> 
> In the first case, the type "a" is not fully known when the coercion
> "(c :> a)" is performed, as the classes are mutually recursive.  The
> compiler handles this case as if it knew nothing about the structure
> of the type "a".  With this assumption, the only case the compiler can
> be sure that the type of "c" is a subtype of "a" is when the type of
> "c" is "a".  This is not the case, hence the error message.
> 
> The reason for this overly conservative (in this case) assumption is
> that the result of the type inference algorithm could otherwise depend
> on the order in which the program is typed.
> 

Clear !

> If you really need mutually recursive classes, a work-around is to
> explicitely define the classe types before defining the classes.
> 

I don't really need recursive classes, but I started
writing my classes in a top-down manner with forward references to
classes
to be defined. Hence, the use of recursive classes. I can simply change
my definitions order (bottow-up), it solves the problem !

Thanks,

Frederic.
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