Magnus Therning wrote:
Patrick LeBoutillier wrote:
I wanted to parse a file that looks like this:
MONDAY JOHN JIM LINDA TUESDAY BILL BOB WEDNESDAY THURSDAY SAM TODD LARRY LUKE FRIDAY TED
in order to count the number of people for each day. After a (very) long time and a lot of trial and error, I managed to do it with this program:
Nice program, especially your use of function composition is good style.
I think that you've pretty much used accumulators in the way they most often are used. In many cases you don't _have_ to keep count though. Here's one way to get the same result, but without keeping count:
countDays [] = [] countDays ls = let day = head ls count = length $ takeWhile (isSpace . head) $ tail ls in (day, count) : countDays (drop (1 + count) ls)
main = interact (unlines . map show . countDays . lines)
Here's a version using span from the Prelude: main = interact $ unlines . map show . countDays . lines countDays [] = [] countDays (day:xs) = (day, length people) : countDays xs' where (people, xs') = span (isSpace . head) xs Note that this file format is very simple and it's ok to use lines and isSpace to parse it. But the tool of choice are parser combinators like Text.Parsec or Text.ParserCombinators.ReadP . -- http://apfelmus.nfshost.com