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2020-09-20 03:59:17 <lambdabot> True
2020-09-20 03:59:21 <ski> > let memb x [] = False; memb x (y:ys) | x `elem` y:ys = True | otherwise = memb x (y:ys) in memb 3 [0,2,1]
2020-09-20 03:59:27 <lambdabot> mueval-core: Time limit exceeded
2020-09-20 03:59:41 × gestone quits (~gestone@c-98-225-37-68.hsd1.wa.comcast.net) (Ping timeout: 256 seconds)
2020-09-20 04:00:01 <ski> sepi : do you see why it loops ?
2020-09-20 04:00:37 → Rudd0 joins (~Rudd0@185.189.115.118)
2020-09-20 04:00:45 <lechner> Hi, I would like to abstract the calls to the three hash calculations in this code and get the warnings below it. Can I not include 'do' in the function? https://dpaste.com/4ZCGYR975
2020-09-20 04:00:59 × falafel quits (~falafel@2605:e000:1527:d491:f090:20fe:cddf:2a1a) (Remote host closed the connection)
2020-09-20 04:01:25 <sepi> Yeah it checks if its in there, if its not it'll keep calling itself. I suppose I want to know how to stop if it reaches the end of the list
2020-09-20 04:01:39 <ski> compute :: (Char8.ByteString -> Char8.ByteString) -> String -> Char8.ByteString
2020-09-20 04:01:42 <ski> should be
2020-09-20 04:01:43 <ski> compute :: (Char8.ByteString -> Char8.ByteString) -> String -> IO Char8.ByteString
2020-09-20 04:02:13 × bitmagie quits (~Thunderbi@200116b8062b2e00fc59d02ac7bcf06a.dip.versatel-1u1.de) (Quit: bitmagie)
2020-09-20 04:02:15 <lechner> ski: i thought the <- drops the IO?
2020-09-20 04:02:17 <ski> sepi : make sure you take a step forward, rather than walking in place, standing still
2020-09-20 04:02:19 × denisse quits (~spaceCat@gateway/tor-sasl/alephzer0) (Remote host closed the connection)
2020-09-20 04:02:22 <ski> no, lechner
2020-09-20 04:02:35 → denisse joins (~spaceCat@gateway/tor-sasl/alephzer0)
2020-09-20 04:02:40 <ski> the whole `do'-expression will still have type `IO T', for some type `T'
2020-09-20 04:02:47 <ski> (you can't escape)
2020-09-20 04:03:40 × DirefulSalt quits (DirefulSal@gateway/vpn/privateinternetaccess/direfulsalt) (Remote host closed the connection)
2020-09-20 04:03:50 <ski> btw, probably it's better to give a name to `Char8.pack contents', in order to not recompute it ?
2020-09-20 04:03:59 <ski> (in `main', i mean)
2020-09-20 04:04:09 → DirefulSalt joins (DirefulSal@gateway/vpn/privateinternetaccess/direfulsalt)
2020-09-20 04:05:02 <ski> sepi : also .. if you care to tell, what is `memb' supposed to compute ?
2020-09-20 04:05:15 <lechner> i thought perhaps the compiler would be smart enough not to, although I thought that the 'effect' from readFile may force it.
2020-09-20 04:05:40 → mpereira joins (~mpereira@2a02:810d:f40:d96:b46b:1e98:8653:4550)
2020-09-20 04:05:53 <ski> lechner : anyway, if you move the `readFile' out of `compute', you can probably avoid the `IO' in its return type
2020-09-20 04:05:53 × denisse quits (~spaceCat@gateway/tor-sasl/alephzer0) (Remote host closed the connection)
2020-09-20 04:06:09 → denisse joins (~spaceCat@gateway/tor-sasl/alephzer0)
2020-09-20 04:06:22 <lechner> i will, but bear with me for a minute please. i changed the code the way you said, but now the code below fails even though i did not change it.
2020-09-20 04:06:26 <sepi> like if x = ["abc", "def"]. memb says is ["def"] in x?
