[Haskell-beginners] Parsec, parsing 'free text'

[Franco]

Indeed the second solution is more elegant (and the examples very simple to follow, they should be added to Parsec's documentation!).
For the records, before reading this I was using the ductape solution below:

161  
162 -- take a string till t, on that runs parser p. 
163 -- The last parameters sets wheter t will be consumed or  
164 -- not. FILE HANDLING FOR ERRORS? 
165 parseTill :: Parser a -> Parser b -> Parser b 
166 parseTill ter p = manyTill anyChar ter >>= \sndPar -> 
167                   case parse p "" sndPar of 
168                     Left  a -> fail "todo: check how error msg are propagted" 
169                     Right b -> return b 

Thanks again
-F


On Sun, 11 Mar 2012 10:53:50 +0000
Stephen Tetley <stephen.tetley at gmail.com> wrote:

> Hi Franco
> 
> Actually the simple case of finding formatting tags in free text was
> easier in Parsec than my email last night suggested. Perhaps it is
> artificially easy because you can identify tag start and ends with a
> single character so you can use `satisfy`.
> 
> import Text.Parsec
> import Text.Parsec.String
> import Control.Applicative hiding ( (<|>), many )
> 
> 
> data Text1 = FreeText String | Formatted String
>   deriving (Eq,Ord,Show)
> 
> type Text = [Text1]
> 
> runText :: String -> Either ParseError Text
> runText = runP lexer () "no-input"
> 
> 
> notLAngle :: Char -> Bool
> notLAngle = (/= '<')
> 
> notRAngle :: Char -> Bool
> notRAngle = (/= '>')
> 
> lexer :: Parser Text
> lexer = many (formatted <|> free)
> 
> formatted :: Parser Text1
> formatted = Formatted <$>
>     between (char '<') (char '>') (many1 (satisfy notRAngle))
> 
> free :: Parser Text1
> free = FreeText <$> many1 (satisfy notLAngle)
> 
> 
> 
> demo01 = runText "[ someconditions | this is some <red - formatted> text.]"
> demo02 = runText "<red - formatted> more text."


-- 
Franco <franco00 at gmx.com>