Logs: freenode/#haskell

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2020-09-17 14:30:07	→	nan` joins (~nan`@unaffiliated/nan/x-5405850)
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2020-09-17 14:44:28	<z0>	> 9 / (1/0)
2020-09-17 14:44:31	<lambdabot>	0.0
2020-09-17 14:44:47	→	shadowdao joins (~user@unaffiliated/shadowdaemon)
2020-09-17 14:44:59	<z0>	^ can someone explain this to me?
2020-09-17 14:45:07	×	gestone quits (~gestone@c-73-97-137-216.hsd1.wa.comcast.net) (Ping timeout: 246 seconds)
2020-09-17 14:45:13	→	cantstanya joins (~chatting@gateway/tor-sasl/cantstanya)
2020-09-17 14:45:22	<dolio>	1/0 is infinity, and 9/infinity = 0.
2020-09-17 14:46:10	<z0>	i get the theory, but how does Haskell do this?
2020-09-17 14:46:21	<dolio>	It's IEEE754 arithmetic.
2020-09-17 14:46:32	×	mariatsji quits (~mariatsji@2a01:79d:53aa:c66c:59f2:1ee3:fe3e:b848) (Remote host closed the connection)
2020-09-17 14:47:31	×	kuribas quits (~user@ip-188-118-57-242.reverse.destiny.be) (Remote host closed the connection)
2020-09-17 14:47:53	<hyperisco>	so obviously 0*infinity = 9
2020-09-17 14:48:22	<merijn>	z0: What do you mean by "how does Haskell do this??
2020-09-17 14:48:31	<merijn>	s/??/"?
2020-09-17 14:48:38	<hyperisco>	> 0 * (1/0)
2020-09-17 14:48:41	<lambdabot>	NaN
2020-09-17 14:48:58	→	mariatsji joins (~mariatsji@2a01:79d:53aa:c66c:59f2:1ee3:fe3e:b848)
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2020-09-17 14:49:07	<merijn>	The answer is, most likely, "the same way C does this"
2020-09-17 14:49:16	<hyperisco>	maybe "NaN" should mean "more than one number"
2020-09-17 14:49:25	<z0>	@type (1/0)
2020-09-17 14:49:27	<lambdabot>	Fractional a => a
2020-09-17 14:49:34	→	mariatsji joins (~mariatsji@2a01:79d:53aa:c66c:59f2:1ee3:fe3e:b848)
2020-09-17 14:49:37	<z0>	> 1/0
2020-09-17 14:49:40	<lambdabot>	Infinity
2020-09-17 14:49:42	<dmwit>	> 9 / (1/0) :: Rational
2020-09-17 14:49:44	<lambdabot>	*Exception: Ratio has zero denominator
2020-09-17 14:49:46	<z0>	@type Infinity
2020-09-17 14:49:48	<lambdabot>	error:
2020-09-17 14:49:48	<lambdabot>	• Data constructor not in scope: Infinity
2020-09-17 14:49:48	<lambdabot>	• Perhaps you meant variable ‘infinity’ (imported from Data.Number.Natural)
2020-09-17 14:49:49	<ski>	> sqrt (-1)
2020-09-17 14:49:51	<lambdabot>	NaN
2020-09-17 14:49:52	<merijn>	z0: Ah, how does it decide the type of a polymorphic expression?
2020-09-17 14:49:52	<ski>	> log (-1)
2020-09-17 14:49:54	<lambdabot>	NaN
2020-09-17 14:50:05	<merijn>	z0: Was that the question?
2020-09-17 14:50:15	<z0>	merijn: that's right
2020-09-17 14:50:19	<hyperisco>	MoreThanOneNumber, NotInRealPlane
2020-09-17 14:50:34	×	cfricke quits (~cfricke@unaffiliated/cfricke) (Quit: WeeChat 2.9)
2020-09-17 14:50:37	<hyperisco>	FILE_NOT_FOUND probably somewhere in the arithmetic
2020-09-17 14:50:41	<dmwit>	z0: It uses defaulting. The default default is (Integer, Double), I think.
2020-09-17 14:50:41	→	agiza joins (2eef7ad3@larka.olf.sgsnet.se)
2020-09-17 14:50:55	<merijn>	z0: Ok, so there's a bunch of rules in the report that define special cases for polymorphic types for Num/Integral and Fractional/etc.
