alt Hacker NewsIn Haskell I think it's something like:
{-# LANGUAGE OverloadedStrings #-}
import Data.Attoparsec.Text
import qualified Data.Text as T
type ParseError = String
csgParse :: T.Text -> Either ParseError Int
csgParse = eitherResult . parse parser where
parser = do
as <- many' $ char 'a'
let n = length as
count n $ char 'b'
count n $ char 'c'
char '\n'
return n
ghci> csgParse "aaabbbccc\n"
Right 3
The question comes from Haskell, yes: https://byorgey.wordpress.com/2012/01/05/parsing-context-sen...
You used monadic parser, monadic parsers are known to be able to parse context-sensitive grammars. But, they hide the fact that they are combiinators, implemented with closures beneath them. For example, that "count n $ char 'b'" can be as complex as parsing a set of statements containing expressions with an operator specified (symbol, fixity, precedence) earlier in code.
In Haskell, it is easy - parameterize your expression grammar with operators, apply them, parse text. This will work even with Applicative parsers, even unextended.
But in Rust? I haven't seen how it can be done.