Functional Parser

Several applicative parsers / parser combinators, inspired by:

• https://academy.realm.io/posts/tryswift-yasuhiro-inami-parser-combinator/
• https://talk.objc.io/episodes/S01E78-swift-strings-and-substrings
• https://www.youtube.com/watch?v=YSnQ8N760mI
• https://www.pointfree.co/collections/parsing
• https://hackage.haskell.org/package/parsec