Parsec.Combinator：sepEndBy

everyday parser Parsec 
module Main where

import Text.ParserCombinators.Parsec

test1 :: Parser String
test1 =  sepEndBy letter (char ',')

run :: Show a => Parser a -> String -> IO ()
run p input
        = case (parse p "" input) of
            Left err -> do{ putStr "parse error at "
                          ; print err
                          }
            Right x  -> print x

で、

*Main> run test1 ""
""
*Main> run test1 "a"
"a"
*Main> run test1 "a,"
"a"
*Main> run test1 "a,b"
"ab"
*Main> run test1 "a,b,"
"ab"
*Main> run test1 "ab"
"a"