...

There does not seem to be a way to do everything I'd like in GHC even in its most permissive mode (I'm using "-fallow-overlapping-instances -fallow-undecidable-instances".) In particular, I'd like to use bare integer literals together with values of the types I define.

Do you have a code example of what you're trying to do?

Here's a simple example of the problem: class Add a b c | a b -> c where add :: a -> b -> c instance Add Integer Integer Integer where add = (+) pt1 = (3::Integer) `add` (4::Integer) -- Works fine, --ft2 = (5::Integer) `add` 6 -- Fails mike If you uncomment ft2, GHC (as expected) says: /home/gunter/haskell/hdl/PlusTest.hs:20: No instance for `Add Integer b c' arising from use of `add' at /home/gunter/haskell/hdl/PlusTest.hs:20 in the definition of function `ft2': (5 :: Integer) `add` 6 /home/gunter/haskell/hdl/PlusTest.hs:20: Ambiguous type variable(s) `b' in the constraint `Num b' arising from the literal `6' at /home/gunter/haskell/hdl/PlusTest.hs:20 In the second argument of `add', namely `6'