# swift-parsing
**Repository Path**: bugtree/swift-parsing
## Basic Information
- **Project Name**: swift-parsing
- **Description**: No description available
- **Primary Language**: Unknown
- **License**: MIT
- **Default Branch**: abc
- **Homepage**: None
- **GVP Project**: No
## Statistics
- **Stars**: 0
- **Forks**: 0
- **Created**: 2025-04-30
- **Last Updated**: 2025-04-30
## Categories & Tags
**Categories**: Uncategorized
**Tags**: None
## README
# swift-parsing
[](https://swiftpackageindex.com/pointfreeco/swift-parsing)
[](https://swiftpackageindex.com/pointfreeco/swift-parsing)
A library for turning nebulous data into well-structured data, with a focus on composition, performance, generality, and ergonomics:
* **Composition**: Ability to break large, complex parsing problems down into smaller, simpler ones. And the ability to take small, simple parsers and easily combine them into larger, more complex ones.
* **Performance**: Parsers that have been composed of many smaller parts should perform as well as highly-tuned, hand-written parsers.
* **Generality**: Ability to parse _any_ kind of input into _any_ kind of output. This allows you to choose which abstraction levels you want to work on based on how much performance you need or how much correctness you want guaranteed. For example, you can write a highly tuned parser on collections of UTF-8 code units, and it will automatically plug into parsers of strings, arrays, unsafe buffer pointers and more.
* **Ergonomics**: Accomplish all of the above in a simple, fluent API that can succinctly describe your parsing problem.
---
* [Motivation](#motivation)
* [Getting started](#getting-started)
* [Benchmarks](#benchmarks)
* [Documentation](#documentation)
* [Other libraries](#other-libraries)
* [License](#license)
## Learn More
This library was designed over the course of many [episodes](https://www.pointfree.co/collections/parsing) on [Point-Free](https://www.pointfree.co), a video series exploring functional programming and the Swift language, hosted by [Brandon Williams](https://twitter.com/mbrandonw) and [Stephen Celis](https://twitter.com/stephencelis). You can watch all of the episodes [here](https://www.pointfree.co/collections/parsing).
## Motivation
Parsing is a surprisingly ubiquitous problem in programming. We can define parsing as trying to take a more nebulous blob of data and transform it into something more well-structured. The Swift standard library comes with a number of parsers that we reach for every day. For example, there are initializers on `Int`, `Double`, and even `Bool`, that attempt to parse numbers and booleans from strings:
```swift
Int("42") // 42
Int("Hello") // nil
Double("123.45") // 123.45
Double("Goodbye") // nil
Bool("true") // true
Bool("0") // nil
```
And there are types like `JSONDecoder` and `PropertyListDecoder` that attempt to parse `Decodable`-conforming types from data:
```swift
try JSONDecoder().decode(User.self, from: data)
try PropertyListDecoder().decode(Settings.self, from: data)
```
While parsers are everywhere in Swift, Swift has no holistic story _for_ parsing. Instead, we typically parse data in an ad hoc fashion using a number of unrelated initializers, methods, and other means. And this typically leads to less maintainable, less reusable code.
This library aims to write such a story for parsing in Swift. It introduces a single unit of parsing that can be combined in interesting ways to form large, complex parsers that can tackle the programming problems you need to solve in a maintainable way.
## Getting started
> This is an abridged version of the ["Getting Started"][getting-started-docs] article in the library's [documentation][swift-parsing-docs].
Suppose you have a string that holds some user data that you want to parse into an array of `User`s:
```swift
var input = """
1,Blob,true
2,Blob Jr.,false
3,Blob Sr.,true
"""
struct User {
var id: Int
var name: String
var isAdmin: Bool
}
```
A naive approach to this would be a nested use of `.split(separator:)`, and then a little bit of extra work to convert strings into integers and booleans:
```swift
let users = input
.split(separator: "\n")
.compactMap { row -> User? in
let fields = row.split(separator: ",")
guard
fields.count == 3,
let id = Int(fields[0]),
let isAdmin = Bool(String(fields[2]))
else { return nil }
return User(id: id, name: String(fields[1]), isAdmin: isAdmin)
}
```
Not only is this code a little messy, but it is also inefficient since we are allocating arrays for the `.split` and then just immediately throwing away those values.
It would be more straightforward and efficient to instead describe how to consume bits from the beginning of the input and convert that into users. This is what this parser library excels at 😄.
We can start by describing what it means to parse a single row, first by parsing an integer off the front of the string, and then parsing a comma. We can do this by using the `Parse` type, which acts as an entry point into describing a list of parsers that you want to run one after the other to consume from an input:
```swift
let user = Parse {
Int.parser()
","
}
```
Already this can consume the beginning of the input:
```swift
// Use a mutable substring to verify what is consumed
var input = input[...]
try user.parse(&input) // 1
input // "Blob,true\n2,Blob Jr.,false\n3,Blob Sr.,true"
```
> Note that we use a `Substring` instead of `String` because it allows for more efficient mutations and copying. See the article ["String Abstractions"][string-abstractions-docs] for more information.
