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2020-10-12 01:24:55 × st8less quits (~st8less@2603:a060:11fd:0:9c66:9b18:c21:60c) (Ping timeout: 244 seconds)
2020-10-12 01:26:28 × raehik quits (~raehik@cpc96984-rdng25-2-0-cust109.15-3.cable.virginm.net) (Ping timeout: 244 seconds)
2020-10-12 01:26:45 × xerox_ quits (~xerox@unaffiliated/xerox) (Ping timeout: 240 seconds)
2020-10-12 01:26:48 × snakemas1 quits (~snakemast@213.100.206.23) (Ping timeout: 260 seconds)
2020-10-12 01:27:04 <proofofme> it's installing successfully so far :)
2020-10-12 01:28:04 <cohn> I'm playing around with the Text.CSV module. Hopefully this is an easy one: how can I get the "head" of the CSV data (the column names)?
2020-10-12 01:28:15 <cohn> when I do this: dat <- parseCSVFromFile "foo.csv"
2020-10-12 01:28:28 <cohn> the result has this type: dat :: Either parsec-3.1.14.0:Text.Parsec.Error.ParseError CSV
2020-10-12 01:28:48 → st8less joins (~st8less@2603:a060:11fd:0:9c66:9b18:c21:60c)
2020-10-12 01:28:55 <cohn> so it's wrapped in an "Either"... just need to get the Right value.
2020-10-12 01:29:19 → olligobber joins (olligobber@gateway/vpn/privateinternetaccess/olligobber)
2020-10-12 01:31:21 → aaaaaa joins (~ArthurStr@host-91-90-11-13.soborka.net)
2020-10-12 01:31:23 <proofofme> pattern matching and `case` is my best guess. I'm pretty novice though ...
2020-10-12 01:32:33 <proofofme> https://stackoverflow.com/questions/46944347/how-to-get-value-from-either Does this help?
2020-10-12 01:33:05 <cohn> yep, thanks proofofme!
2020-10-12 01:33:57 → ensyde joins (~ensyde@2600:1702:2e30:1a40:9170:421:4d7b:753d)
2020-10-12 01:34:47 → conal joins (~conal@64.71.133.70)
2020-10-12 01:34:50 <proofofme> apparently, you can use `fromRight` as well, but that can come with some issues, if not accounted for. I used `fromJust` to unwrap a Maybe from an IO monad to get to the [String] beneath yesterday. Took some time to figure it out lol
2020-10-12 01:34:57 × olligobber quits (olligobber@gateway/vpn/privateinternetaccess/olligobber) (Ping timeout: 258 seconds)
2020-10-12 01:35:03 × polyrain quits (~polyrain@2001:8003:e501:6901:1d4a:4b8a:8ea1:adc0) (Quit: My MacBook has gone to sleep. ZZZzzz…)
2020-10-12 01:37:55 → vonfry joins (~user@li1870-189.members.linode.com)
2020-10-12 01:38:17 <ski> proofofme : probably better to handle the error case explicitly .. unless maybe if you're really sure it can't happen
2020-10-12 01:38:45 → wroathe_ joins (~wroathe@c-68-54-25-135.hsd1.mn.comcast.net)
2020-10-12 01:39:01 <ski> (but even then, it can be better to have an explicit pattern-match, rather than `fromJust',`fromRight',`head',`tail', since with those, you don't get a location if things go south)
2020-10-12 01:39:05 × wroathe quits (~wroathe@c-73-24-27-54.hsd1.mn.comcast.net) (Ping timeout: 240 seconds)
2020-10-12 01:39:19 <cohn> crikey... not woring
2020-10-12 01:39:22 <proofofme> so you would use `case` and pattern matching for that just by default, yeah?
2020-10-12 01:39:23 <cohn> *working
2020-10-12 01:40:24 <proofofme> cohn, let me see if I can get the same thing working on my end
2020-10-12 01:40:42 × Gurkenglas quits (~Gurkengla@unaffiliated/gurkenglas) (Ping timeout: 265 seconds)
2020-10-12 01:41:05 × CMCDragonkai1 quits (~Thunderbi@124.19.3.250) (Ping timeout: 240 seconds)
2020-10-12 01:41:14 <ski> proofofme : you could use `Right x = ...' in a `let' or where. or apply `\(Right x) -> x' to the result
2020-10-12 01:41:28 × aaaaaa quits (~ArthurStr@host-91-90-11-13.soborka.net) (Ping timeout: 258 seconds)
2020-10-12 01:41:33 <cohn> for the curious: https://pastebin.com/MYixX2vp
2020-10-12 01:42:08 → aaaaaa joins (~ArthurStr@host-91-90-11-13.soborka.net)
2020-10-12 01:43:46 <cohn> this is what frustrates me about Haskell. It's easy to pick up the basics of the language but when it comes time to use library modules, it's a PITA.
2020-10-12 01:44:14 <proofofme> what is `dat`?
2020-10-12 01:44:23 <lemmih> cohn: Your problem is with static typing, though, not libraries.
2020-10-12 01:44:28 hackage churros 0.1.0.3 - Channel/Arrow based streaming computation library. https://hackage.haskell.org/package/churros-0.1.0.3 (LyndonMaydwell)
2020-10-12 01:45:04 <lemmih> cohn: What's the type of your expression?
2020-10-12 01:45:18 <cohn> proofofme: it's the result of reading the CSV file
2020-10-12 01:45:25 <cohn> https://hackage.haskell.org/package/csv-0.1.2/docs/Text-CSV.html
2020-10-12 01:45:26 <proofofme> ah
2020-10-12 01:45:37 <cohn> lemmih: I would agree
2020-10-12 01:45:43 <ski> cohn : probably `head d' doesn't have type `String'
2020-10-12 01:46:24 <lemmih> cohn: Static typing is not optional in Haskell. You just gotta bite the bullet and always keep types in mind.
