testsuite: Add testcase for #16394
[ghc.git] / testsuite / tests / typecheck / should_fail / T16394.hs
1 {-# LANGUAGE PolyKinds, TypeFamilies, DataKinds #-}
2
3 class C a where
4 type T (n :: a)
5
6 instance C a => C b => C (a, b) where
7 type T '(n, m) = (T n, T m)
8
9 -- but this worked fine:
10 --
11 -- instance (C a, C b) => C (a, b) where
12 -- type T '(n, m) = (T n, T m)