Haskell : Show instance Ambiguity

Question

I am trying to write a show instance to display well formed formula but after miming whole syntax I am still facing the same error as below.

Hugs> :load \"C:         


        

Answer 1

In haskell, whitespace is important. You need to indent the show's that belong to your instance of Show.

instance Show Wff where
   show (VAR x)     = show x
   show (NEG x)     = "~" ++ show x
   show (AND x y)   = "(" ++ show x ++ "^" ++ show y ++ ")"
   show (OR x y)    = "(" ++ show x ++ "v" ++ show y ++ ")"
   show (IMPL x y)  = "(" ++ show x ++ "-->" ++ show y ++ ")"

Also, you do not need parenthesis to pass the parameters to show. show(x) should be show x.

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