CSV <-> Array<OrderedDictionary>

csv.swift

/*
In Computer Science class I was tasked with writing a function takes a raw CSV table and returns a list of OrderedDictionaries and vice versa – but in Python.
It felt messy, convoluted and slow, so I wanted to what it would look like in Swift, especially with Pointfree's swift-parsing library and their experimental parser-builder branch.
This is as high performance as possible while using the swift-parsing library. Consequently, this doesn't support special characters such as é or æ due to the use of UTF8 code units.
*/

import Algorithms
import OrderedCollections
import Parsing

func csvToDictionaries(csv: String) -> [OrderedDictionary<String, String>]? {
    let quoteOrField = Parse {
        OneOf {
            Parse {
                "\"".utf8
                Prefix { $0 != .init(ascii: "\"") }
                "\"".utf8
            }
            Prefix { $0 != .init(ascii: ",") && $0 != .init(ascii: "\n") }
        }
        .map { String(Substring($0)) }
    }

    let csvParser = Parse {
        Many {
            Many {
                quoteOrField
            } separator: {
                ",".utf8
            }
        } separator: {
            "\n".utf8
        }
        .map { input -> Array<OrderedDictionary<String, String>> in
            let headers = input.first!
            var output: Array<OrderedDictionary<String, String>> = []
            output.reserveCapacity(input.count - 1)
            
            input[1...].forEach { row in
                output.append(OrderedDictionary(uncheckedUniqueKeys: headers, values: row))
            }
            return output
        }
    }

    return csvParser.parse(csv)
}

func dictionariesToCSV(dics dictionaries: [OrderedDictionary<String, String>]) -> String {
    var bytes: [UTF8.CodeUnit] = []
    
    bytes.append(
        contentsOf: dictionaries.first!.keys
            .interspersed(with: ",")
            .flatMap(\.utf8)
    )
    bytes.append(.init(ascii: "\n"))
    
    dictionaries.map(\.values).forEach { row in
        bytes.append(
            contentsOf: row
                .interspersed(with: ",")
                .flatMap(\.utf8)
        )
        bytes.append(.init(ascii: "\n"))
    }
    
    return String(decoding: bytes, as: UTF8.self)
}