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(a) we wish to accept the NoDatatypeContexts proposal http://hackage.haskell.org/trac/haskell-prime/wiki/NoDatatypeContexts

The Trac-Wiki says: "What removing the datatype contexts from a source file will do is make some previously illegal programs legal." What is an example?

As on the wiki, data Eq a => Foo a = Constr a getVal :: Foo a -> a getVal (Constr x) = x would previously have been rejected. Once the compiler forces the user to remove the Eq a => context on the datatype, the rest of the program will be accepted. Regards, Malcolm