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2020-11-13 14:10:26 <royal_screwup21> ski hmm yeah you're right
2020-11-13 14:10:36 <royal_screwup21> it seems really weird
2020-11-13 14:10:41 <royal_screwup21> the currrent impl
2020-11-13 14:11:50 <ski> that `Show' instance would generate mostly readable output, getting relatively close to what your pretty-printing intended, while still generating a valid Haskell expression
2020-11-13 14:12:17 <royal_screwup21> ski I'm not sure I understand what's wrong with wrt to precedence
2020-11-13 14:12:26 <ski> of course, you can do your own pretty-printing as well (or instead), if you like. but please don't put that pretty-printing into `Show'
2020-11-13 14:12:45 <royal_screwup21> so if the ziplist is [1, 2] 3 [5]. Then when I run "before", I should get "1"
2020-11-13 14:12:58 → gproto0023 joins (~gproto23@unaffiliated/gproto23)
2020-11-13 14:14:52 <royal_screwup21> that is, will it turn into [2] 1 [3,5]
2020-11-13 14:15:25 <ski> `Show' instances are intended to work together with each other. if you declare an instance for a type, then it will automatically be combined with other existing instances, like for `Maybe',`[]',`Ratio',&c. whenever the user asks to show an input of a type combining your data type with these other types .. you have to consider how such interactions can look like. if you deviate from generating Haskell
2020-11-13 14:15:32 <ski> expressions in `Show', then you will get weird mixes of Haskell and non-Haskell syntax, as a result of such combinations
2020-11-13 14:15:42 × gproto023 quits (~gproto23@unaffiliated/gproto23) (Ping timeout: 265 seconds)
2020-11-13 14:16:02 <ski> royal_screwup21 : "so if the ziplist is [1, 2] 3 [5]" -- what do you mean by this ? do you mean `ZL [1,2] 3 [5]', or do you mean `ZL [2,1] 3 [5]' ?
2020-11-13 14:16:24 <ski> (it's not at all clear which you intended)
2020-11-13 14:16:29 <royal_screwup21> the former
2020-11-13 14:17:17 <ski> so, yes, `before (toZipList [2,1] 3 [5])' will return `toZipList [2] 1 [3,5]'
2020-11-13 14:17:38 × bitmapper quits (uid464869@gateway/web/irccloud.com/x-pozlvwyabhwikscl) (Quit: Connection closed for inactivity)
2020-11-13 14:17:45 <ski> iow, `before (ZL [1,2] 3 5)' will return `ZL [2] 1 [3,5]' -- this is the same thing
2020-11-13 14:20:19 <royal_screwup21> ski the core idea behind this impl is that preprending an element to a list is inexpensive, whereas append is expensive -- am i thinking correctly?
2020-11-13 14:21:41 → blankhart joins (~blankhart@pool-100-35-219-3.nwrknj.fios.verizon.net)
2020-11-13 14:23:05 × Qui_Sum1 quits (~Qui_Sum@178.162.212.214) ()
2020-11-13 14:25:01 <ski> royal_screwup21 : yes, that's correct
2020-11-13 14:25:06 <royal_screwup21> ok cool :)
2020-11-13 14:25:15 <royal_screwup21> thanks for much for all your help - much appreciated
2020-11-13 14:25:55 × bitmagie quits (~Thunderbi@200116b8068f010041b23aab865e3023.dip.versatel-1u1.de) (Quit: bitmagie)
2020-11-13 14:26:52 <ski> "I'm not sure I understand what's wrong with wrt to precedence" -- hmm, not the best example, but consider `NotFocus (-3) % Focus 2', of type `Ratio (ZipElem Int)'. if you `show' this, you would presumably get `" -3 % (2)"', where that negation isn't protected by brackets, while precedence indicates that it ought to be
2020-11-13 14:27:26 → bitmagie joins (~Thunderbi@200116b8068f010041b23aab865e3023.dip.versatel-1u1.de)
2020-11-13 14:27:59 <ski> i'm sure you can construct better (that is, worse) examples, but i was trying to think of one that's in the base library
2020-11-13 14:28:52 × neiluj quits (~jco@unaffiliated/neiluj) (Ping timeout: 256 seconds)
2020-11-13 14:29:06 <merijn> ski: eh...did you use ZipList for a list zipper? That seems needlessly confusing, given the existing ZipList...
2020-11-13 14:29:07 × bitmagie quits (~Thunderbi@200116b8068f010041b23aab865e3023.dip.versatel-1u1.de) (Client Quit)
2020-11-13 14:29:18 <ski> the point is that `Show' is supposed to protect parts (like your `x' in `NotFocus x' and `Focus x') with wrapping brackets, if required to force the intended reading, due to precedence of operators
2020-11-13 14:29:37 <geekosaur> merijn, royal_screwup21 did and was already told about the collision
2020-11-13 14:29:41 <merijn> ah
2020-11-13 14:29:49 <ski> merijn : "<dminuoso> royal_screwup21: btw, thats better called a zipper than a ziplist","<dminuoso> We have a newtype ZipList which provides an alternate Alternative instance for [], but it's unrelated to your thing"
2020-11-13 14:31:43 <ski> royal_screwup21 : usually, except in very simple cases, when you're writing a `Show' instance manually, you should define `showsPrec', not `show'
2020-11-13 14:33:17 <ski> you can define `show' if each possible value is "atomic", never requires wrapping brackets. e.g. `data Bool = False | True' has only "constant data constructors", none of them are parameterized, they don't take arguments, don't have components
2020-11-13 14:36:04 <ski> royal_screwup21 : oh, and sorry. `showsChar' above should be `showChar'
2020-11-13 14:36:28 → jamm_ joins (~jamm@unaffiliated/jamm)
2020-11-13 14:36:31 <royal_screwup21> :)
2020-11-13 14:38:18 <ski> sometimes it makes sense to not expose the implementation (in your case the `ZL' data constructor) in the `Show' instance. but then, imho, one ought to output an expression in terms of the exported operations, the public API, of the module (assuming the data type itself is exported)
2020-11-13 14:38:32 × darjeeling_ quits (~darjeelin@122.245.210.116) (Ping timeout: 260 seconds)
2020-11-13 14:38:52 → britva joins (~britva@2a02:aa13:7240:2980:bc4b:509a:98e6:5bb0)
2020-11-13 14:38:58 × geekosaur quits (82659a09@host154-009.vpn.uakron.edu) (Remote host closed the connection)
2020-11-13 14:39:07 → renzhi joins (~renzhi@2607:fa49:655f:e600::28da)
2020-11-13 14:39:11 <ski> @let tabulate :: Ix i => (i,i) -> (i -> e) -> Array i e; tabulate ix f = listArray ix [f i | i <- range ix]
2020-11-13 14:39:12 <lambdabot> Defined.
