On Sun, Feb 12, 2006 at 01:57:07PM +0100, Daniel Fischer wrote:
Am Sonntag, 12. Februar 2006 04:23 schrieb Juan Carlos Arevalo Baeza:
optional :: GenParser tok st a -> GenParser tok st () optional p = do{ p; return ()} <|> return ()
Now, this completely loses the result of the optional parser. Better would be:
optional :: GenParser tok st a -> GenParser tok st (Maybe a) optional p = do{ x <- p; return (Just x) } <|> return Nothing
Your above parser would be
option Nothing (fmap Just p) -- or you might use liftM.
Both are easy enough. If you think the naming is unfortunate, I wouldn't flatly contradict, but it's too late now, I believe.
They are easy, but writing "option Nothing (liftM Just p)" for the nth time tends to be boring. I could write my own combinator, but all the good names are already taken. I too wish optional returned (Maybe a) and I wonder how many programs would be broken if it was changed now. Best regards Tomasz -- I am searching for programmers who are good at least in (Haskell || ML) && (Linux || FreeBSD || math) for work in Warsaw, Poland