On Thu, 19 Jul 2012, Herbert Valerio Riedel wrote:

Recently, I was a bit suprised that GHC didn't warn about useless `where` definitions such as the following when using `-Wall` (and I couldn't find a respective warning GHC CLI flag which would have enabled reporting a warning in this case -- unless I missed it)

module Foo where

foo :: Int -> Int foo n = n + 1 where Nothing = Just n

I think that where x@Nothing = Just n could be useful, if 'x' is evaluated somewhere.

You're right. That's a good case for a feature request. In fact any binding that binds no variables should be warned about: let Just _ = ... Cheers Christian Am 19.07.2012 12:50, schrieb Herbert Valerio Riedel:

Hello,

Recently, I was a bit suprised that GHC didn't warn about useless `where` definitions such as the following when using `-Wall` (and I couldn't find a respective warning GHC CLI flag which would have enabled reporting a warning in this case -- unless I missed it)

module Foo where

foo :: Int -> Int foo n = n + 1 where Nothing = Just n

...wouldn't it be a sensible thing for GHC to warn in such cases (i.e. when the LHS of a pattern binding is a nullary constructor), or is there a useful application for this construct?

(In my original case, I ended up with such a "dead" construct after some "unsound" code refactoring, and it would have helped me catch my error earlier, if GHC would have pointed out that somethings fishy with my code)