tcfail002.hs:4:7:
    Occurs check: cannot construct the infinite type: t ~ [t]
    Relevant bindings include
      z :: [t] (bound at tcfail002.hs:4:3)
      c :: [t] -> t (bound at tcfail002.hs:3:1)
    In the expression: z
    In an equation for ‘c’: c z = z