Parsec.Error：errorPos

everyday parser Parsec 
Prelude> :m Text.ParserCombinators.Parsec
Prelude Text.ParserCombinators.Parsec> :t errorPos
errorPos :: ParseError -> SourcePos

module Main where

import Text.ParserCombinators.Parsec
import Text.ParserCombinators.Parsec.Token
import Text.ParserCombinators.Parsec.Language

lexer  :: TokenParser ()
lexer  =  makeTokenParser(javaStyle)

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

で、

Prelude> :l 20090129_parsec00.hs
[1 of 1] Compiling Main             ( 20090129_parsec00.hs, interpreted )
Ok, modules loaded: Main.
*Main> run (identifier lexer) "abc"
Loading package parsec-2.0 ... linking ... done.
"abc"
*Main> run (identifier lexer) "123"
parse error at (line 1, column 1)
*Main> :l 20081127_parsec00.hs
[1 of 1] Compiling Main             ( 20081127_parsec00.hs, interpreted )
Ok, modules loaded: Main.
*Main> run (identifier lexer) "123"
parse error at (line 1, column 1):
unexpected "1"
expecting identifier