使用parsec在字符串中查找子字符串

Question

例如，我想从"aabbccabc"获得​​，使用正则表达式应该很容易。但我想使用parsec。看来，try能做到这一点，但是这必须是非常低效的...

我想：

import Text.ParserCombinators.Parsec 
ps pser txt = case (parse pser "" txt) of 
    Left e -> show e 
    Right v -> v 

，并得到以下结果：

λ> ps (string "asf") " dsfdsasf" 
"(line 1, column 1):\nunexpected \" \"\nexpecting \"asf\"" 

Answer 1

你可以做这样的事情：

{-# LANGUAGE FlexibleContexts #-} 

import Text.Parsec 
import Text.Parsec.Char 

findSubString str = try (string str) <|> (anyChar *> findSubString str) 

foo = do 
    findSubString "abc" 
    findSubString "def" 

test1 = parseTest foo "this is abc"   -- fails: expecting def 

test2 = parseTest foo "this is abc and de" -- fails: expecting def 

test3 = parseTest foo "this is abc and def" -- succeeds