Warn when using Enum instance for Float or Double
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 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.