Hi all, When I try to compile the following in GHC (v 6.6) (with -fno-monomorphism-restriction -fimplicit-params) class Configuration a where thestring:: a -> String foo c = let { ?c = c } in bar bar = thestring ?c I get: Ambiguous type variable `a' in the constraint: `Configuration a' arising from use of `thestring' at /home/grzegorz/Foo.hs:9:6-17 Possible cause: the monomorphism restriction applied to the following: bar :: (?c::a) => String (bound at /home/grzegorz/Foo.hs:9:0) foo :: a -> String (bound at /home/grzegorz/Foo.hs:8:0) Probable fix: give these definition(s) an explicit type signature or use -fno-monomorphism-restriction Adding the type signature bar :: (Configuration a,?c :: a) => String the compiler says: Ambiguous constraint `Configuration a' At least one of the forall'd type variables mentioned by the constraint must be reachable from the type after the '=>' In the type signature for `bar': bar :: (Configuration a, ?c :: a) => String Similar code without use of implicit params compiles fine: class Configuration a where thestring:: a -> String foo c = thestring c Why do implicit params cause this error and is there a way to make it work? Thanks, -- Grzegorz