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2020-10-05 17:22:34 <ski> @type lookup
2020-10-05 17:22:35 <lambdabot> Eq a => a -> [(a, b)] -> Maybe b
2020-10-05 17:22:36 <ski> @type M.lookup
2020-10-05 17:22:37 <lambdabot> Ord k => k -> M.Map k a -> Maybe a
2020-10-05 17:22:42 <int-e> . o O ( Lens s t a b )
2020-10-05 17:22:45 <monochrom> The greatest hypocrisy of people bragging about descriptive names is they go on to give you foo, bar, quux.
2020-10-05 17:22:48 <ski> `k' here is reasonable, abbreviating "key"
2020-10-05 17:23:00 <zoom84> back to my original question now
2020-10-05 17:23:01 <monochrom> Proving that for generic things there is no such thing as descriptive names.
2020-10-05 17:23:23 <ski> spelling out `key',`token',`stream',&c. all the time, might make some type signatures long enough, that they're harder to comprehend, though
2020-10-05 17:23:27 <int-e> I'm really a fan of having the length (and hence "descriptiveness") of the name increase with its scope.
2020-10-05 17:23:37 → borne joins (~fritjof@200116b86471bb007fe01feb1760d29e.dip.versatel-1u1.de)
2020-10-05 17:23:41 × Lowl3v3l quits (~Lowl3v3l@dslb-090-186-188-115.090.186.pools.vodafone-ip.de) (Remote host closed the connection)
2020-10-05 17:23:44 <ski> yes, that's a good guideline
2020-10-05 17:24:01 <zoom84> instance Functor (MyEither a) where
2020-10-05 17:24:01 → Lowl3v3l joins (~Lowl3v3l@dslb-090-186-188-115.090.186.pools.vodafone-ip.de)
2020-10-05 17:24:06 <zoom84> fmap f (MyRight b) = MyRight (f b)
2020-10-05 17:24:13 <zoom84> fmap f (MyLeft x) = MyLeft x
2020-10-05 17:24:41 <zoom84> so for my fmap instances, the "a" in Either a b is not available. Only the "b" is available, correct?
2020-10-05 17:25:11 <monochrom> Or you write "Either x" like I do, so a is available again.
2020-10-05 17:25:12 <dsal> Correct.
2020-10-05 17:25:18 <ski> zoom84 : which `Either a b' ?
2020-10-05 17:25:27 <zoom84> good. how then does MyLeft x work then? Since MyLeft uses "a"
2020-10-05 17:25:35 <ski> zoom84 : are you talking about the definition of the `data' type `Either' ?
2020-10-05 17:25:40 → ericsagnes joins (~ericsagne@2405:6580:0:5100:e0:d1d9:7c60:99ac)
2020-10-05 17:25:45 <int-e> :t fmap :: (b -> c) -> Either a b -> Either a c
2020-10-05 17:25:47 <lambdabot> (b -> c) -> Either a b -> Either a c
2020-10-05 17:25:50 <dolio> I think "correct" might be the wrong answer.
2020-10-05 17:26:05 <ski> zoom84 : the `b' in `MyRight b' has nothing to do with the `b' in `MyEither a b' or `MyEither x b'
2020-10-05 17:26:06 <int-e> That's the only possible Functor instance for Either.
2020-10-05 17:26:20 <zoom84> I created my own MyEither. It's the same as Either. I did it so I can experiment trying to learn this aspect. Either vs MyEither interchangeable
2020-10-05 17:26:23 × conal quits (~conal@64.71.133.70) (Quit: Computer has gone to sleep.)
