[ghc-steering-committee] Please review: deriving for empty, Shepherd: Iavor Diatchki

[Joachim Breitner]

Hi,

Am Mittwoch, den 16.08.2017, 18:19 +0000 schrieb Iavor Diatchki:
> I don't have a strong opinion about the pragma issue---to me this
> kind of divergence from Haskell 2010 is not important, as I really
> don't see what could possibly go wrong if you were to accidentally
> accept a program with a deriving clause on an empty data declaration.

that touches on a more fundamental question: How strict do we want to
be with the “every divergence from the standard requires an extension”
rule. My impression is that we have been rather strict with it,
requiring extensions for things that are rather unambiguous (deriving
various extra classes comes to mind).

Before we diverge from this rule we should agree on the criteria as to
when we allow ourselves to diverge. (E.g. something along the line:
Divergence is only allowed around already rather obscure features. This
would allow empty data declarations to derive stuff without language
extension, but not allow additional derived type classes – but I just
wrote this for illustrative purposes.)

Greetings,
Joachim



-- 
Joachim Breitner
  mail at joachim-breitner.de
  http://www.joachim-breitner.de/
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