Hello Omer,
It is almost certainly the case that the implementation of these
functions should not be the constant return True function. Furthermore,
the implementation should probably be done using:
http://ghc.haskell.org/trac/ghc/ticket/2431
Edward
Excerpts from Ömer Sinan Ağacan's message of Fri Aug 09 08:06:19 -0700 2013:
> Hi all,
>
> I just started GHC development made a commit for ticket 7401:
> http://ghc.haskell.org/trac/ghc/ticket/7401
>
> My patch is here:
> https://github.com/osa1/ghc/commit/3ec257ff48372de30df59cd8854ce28954c9db95
>
>
> `make test` succeeds. My test case for this patch is something like this:
>
>
> data D deriving Eq
>
> main :: IO ()
> main = print ((undefined :: D) == (undefined :: D))
>
>
> example:
>
>
> ➜ haskell ./ghc/inplace/bin/ghc-stage2 --interactive derive.hs
> GHCi, version 7.7.20130806: http://www.haskell.org/ghc/ :? for help
> Loading package ghc-prim ... linking ... done.
> Loading package integer-gmp ... linking ... done.
> Loading package base ... linking ... done.
> [1 of 1] Compiling Main ( derive.hs, interpreted )
> Ok, modules loaded: Main.
> ghci> main
> True
> it :: ()
>
>
> This behavior(returning True) is consistent with standalone deriving version:
>
>
> ➜ haskell cat derive_standalone.hs
> {-# LANGUAGE StandaloneDeriving #-}
>
> data D
>
> deriving instance Eq D
>
> main :: IO ()
> main = print ((undefined :: D) == (undefined :: D))
>
> ➜ haskell ./ghc/inplace/bin/ghc-stage2 --interactive
> derive_standalone.hs
> GHCi, version 7.7.20130806: http://www.haskell.org/ghc/ :? for help
> Loading package ghc-prim ... linking ... done.
> Loading package integer-gmp ... linking ... done.
> Loading package base ... linking ... done.
> [1 of 1] Compiling Main ( derive_standalone.hs, interpreted )
> Ok, modules loaded: Main.
> ghci> main
> True
> it :: ()
> ghci>
> Leaving GHCi.
>
>
>
> However, if you want (==) implementation in this case to be `error
> "Void (==)`, I think I can also do that by first fixing the code
> generated by StandaloneDeriving extension and then fixing my current
> patch.
>
>
>
> Any comments and reviews would be appreciated!
>
>
> ---
> Ömer Sinan Ağacan
> http://osa1.net
>
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