Find substring in a string with parsec

Question

For example, I want to get "abc" from "aabbccabc", which should be easy with regex. But i want to use parsec. It seems that try can do that, but that must be quite inefficient...

I tried:

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

and got the following result:

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

Answer 1

You can do something like this:

{-# 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