[Haskell-cafe] Request: warn about language extensions that are not used

Peter Verswyvelen bugfact at gmail.com
Thu Mar 12 10:27:18 EDT 2009

Thanks Conal.

For people interested, here's the ticket.


Martijn Van Steenbergen indirectly revealed a feature request to the feature
request feature of the feature database :-) Okay, I'll stop the nonsense: it
would be nice if the community could rate the popularity of a feature
request, which Martijn now just did by adding a comment.

On Thu, Mar 12, 2009 at 3:12 PM, Conal Elliott <conal at conal.net> wrote:

> Thanks Peter.  I'd love to have this feature also.  I go back every so
> often and try removing each of the extensions listed in my LANGUAGE pragma.
> Didn't occur to me that the compiler could be doing it for me.  Regards,  -
> Conal
> 2009/3/11 Peter Verswyvelen <bugfact at gmail.com>
>> Okay, I submitted it as a GHC feature request. Thanks for the feedback.
>> On Wed, Mar 11, 2009 at 5:16 PM, Creighton Hogg <wchogg at gmail.com> wrote:
>>> 2009/3/11 Peter Verswyvelen <bugfact at gmail.com>:
>>> > When I put
>>> > {-# OPTIONS_GHC -Wall -Werror #-}
>>> > in my source file, I don't get compiler (GHC) warnings about redundant
>>> > language extensions that I enabled.
>>> > It would be nice if the compiler gave warnings about this, since after
>>> > refactoring, some language extensions might not be needed anymore, and
>>> hence
>>> > should be removed since fewer language extensions mean more stable and
>>> > portable code no?
>>> > What do you think?
>>> So you mean something like if you put {-# LANGUAGE
>>> GeneralizedNewtypeDeriving #-} in a file, but never do newtype
>>> deriving, it would warn you?
>>> I have no idea how hard that'd be to implement, but that sounds kind
>>> of cool.  Useful for both refactoring and when you've inherited old
>>> code.
>>> Cheers,
>>> C
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