data-default WAS: [containers] Proposal: Change to the Data.Map Monoid

[Roman Cheplyaka]

I don't agree to Empty either. As I mentioned, the most compelling use cases for
Default I see are things like ParserOptions and ConnectionInfo.

Empty could be a separate typeclass with a different set of instances. It should
probably come with laws (its monofoldable length/size should be 0).

Roman

* João Cristóvão <jmacristovao at gmail.com> [2014-05-22 12:36:24+0100]
> Hi Roman, Daniel,
> 
> I do see your point, and I don't find it a problem. In those particular
> cases perhaps it only makes sense to define a Default value for the same
> cases as mempty applies, namely for Sum and Product.
> 
> So, I'm fine with not including default values for Int, Bool, Float...
> 
> However, I'm not sure I agree with calling it Empty.
> You might want to use Default with your own Algebraic data type where the
> concept of Default makes sense, but the concept of Empty does not.
> The Empty name may be a little too misleading (as mempty is already for
> Monoid, see the Product newtype).
> 
> Cheers,
> João
> 
> 
> 2014-05-22 9:10 GMT+01:00 Daniel Trstenjak <daniel.trstenjak at gmail.com>:
> 
> >
> > Hi João,
> >
> > > ... with an obvious default value ...
> >
> > I think that's the problem some people have, that the default values
> > for several types aren't obvious at all and therefore you have to know
> > the default values of several types to easily read code using 'def'.
> >
> > The default values for container like types - like String or List - are
> > mostly quite obvious, they're just the empty ones. But the default
> > values for types like Int, Bool of Float aren't that obvious and they
> > certainly don't make sense in any use case.
> >
> > That's also the reason why an Empty type class was advocated instead
> > of the Default one, because than it's really obvious what the result
> > for container like types is.
> >
> >
> > Greetings,
> > Daniel
> > _______________________________________________
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> >

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