[GHC] #14377: some results not expected with the addition

[GHC]

#14377: some results not expected with the addition
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        Reporter:  vanto             |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:  invalid           |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by svenpanne):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 I fully understand that you want to change the standard way of `Show`ing
 `Double`s, but this won't happen: There is an informal understanding that
 `read` and `show` are a (weak) kind of inverses:

 {{{
 #!haskell
 almostIdentity x = read (show x) `asTypeOf` x
 }}}

 There is no formal requirement in the Haskell Report for this, but you can
 be sure that lots of code out there would break for no good reason if the
 standard `Show` instance would simply lower the precision. Improving the
 implementation so that it would output as few characters as possible while
 retaining precision ''and'' performance would be another story, as has
 already been pointed out. Again: If you want some special formatting, use
 e.g.:

 {{{
 Prelude> Text.Printf.printf "%.5g\n" 12.3456789
 12.34568
 }}}

 Just for the record: Try the equivalent of your examples in Chrome's
 JavaScript console, in Firefox, Python 3.6's IDLE, in DrRacket's console
 etc. etc., and you will see the same results as in GHC(i), and for a good
 reason.

 Another thing: A bug tracker is not really the right place to discuss wild
 new ideas, IRC e.g. might be a better place to get some initial feedback
 and perhaps learn why things are done they way they are.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14377#comment:13>
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