[Haskell-cafe] Class Synonyms - example 2

[Jorge Adriano Aires]

> Jorge,
>
> > Besides the case where 'a' is the same as 'b', there is also another
> > interesting case. That is when you have both, Foo A B and Foo B A.
> > This is a
> > known property (named DoubleFoo) [...]
>
> Again, with -fallow-undecidable-instances:
>
> \begin{code}
> class (Foo a b, Foo b a) => DoubleFoo a b
> instance (Foo a b, Foo b a) => DoubleFoo a b
> \end{code}

Ah! Got it.
Thanks  Stefan,

J.A.