Re: yet another very simple overlapping instance example

[Razvan Musaloiu-E.]

Hi!

Koen Claessen wrote:
 | instance (Num a) => Op_plus a MyInt where
 |      i `plus` (MyInt b) = i + b
Remember that b is of type Int, but you also say that i is
of any Num type. This clashes, since + requires both if its
arguments to hve the same types.
You are right! I did't notice that error. Here is a version of the 
example free (if a remove the last instance compiles cleanly) of this 
mistake.

	data MyInt = MyInt Integer deriving Show

        class Op_plus a b where
            plus :: a -> b -> Integer
        instance Op_plus MyInt MyInt where
            (MyInt a) `plus` (MyInt b) = a + b
        instance (Integral a) => Op_plus a MyInt where
            i `plus` (MyInt b) = (toInteger i) + b
Obs: perhaps MyInt should be now MyInteger. :-)

--
Razvan ME
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