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

[GHC]

#9240: "read . show ≡ id" not satisfied by Data.Fixed
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        Reporter:  hvr               |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:  7.10.1
       Component:  libraries/base    |          Version:  7.2.1
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  #9231
-------------------------------------+------------------------------------
Changes (by hvr):

 * related:  #9213 => #9231


Old description:

> 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

New description:

 As pointed out in #9231, the desired property "read . show ≡ id" is not
 satisfied for all resolutions. For instance, consider the following
 example:

 {{{#!hs
 > 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#comment:1>
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