[GHC] #12970: Add default implementation for Bits.bitSize

[GHC]

#12970: Add default implementation for Bits.bitSize
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           Reporter:  txnull         |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:                 |           Version:
  libraries/base                     |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I think it would be a good idea to provide a default implementation for
 bitSize, example:

 {{{#!hs
   bitSize b = fromMaybe (error "bitSize is undefined") (bitSizeMaybe b)
 }}}

 The advantage is that from now on new instances of Bits no longer need to
 define bitSize.

 And once bitSize has been removed there will be no errors about it not
 being a method of class Bits.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12970>
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