Derived Read instances for recursive datatypes with infix constructors are too inefficient
Consider this definition:
data Exp = C | Exp :+: Exp | Exp :-: Exp deriving ( Read, Show )
Now, try something like:
> read "((((((((((C))))))))))" :: Exp
Even this simple expression may take several seconds to parse. It gets worse if you keep adding parenthesis. And even worse if you add more infix constructors....
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