Question

我有以下树：

data Questionario = Answer String
                  | Question String Questionario Questionario

左侧的子树是否定答案，右侧的子树是肯定答案。

我想将Questionario定义为一个实例，显示所有可能的路径。例如：

q = Question "a >= b"
      (Question "a >= c"
         (Question "b >= c"
              (Answer "a b c")
              (Answer "a c b"))
         (Answer "c a b"))
      (Question "a >= c"
         (Answer "b a c")
         (Question "b >= c"
             (Answer "b c a")
             (Answer "c b a")))

必须显示为：

*Main> q
a >= b? No a >= c? No b >= c? No ANSWER: a b c
a >= b? No a >= c? No b >= c? Yes ANSWER: a c b
a >= b? No a >= c? Yes ANSWER: c a b
a >= b? Yes a >= c? No ANSWER: b a c
a >= b? Yes a >= c? Yes b >= c? No ANSWER: b c a
a >= b? Yes a >= c? Yes b >= c? Yes ANSWER: c b a

我已经写过：

instance Show Questionario where
    show (Answer x) = "ANSWER " ++ x
    show (Question q r l) = q ++ "? "

但我不确定如何让它显示出每一条可能的道路。我该怎么做？感谢。

Answer 1

您希望函数生成所有路径。可能的方法是：

paths :: Questionario -> [String]
paths (Answer x) = ["ANSWER " ++ x]
paths (Question q l r) = [q ++ "? No  " ++ s | s <- paths l] ++
                         [q ++ "? Yes " ++ s | s <- paths r]

Answer只有一条路径。相反，Question的路径是：

的并集

与否定答案有关的问题，前面有问题和＆＃34;否＆＃34;和
与肯定答案相关的问题，前面有问题和＆＃34;是＆＃34;。

您可能希望使用map而不是列表推导 - 这只是个人品味的问题。

在实例上显示不同的路径

1 个答案: