T9144.hs:34:26: error:
    • Couldn't match type ‘Integer’ with ‘FooTerm’
      Expected: DemoteRep @Nat ('KProxy @Nat)
        Actual: DemoteRep @Foo ('KProxy @Foo)
    • In the first argument of ‘toSing’, namely ‘n’
      In the expression: toSing n
      In the expression:
        case toSing n of SomeSing n' -> SomeSing (SBar n')