data Binary = Zero | One deriving (Enum, Eq, Show)
data BinState = S0 | S1 | S2 deriving (Enum, Eq, Show)

singleOne :: FSM BinState Binary BinState
singleOne =
  FSM
    { start = S0,
      trans = trans,
      accept = [S1],
      out = Moore $ id
    }
  where
    -- Can be read in a tabular style
    trans :: BinState -> Binary -> BinState
    trans S0 Zero = S0
    trans S0 One = S1
    trans S1 Zero = S1
    trans S1 One = S2
    trans S2 _ = S2