{-# LANGUAGE MultiParamTypeClasses #-}

class F a b where
    f :: a -> b

class O a where
    o :: a

data K = K
data L = L
data M = M

instance O K where
    o = K

instance O L where
    o = L

instance F K L where
    f K = L

instance F L K where
    f L = K

instance F L L where
    f L = L

instance F M K where
    f M = K

F K L
F L K
F L L
F M K

O K
O L

f o :: K

*Main> f o :: K

<interactive>:2:1:
    No instance for (F a0 K) arising from a use of `f'
    The type variable `a0' is ambiguous
    Possible fix: add a type signature that fixes these type variable(s)
    Note: there are several potential instances:
      instance F M K -- Defined at hw.hs:28:10
      instance F L K -- Defined at hw.hs:22:10
    Possible fix: add an instance declaration for (F a0 K)
    In the expression: f o :: K
    In an equation for `it': it = f o :: K

<interactive>:2:3:
    No instance for (O a0) arising from a use of `o'
    The type variable `a0' is ambiguous
    Possible fix: add a type signature that fixes these type variable(s)
    Note: there are several potential instances:
      instance O L -- Defined at hw.hs:16:10
      instance O K -- Defined at hw.hs:13:10
    In the first argument of `f', namely `o'
    In the expression: f o :: K
    In an equation for `it': it = f o :: K