Permitting trailing commas for record syntax ADT declarations

[Herbert Valerio Riedel]

On 2014-09-24 at 08:50:22 +0200, Edward Kmett wrote:
> I'm personally of the "it should be a language extension like everything
> else" mindset. 

Me too. Mostly for being able to have more useful error messages with
older GHCs and other Haskell parsers. 

Because if it's a lang-ext pragma, you have to specify it somewhere
explicitly ({-# LANGUAGE .. #-} and/or {other,default}-extenions in the
cabal file), and if the parser used doesn't know that extension you get
a more useful hint pointing you directly at your problem if you throw
spurious-commas at a Haskell parser which doesn't support that extension
(yet), or with Cabal involved, you'd even get a error message that the
current compiler doesn't support that extension.