regex-applicative is a parsing combinator library for Haskell based on regular expressions.
import Text.Regex.Applicative data Protocol = HTTP | FTP deriving Show protocol :: RE Char Protocol protocol = HTTP <$ string "http" <|> FTP <$ string "ftp" type Host = String type Location = String data URL = URL Protocol Host Location deriving Show host :: RE Char Host host = many $ psym $ (/= '/') url :: RE Char URL url = URL <$> protocol <* string "://" <*> host <* sym '/' <*> many anySym main = print $ "http://stackoverflow.com/questions" =~ url
See the API reference.
For common tasks, this package is several times slower than monadic parser combinator libraries like parsec. However, this library has a roughly linear complexity, whereas monadic parser combinators have exponential worst-time complexity (see here).
Some tips to make your regex run faster:
If you don't care about the result of the whole regex or its part, only whether it matches or not, mark it with
<$. Recognition is faster than parsing.
If you apply the same regex to multiple strings, partially apply it like so:
let matcher = match my_regex in map matcher my_strings
This way the compiled regex is stored in the
matchervalue and shared among the strings.
Only GHC versions >= 8.0 are supported, although older versions may work too.