A.hs:8:6:
    No instance for (Num (Int :- Int))
      arising from the literal `1'
    Possible fix: add an instance declaration for (Num (Int :- Int))
    In the expression: 1
    In the expression: (1, (2, 3))
    In an equation for `f': f = (1, (2, 3))

A.hs:8:8:
    Couldn't match expected type `Int' with actual type `(t0, t1)'
    In the expression: (2, 3)
    In the expression: (1, (2, 3))
    In an equation for `f': f = (1, (2, 3))