How to replace a string with another in haskell

问题

I want to replace a string from an input file with a different string. I was searching for a method but it seems i can only alter the string character by character. For example in the my code below

replace :: String -> String 
replace [] = [] 
replace (x:xs) = if x == '@' then 'y':replace xs --y is just a random char
                             else x:replace xs

searching :: String -> IO String
searching filename = do
    text <- readFile filename
    return(replace text)


main :: IO ()
main = do

  n <- searching "test.sf"
  writeFile "writefile.html" n 

I want to find the first occurrence of the string "@title", but i cant seem to find a method to do so as mentioned before, i can only access the char '@'. Is there a method for doing such a task.

回答1:

You can use Data.List.Utils replace, it's lazy and you can process a big file with some like:

main = getContents >>= putStr . replace "sourceString" "destinationString"

That's all!

A possible replace function could be

rep a b s@(x:xs) = if isPrefixOf a s

                     -- then, write 'b' and replace jumping 'a' substring
                     then b++rep a b (drop (length a) s)

                     -- then, write 'x' char and try to replace tail string
                     else x:rep a b xs

rep _ _ [] = []

another smart way (from Data.String.Utils)

replace :: Eq a => [a] -> [a] -> [a] -> [a]
replace old new l = join new . split old $ l

来源：https://stackoverflow.com/questions/14907600/how-to-replace-a-string-with-another-in-haskell