2020-10-05 17:27:17 <ski> zoom84 : yea, in `data MyEither a b = MyLeft a | MyRight b deriving Show', `a' and `b' are local names. they are not available outside this definition of `MyEither'
2020-10-05 17:27:22 → mananamenos_ joins (~mananamen@vpn236-17.vpns.upv.es)
2020-10-05 17:27:56 <ski> if you wanted to, you could define it as `data MyEither coffee tea = MyLeft coffee | MyRight tea deriving Show', and it would not affect other code at all
2020-10-05 17:28:12 → bitmagie joins (~Thunderbi@200116b806da5f00187a54deb389527f.dip.versatel-1u1.de)
2020-10-05 17:28:16 <int-e> zoom84: note that you had to write `instance Functor (MyEither a) where`, with only the last type parameter left out; that's all Haskell can do.
2020-10-05 17:28:51 <int-e> (You could use a different variable name for that `a` though.)
2020-10-05 17:29:21 <ski> zoom84 : it's just a convention to start naming the parameters `a',`b',`c',..., unless there's some particular significance (rôle) one may want to hint, like `k' for "key", `t' for "token", `f' for "functor", &c.
2020-10-05 17:29:29 <zoom84> yeah, convention still tripping me up
2020-10-05 17:29:35 <int-e> . o O ( instance Functor (Either idontcarewhatthisisaslongasitsneitheranorb) where ... )
2020-10-05 17:29:44 <dsal> Oh, is it the variable name that is confusing?
2020-10-05 17:29:48 × mirrorbird quits (~psutcliff@2a00:801:2d5:9d73:ff00:6553:d451:a276) (Ping timeout: 244 seconds)
2020-10-05 17:30:06 <monochrom> I think it is the notion of dummy variables.
2020-10-05 17:30:10 <zoom84> rewriting my sample now with totally different names
2020-10-05 17:30:25 × bitmagie quits (~Thunderbi@200116b806da5f00187a54deb389527f.dip.versatel-1u1.de) (Client Quit)
2020-10-05 17:30:27 × alp quits (~alp@2a01:e0a:58b:4920:79a7:73ea:36f8:a1c9) (Ping timeout: 240 seconds)
2020-10-05 17:30:28 <zoom84> to make it obvious...i'll see if it clicks then
2020-10-05 17:30:51 × mananamenos quits (~mananamen@84.122.202.215.dyn.user.ono.com) (Ping timeout: 258 seconds)
2020-10-05 17:30:57 <ski> zoom84 : it's also quite common, if you have say type variables `a',`b',`c' in a type signature, to also name corresponding values, in the definition, `a',`b',`c'. but one could instead name these `x',`y',`z' (so that we get `x :: a',`y :: b',`z :: c', which looks less confusing than `a :: a',`b :: b',`c :: c')
2020-10-05 17:31:10 → Buntspecht joins (~user@unaffiliated/siracusa)
2020-10-05 17:31:42 <ski> (or, if you have a list of values of type `a', it could commonly be called `as', so that you have `as :: [a]'. but you could instead call it `xs', so that you have `xs :: [a]')
2020-10-05 17:31:46 <zoom84> data MyEither dog cat = MyLeft dog | MyRight cat deriving(Show)
2020-10-05 17:31:53 <zoom84> instance Functor (MyEither doodad) where
2020-10-05 17:31:58 <zoom84> fmap f (MyRight x) = MyRight (f x)
2020-10-05 17:32:14 <zoom84> fmap f (MyLeft x) = MyLeft x
2020-10-05 17:32:23 × mav1 quits (~mav@i59F4E23A.versanet.de) (Ping timeout: 258 seconds)
2020-10-05 17:32:25 <ski> zoom84 : did you try my `InstanceSigs' suggestion from above ?
