tcfail133.hs:2:61:
    Warning: -XDatatypeContexts is deprecated: It was widely considered a misfeature, and has been removed from the Haskell language.

tcfail133.hs:68:14:
    No instance for (AddDigit (Zero :@ (One :@ One)) One a0)
      arising from a use of `add'
    Possible fix:
      add an instance declaration for
      (AddDigit (Zero :@ (One :@ One)) One a0)
    In the second argument of `($)', namely
      `add (One :@ Zero) (One :@ One)'
    In the expression: show $ add (One :@ Zero) (One :@ One)
    In an equation for `foo':
        foo = show $ add (One :@ Zero) (One :@ One)