sepBy.hs

import Text.ParserCombinators.ReadP
import Data.Char

schar :: Char -> ReadP Char
schar c = skipSpaces >> char c

word :: ReadP String
word = skipSpaces >> munch1 isAlphaNum

wordlist :: ReadP [String]
wordlist = sepBy word (schar ',')

input :: ReadP [String]
input = do ls <- wordlist
           skipSpaces
           eof
           return ls

main :: IO ()
main = do line <- getLine
          print $ show $ readP_to_S input line