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

[Ivan Lazar Miljenovic]

On 15 June 2015 at 14:56, Michael Baikov <manpacket at gmail.com> wrote:
> I guess we can have something similar for rationals as well, I haven't
> considered those.

I wouldn't call it IsNumeric then, as to me it implies it could be *any* number.

IsIntegral maybe though.

But I too would like something like this, whatever the name.

>
> 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



-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
http://IvanMiljenovic.wordpress.com