rules for type casting

[S.D.Mechveliani]

Another question on *rules*.
Could they help the implicit type casting? 
For example, with 
                          {rules Num a=> x::a, y::[a] ==> x+y = [x]+y}
                          instance Num a => Num [a] where ...
one could expect for  x :: Num b=>b  the casting
                                             x + [x,y] --> [x] + [x,y]

It looks like this deals with the rule application at the stage of 
type solving.
Computer algebra gives much more sensible examples of type casting;
you, would probably, believe that they exist.


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Sergey Mechveliani
[EMAIL PROTECTED]