#endif /* GHCI */
\end{code}
-Note [Multiple instantiation]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
-For example, consider
- f :: forall a. Eq a => forall b. Ord b => a -> b
-At a call to f, at say [Int, Bool], it's tempting to translate the call to
-
- f_m1
- where
- f_m1 :: forall b. Ord b => Int -> b
- f_m1 = f Int dEqInt
-
- f_m2 :: Int -> Bool
- f_m2 = f_m1 Bool dOrdBool
-
-But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
-a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
- f_m1 = f_mx
-But it's entirely possible that f_m2 will continue to float out, because it
-mentions no type variables. Result, f_m1 isn't in scope.
-
-Here's a concrete example that does this (test tc200):
-
- class C a where
- f :: Eq b => b -> a -> Int
- baz :: Eq a => Int -> a -> Int
-
- instance C Int where
- baz = f
-
-Current solution: only do the "method sharing" thing for the first type/dict
-application, not for the iterated ones. A horribly subtle point.
-
%************************************************************************
%* *