Base1.hs:20:13: error:
    • Couldn't match type ‘a0 -> a0’ with ‘forall a. a -> a’
      Expected type: MEither Sid b
        Actual type: MEither (a0 -> a0) b
    • In the expression: MLeft fid
      In an equation for ‘test1’: test1 fid = MLeft fid

Base1.hs:25:39: error:
    • Couldn't match type ‘a1 -> a1’ with ‘forall a. a -> a’
      Expected type: Maybe (Sid, Sid)
        Actual type: Maybe (a1 -> a1, a2 -> a2)
    • In the expression: Just (x, y)
      In a case alternative: MRight y -> Just (x, y)
      In the expression:
        case m of
          MRight y -> Just (x, y)
          _ -> Nothing