tcfail008.hs:3:5: error:
    Ambiguous type variable ‘a0’ arising from the literal ‘1’
    prevents the constraint ‘(Num a0)’ from being solved.
    Relevant bindings include o :: [a0] (bound at tcfail008.hs:3:1)
    Probable fix: use a type annotation to specify what ‘a0’ should be.
    These potential instances exist:
      instance Num Integer -- Defined in ‘GHC.Num’
      instance Num Double -- Defined in ‘GHC.Float’
      instance Num Float -- Defined in ‘GHC.Float’
      ...plus two others
      (use -fprint-potential-instances to see them all)
    In the first argument of ‘(:)’, namely ‘1’
    In the expression: 1 : 2
    In an equation for ‘o’: o = 1 : 2

tcfail008.hs:3:7: error:
    No instance for (Num [a0]) arising from the literal ‘2’
    In the second argument of ‘(:)’, namely ‘2’
    In the expression: 1 : 2
    In an equation for ‘o’: o = 1 : 2