2020-10-05 17:32:56 <ski> try adding the line
2020-10-05 17:32:57 <ski> {-# LANGUAGE InstanceSigs #-}
2020-10-05 17:33:04 <ski> at the top of your source file
2020-10-05 17:33:14 <zoom84> if I do the following in ghci: fmap (*2) (MyLeft 10)
2020-10-05 17:33:15 <monochrom> Koodos for writing code to test your understanding
2020-10-05 17:33:24 geekosaur hopes there was some indentation there, also
2020-10-05 17:33:39 <ski> then, just above the definition of `fmap' in your instance, you can write the type signature for `fmap' that you expect, for `MyEither'
2020-10-05 17:33:42 → is_null joins (~jpic@pdpc/supporter/professional/is-null)
2020-10-05 17:34:03 <ski> zoom84 : try `fmap (* 2) (MyLeft 10) :: MyEither Integer Bool'
2020-10-05 17:34:34 <zoom84> my original statement works
2020-10-05 17:34:42 → phaul joins (~phaul@ruby/staff/phaul)
2020-10-05 17:34:52 <zoom84> i'm trying to understand what that fmap instance actually receives
2020-10-05 17:34:54 <ski> hm, actually, say `fmap (* 2) (MyLeft 10) :: MyEither Integer Double'
2020-10-05 17:35:02 <monochrom> ski, there is ExtendedDefaulting to default to MyEither Integer () :)
2020-10-05 17:35:17 <ski> yea, i just recalled :)
2020-10-05 17:35:29 → fog joins (c1b057e2@gateway/web/cgi-irc/kiwiirc.com/ip.193.176.87.226)
2020-10-05 17:36:05 <fog> its not my fault! its election season - all the lobbying efforts and competing partisan spending distorts the fabric of reality
2020-10-05 17:36:50 ChanServ sets mode +o monochrom
2020-10-05 17:36:55 monochrom sets mode +b *!*@gateway/web/cgi-irc/kiwiirc.com/ip.193.176.87.226
2020-10-05 17:36:55 fog is kicked by monochrom (fog)
2020-10-05 17:37:34 → Guest_57 joins (590fec7f@x590fec7f.dyn.telefonica.de)
2020-10-05 17:37:55 <zoom84> does this implicit type signature look about right: (a -> b) -> MyEither doodad foobar -> MyEither a b
2020-10-05 17:38:05 <ski> no
2020-10-05 17:38:17 <ski> try writing
2020-10-05 17:38:22 <ski> fmap :: (a -> b) -> MyEither doodad foobar -> MyEither a b
2020-10-05 17:38:28 hackage fused-effects-mwc-random 0.1.0.0 - High-quality random number generation as an effect. https://hackage.haskell.org/package/fused-effects-mwc-random-0.1.0.0 (patrick_thomson)
2020-10-05 17:38:29 <ski> above your definition, and see how it complains
2020-10-05 17:38:37 <zoom84> not writing the signaturte
2020-10-05 17:38:47 <zoom84> trying to impute the equivalent
2020-10-05 17:38:58 <ski> you can check your understanding, by writing the signature that you expect
2020-10-05 17:39:12 × John20 quits (~John@82.46.59.122) (Ping timeout: 256 seconds)
2020-10-05 17:39:26 <ski> where did `doodad' and `foobar' come from ?
2020-10-05 17:39:32 <ski> where did `a' and `b' come from ?
2020-10-05 17:39:55 × kritzefitz quits (~kritzefit@212.86.56.80) (Ping timeout: 240 seconds)
2020-10-05 17:39:57 <zoom84> where i can specify that signature?
2020-10-05 17:40:07 <ski> just above the definition of `fmap'
2020-10-05 17:40:40 <zoom84> The type signature for ‘fmap’ lacks an accompanying binding (The type signature must be given where ‘fmap’ is declared) |795 | fmap :: (a -> b) -> MyEither doodad foobar -> MyEither a b
2020-10-05 17:41:10 <zoom84> fmap is in a library source file. you're saying i should put it there?
2020-10-05 17:41:34 geekosaur again points to indentation
2020-10-05 17:42:08 × idhugo quits (~idhugo@563472ae.rev.stofanet.dk) (Ping timeout: 260 seconds)
2020-10-05 17:42:18 <MarcelineVQ> This requires InstanceSigs
2020-10-05 17:42:32 <ski> (as was already mentioned, twice or thrice :)
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