I want to create a while loop to concatenate strings in the xs list
until I find an empty string, but it seems neither we have a chance to
increment an Int nor create a while loop.
So this looks like a pseudo code for Haskell, but how can I actually implement my solution?
prt :: String -> [String] -> Int -> String
prt str xs x = do
while((xs !! (x)) /= "")
str = str ++ (xs !! (x++))
Forget array indexes: they are often not needed. All you have to do for your task is getting the longest prefix of your list containing only non-empty strings.
takeWhile (not . null) xs
-- or
takeWhile (/= "") xs
Then you want to concatenate these strings.
concat $ takeWhile (/= "") xs
If you want to start after n strings for some reason, just drop the first n before beginning:
concat $ takeWhile (/= "") $ drop n xs
If you really want to do a custom "loop", use recursion:
g xs n = f $ drop n xs
f [] = ""
f ("":xs) = ""
f (x:xs) = x ++ f xs
x: maybe add a drop in there or something?
not . null, should generally be preferred to (/= "") because it works for types other than strings.