haskell - 使用 parsec 在字符串中查找子字符串

Question

例如，我想从 "aabbccabc" 获取 "abc"，使用正则表达式应该很容易。但我想使用秒差距。看起来 try 可以做到这一点，但那肯定是相当低效的......

我试过:

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

得到如下结果:

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

Answer 1

你可以这样做:

{-# 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