[Haskell-cafe] Is there already a lib to parse a line of string with a pattern and generate key-value map or a record?

[Neil Mayhew]

I’m a fan of |regex-applicative|. It’s a combinator library modelled on 
the parsec family but because it parses only regular languages rather 
than context-free ones, it’s a bit simpler to use and is a better match 
for some tasks. It uses |OverloadedStrings| to make it easier to include 
literal string matches and provides a non-greedy repeating combinator 
called |few| that avoids having to specify exclusive matches. I think it 
solves this problem quite nicely:

|{-# LANGUAGE OverloadedStrings #-} import Text.Regex.Applicative -- 
This is just <*> with right associativity (<&>) :: Applicative f => f (a 
-> b) -> f a -> f b (<&>) = (<*>) infixr 3 <&> type Item = (String, 
String) item :: String -> RE Char ([Item] -> [Item]) item key = (:) . 
(,) key <$> few anySym -- ${year}/${month}/${day} ${hour}:${minute} User 
${username} runs command ${command}. pattern :: RE Char [Item] pattern = 
item "year" <* "/" <&> item "month" <* "/" <&> item "day" <* " " <&> 
item "hour" <* ":" <&> item "minute" <* " User " <&> item "username" <* 
" runs command " <&> item "command" <* "." <&> pure [] input :: String 
input = "2019/04/17 17:27 User magicloud runs command ls." output :: 
Maybe [Item] output = match pattern input -- Just 
[("year","2019"),("month","04"),("day","17"),("hour","17"),("minute","27"),("username","magicloud"),("command","ls")] 
|

(Also available as a gist 
<https://gist.github.com/neilmayhew/e4fc90b7eaeb7bbcfeb6d6938544ecc9>.)

Obviously the combinator version is less compact and therefore could be 
considered less readable, but the implementation details could probably 
be tweaked a bit. It would also be relatively easy to write a 
quasi-quoter that turns the original input syntax (with |${variable}|) 
into the equivalent I’ve shown here.

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