2020-09-20 04:06:34 <sepi> True
2020-09-20 04:06:51 <lechner> https://dpaste.com/553FLPZG5
2020-09-20 04:06:54 <ski> lechner : smart enough not to do what ? recompute the calls to `Char8.pack' ? or reread the file ?
2020-09-20 04:07:03 × ChaiTRex quits (~ChaiTRex@gateway/tor-sasl/chaitrex) (Ping timeout: 240 seconds)
2020-09-20 04:07:04 × toorevitimirp quits (~tooreviti@117.182.182.33) (Ping timeout: 272 seconds)
2020-09-20 04:07:17 <ski> sepi : now try `memb "ghij" x'
2020-09-20 04:07:47 <lechner> ski: i thought the effectful action of readFile might retrigger the remaining computation, but without that the compiler should not repack
2020-09-20 04:08:14 → shad0w_ joins (~shad0w_@160.202.36.27)
2020-09-20 04:08:16 <ski> GHC only does limited CSE
2020-09-20 04:08:21 → ChaiTRex joins (~ChaiTRex@gateway/tor-sasl/chaitrex)
2020-09-20 04:09:22 <ski> lechner : anyway, the second error message is because you still have a mistake in `compute'. but perhaps you want to keep the `IO' out of it ?
2020-09-20 04:09:22 <sepi> It'll just sit there and I have to suspend it rather than being false
2020-09-20 04:09:54 <ski> (in that case, it would be better to fix that first. although, if you want to, you could fix the other error)
2020-09-20 04:10:02 <ski> sepi : and why's that ?
2020-09-20 04:10:18 <lechner> ski: i see. sorry i misread the error message. it's my first day with Haskell
2020-09-20 04:10:33 <ski> it's okay
2020-09-20 04:10:55 <ski> it's not that uncommon that fixing an error in one place will trigger an error to be flagged in another location
2020-09-20 04:11:29 <ski> sometimes it can be hard to know whether one will get out of the "tunnel(s) of error", fixing one after the other
2020-09-20 04:11:40 <ski> with more experience, you should be able to tell this, quicker
2020-09-20 04:12:12 × mpereira quits (~mpereira@2a02:810d:f40:d96:b46b:1e98:8653:4550) (Ping timeout: 260 seconds)
2020-09-20 04:12:25 <lechner> ski: How do I add the IO to the result?
2020-09-20 04:13:03 <sepi> its going to keep looking for the match because recursion, because I suppose there isn't a "if it reaches end, false" statement
2020-09-20 04:13:18 <lechner> and why is the expected type now without the IO even though I just added it up top?
2020-09-20 04:13:56 <ski> (this effect can also be noticed, when refactoring, changing the type signature. this can often trigger an error in other places, and fixing those can trigger further errors, like a ripple effect. this is normally a good thing, the implementation telling you all places you must fix, after having changed one place, in order to not encounter problems when running the code)
2020-09-20 04:14:32 × elliott_ quits (~elliott@2607:fb90:18d6:fc61:a84:10d2:ef86:f415) (Ping timeout: 260 seconds)
2020-09-20 04:14:52 <lechner> but why did it not accept the actual type without the IO in the first place. just because of the 'do'?
2020-09-20 04:15:16 <ski> sepi : there is a "if it reaches end, false" case, that's `memb x [] = False'. the problem is that you never take a step closer to it, you're moving your legs up and down, standing still
2020-09-20 04:16:04 <ski> lechner : "but why did it not accept the actual type without the IO in the first place. just because of the 'do'?" -- no, because of the `readFile'
2020-09-20 04:16:14 × danso quits (~dan@107-190-41-58.cpe.teksavvy.com) (Read error: Connection reset by peer)
2020-09-20 04:16:32 <ski> "How do I add the IO to the result?" -- result of what ? `compute' ?
