[GHC] #9240: "read . show ≡ id" not satisfied by Data.Fixed

[GHC]

#9240: "read . show ≡ id" not satisfied by Data.Fixed
------------------------------------+-------------------------------------
       Reporter:  hvr               |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:  7.10.1
      Component:  libraries/base    |           Version:  7.2.1
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:  #9213             |
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 As pointed out in #9213, the desired property "read . show ≡ id" is not
 satisfied for all resolutions. For instance, consider the following
 example:

 {{{
 > data B7
 > instance HasResolution B7 where resolution _ = 128

 > 1.070 :: Fixed B7
 1.062
 > 1.062 :: Fixed B7
 1.054

 > read "1.070" :: Fixed B7
 1.062
 > read "1.062" :: Fixed B7
 1.054
 }}}

 This behaviour can be reproduced all the way back to GHC 7.2.1

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9240>
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