Re: [Haskell-cafe] Class Synonyms - example 2

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} HTH, Stefan