2020-09-20 04:16:50 <lechner> hashMethod $ Char8.pack contents
2020-09-20 04:16:52 → danso joins (~dan@107-190-41-58.cpe.teksavvy.com)
2020-09-20 04:17:07 <ski> "and why is the expected type now without the IO even though I just added it up top?" -- what do you mean ? in <https://dpaste.com/553FLPZG5>, the expected type does have an `IO'
2020-09-20 04:17:20 <ski> lechner : `return :: a -> IO a'
2020-09-20 04:17:26 <lechner> yes, but only because I added it up top
2020-09-20 04:17:34 → jedws joins (~jedws@121.209.139.222)
2020-09-20 04:18:06 <lechner> thanks. where do I place this return statement, please? and do I retain the name 'a'?
2020-09-20 04:18:13 <ski> it's complaining that `hashMethod :: Char8.ByteString -> Char8.ByteString', while you're attempting to use it as if it was `hashMethod :: Char8.ByteString -> IO Char8.ByteString'
2020-09-20 04:18:24 <lechner> right
2020-09-20 04:18:44 <ski> `a' is a type variable. in your case, `a' would become `Char8.ByteString'
2020-09-20 04:19:01 <ski> (so that you get `return :: Char8.ByteString -> IO Char8.ByteString' ..)
2020-09-20 04:19:54 → merijn joins (~merijn@83-160-49-249.ip.xs4all.nl)
2020-09-20 04:19:57 → drbean joins (~drbean@TC210-63-209-59.static.apol.com.tw)
2020-09-20 04:20:25 <ski> (another way to fix the type mismatch for `hashMethod' would be to change the signature of `compute' so that the specified callback (that's `hashMethod'), actually had type `Char8.ByteString -> IO Char8.ByteString' .. but i'm not convinced you actually want to do this)
2020-09-20 04:21:07 → Saukk joins (~Saukk@2001:998:dc:4a67:1c59:9bb5:b94c:4)
2020-09-20 04:21:09 <lechner> I will eventually remove the IO out of that function. right now, I am just learning. Where does that return statement go, please?
2020-09-20 04:21:14 × jedws quits (~jedws@121.209.139.222) (Client Quit)
2020-09-20 04:21:29 <lechner> and is this thing still called a function?
2020-09-20 04:21:52 <ski> (usually, especially as a beginner, one should think twice, before putting `IO' inside argument types. it's not that it's dangerous, but rather that it adds extra power, with possibility for extra confusion, that one relatively rarely needs)
2020-09-20 04:22:01 <ski> `compute' ? sure
2020-09-20 04:22:11 <ski> `hashMethod' as well
2020-09-20 04:22:11 <lechner> i agree with that
2020-09-20 04:22:34 <lechner> i thought perhaps the 'do' would turn compute into a monad
2020-09-20 04:22:38 <ski> no
2020-09-20 04:22:55 <ski> monads are not values that you deal with, at run-time
2020-09-20 04:22:58 hackage reanimate 1.0.0.0 - Animation library based on SVGs. https://hackage.haskell.org/package/reanimate-1.0.0.0 (DavidHimmelstrup)
2020-09-20 04:23:06 <ski> take e.g. `getLine :: IO String'
2020-09-20 04:23:15 <ski> `getLine' is not a monad. `IO' is the monad
2020-09-20 04:23:23 <lechner> i see. that's not a monad either
2020-09-20 04:23:28 <lechner> or is it?
2020-09-20 04:23:28 <ski> `getLine' is a monadic action, or just action, for short
2020-09-20 04:23:35 <ski> if you have
2020-09-20 04:23:39 <ski> compute :: (Char8.ByteString -> Char8.ByteString) -> String -> IO Char8.ByteString
2020-09-20 04:23:43 <lechner> the IO is the monad?
2020-09-20 04:23:57 <ski> then `compute hashMethod fileName' will also be an action. an `IO'-action (since `IO' is the monad here)
2020-09-20 04:24:00 <ski> yes
2020-09-20 04:24:32 <ski> the type `IO' (together with its instance of the `Monad' type class) is the monad
2020-09-20 04:25:07 <lechner> okay, sorry to be persistent. in which line do i stick that return statement, please?
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