LanguageDef：commentLine

everyday parser Parsec 
Prelude> :m Text.ParserCombinators.Parsec.Language
Prelude Text.ParserCombinators.Parsec.Language> commentLine haskellStyle
Loading package parsec ... linking ... done.
"--"
Prelude Text.ParserCombinators.Parsec.Language> commentLine javaStyle
"//"
Prelude Text.ParserCombinators.Parsec.Language> commentLine emptyDef
""
Prelude Text.ParserCombinators.Parsec.Language> commentLine haskellDef
"--"
Prelude Text.ParserCombinators.Parsec.Language> commentLine mondrianDef
"//"