T12844.hs:12:9: warning: [-Wpartial-type-signatures (in -Wdefault)]
    • Found type wildcard ‘_’
        standing for ‘(Foo rngs, Head rngs ~ '(r, r'))’
      Where: ‘rngs’, ‘r’, ‘k’, ‘r'’, ‘k1’
               are rigid type variables bound by
               the inferred type of
                 bar :: (Foo rngs, Head rngs ~ '(r, r')) => FooData rngs
               at T12844.hs:13:1-9
    • In the type signature: bar :: _ => FooData rngs