[GHC] #12020: Error message on use of != should suggest use of /=

[GHC]

#12020: Error message on use of != should suggest use of /=
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        Reporter:  mhoermann         |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 Replying to [comment:1 nomeata]:

 I like it, comments:

 Do you have more motivational examples, I have a feeling this would mostly
 be used for operators.

 Would it appear in `:info (/=)` output? What about `:info (!=)` whether or
 not it's defined.

 Would it be attached to the definition or definable in a separate module?

 Adding a custom error message.

 I take it that the first definition was supposed to be `(/=) :: a -> a ->
 Bool`:

 {{{#!hs
 class Eq a where
   (==) :: a -> a -> Bool
   (/=) :: a -> a -> Bool
   {-# MISSPELLINGS (/=) AS (!=) "‘Not equal to’ is (/=), syntactically
 emulating the the math symbol ≠" #-}

 class Eq a => Bits a where
   (.&.) :: a -> a -> a
   {-# MISSPELLINGS (.&.) AS (&) "Bitwise and is (.&.)." #-}
   (.|.) :: a -> a -> a
   {-# MISSPELLINGS (.|.) AS (|) "Bitwise or is (.|.)." #-}
   ...
   shiftL :: a -> Int -> a
   {-# MISSPELLINGS shiftL AS (<<) "Left shift" #-}
 }}}

 `(|)` doesn't parse but oh well

 {{{
 ghci> 4 != 10

 _--_           It looks like you're trying
 Ö  Ö      ,- to code. ‘Not equal to’ is (/=), syntactically
 || |     '   emulating the the math symbol ≠. Try writing
 |\_|/          ‘4 /= 10’ instead.
  \_/
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12020#comment:2>
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