実装基準がよくわからない。

import System.Environment(getArgs)
import Data.List(isInfixOf,isPrefixOf,tails,findIndices)

search1 = isInfixOf
search2 word = length . filter (isPrefixOf word) . tails
search3 word content = (ps /= [], length ps, ps)
　where ps = concat . zipWith indices [0..] $ lines content
　　　　indices l = zip (repeat l) . findIndices (isPrefixOf word) . tails

main = do
　(file:word:_) <- getArgs
　print =<< search1 word <$> readFile file
　print =<< search2 word <$> readFile file
　print =<< search3 word <$> readFile file