[Haskell-beginners] question on typeclasses and applicatives

[Daniel Fischer]

On Friday 03 September 2010 00:17:22, Alec Benzer wrote:
> I guess I'm still sort of confused or perturbed with why it's disabled
> by default. If the compiler has the ability to do it and there are no
> problems with doing it, why not just allow it without requiring you to
> pass a flag to the compiler?

It's disabled by default because the language standard laid down different 
rules. Generally, compiler writers tend to avoid enabling too much non-
standard behaviour by default (though chapter 12 of the GHC user's guide 
lists a couple of deviations). However, often there's useful stuff that 
goes against the standard (well, it seemed to be a good idea at the time), 
so many compilers offer extensions to go beyond the standard.