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

[Creighton Hogg]

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