2020-11-13 14:39:40 <ski> > tabulate (0,7) (\i -> i^2 + 1)
2020-11-13 14:39:41 <lambdabot> error:
2020-11-13 14:39:41 <lambdabot> Ambiguous occurrence ‘tabulate’
2020-11-13 14:39:41 <lambdabot> It could refer to
2020-11-13 14:39:46 <ski> > L.tabulate (0,7) (\i -> i^2 + 1)
2020-11-13 14:39:48 <lambdabot> array (0,7) [(0,1),(1,2),(2,5),(3,10),(4,17),(5,26),(6,37),(7,50)]
2020-11-13 14:40:51 <ski> that's an example. `Array' is an abstract data type, so its `Show' instance displays an array value in terms of the `array' operation for constructing them (note that i called `listArray', now `array', above. `listArray' is another operation for constructing them)
2020-11-13 14:40:55 <ski> @type array
2020-11-13 14:40:57 <lambdabot> Ix i => (i, i) -> [(i, e)] -> Array i e
2020-11-13 14:40:59 <ski> @type listArray
2020-11-13 14:41:00 <lambdabot> Ix i => (i, i) -> [e] -> Array i e
2020-11-13 14:42:02 <ski> (`listArray' assumes the elements come in a standard order. `array' doesn't assume that, you can list index-element pairs in any order)
2020-11-13 14:42:13 × christo quits (~chris@81.96.113.213) (Remote host closed the connection)
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2020-11-13 14:54:22 × jakalx quits (~jakalx@base.jakalx.net) (Ping timeout: 256 seconds)
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2020-11-13 14:57:13 × gproto0023 quits (~gproto23@unaffiliated/gproto23) (Ping timeout: 264 seconds)
2020-11-13 15:00:42 <motte> hi, how can i find all possible combinations of a nested list? the result should contain only one element from a given index
2020-11-13 15:00:54 → lucasb joins (uid333435@gateway/web/irccloud.com/x-oypdzthrgbpglsbk)
2020-11-13 15:01:09 <motte> e.g. [[1,2], [4,5]] should turn into [[1,2], [1,5], [2,4], [2,5]]
2020-11-13 15:01:54 <merijn> > traverse sequence [[1,2], [4,5]]
2020-11-13 15:01:56 <lambdabot> error:
2020-11-13 15:01:56 <lambdabot> • Ambiguous type variables ‘f0’,
2020-11-13 15:01:56 <lambdabot> ‘a0’ arising from a use of ‘show_M31303913069...
2020-11-13 15:01:59 <merijn> aww
2020-11-13 15:02:26 × xff0x quits (~fox@2001:1a81:53f2:4b00:f0ff:5175:9775:725d) (Ping timeout: 264 seconds)
2020-11-13 15:03:52 <xerox_> > sequence [[1,2],[4,5]]
2020-11-13 15:03:54 <lambdabot> [[1,4],[1,5],[2,4],[2,5]]
2020-11-13 15:04:05 <merijn> rats, it *is* just sequence?
2020-11-13 15:04:18 → heatsink joins (~heatsink@107-136-5-69.lightspeed.sntcca.sbcglobal.net)
2020-11-13 15:04:35 <motte> oh i messed it up, the result should be [[1,4], [1,5], [2,4], [2,5]]
2020-11-13 15:04:40 <xerox_> ding!
2020-11-13 15:05:24 <merijn> xerox_: I thought that first, but thought the type didn't match >.>
2020-11-13 15:06:25 × acarrico quits (~acarrico@dhcp-68-142-39-249.greenmountainaccess.net) (Ping timeout: 240 seconds)
2020-11-13 15:07:24 × FreeBirdLjj quits (~freebirdl@101.228.42.108) ()
2020-11-13 15:07:33 → conal joins (~conal@66.115.157.159)
2020-11-13 15:08:28 <motte> huh it really is sequence
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2020-11-13 15:09:13 × heatsink quits (~heatsink@107-136-5-69.lightspeed.sntcca.sbcglobal.net) (Ping timeout: 264 seconds)
2020-11-13 15:09:22 <bqv> well what d'you know, it really is just sequence
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2020-11-13 15:09:29 × kritzefitz quits (~kritzefit@fw-front.credativ.com) (Remote host closed the connection)
2020-11-13 15:09:44 ← jsmolic parts (~quassel@95.168.121.30) ("https://quassel-irc.org - Chat comfortably. Anywhere.")
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