CSV.swift

    func testCSV() throws {
        let plainField = Prefix { $0 != .init(ascii: ",") && $0 != .init(ascii: "|") && $0 != .init(ascii: "\n") }

        let quotedField = Parse {
            "|".utf8
            Many {
                OneOf {
                    Parse { "||".utf8 }.map { Substring("").utf8 }
                    Prefix { $0 != .init(ascii: "|") }
                }
            } separator: {
                "".utf8
            } 
            "|".utf8
        }.map { array in
            array.map(Substring.init).joined(separator: "")[...].utf8
        }
//            .eraseToAnyParser()

        let field = OneOf {
            quotedField
            plainField
        }
            .map { String(Substring($0)) }

        let line = Many {
            field
        } separator: {
            ",".utf8
        }

        let csv = Many {
            line
        } separator: {
            "\n".utf8
        } terminator: {
            End()
        }

        let input = #"""
            123,Alice
            789,|Clarice|
            456,|Bob ||Baumeister|||
            """#
        let result = try csv.parse(input)
        XCTAssertNoDifference([["123", "Alice"], ["789", "Clarice"], ["456", "Bob |Baumeister|"]], result)
    }