T6054.hs:7:14: error:
    • No instance for (Bar '() a0)
        arising from an expression type signature
    • In the first argument of ‘print’, namely
        ‘(Proxy :: Bar '() a => Proxy a)’
      In the expression: print (Proxy :: Bar '() a => Proxy a)
      In an equation for ‘foo’:
          foo = print (Proxy :: Bar '() a => Proxy a)