Next we want to take everything up until the next comma for the user's name, and then consume the comma:
```swift
let user = Parse {
Int.parser()
","
Prefix { $0 != "," }
","
}
```
And then we want to take the boolean at the end of the row for the user's admin status:
```swift
let user = Parse {
Int.parser()
","
Prefix { $0 != "," }
","
Bool.parser()
}
```
Currently this will parse a tuple `(Int, Substring, Bool)` from the input, and we can `.map` on that to turn it into a `User`:
```swift
let user = Parse {
Int.parser()
","
Prefix { $0 != "," }
","
Bool.parser()
}
.map { User(id: $0, name: String($1), isAdmin: $2) }
```
To make the data we are parsing to more prominent, we can instead pass the transform closure as the first argument to `Parse`:
```swift
let user = Parse {
User(id: $0, name: String($1), isAdmin: $2)
} with: {
Int.parser()
","
Prefix { $0 != "," }
","
Bool.parser()
}
```
Or we can pass the `User` initializer to `Parse` in a point-free style by transforming the `Prefix` parser's output from a `Substring` to ` String` first:
```swift
let user = Parse(User.init(id:name:isAdmin:)) {
Int.parser()
","
Prefix { $0 != "," }.map(String.init)
","
Bool.parser()
}
```
That is enough to parse a single user from the input string, leaving behind a newline and the final two users:
```swift
try user.parse(&input) // User(id: 1, name: "Blob", isAdmin: true)
input // "\n2,Blob Jr.,false\n3,Blob Sr.,true"
```
To parse multiple users from the input we can use the `Many` parser to run the user parser many times:
```swift
let users = Many {
user
} separator: {
"\n"
}
try users.parse(&input) // [User(id: 1, name: "Blob", isAdmin: true), ...]
input // ""
```
Now this parser can process an entire document of users, and the code is simpler and more straightforward than the version that uses `.split` and `.compactMap`.
Even better, it's more performant. We've written [benchmarks](Sources/swift-parsing-benchmark/ReadmeExample.swift) for these two styles of parsing, and the `.split`-style of parsing is more than twice as slow:
```
name time std iterations
------------------------------------------------------------------
README Example.Parser: Substring 3426.000 ns ± 63.40 % 385395
README Example.Ad hoc 7631.000 ns ± 47.01 % 169332
Program ended with exit code: 0
```
Further, if you are willing write your parsers against `UTF8View` instead of `Substring`, you can eke out even more performance, more than doubling the speed:
```
name time std iterations
------------------------------------------------------------------
README Example.Parser: Substring 3693.000 ns ± 81.76 % 349763
README Example.Parser: UTF8 1272.000 ns ± 128.16 % 999150
README Example.Ad hoc 8504.000 ns ± 59.59 % 151417
```
We can also compare these times to a tool that Apple's Foundation gives us: `Scanner`. It's a type that allows you to consume from the beginning of strings in order to produce values, and provides a nicer API than using `.split`:
```swift
var users: [User] = []
while scanner.currentIndex != input.endIndex {
guard
let id = scanner.scanInt(),
let _ = scanner.scanString(","),
let name = scanner.scanUpToString(","),
let _ = scanner.scanString(","),
let isAdmin = scanner.scanBool()
else { break }
users.append(User(id: id, name: name, isAdmin: isAdmin))
_ = scanner.scanString("\n")
}
```
However, the `Scanner` style of parsing is more than 5 times as slow as the substring parser written above, and more than 15 times slower than the UTF-8 parser:
```
name time std iterations
-------------------------------------------------------------------
README Example.Parser: Substring 3481.000 ns ± 65.04 % 376525
README Example.Parser: UTF8 1207.000 ns ± 110.96 % 1000000
README Example.Ad hoc 8029.000 ns ± 44.44 % 163719
README Example.Scanner 19786.000 ns ± 35.26 % 62125
```
That's the basics of parsing a simple string format, but there's a lot more operators and tricks to learn in order to performantly parse larger inputs. Read the [documentation][swift-parsing-docs] to dive more deeply into the concepts of parsing, and view the [benchmarks](Sources/swift-parsing-benchmark) for more examples of real life parsing scenarios.
