If it ducks like a quack, and it smells like a quack, it's probably a x-www-urlencoded URI query string.
Super simple parser combinators for URI query strings!
It just piggy-backs on existing high-performance parser combinators like
attoparsec and
aeson to parse data that looks
like [(Text, Maybe Text)]. Check it out:
import Data.Attoparsec.Text
import Data.Uri.Query
runParser (overEquals (,) (attoparsec double) (attoparsec double))
[("123", Just "456"), ("123", Nothing), ("123", Just "456")]returns
Right (123,456)It tries to follow the same semantics as attoparsec; backtrack on failure. It's implemented with a really really simple zipper between "parsed so far" and "to parse", if that makes sense - the head of "to parse" is the subject, while failure just reverts the append.
Also, many, some and friends all work too:
runParser (some . unlabeled $ attoparsec double)
[("1234",Nothing),("5678",Nothing)]returns
Right [1234,5678]