2020-09-17 14:51:02	ski	. o O ( `abs (0/0)' )
2020-09-17 14:51:03	<z0>	merijn: and what is Infinity treated as a value of type Fractional a => a
2020-09-17 14:51:18	<dmwit>	Infinity is not a value of type Fractional a => a.
2020-09-17 14:51:24	×	agiza quits (2eef7ad3@larka.olf.sgsnet.se) (Remote host closed the connection)
2020-09-17 14:51:24	<dmwit>	It is a value of type Double, and a value of type Float.
2020-09-17 14:51:25	<merijn>	z0: Which basically say "if you've got a polymorphic expression that's Num or Integral, default it to Integer" and "Double" for Fractional
2020-09-17 14:51:38	<dmwit>	> (read "Infinity" :: Double, read "Infinity" :: Rational)
2020-09-17 14:51:41	<lambdabot>	(Infinity,*Exception: Prelude.read: no parse
2020-09-17 14:51:50	<merijn>	z0: This is covered by the "defaulting rules"
2020-09-17 14:51:54	→	alp_ joins (~alp@2a01:e0a:58b:4920:102b:86e3:d072:38a0)
2020-09-17 14:51:54	<hyperisco>	yes, the seldom talked about defaults feature
2020-09-17 14:52:02	<merijn>	z0: If you enable -Wall you should get warnings for defaulting, iirc
2020-09-17 14:52:10	<dolio>	Well, Infinity isn't a valid expression unless you define a data type with a constructor of that name.
2020-09-17 14:52:19	<ski>	(or pattern synonym)
2020-09-17 14:52:24	<dolio>	Yeah, or that.
2020-09-17 14:52:28	<z0>	dolio: i think that's what is confusing me
2020-09-17 14:52:52	→	bahamas joins (~lucian@188.24.181.166)
2020-09-17 14:52:52	×	bahamas quits (~lucian@188.24.181.166) (Changing host)
2020-09-17 14:52:52	→	bahamas joins (~lucian@unaffiliated/bahamas)
2020-09-17 14:52:53	<dolio>	1/0 is an expression, and what it does depends on the type.
2020-09-17 14:53:09	<merijn>	z0: "(1/0) :: Fractional a => a" gets defaulted to type "Double" and when you compute 1/0 for Double the result is a Double (which happens to have value Infinity)
2020-09-17 14:53:27	<ski>	> 1 / 0 :: Rational
2020-09-17 14:53:30	<lambdabot>	*Exception: Ratio has zero denominator
2020-09-17 14:53:47	<z0>	> ((1/0) :: Double, (1/0) :: Rational, Infinity :: Double, Infinity :: Rational)
2020-09-17 14:53:48	×	jonathanx quits (~jonathan@dyn-8-sc.cdg.chalmers.se) (Remote host closed the connection)
2020-09-17 14:53:50	<lambdabot>	error:
2020-09-17 14:53:50	<lambdabot>	• Data constructor not in scope: Infinity :: Double
2020-09-17 14:53:50	<lambdabot>	• Perhaps you meant variable ‘infinity’ (imported from Data.Number.Natur...
2020-09-17 14:54:06	<z0>	> ((1/0) :: Double, (1/0) :: Rational)
2020-09-17 14:54:09	×	mariatsji quits (~mariatsji@2a01:79d:53aa:c66c:59f2:1ee3:fe3e:b848) (Ping timeout: 244 seconds)
2020-09-17 14:54:09	<lambdabot>	(Infinity,*Exception: Ratio has zero denominator
2020-09-17 14:54:22	<z0>	> (Infinity :: Double)
2020-09-17 14:54:25	<lambdabot>	error:
2020-09-17 14:54:25	<lambdabot>	• Data constructor not in scope: Infinity :: Double
2020-09-17 14:54:25	<lambdabot>	• Perhaps you meant variable ‘infinity’ (imported from Data.Number.Natural)
2020-09-17 14:54:32	<z0>	hum
2020-09-17 14:54:40	<merijn>	z0: Infinity is the string representation of a Double value
2020-09-17 14:54:48	<merijn>	z0: That double value has no literal way to write it

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