## Benchmarks
This library comes with a benchmark executable that not only demonstrates the performance of the library, but also provides a wide variety of parsing examples:
* [Hex color](Sources/swift-parsing-benchmark/Color.swift)
* [Simplified CSV](Sources/swift-parsing-benchmark/CSV.swift)
* [Simplified JSON](Sources/swift-parsing-benchmark/JSON.swift)
* [ISO8601 date](Sources/swift-parsing-benchmark/Date.swift)
* [HTTP request](Sources/swift-parsing-benchmark/HTTP.swift)
* [DNS header](Sources/swift-parsing-benchmark/BinaryData.swift)
* [Arithmetic grammar](Sources/swift-parsing-benchmark/Arithmetic.swift)
* [URL router](Sources/swift-parsing-benchmark/Routing.swift)
* [Xcode test logs](Sources/swift-parsing-benchmark/XCTestLogs.swift)
* and more
These are the times we currently get when running the benchmarks:
```text
MacBook Pro (16-inch, 2021)
Apple M1 Pro (10 cores, 8 performance and 2 efficiency)
32 GB (LPDDR5)
name time std iterations
----------------------------------------------------------------------------------
Arithmetic.Parser 8042.000 ns ± 5.91 % 174657
BinaryData.Parser 42.000 ns ± 56.81 % 1000000
Bool.Bool.init 41.000 ns ± 60.69 % 1000000
Bool.Bool.parser 42.000 ns ± 57.28 % 1000000
Bool.Scanner.scanBool 1041.000 ns ± 25.98 % 1000000
Color.Parser 209.000 ns ± 13.68 % 1000000
CSV.Parser 4047750.000 ns ± 1.18 % 349
CSV.Ad hoc mutating methods 898604.000 ns ± 1.49 % 1596
Date.Parser 6416.000 ns ± 2.56 % 219218
Date.DateFormatter 25625.000 ns ± 2.19 % 54110
Date.ISO8601DateFormatter 35125.000 ns ± 1.71 % 39758
HTTP.HTTP 9709.000 ns ± 3.81 % 138868
JSON.Parser 32292.000 ns ± 3.18 % 41890
JSON.JSONSerialization 1833.000 ns ± 8.58 % 764057
Numerics.Int.init 41.000 ns ± 84.54 % 1000000
Numerics.Int.parser 42.000 ns ± 72.17 % 1000000
Numerics.Scanner.scanInt 125.000 ns ± 20.26 % 1000000
Numerics.Comma separated: Int.parser 8096459.000 ns ± 0.44 % 173
Numerics.Comma separated: Scanner.scanInt 49178770.500 ns ± 0.24 % 28
Numerics.Comma separated: String.split 14922583.500 ns ± 0.67 % 94
Numerics.Double.init 42.000 ns ± 72.61 % 1000000
Numerics.Double.parser 125.000 ns ± 58.57 % 1000000
Numerics.Scanner.scanDouble 167.000 ns ± 18.84 % 1000000
Numerics.Comma separated: Double.parser 11313395.500 ns ± 0.96 % 124
Numerics.Comma separated: Scanner.scanDouble 50431521.000 ns ± 0.19 % 28
Numerics.Comma separated: String.split 18744125.000 ns ± 0.46 % 75
PrefixUpTo.Parser: Substring 249958.000 ns ± 0.88 % 5595
PrefixUpTo.Parser: UTF8 13250.000 ns ± 2.96 % 105812
PrefixUpTo.String.range(of:) 43084.000 ns ± 1.57 % 32439
PrefixUpTo.Scanner.scanUpToString 47500.000 ns ± 1.27 % 29444
Race.Parser 34417.000 ns ± 2.73 % 40502
README Example.Parser: Substring 4000.000 ns ± 3.79 % 347868
README Example.Parser: UTF8 1125.000 ns ± 7.92 % 1000000
README Example.Ad hoc 3542.000 ns ± 4.13 % 394248
README Example.Scanner 14292.000 ns ± 2.82 % 97922
Routing.Parser 21750.000 ns ± 3.23 % 64256
String Abstractions.Substring 934167.000 ns ± 0.60 % 1505
String Abstractions.UTF8 158750.000 ns ± 1.36 % 8816
UUID.UUID.init 209.000 ns ± 15.02 % 1000000
UUID.UUID.parser 208.000 ns ± 24.17 % 1000000
Xcode Logs.Parser 3768437.500 ns ± 0.56 % 372
```
## Documentation
The documentation for releases and main are available here:
* [main][swift-parsing-docs]
* [0.7.1](https://pointfreeco.github.io/swift-parsing/0.7.1/documentation/parsing)
Other versions
* [0.7](https://pointfreeco.github.io/swift-parsing/0.7.0/documentation/parsing)
* [0.6](https://pointfreeco.github.io/swift-parsing/0.6.0/documentation/parsing)
* [0.5](https://pointfreeco.github.io/swift-parsing/0.5.0/documentation/parsing)
## Other libraries
There are a few other parsing libraries in the Swift community that you might also be interested in:
* [Consumer](https://github.com/nicklockwood/Consumer)
* [Sparse](https://github.com/johnpatrickmorgan/Sparse)
* [SwiftParsec](https://github.com/davedufresne/SwiftParsec)
## License
This library is released under the MIT license. See [LICENSE](LICENSE) for details.
[getting-started-docs]: https://pointfreeco.github.io/swift-parsing/main/documentation/parsing/gettingstarted
[string-abstractions-docs]: https://pointfreeco.github.io/swift-parsing/main/documentation/parsing/stringabstractions
[swift-parsing-docs]: https://pointfreeco.github.io/swift-parsing