State of DData

[Simon Marlow]

> > > In my opinion, even "advanced users" should adhere to The
> > > Haskell Report which says that (==) means equality.
> >
> > Where does the report say that?  As far as I can see, the 
> closest quote is
> > this:
> >
> >    The Eq class provides equality (==) and inequality (/=) methods.
> >
> > (section 6.3.1).  The report doesn't explicitly say 
> anywhere that any
> > assumptions about the properties of == are ever made.
> 
> If the Report calles (==) an equality method then (==) should 
> implement equality for every Eq instance.

Arguably then, anything which is an instance of Monad should be a monad.

And '+' should be addition.  etc. etc.

Haskell doesn't require any of these to be true, and similarly it
doesn't require that every instance of '==' is equality.

Cheers,
	Simon