[Haskell-cafe] an idea for modifiyng data/newtype syntax: use `::=` instead of `=`

[MigMit]

It's generally considered OK to break small parts of code. For example, the infamous n+k patterns — if I remember correctly, they are still here, but you have to enable them explicitly. It breaks SOME code, but not a lot of it.

We might even break a lot of code, but we surely need a VERY good reason to do that.

> On 08 Aug 2015, at 23:27, Hilco Wijbenga <hilco.wijbenga at gmail.com> wrote:
> 
> On 8 August 2015 at 14:03, Brandon Allbery <allbery.b at gmail.com> wrote:
>> This is quite important, folks. Don't tell us how tools will mitigate this.
>> Go look at Python 3's adoption rate --- and it does have the tools --- and
>> tell me again how well that path works for an established language. (Hint:
>> every Python package I use has no intention of moving to Python 3.)
> 
> That seems like a red herring to me. Python does not have a type
> system to speak of so even simple refactoring is painful. Let alone
> making changes to the language itself...
> 
>> Haskell may be new to you personally. That does not mean that it's okay to
>> break what, more than 15 years worth of code?
> 
> So when is it okay? :-) Still, if proper tooling automates it, why not?
> 
> (I'm not advocating making language changes willy-nilly but the
> argument "it breaks existing code" [in and of itself] implies we are
> stuck with all mistakes made in the past. Language designers are human
> too. We need a way forward.)