Haskell by Example: String Functions

original

import Data.List
import Data.Char

include :: String -> String -> Bool
include xs ys = or . map (isPrefixOf ys) . tails $ xs

joinWith :: [String] -> String -> String
joinWith xs sep = concat . init . concat $ [[x, sep] | x <- xs]

split :: String -> Char -> [String]
split "" _ = []
split xs c = let (ys, zs) = break (== c) xs
             in  if null zs then [ys] else ys : split (tail zs) c

main = do
    putStrLn $ "Contains:  " ++ show ("test" `include` "es")
    putStrLn $ "Count:     " ++ show (length . filter (=='t') $ "test")
    putStrLn $ "HasPrefix: " ++ show (isPrefixOf "te" "test")
    putStrLn $ "HasSuffix: " ++ show (isSuffixOf "st" "test")
    putStrLn $ "Index:     " ++ show (elemIndex 'e' "test")
    putStrLn $ "Join:      " ++ show (["a", "b"] `joinWith` "-")
    putStrLn $ "Repeat:    " ++ show (replicate 5 'a')
    putStrLn $ "Replace:   " ++ show (map (\x -> if x == 'o' then '0' else x) "foo")
    putStrLn $ "Split:     " ++ show (split "a-b-c-d-e" '-')
    putStrLn $ "ToLower:   " ++ map toLower "TEST"
    putStrLn $ "ToUpper:   " ++ map toUpper "test"
    putStrLn ""
    putStrLn $ "Len: " ++ show (length "hello")
    putStrLn $ "Char:" ++ show ("hello" !! 1)

$ runhaskell string-functions.hs
Contains:  True
Count:     2
HasPrefix: True
HasSuffix: True
Index:     Just 1
Join:      "a-b"
Repeat:    "aaaaa"
Replace:   "f00"
Split:     ["a","b","c","d","e"]
ToLower:   test
ToUpper:   TEST

Len: 5
Char:'e'

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