我正在尝试使用以下代码进行正则表达式替换
import Text.RE.Replace
import Text.RE.TDFA.String
onlyLetters :: String -> String
onlyLetters s = replaceAll "" $ s *=~ [re|$([^a-zA-Z])|]
我发现很难找到任何可理解的文档。这会产生编译错误:
src\Pangram.hs:6:53: error: parse error on input `]'
|
6 | onlyLetters s = replaceAll "" $ (s *=~ [re|[a-zA-Z]|])
| ^
Progress 1/2
-- While building package pangram-2.0.0.12 (scroll up to its section to see the error) using:
C:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_Z6RU0evB_3.0.1.0_ghc-8.8.4.exe --builddir=.stack-work\dist\29cc6475 build lib:pangram test:test --ghc-options " -fdiagnostics-color=always"
Process exited with code: ExitFailure 1
PS C:\Users\mcleg\Exercism\haskell\pangram> stack test
pangram> configure (lib + test)
Configuring pangram-2.0.0.12...
pangram> build (lib + test)
Preprocessing library for pangram-2.0.0.12..
Building library for pangram-2.0.0.12..
[1 of 2] Compiling Pangram
src\Pangram.hs:7:56: error: parse error on input `]'
|
7 | onlyLetters s = replaceAll "" $ s *=~ [re|$([^a-zA-Z])|]
| ^
Progress 1/2
-- While building package pangram-2.0.0.12 (scroll up to its section to see the error) using:
C:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_Z6RU0evB_3.0.1.0_ghc-8.8.4.exe --builddir=.stack-work\dist\29cc6475 build lib:pangram test:test --ghc-options " -fdiagnostics-color=always"
Process exited with code: ExitFailure 1
该支架有什么问题,我该如何正确执行?谢谢-斯凯
该[…|…|]
是准报价语法[哈斯克尔维基]。这是Haskell语法的扩展,默认情况下未启用。
你可以使用一个LANGUAGE
编译指示来打开它:
{-# LANGUAGE QuasiQuotes #-}
import Text.RE.Replace
import Text.RE.TDFA.String
onlyLetters :: String -> String
onlyLetters s = replaceAll "" $ s *=~ [re|$([^a-zA-Z])|]
准引用将生成Haskell代码,然后在Haskell程序中使用该代码。这意味着通过准报价,可以在编译时对正则表达式进行验证,与在运行时编译正则表达式相比,它甚至可以稍微优化效率。
对于给定的onlyLetters
函数,我们将得到:
*Main> onlyLetters "fo0b4r"
"fobr"
就是这样,非常感谢