"=〜"raise"没有实例(RegexContext Regex [Char] [String])"

Question

操作系统:MacOSX 10.7.1来自brew的GHC和Haskell平台.

   GHCi, version 7.0.4: http://www.haskell.org/ghc/  :? for help
    Loading package ghc-prim ... linking ... done.
    Loading package integer-gmp ... linking ... done.
    Loading package base ... linking ... done.
    Loading package ffi-1.0 ... linking ... done.
    Prelude> :m +Text.Regex.Posix
    Prelude Text.Regex.Posix> "foo" =~ "o" :: [String]

    <interactive>:1:7:
        No instance for (RegexContext Regex [Char] [String])
          arising from a use of `=~'
        Possible fix:
          add an instance declaration for
          (RegexContext Regex [Char] [String])
        In the expression: "foo" =~ "o" :: [String]
        In an equation for `it': it = "foo" =~ "o" :: [String]
    Prelude Text.Regex.Posix> "foo" =~ "o" :: String
    Loading package array-0.3.0.2 ... linking ... done.
    Loading package bytestring-0.9.1.10 ... linking ... done.
    Loading package containers-0.4.0.0 ... linking ... done.
    Loading package transformers-0.2.2.0 ... linking ... done.
    Loading package mtl-2.0.1.0 ... linking ... done.
    Loading package regex-base-0.93.2 ... linking ... done.
    Loading package regex-posix-0.95.1 ... linking ... done.
    "o"

我相信图书馆更新了.我认为输出"foo" =~ "o" :: [String]是["o", "o"]

任何建议将不胜感激.

Answer 1

ghci> getAllTextMatches ("foo" =~ "o" :: AllTextMatches [] String)
["o", "o"]

我没有在Haskell中使用正则表达式(我认为Dan Burton的答案更为惯用).

所以我想出来的方式是我看了你的类型错误No instance for (RegexContext Regex [Char] [String]),并弹出到ghci:

ghci> :t (=~)
(=~)
  :: (RegexMaker Regex CompOption ExecOption source,
      RegexContext Regex source1 target) =>
     source1 -> source -> target

所以RegexContext Regex [Char] [String]是一个包含返回类型的类"foo" =~ "o" :: [String].所以我看看这个类确实存在哪些实例,所以我可以找出允许返回值的内容:

ghci> :i RegexContext
class RegexLike
        regex source => RegexContext regex source target where
  match :: regex -> source -> target
  matchM :: Monad m => regex -> source -> m target
        -- Defined in Text.Regex.Base.RegexLike
instance RegexContext Regex String String
  -- Defined in Text.Regex.Posix.String
instance RegexLike a b => RegexContext a b [[b]]
  -- Defined in Text.Regex.Base.Context
...
instance RegexLike a b => RegexContext a b (AllTextMatches [] b)
  -- Defined in Text.Regex.Base.Context
...

这个AllTextMatches名字似乎表明你在寻找什么,所以我检查了一下:

ghci> :i AllTextMatches
newtype AllTextMatches f b
  = AllTextMatches {getAllTextMatches :: f b}
        -- Defined in Text.Regex.Base.RegexLike
instance RegexLike a b => RegexContext a b (AllTextMatches [] b)
  -- Defined in Text.Regex.Base.Context

所以这是用于提取所有文本匹配的类型,正如我怀疑的那样.我需要做的就是表明我想要一个这种类型的返回值.

还要注意可能的返回类型[[b]],我假设它返回包含每个完整匹配及其所有子匹配的列表列表:

ghci> "foo" =~ "o" :: [[String]]
[["o"],["o"]]
ghci> "foo bar baz" =~ "[aeiou](.)" :: [[String]]
[["oo","o"],["ar","r"],["az","z"]]

所以也许这是你打算使用的类型,而不是[String].我可以看到存在[String]时有点模棱两可[[String]]- 应该"foo bar baz" =~ "[aeiou](.)" :: [String]是fst ("foo bar baz" =~ "[aeiou](.)" :: [[String]])或者map fst ("foo bar baz" =~ "[aeiou](.)" :: [[String]]).

Answer 2

这也有效

ghci> getAllTextMatches $ "foo" =~ "o" :: [String]
["o","o"]

Answer 3

尝试这个：

Prelude Text.Regex.Posix> getAllTextMatches ("foo" =~ "o" :: AllTextMatches [] String)
["o","o"]