[GHC] #8012: Warn when using Enum instance for Float or Double

[GHC]

#8012: Warn when using Enum instance for Float or Double
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Reporter:  gidyn             |          Owner:                  
    Type:  feature request   |         Status:  new             
Priority:  normal            |      Component:  Compiler        
 Version:  7.6.3             |       Keywords:                  
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
 Failure:  None/Unknown      |      Blockedby:                  
Blocking:                    |        Related:                  
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 The Enum instances for Float and Double have dubious semantics which cause
 endless confusion, e.g.
 [http://stackoverflow.com/questions/13203471/the-math-
 behind-1-0999999999999999-in-haskell],
 [http://stackoverflow.com/questions/9810002/floating-point-list-
 generator],
 [http://stackoverflow.com/questions/7290438/haskell-ranges-and-floats],
 [http://stackoverflow.com/questions/10328435/how-to-solve-floating-point-
 number-getting-wrong-in-list-haskell],
 and many more.

 It is therefore proposed that the usage of an Enum instance for Float or
 Double generate a compiler warning, such as "The Enum instance for Float
 is subject to rounding errors".

 A discussion of this on [http://haskell.1045720.n5.nabble.com/Proposal-
 Warn-when-using-Enum-instance-of-Float-or-Double-td5731620.html the
 libraries list] suggested that such a warning would be desired, although
 the discussion mostly focused on whether the libraries list is an
 appropriate place for this discussion.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/8012>
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