[Haskell-beginners] ghci: inconsistent return values for succ

[Kostiantyn Rybnikov]

If you use Decimal package [0], you can have what you want:

λ succ (3.14 :: Decimal)
4.14

[0]: https://hackage.haskell.org/package/Decimal

On Sun, Oct 18, 2015 at 5:17 AM, Frothy Bits <neuralpancake at gmail.com>
wrote:

> Greetings,
>
> Absolutely brand new to Haskell.  Taking ghci v7.10.2 out for a spin, and
> I find I get inconsistent return values for succ n:
>
> ghci> succ 3.14
> 4.1400000000000001
>
> for example instead of the expected 4.14
>
> succ 2.14 and 4.14 give the expected results. but succ 2.14 returns
> 2.1399999999999997.  This anomalous behavior runs through the range of
> n.nn;  in the n.01 range, for example, 16.01 and 63.01 return wonky results
> per above.
>
> I tested this on Windows and Linux (various flavors) and I get the same
> results there and in the interactive test code space on haskell.org.
>
> I'm not familiar enough with the language, yet, to go debugging this on my
> own, but it would seem to be at least a problem with how succ is
> implemented, if not how values are handled in general.....which could
> potentially be bad if you were trying to do anything requiring precise
> calculations....
>
>
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