Otakar Smrz schrieb:
The conflict arises when I define my own instance for reading a non-polymorphic list, like in:
instance Read [SomeType]
1.) This is not haskell98 2.) should not readList be defined rather than readsPrec? instance Read SomeType where readList ...
Fortunately, I do not need the Data.Set library, and can prevent the problem by an explicit empty import:
import Data.Set ()
Can't you omit the whole line (if sets are not involved)?
However, a simple fix for it might be welcome by others as well:
instance (Read a, Read [a], Ord a) => Read (Set a) where ...
"Illegal Haskell 98 class constraint in instance declaration" There is an instance: instance Read a => Read [a] so the given "instance (Read a, Ord a) => Read (Set a)" would overlap. (Per type only one instance can be used.) I hope I did not completely missunderstood you Christian