[GHC] #7045: The `Read` instance of `Rational` does not support exponential notation (was: the compiler and the library functions should read literals in the same way)

[GHC]

#7045: The `Read` instance of `Rational` does not support exponential notation
-------------------------------+--------------------------------------------
  Reporter:  maeder            |          Owner:                  
      Type:  bug               |         Status:  new             
  Priority:  normal            |      Milestone:  7.6.1           
 Component:  libraries/base    |        Version:  7.4.2           
Resolution:                    |       Keywords:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown      |     Difficulty:  Unknown         
  Testcase:                    |      Blockedby:                  
  Blocking:                    |        Related:  #7044, #5692    
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Changes (by pcapriotti):

  * milestone:  => 7.6.1


Comment:

 We can change that they are converted to `Rational` internally, but not
 that they are ultimately converted to `Fractional a => a`, since that's a
 visible and non-backwards compatible change.

 Since `Rational` has a `Fractional` instance, I think `1e10 :: Rational`
 should be accepted. The fact that you can blow the compiler up by giving
 it a big exponent is indeed a problem, but that's tracked by #5692 (and I
 believe the solution is to make it "fail" at runtime).

 However, we can keep this ticket as a feature request for the `Read`
 instance of `Rational`.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7045#comment:5>
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