tcfail125.hs:1:14: warning: [-Wdeprecated-flags (in -Wdefault)]
    -XDatatypeContexts is deprecated: It was widely considered a misfeature, and has been removed from the Haskell language.

tcfail125.hs:11:4: error: [GHC-39999]
    • No instance for ‘Show a’ arising from a use of ‘LiftObs’
      Possible fix:
        add (Show a) to the context of
          the type signature for:
            f :: forall a. Obs a -> String
    • In the pattern: LiftObs _ _
      In an equation for ‘f’: f (LiftObs _ _) = "yes"