TryParsec

Monadic Parser Combinator for try! Swift.

• Inspired by Haskell Attoparsec & Aeson, Swift Argo.
• Supports CSV, XML, JSON (+ mapping)
• Doesn't try, but please try :)

NOTE: This library is still in early development. Please see TODO & FIXME.

Quick Play

Open Examples/TryParsecPlayground.playground.

$ sudo gem install fastlane
$ fastlane play   # prepares Xcode Playground

How to use

// Simple Arithmetic
let ans = parseArithmetic(" ( 12 + 3 )         * 4+5").value
expect(ans) == 65

// CSV
let csv = parseCSV("foo,bar,baz\r\n1,22,333\r\n").value
expect(csv) == [["foo", "bar", "baz"], ["1", "22", "333"]]

// XML
let xmlString = "<p class=\"welcome\"><a href=\"underground.html\" target=\"_blank\">Hello</a><?php echo ' Cruel'; ?> World<!-- 💀 --><![CDATA[💣->😇]]></p>"
let xml = parseXML(xmlString).value
expect(xml) == [.element("p", [XML.Attribute("class", "welcome")], [.element("a", [XML.Attribute("href", "underground.html"), XML.Attribute("target", "_blank")], [.text("Hello")]), .processingInstruction("php echo ' Cruel'; "), .text(" World"), .comment(" 💀 "), .text("💣->😇")])]

// JSON
let jsonString = "{ \"string\" : \"hello\", \"array\" : [1, \"two\", [true, null]] }"
let json = parseJSON(jsonString).value
expect(json) == JSON.object([
    "string" : .string("hello"),
    "array" : .array([.number(1), .string("two"), .array([.bool(true), .null])])
])

JSON Decoding & Encoding

import Curry

struct Model: FromJSON, ToJSON
{
    let string: String
    let array: [Any]?

    static func fromJSON(json: JSON) -> Result<Model, JSON.ParseError>
    {
        return curry(self.init)
            <^> json !! "string"
            <*> json !? "array"
    }

    static func toJSON(model: Model) -> JSON
    {
        return toJSONObject([
            "string" ~ model.string,
            "array" ~ model.array
        ])
    }
}

let jsonString = "{ \"string\" : \"hello\", \"array\" : [1, \"two\", [true, null]] }"

// JSON String -> Model
let decoded: Result<Model, JSON.ParseError> = decode(jsonString)

// Model -> JSON String
let encoded: String = encode(decoded.value!)

For currying, see thoughtbot/Curry for more information.

Supported functions

• Basic Operators: >>-, <^>, <*>, *>, <*, <|>, <?>
• Combinators: zeroOrOne, many, many1, manyTill, skipMany, skipMany1, sepBy, sepBy1, sepEndBy, sepEndBy1, count, chainl, chainl1, chainr, chainr1
• Text (UnicodeScalarView): peek, endOfInput, satisfy, skip, skipWhile, take, takeWhile, any, char, not, string, asciiCI, oneOf, noneOf, digit, hexDigit, lowerAlphabet, upperAlphabet, alphabet, alphaNum, space, skipSpaces, endOfLine, number

TODO & FIXME

• Improve overall performance
  • Current JSON parsing is 70x~ slower than NSJSONSerialization (even with whole-module-optimization)
• Improve error reporting
• Support indent parser (e.g. YAML)
• Once apple/swift supports Higher Kinded Types...
  • Support incremental input
  • Remove workarounds e.g. reflection-based JSON encoding

Acknowledgement

This library is heavily inspired by following developers & libraries:

• Bryan O'Sullivan: Author of Attoparsec & Aeson (Haskell)
• Daan Leijen: Author of Parsec (Haskell)
• thoughtbot: Author of Argo (Swift JSON decoding library)

References

• Parser Combinators in Swift (video)
• Parser Combinator in Swift // Speaker Deck (slide)

Licence

MIT