Haskell type class instantiation -

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i trying set (polya a) , (polyb a) instances of class polynomial, want implement coeffs, fromcoeffs, coeffsb, fromcoeffsb. not quite sure doing wrong, because receive error message saying functions not visible class polynomial. please?

class polynomial p  --default implementations data polya = coeffs [a]            deriving (show) data polyb = const | x (polyb a)            deriving (show)  --instances instance polynomial (polya a)     coeffs (coeffs f)=f     fromcoeffs f= coeffs f   instance polynomial (polyb a)  coeffsb (const f)= [f]  coeffsb (x f a)= coeffsb f ++ [a]  fromcoeffsb [] = error "wrong input!"  fromcoeffsb [f]= const f  fromcoeffsb lis@(_:t)= x (fromcoeffsb (init lis)) (last lis)

the following code compiles me:

class polynomial p   coeffs :: p -> [a]   fromcoeffs :: [a] -> p  --default implementations data polya = coeffs [a]            deriving (show) data polyb = const | x (polyb a)            deriving (show)  --instances instance polynomial polya     coeffs (coeffs f)=f     fromcoeffs f= coeffs f  instance polynomial polyb  coeffs (const f)= [f]  coeffs (x f a)= coeffs f ++ [a]  fromcoeffs [] = error "wrong input!"  fromcoeffs [f]= const f  fromcoeffs lis@(_:t)= x (fromcoeffs (init lis)) (last lis)

summary of changes:

  • add methods polynomial class declaration.
  • remove type arguments in instance declarations.
  • change coeffsb coeffs , fromcoeffsb fromcoeffs everywhere.
  • outdent polyb instance declaration 1 space.

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