Logs: freenode/#haskell
| 2021-03-17 16:57:03 | <koz_> | Come up with a simple (as in, two lines) input with indentation. |
| 2021-03-17 16:57:06 | <koz_> | One correct, one wrong. |
| 2021-03-17 16:57:11 | <koz_> | And try and write a parser for that. |
| 2021-03-17 16:57:17 | <koz_> | Such that the right one parses, and the wrong one errors. |
| 2021-03-17 16:57:23 | <koz_> | _Then_ try to generalize. |
| 2021-03-17 16:57:24 | <shapr> | jumper149: do you have blucontrol hooked into your nix setup as a user level service? |
| 2021-03-17 16:57:25 | × | cuz quits (~user@38.140.58.234) (Ping timeout: 276 seconds) |
| 2021-03-17 16:57:42 | <shapr> | aw, Jordandave23 didn't want to re-learn Haskell after all :-( |
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| 2021-03-17 16:57:49 | <dhruvasagar> | koz_: ok, thanks for your help |
| 2021-03-17 16:58:16 | <jumper149> | shapr: I simply call it in my .xprofile https://github.com/jumper149/dotfiles/blob/master/.xprofile#L22 |
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| 2021-03-17 16:58:44 | <koz_> | (ok, maybe three lines) |
| 2021-03-17 16:58:55 | <koz_> | (but the point is, it should be fairly short and mostly about the indentation) |
| 2021-03-17 16:59:00 | <shapr> | jumper149: ah, thanks |
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| 2021-03-17 16:59:08 | <jumper149> | Never had it crash so I never felt the need to write a service. It would be cool to have though |
| 2021-03-17 16:59:55 | <bobweb> | koz_: Yes, I resolved the previous issue by not trying to access the elements inside the data constructor: that was the part of the exercise that I was misunderstanding. In the present issue, (<>) is supposed to return the first (Snd x) value (or the right-most value if both are (Fst _). So """Fst 1 <> Snd 2""" should just return """Snd 2""" as |
| 2021-03-17 16:59:55 | <bobweb> | there is no manipulation of the data variables (1 and 2, in this case). E.G., """Fst 1""" returns """Fst 1""" and """Snd 2""" returns """Snd 2""", no problem because the (Or a b) type derives Show. So why does """Fst 1 <> Snd 2""" refuse to show """Snd 2"""? |
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| 2021-03-17 17:00:42 | <koz_> | bobweb: Again, firstly what geekosaur mentioned. Secondly, since I can't see the code for the tests themselves, it's very difficult for me to say anything. |
| 2021-03-17 17:00:55 | <koz_> | The thing you're pasting that it's running doesn't have strings in it. |
| 2021-03-17 17:00:55 | <jumper149> | shapr: And I also have this https://github.com/jumper149/dotfiles/blob/master/.xprofile#L22 |
| 2021-03-17 17:01:00 | <koz_> | (or Strings, same diff) |
| 2021-03-17 17:01:14 | <jumper149> | shapr: wrong link: https://github.com/jumper149/dotfiles/blob/nixos/.config/nixpkgs/overlays-custom/main.nix#L47 |
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| 2021-03-17 17:05:46 | <shapr> | ah, that's the kind of thing I need |
| 2021-03-17 17:07:12 | <jumper149> | shapr: I might as well just make a PR for nixpkgs. :D |
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| 2021-03-17 17:07:31 | <jumper149> | The derivation is already done anyways |
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| 2021-03-17 17:10:35 | jumper149 | puts it into nixpkgs right now :) |
| 2021-03-17 17:10:37 | <shapr> | jumper149: yay! |
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| 2021-03-17 17:16:23 | hackage | musicw 0.3.8 - Sound synthesis library, to be used with GHCJS and Web Audio API https://hackage.haskell.org/package/musicw-0.3.8 (dktr0) |
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| 2021-03-17 17:24:07 | <bobweb> | Here is an expanded and annotated version of my issue: https://paste.tomsmeding.com/ Basically everything works except that (<>) won't print e.g., Fst 1 <> Snd 2 returns an error instead of returning Snd 2. As (<>) on (Or a b = Fst a | Snd b deriving (Eq, Show)) is not defined to operate on the x in Snd x, it should have no problem printing (by |
| 2021-03-17 17:24:08 | <bobweb> | my understanding). Thanks. |
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| 2021-03-17 17:25:39 | <geekosaur> | the error message you showed earlier was about defaulting, which is why I suggested ExtendedDefaultRules to get around it. (also your link above is wrong, it's the URL of the paste site and not of a paste) |
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| 2021-03-17 17:26:46 | <geekosaur> | in the absence of ExtendedDefaultRules, ghc can't see through Semigroup to see that the thing inside it has a type with a Show instance |
| 2021-03-17 17:26:51 | <bobweb> | geekosaur: Oops! Sorry. Here: https://paste.tomsmeding.com/t2eAq6e2 |
| 2021-03-17 17:27:34 | <geekosaur> | interesting, that's in ghci so ExtendedDefaultRules isn't enough |
| 2021-03-17 17:28:28 | <bobweb> | The author expects that this should be a simple exercise, I think. |
| 2021-03-17 17:28:28 | <geekosaur> | I'm betting it works if you give 2 an explicit type, though |
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| 2021-03-17 17:28:45 | <bobweb> | Yes, as long as its a string. |
| 2021-03-17 17:28:50 | <geekosaur> | maybe you turn ExtendedDefaultRules off in a .ghci file? |
| 2021-03-17 17:28:58 | <sam9000> | exit |
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| 2021-03-17 17:29:21 | <geekosaur> | Snd (2 :: Int) -- should also work |
| 2021-03-17 17:29:38 | <geekosaur> | or :: Integer if you prefer |
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| 2021-03-17 17:30:31 | <geekosaur> | conversely strings would stop working if you enabled OverloadedStrings |
| 2021-03-17 17:31:02 | <bobweb> | See errors here: https://paste.tomsmeding.com/4djxlyKQ |
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| 2021-03-17 17:31:56 | <geekosaur> | oh, hm, right, so it's actually using some other instance there. or failing to find an instance at all and reporting it poorly |
| 2021-03-17 17:32:51 | <bobweb> | I'm in Stack project if that matters... |
| 2021-03-17 17:33:04 | <geekosaur> | (it shouldn't even reach Show if it has no Num instance for something with a Semigroup instance, but most things with Num instances have at least two possible Semigroups and neither one is better than the other so ghc refuses to pick one as "the" Semigroup) |
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| 2021-03-17 17:33:49 | <geekosaur> | (Sum and Product to be specific) |
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| 2021-03-17 17:34:45 | <geekosaur> | did the earlier exercise have you specify a Monoid or Semigroup instance for any other type than Or? |
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| 2021-03-17 17:35:27 | <geekosaur> | because, as I said, ghc doesn't pick either Sum or Produce by default as "the" Monoid or Semigroup over any Num instance |
| 2021-03-17 17:35:39 | <geekosaur> | but the code you showed assumes one has been picked somehow |
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| 2021-03-17 17:36:12 | <geekosaur> | or maybe they provide a different Num instance somewhere |
| 2021-03-17 17:38:30 | <monochrom> | There are multiple problems forbidding "Fst 1 <> Snd 2" to work automatically, even after extended defaults and type annotations. |
| 2021-03-17 17:38:48 | <geekosaur> | yes |
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| 2021-03-17 17:39:40 | <monochrom> | One issue is you're now looking for a type X such that X is an instance of Num and Semigroup. (Show is too easy.) There is none. |
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