On Fri, Sep 24, 2010 at 9:28 PM, Evan Laforge
simpleComment = do{ string "<!--" ; manyTill anyChar (try (string "-->")) }
Note the overlapping parsers anyChar and string "", ...
Yes, I think the doc just made a mistake there. In fact, it looks like the same mistake is in the current doc at http://hackage.haskell.org/packages/archive/parsec/3.1.0/doc/html/Text-Parse...
Evan, Thanks very much for the typo confirmation, the explanation about backtracking below, and the tip about the source distribution for the examples. I need to remember that multiple char strings imply backtracking, and that backtracking is not the default, hence "try". Thanks. -- Peter
Second, manyTill, by definition, keeps applying p (anyChar) until end (string "-->") is satisfied, so I would expect one could just write:
manyTill anyChar (string "-->")
The problem is that "-->" has multiple characters. So if you have "-not end comment", it will match the '-' against the (string "-->"). Since it doesn't backtrack by default, it's committed now and will fail when it hits the 'n'. The 'try' will make it backtrack to 'anyChar' when the second '-' fails to match.
(If anyone knows of a collection of parsec demos or good examples, I would appreciate a link; thanks)
I thought the parsec source included some example parsers for simple languages? In any case, there is lots of material floating around, though I found parsec so intuitive and the docs so good that I just started hacking. I think the 'build scheme in haskell' tutorial uses parsec for the parsing.