tcfail218.hs:16:5: error: [GHC-43085]
    • Overlapping instances for C [a] Bool arising from a use of ‘foo’
      Matching instance:
        instance C [a] b -- Defined at tcfail218.hs:8:29
      Potentially matching instance:
        instance C [Int] Bool -- Defined at tcfail218.hs:7:29
      (The choice depends on the instantiation of ‘a’
       To pick the first instance above, use IncoherentInstances
       when compiling the other instance declarations)
    • In the expression: foo
      In an equation for ‘x’: x = foo