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[Chih-Ping Chen]

Hi,
        I met some problems while deriving Text instances.

        Firstly, I build the following module:

module A(Poly(Glue)) where
data (Num a) => Poly a = Glue a (Poly a) deriving (Eq, Text)

        Then, I try to evaluate 'zero' in module Test.

module Test(p1) where
import A(Poly(Glue))
zero = Glue 0 zero

I got the error message:

Evaluating (in file hw4.hs): zero
Glue 
>>Error: The symbol #:|sel-Num/showsPrec6428| has no global value

LISP:SYMBOL-VALUE:
   Required arg 0 (S): #:|sel-Num/showsPrec6428|
:C  0: Try evaluating #:|sel-Num/showsPrec6428| again
    1: Restart Haskell.

Is there anything wrong with my code? Or 'zero' can't be output even it's
Text instance has been derived? 

Thank you!