2020-10-12 01:46:39 <jchia> Why is there a head fold but no 'tail' in Control.Foldl? Is a tail old that hard to define properly?
2020-10-12 01:46:45 <ski> cohn : do you know what you want to happen/do, in the error case ?
2020-10-12 01:46:59 <cohn> so, `dat <- parseCSVFromFile "foo.csv"`
2020-10-12 01:47:14 <cohn> ski: just print an error message.
2020-10-12 01:47:20 <ski> what is `CSV' ?
2020-10-12 01:47:27 <ski> a type synonym ?
2020-10-12 01:47:31 → olligobber joins (olligobber@gateway/vpn/privateinternetaccess/olligobber)
2020-10-12 01:47:38 × aaaaaa quits (~ArthurStr@host-91-90-11-13.soborka.net) (Ping timeout: 256 seconds)
2020-10-12 01:47:39 <cohn> yes
2020-10-12 01:47:45 <ski> cohn : and abort the program, or not ?
2020-10-12 01:47:48 <lemmih> type CSV = [[String]]
2020-10-12 01:47:51 <ski> ok
2020-10-12 01:48:15 <cohn> ski: I'm playing around in GHCi, so no need to exit. : )
2020-10-12 01:48:17 → _vaibhavingale_ joins (~Adium@203.188.228.27)
2020-10-12 01:48:17 × GyroW_ quits (~GyroW@unaffiliated/gyrow) (Quit: Someone ate my pie)
2020-10-12 01:48:28 → GyroW joins (~GyroW@d54c03e98.access.telenet.be)
2020-10-12 01:48:29 × GyroW quits (~GyroW@d54c03e98.access.telenet.be) (Changing host)
2020-10-12 01:48:29 → GyroW joins (~GyroW@unaffiliated/gyrow)
2020-10-12 01:48:57 <ski> cohn : yes, but i'm asking you what you want your program to do, when there's a parse error
2020-10-12 01:49:09 <cohn> just print an error message
2020-10-12 01:49:11 <ski> should it continue processing, somehow ?
2020-10-12 01:49:13 <ski> or just stop ?
2020-10-12 01:49:24 <cohn> yes, just stop and print an error message
2020-10-12 01:49:27 → polyrain joins (~polyrain@2001:8003:e501:6901:1d4a:4b8a:8ea1:adc0)
2020-10-12 01:49:39 <ski> then call `error' in the `Left' parameter case for `either'
2020-10-12 01:50:02 <ski> (that will also fix this type mismatch error)
2020-10-12 01:50:18 → _vaibhavingale_1 joins (~Adium@203.188.228.27)
2020-10-12 01:50:36 <cohn> whoa! that worked! thanks, ski!
2020-10-12 01:50:37 × merijn quits (~merijn@83-160-49-249.ip.xs4all.nl) (Ping timeout: 264 seconds)
2020-10-12 01:50:43 <ski> because
2020-10-12 01:50:47 <ski> @type error
2020-10-12 01:50:48 <lambdabot> [Char] -> a
2020-10-12 01:51:03 <ski> `error' promises that its return value will be of any type `a' that the caller would like
2020-10-12 01:51:21 <ski> (this works, because `error' doesn't return a value, instead it aborts computation)
2020-10-12 01:52:00 <ski> cohn : btw, you can simplify ("eta-reduce") `\d -> head d', to just `head'
2020-10-12 01:52:01 <cohn> ah, okay. so because I didn't use `error`, the computation didn't abort, which caused the type mismatch message in my paste?
2020-10-12 01:52:13 <ski> (but possibly you want to put more code into that alternative ..)
2020-10-12 01:52:16 → _vaibhavingale_2 joins (~Adium@203.188.228.27)
2020-10-12 01:52:19 <ski> yes, cohn
2020-10-12 01:52:25 × olligobber quits (olligobber@gateway/vpn/privateinternetaccess/olligobber) (Ping timeout: 240 seconds)
2020-10-12 01:52:39 <ski> it tried to check that the result type of both "branches" was the same .. and they weren't
2020-10-12 01:52:47 × _vaibhavingale_ quits (~Adium@203.188.228.27) (Ping timeout: 265 seconds)
2020-10-12 01:53:12 <cohn> ok, so...
2020-10-12 01:53:16 <cohn> @type either
2020-10-12 01:53:18 <lambdabot> (a -> c) -> (b -> c) -> Either a b -> c
2020-10-12 01:53:35 <cohn> so the type of 'c' was different?
2020-10-12 01:53:45 → ttc joins (tomtauma1@gateway/shell/matrix.org/x-dyilsezwqgixpwcl)
2020-10-12 01:53:47 × polyrain quits (~polyrain@2001:8003:e501:6901:1d4a:4b8a:8ea1:adc0) (Client Quit)
2020-10-12 01:54:12 × _vaibhavingale_2 quits (~Adium@203.188.228.27) (Read error: Connection reset by peer)
2020-10-12 01:54:15 → _vaibhavingale_ joins (~Adium@203.188.228.27)
2020-10-12 01:54:35 × hiptobecubic quits (~john@unaffiliated/hiptobecubic) (Remote host closed the connection)
2020-10-12 01:54:43 × _vaibhavingale_1 quits (~Adium@203.188.228.27) (Ping timeout: 265 seconds)
2020-10-12 01:55:09 × _vaibhavingale_ quits (~Adium@203.188.228.27) (Read error: Connection reset by peer)
2020-10-12 01:55:11 <cohn> and yes, it works with eta reduction: `either (\err -> error "Didn't work") head dat`
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