:57 <ski> if you look at `fmap :: (a -> b) -> MyEither doodad foobar -> MyEither a b', and compare it with the definition equation `fmap f (MyLeft x) = MyLeft x', you can see that the first parameter,`f', gets type `a -> b', and the second parameter, `MyLeft x', gets type `MyEither doodat foobar', and that the result `MyLeft x' is to have type `MyEither a b'
2020-10-05 17:53:34 <ski> zoom84 : do you understand that part, matching up parameters and result, in a definition equation like `fmap f (MyLeft x) = MyLeft x', with the corresponding parameter types and result type, in the type signature ?
2020-10-05 17:53:54 ← nievlo parts (bd801243@189.128.18.67) ()
2020-10-05 17:55:30 → bloodstalker joins (~bloodstal@46.166.187.154)
2020-10-05 17:55:32 × thir quits (~thir@p200300f27f0fc60038c1b16891cbfa03.dip0.t-ipconnect.de) (Ping timeout: 260 seconds)
2020-10-05 17:56:20 → shatriff joins (~vitaliish@217.27.153.240)
2020-10-05 17:57:16 <zoom84> still working on it...
2020-10-05 17:57:29 <ski> zoom84 : a "yes" or "no" would be nice
2020-10-05 17:57:31 <zoom84> understand what you wrote ski...making changes to understand
2020-10-05 17:57:35 <ski> ok
2020-10-05 17:58:05 × alx741_ quits (~alx741@186.178.110.22) (Ping timeout: 240 seconds)
2020-10-05 17:58:20 <zoom84> zoom, I understand. in isolation it makes sense, ie for simpler functions. in this context I get confused
2020-10-05 17:58:33 <ski> next step, it to actually check that the matching up of formal parameters (aka patterns) and result (expression), with the parameter and result types, actually makes sense
2020-10-05 17:58:48 <ski> so, let's think about that
2020-10-05 17:58:53 <ski> we know
2020-10-05 17:58:55 <zoom84> give me a sec..
2020-10-05 17:59:05 <ski> fmap :: (a -> b) -> MyEither doodad foobar -> MyEither a b
2020-10-05 17:59:06 <zoom84> can only work on one thought experiemnt at a time
2020-10-05 17:59:07 <ski> fmap f (MyLeft x) = MyLeft x
2020-10-05 17:59:32 <ski> and, from matching up parameters and result with corresponding types in signature, we get
2020-10-05 17:59:35 <ski> f :: a -> b
2020-10-05 17:59:42 <ski> MyLeft x :: MyEither doodad foobar
2020-10-05 17:59:48 <ski> MyLeft x :: MyEither a b
2020-10-05 18:00:02 × Usurp quits (~Usurp@217.146.82.202) ()
2020-10-05 18:00:22 × is_null quits (~jpic@pdpc/supporter/professional/is-null) (Ping timeout: 244 seconds)
2020-10-05 18:00:45 × oisdk quits (~oisdk@2001:bb6:3329:d100:2471:1ee3:650d:c8f7) (Quit: oisdk)
2020-10-05 18:00:54 <ski> (that's the same as i mentioned before, just spelled out a little more explicitly, using the `::' ("has type") notation)
2020-10-05 18:01:08 ski waits for zoom84
2020-10-05 18:01:42 × dyeplexer quits (~lol@unaffiliated/terpin) (Read error: Connection reset by peer)
2020-10-05 18:02:01 <monochrom> I wonder if it's helpful again to do my trick. By going "instance Functor (MyEither doodad)", you saying: in "(a -> b) -> f a -> f b" you're setting "f" to "MyEither doodad". So do that consistently and see what you get.
2020-10-05 18:02:26 → mananamenos joins (~mananamen@84.122.202.215.dyn.user.ono.com)
2020-10-05 18:04:34 ← cohn parts (~noone@unaffiliated/cohn) ()
2020-10-05 18:06:03 × mananamenos_ quits (~mananamen@vpn236-17.vpns.upv.es) (Ping timeout: 260 seconds)
2020-10-05 18:06:21 → justsomeguy joins (~justsomeg@unaffiliated/--/x-3805311)
2020-10-05 18:06:29 <zoom84> :r
2020-10-05 18:07:00 <ski> Ok, one module loaded.
2020-10-05 18:07:19 × heatsink quits (~heatsink@107-136-5-69.lightspeed.sntcca.sbcglobal.net) (Remote host closed the connection)
2020-10-05 18:09:46 <zoom84> finally have a signature that correctly compiles...reading over to understand fully.
2020-10-05 18:09:48 × bitmapper quits (uid464869@gateway/web/irccloud.com/x-umfptdbczzisdhag) (Quit: Connection closed for inactivity)
2020-10-05 18:09:50 × mirrorbird quits (~psutcliff@2a00:801:2d5:9d73:ff00:6553:d451:a276) (Quit: Leaving)
2020-10-05 18:09:55 <ski> ok
2020-10-05 18:10:28 → cohn joins (~noone@unaffiliated/cohn)
2020-10-05 18:10:55 × mananamenos quits (~mananamen@84.122.202.215.dyn.user.ono.com) (Ping timeout: 240 seconds)
2020-10-05 18:11:28 → mananamenos joins (~mananamen@84.122.202.215.dyn.user.ono.com)
2020-10-05 18:11:51 → vicfred joins (~vicfred@unaffiliated/vicfred)
2020-10-05 18:13:21 × jiribenes quits (~jiribenes@rosa.jiribenes.com) (Read error: Connection reset by peer)
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