Inject attoparsec parser with backtracking into non-backtracking scanner
Backtracking kills performance, so scanner package doesn't support it. But sometimes you just need it. E.g. you have a mostly non-backtracking parser, but a small bit of its grammar is too complex to transform it to non-backtracking form. In that case you can inject a backtracking attoparsec parser into otherwise non-backtracking scanner.