Re: Data.Fixed Missing E4, E5, etc

If Data.Fixed in base is changed, might it make more sense to switch to type level naturals and KnownNat as a class? It implements exactly the same functionality but in a more readable and general way. Erik On 3 August 2016 at 19:46, Andrew Martin wrote:

Thanks for your response. I'm actually already doing you recommended in my library. It does work, but I still think it would be better to have this in base.

-Andrew Martin

On Wed, Aug 3, 2016 at 11:46 AM, Merijn Verstraaten wrote:

...

Hi Andrew,

Data.Fixed actually already provides all the tools you need to support any arbitrary precision. As such, I don't see the need to add obscure precisions to the library in addition to the existing common ones. Using Data.Fixed with a 4 digit precision like you want can be achieved in 3 lines of code in you geolite library. Simply define:

data MyPrecision instance HasResolution MyPrecision where resolution _ = 4

and use "Fixed MyPrecision" as type in your library. As you can see in the haddocks, the Num, Real, RealFrac, etc. instances work for any arbitrary instance of HasResolution.

Cheers, Merijn

...

On 3 Aug 2016, at 13:57, Andrew Martin wrote:

I've been working on a library for parsing geolite's GeoIP csv file

(http://hackage.haskell.org/package/geolite-csv-0.2/docs/Geolite-Types.html). In this file, the latitude and longitude are always given to four decimal points of precision. It seems like the Fixed data type (from Data.Fixed in base) is the best choice for representing this.

However, the precision levels provided are:

- E0 - E1 - E2 - E3 - E6 - E9 - E12

I would like to propose adding all of the missing ones into Data.Fixed as well. Even though needed a four-decimal-point-precision number is uncommon, it's not unheard of. Admittedly, the precision offered by E11 seems unlikely to ever be needed, but I think it would be nice for completeness. I would be happy to PR this if others agree that it's a good idea.

-Andrew Martin

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-- -Andrew Thaddeus Martin

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