Question

问题陈述：解析"AB"

中的字符串"ABCDFGABIJABGHA"

约束：使用ReadP

预期解决方案：(["AB","AB","AB"],"whatever is left")

尝试：

getAll :: ReadP a -> ReadP [a]
getAll p = many loop
  where
    loop = p <|> (get >> loop)

readP_to_S (getAll $ string "AB") "ABCDFGABIJABGHA"
[([],"ABCDFGABIJABGHA"),(["AB"],"CDFGABIJABGHA"),(["AB","AB"],"IJABGHA"),(["AB"],"IJABGHA"),(["AB","AB","AB"],"GHA"),(["AB","AB"],"GHA"),(["AB","AB"],"GHA"),(["AB"],"GHA")]

我希望最后一个州成为(["AB","AB","AB"],"GHA")。是否可以使用ReadP？

执行相同的操作

Answer 1

问题在于您正在使用<|>进行对称选择。如果您希望解析器毫无例外地匹配所有p，请使用提供的左偏置选项：<++。

getAll :: ReadP a -> ReadP [a]
getAll p = many loop
  where
    loop = p <++ (get >> loop)

使用ReadP解析字符串的多个实例

1 个答案: