XestiSexp

An S-expression encoder and decoder.

Overview

The XestiSexp framework provides a Swift encoder and decoder that represents values as S-expressions like in Scheme. Encoding and decoding revolve around two Codable-style types:

Stage	Type	Input → Output
Encode	SexpEncoder	Encodable → Data
Decode	SexpDecoder	Data → Decodable

Underneath, a Sexp represents any S-expression datum — boolean, bytevector, character, null, number, pair, string, symbol, or vector — and Sexp.Parser and Sexp.Formatter convert between a Sexp and its textual representation, under either the R⁵RS or the (partial) R⁷RS syntax standard.

Requirements

• iOS 18.0+ / macOS 15.0+
• Swift 6 language mode

Installation

Swift Package Manager

XestiSexp is distributed exclusively through the Swift Package Manager.

To add XestiSexp to a Swift package, add it to the dependencies in your Package.swift:

dependencies: [
    .package(url: "https://github.com/eBardX/XestiSexp.git",
             .upToNextMajor(from: "4.1.0"))
]

Then add XestiSexp to the dependencies of any target that uses it:

.target(name: "MyTarget",
        dependencies: [.product(name: "XestiSexp",
                                package: "XestiSexp")])

To add XestiSexp to an Xcode project, choose File ▸ Add Package Dependencies… and enter the repository URL:

https://github.com/eBardX/XestiSexp.git

Quick Start

Encode any Codable value to S-expression data, then decode it back:

import Foundation
import XestiSexp

struct Greeting: Codable {
    let lang: String
    let text: String
}

let greeting = Greeting(lang: "en",
                        text: "Hello!")

// 1. Encode a value into S-expression data.
let data = try SexpEncoder().encode(greeting)

String(data: data, encoding: .utf8)
// ((lang en) (text Hello!))

// 2. Decode S-expression data back into a value.
let decoded = try SexpDecoder().decode(Greeting.self, from: data)

decoded.lang   // "en"
decoded.text   // "Hello!"

To work directly with S-expression text — without going through Codable — parse and format a Sexp value instead:

let sexp   = try Sexp.Parser(syntax: .r7rsPartial,
                             tracing: .silent).parse(input: "(1 2 3)")
let output = try Sexp.Formatter(prettyPrint: false,
                                syntax: .r7rsPartial,
                                tracing: .silent).format(sexp)

Documentation

Every public declaration carries a DocC comment; SexpEncoder, SexpDecoder, Sexp.Parser, and Sexp.Formatter in particular describe their behavior — and limitations — in detail.

Reference Documentation

Full reference documentation is available courtesy of DocC.

Credits

John Gary Pusey (ebardx@gmail.com)

License

XestiSexp is available under the MIT license.