Logs: liberachat/#haskell
| 2025-12-12 21:02:59 | <lambdabot> | "1.23" |
| 2025-12-12 21:03:02 | <Lycurgus> | *fun |
| 2025-12-12 21:03:14 | <EvanR> | yes Nothing seems to evoke the blessed algorithm |
| 2025-12-12 21:03:45 | <monochrom> | > showFFloat (Just 100) 0 "" |
| 2025-12-12 21:03:46 | <lambdabot> | "0.0000000000000000000000000000000000000000000000000000000000000000000000000... |
| 2025-12-12 21:03:51 | <EvanR> | which is fine but it takes Just something for seemingly a reason |
| 2025-12-12 21:04:49 | <monochrom> | So I think the author just decided that if you have "Just n" then it unconditionally ensures n digits. |
| 2025-12-12 21:05:01 | <EvanR> | maybe if you ask for over 17 significant digits it just slaps 0 on the rest |
| 2025-12-12 21:05:04 | <monochrom> | Even if you're just printing 0. |
| 2025-12-12 21:05:16 | <EvanR> | I know |
| 2025-12-12 21:05:28 | <EvanR> | but in the case of 1.23 it's not the correct digits |
| 2025-12-12 21:05:53 | <EvanR> | (1.229999999999999982236431605997495353221893310546875) |
| 2025-12-12 21:06:15 | <monochrom> | Oh! Now I see what you mean. |
| 2025-12-12 21:09:42 | <monochrom> | > length "1.2299999999999999" |
| 2025-12-12 21:09:43 | <lambdabot> | 18 |
| 2025-12-12 21:11:05 | <EvanR> | basically it's taking the liberty of rounding up |
| 2025-12-12 21:11:07 | <EvanR> | in this case |
| 2025-12-12 21:11:16 | <EvanR> | not really, I'm sure, but that's the effect |
| 2025-12-12 21:12:12 | <monochrom> | let s = "1.22999999999999999" in (length s, read s :: Double) |
| 2025-12-12 21:12:16 | <monochrom> | > let s = "1.22999999999999999" in (length s, read s :: Double) |
| 2025-12-12 21:12:17 | <lambdabot> | (19,1.23) |
| 2025-12-12 21:12:36 | <EvanR> | leading me to the conclusion that: truncating "the string" of a positive float is not the same as rounding down |
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| 2025-12-12 21:12:55 | <EvanR> | which I was trying to demonstrate for reasons |
| 2025-12-12 21:13:09 | <monochrom> | I think it's because at the limited precision of 18 digits, the thing is indistinguishable from 1.23 |
| 2025-12-12 21:13:28 | <EvanR> | yes, 1.23 |
| 2025-12-12 21:13:57 | <EvanR> | but not 1.23 plus 100 zeros |
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| 2025-12-12 22:34:14 | <sindu> | /quit |
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| 2025-12-12 22:44:48 | <mauke> | > 1.229999999999999982236431605997495353221893310546875 == 1.23 |
| 2025-12-12 22:44:49 | <lambdabot> | True |
| 2025-12-12 22:45:05 | <mauke> | can't show what's not there |
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| 2025-12-12 22:51:07 | <EvanR> | 1.23 is showing plenty that is "not there" |
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| 2025-12-12 22:59:53 | <int-e> | EvanR: Have you asked this previously? The topic certainly sounds familiar. I traces back to everybody using https://gitlab.haskell.org/ghc/ghc/-/blob/master/libraries/ghc-internal/src/GHC/Internal/Float.hs?ref_type=heads#L1121-1209 (even text-show has a copy of that function) for printing floating point values and for 1.23 that returns ([1,2,3],1) |
| 2025-12-12 23:02:44 | <EvanR> | it does sound familiar |
| 2025-12-12 23:03:26 | <EvanR> | > showFFloat (Just 0) 1.23 "" |
| 2025-12-12 23:03:27 | <lambdabot> | "1" |
| 2025-12-12 23:03:30 | <EvanR> | > showFFloat (Just 1) 1.23 "" |
| 2025-12-12 23:03:32 | <lambdabot> | "1.2" |
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| 2025-12-12 23:03:37 | <EvanR> | > showFFloat (Just 2) 1.23 "" |
| 2025-12-12 23:03:38 | <lambdabot> | "1.23" |
| 2025-12-12 23:03:41 | <EvanR> | > showFFloat (Just 3) 1.23 "" |
| 2025-12-12 23:03:43 | <lambdabot> | "1.230" |
| 2025-12-12 23:03:57 | <EvanR> | ok it just reveals more of what floatToDigits returns |
| 2025-12-12 23:05:42 | <EvanR> | the question you are referring to was, what actual algorithm is used in the Show instance for floats |
| 2025-12-12 23:06:17 | <EvanR> | is the question to the linked answer |
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