Hi,

I am trying, without sucess, to run the code below from [1] (Section 4.3).

Obviouly I am missing something.

I would like to keep as close to the original code as possible.

Any help would be apreciated.

Regards,

Pat

[1] http://publik.tuwien.ac.at/files/pub-geo_2321.pdf

data MyNumbers a = MyNum a deriving Show

class (Floating a) => Numbers a where

sqr :: a -> a

-- Not sure if i need these

-- instance Num (MyNumbers a) where

-- instance Fractional (MyNumbers a) where

class Lifts b a where

lift0 :: a -> b a

lift1 :: (a -> a) -> b a -> b a

instance Lifts MyNumbers a where

lift0 x = MyNum x

lift1 o x = MyNum (o x) -- ** Couldn't match expected type `a' with actual type `MyNumbers a' **

instance (Floating (MyNumbers Float)) => Numbers (MyNumbers Float) where

sqr x = lift1 sqr x -- ** could not deduce (Numbers Float) arising from a use of `sqr' **

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