Am Freitag 30 Oktober 2009 14:40:13 schrieb Luca Ciciriello:
Hi all.
Just a very basic question.
I need to write a function str2lsts :: String -> [[String]] in order to transorm a string like:
"\"1\",\"cat\",\"dog\"§\"2\",\"duck\",\"goose\""
in the list of lists:
[["1","cat","dog"],["2","duck","goose"]]
I've tried to mix recursion, pattern matching and list comprehension, but the obtained result was embarrassing complex (> 20 lines of awful code). I think that a more simple solution certainly exists.
splitOnToken :: Eq a => a -> [a] -> [[a]] splitOnToken t xs = case break (== t) xs of (hd,tl) -> hd:case tl of (_:r@(_:_)) -> splitOnToken t r _ -> [] str2lsts = map (map read . splitOnToken ',') . splitOnToken '§' if things weren't enclosed in quotation marks inside the string, it would be the nicer map (splitOnToken ',') . splitOnToken '§' , provided of course, neither ',' nor '§' are valid characters for the target strings. import Text.ParserCombinators.Parsec simple = between (char '"') (char '"') (many (staisfy (/= '"'))) -- alternative: simple = char '"' >> manyTill anyChar (char '"') multiple = sepBy simple (char ',') total = sepBy multiple (char '§') str2lsts str = case parse total "" str of Left err -> error (show err) Right lsts -> lsts
Thanks in advance for any idea.
Luca