[Haskell-cafe] Add IsNumeric (similar to IsString and IsList)

[Michael Baikov]

I guess we can have something similar for rationals as well, I haven't
considered those.

On Mon, Jun 15, 2015 at 12:41 PM, Ivan Lazar Miljenovic
<ivan.miljenovic at gmail.com> wrote:
> On 12 June 2015 at 17:04, Michael Baikov <manpacket at gmail.com> wrote:
>> Hi Cafe!
>>
>> Now that we have OverloadedList and OverloadedStrings extensions it
>> might make sense to add something similar for numerals - right now if
>> you want to be able to specify some items as numbers
>> you have to implement Num instance, unfortunately not everything that
>> can be represented as number can have sensible operations required by
>> Num: negation makes no sense for set  of natural numbers for example,
>> multiplication for some applications of currency values which results
>> in Num instance full of (*) = error "No multipication for Foos", (+) =
>> error "No addition for Foos".
>>
>> I don't have any statistics from hackage or github, but in codebase
>> I'm working with there are 3 such instances.
>>
>> Proposal: add OverloadedNumerals language pragma, IsNumeric typeclass
>> and some methods to make that class useful with behavior similar to
>> Lists and Strings.
>
> Is this strictly to replace/augment fromInteger or are you proposing
> one for fromRational as well?
>
> --
> Ivan Lazar Miljenovic
> Ivan.Miljenovic at gmail.com
> http://IvanMiljenovic.wordpress.com