https://github.com/palle-k/covfefe
A parser for nondeterministic context free languages
https://github.com/palle-k/covfefe
abnf backus-naur-form context-free-grammar context-free-language covfefe cyk cyk-parser earley earley-algorithm earley-parser ebnf grammar mathematical-expressions parser parser-framework parser-generator parser-library parsing swift syntax-tree
Last synced: 4 days ago
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A parser for nondeterministic context free languages
- Host: GitHub
- URL: https://github.com/palle-k/covfefe
- Owner: palle-k
- License: mit
- Created: 2017-08-11T19:21:10.000Z (over 8 years ago)
- Default Branch: master
- Last Pushed: 2022-02-23T16:38:30.000Z (almost 4 years ago)
- Last Synced: 2026-02-17T09:55:43.161Z (6 days ago)
- Topics: abnf, backus-naur-form, context-free-grammar, context-free-language, covfefe, cyk, cyk-parser, earley, earley-algorithm, earley-parser, ebnf, grammar, mathematical-expressions, parser, parser-framework, parser-generator, parser-library, parsing, swift, syntax-tree
- Language: Swift
- Homepage: https://palle-k.github.io/Covfefe/
- Size: 4.58 MB
- Stars: 66
- Watchers: 4
- Forks: 8
- Open Issues: 3
-
Metadata Files:
- Readme: README.md
- License: License
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README
# Covfefe
[](https://travis-ci.org/palle-k/Covfefe)
[](https://palle-k.github.io/Covfefe/)
[](https://cocoapods.org/pods/Covfefe)
[](https://github.com/palle-k/Covfefe/blob/master/License)
Covfefe is a parser framework for languages generated by any (deterministic or nondeterministic) context free grammar.
It implements the [Earley](https://en.wikipedia.org/wiki/Earley_parser) and [CYK](https://en.wikipedia.org/wiki/CYK_algorithm) algorithm.
## Usage
### Swift Package Dependency in Xcode
1. Go to "File" > "Swift Packages" > "Add Package Dependency..."
2. Enter "https://github.com/palle-k/Covfefe.git" as the repository URL.
3. Select "Version", "Up to next major", "0.6.1" < "1.0.0"
4. Add Covfefe to your desired target.
### Swift Package Manager
This framework can be imported as a Swift Package by adding it as a dependency to the `Package.swift` file:
```swift
.package(url: "https://github.com/palle-k/Covfefe.git", from: "0.6.1")
```
### CocoaPods
Alternatively, it can be added as a dependency via CocoaPods (iOS, tvOS, watchOS and macOS).
```ruby
target 'Your-App-Name' do
use_frameworks!
pod 'Covfefe', '~> 0.6.1'
end
```
## Example
Grammars can be specified in a superset of EBNF or a superset of BNF, which adopts some features of EBNF (documented [here](/BNF.md)).
Alternatively, ABNF is supported.
```swift
let grammarString = """
expression = binary-operation | brackets | unary-operation | number | variable;
brackets = '(', expression, ')';
binary-operation = expression, binary-operator, expression;
binary-operator = '+' | '-' | '*' | '/';
unary-operation = unary-operator, expression;
unary-operator = '+' | '-';
number = {digit};
digit = '0' ... '9';
variable = {letter};
letter = 'A' ... 'Z' | 'a' ... 'z';
"""
let grammar = try Grammar(ebnf: grammarString, start: "expression")
```
This grammar describes simple mathematical expressions consisting of unary and binary operations and parentheses.
A syntax tree can be generated, which describes how a given word was derived from the grammar above:
```swift
let parser = EarleyParser(grammar: grammar)
let syntaxTree = try parser.syntaxTree(for: "(a+b)*(-c)")
```
For a more complete example, i.e. how to evaluate syntax tree, check out [ExpressionSolver](https://github.com/palle-k/ExpressionSolver).