<div dir="ltr"><div><div><div><div><div><div><div><div><div><div><div><div><div><div><div><div><div><div>Hi,<br><br></div> I'm trying to parse ical files but the source material doesn't matter much. First, I know there is an icalendar library on hackage, but I'm trying to learn as well through this.<br>
<br></div> Now the format is really quite simple and actually I'm parsing it, it works, but I don't like the code I'm writing, it feels wrong and I'm sure there is a better way. Actually for now I'm parsing it to an array of arrays, but I want to fill a proper "data" structure.<br>
<br></div> For my purpose the file contains a bunch of records like this:<br><br>BEGIN:VEVENT<br>DTSTART:20121218T103000Z<br>DTEND:20121218T120000Z<br>[..]<br>DESCRIPTION:<br>[..]<br>END:VEVENT<br><br></div>There are a bunch of records I don't care about and also I want to parse no matter what is the order of directives (so, i want to parse also if DTEND appears before DTSTART for instance, and so on).<br>
<br></div>That last part is my one problem. I can't do:<br><br></div>parseBegin<br></div>start <- parseStart<br></div>end <- parseEnd<br></div>skipRows<br></div>desc <- parseDesc<br></div>skipRows<br></div>end <- parseEnd<br>
return Event { eventStart = start, eventEnd = end ...}<br><br></div>my current working code is:<br><br>parseEvent = do<br> parseBegin<br> contents <- many1 $ (try startDate)<br> <|> (try endDate)<br>
<|> (try description)<br> <|> unknownCalendarInfo<br> parseEnd<br> return contents<br><br></div>But then contents of course returns an array, while I want to return only one element here.<br>
<br></div>SOMEHOW what I would like is:<br><br>parseEvent = do<br> parseBegin<br> contents <- many1 $ (start <- T.try startDate)<br> <|> (end <- T.try endDate)<br> <|> (desc <- T.try description)<br>
<|> unknownCalendarInfo<br> parseEnd<br> return Event { eventStart = start, eventEnd = end ...}<br><br></div> But obviously as far as Parsec is concerned startDate could occur several times and also it's just not valid Haskell syntax.<br>
<br></div> So, any hint about this problem? Parsing multi-line records with Parsec, when I don't know the order in which the lines will appear? I mean sure I can convert my array to the proper data structure... I find which element in the array contains the start date and then which contains the end date... and build my data structure.. But I'm sure something much nicer can be done... I just can't find how.<br>
<br></div><div> I see the author of iCalendar fixed the problem but I can't completely understand his source, it's too many things at the same time for me, I need to take this one step at a time.<br></div><div><br>
</div> Thank you!<br><br>Emmanuel<br></div>