Haskell中布尔型AST的遍历

data BoolExpr = BoolLit Bool
              | And BoolExpr BoolExpr
              | Or BoolExpr BoolExpr
              | Not BoolExpr

evalBoolExpr :: BoolExpr -> Bool
evalBoolExpr (BoolLit b) = b
evalBoolExpr (And expr1 expr2) = evalBoolExpr expr1 && evalBoolExpr expr2
evalBoolExpr (Or expr1 expr2) = evalBoolExpr expr1 || evalBoolExpr expr2
evalBoolExpr (Not expr) = not (evalBoolExpr expr)

traverseBoolExpr :: BoolExpr -> [Bool]
traverseBoolExpr (BoolLit b) = [b]
traverseBoolExpr (And expr1 expr2) = traverseBoolExpr expr1 ++ traverseBoolExpr expr2
traverseBoolExpr (Or expr1 expr2) = traverseBoolExpr expr1 ++ traverseBoolExpr expr2
traverseBoolExpr (Not expr) = traverseBoolExpr expr