A universal lexer library in Swift.
In computer science a Lexer or a tokenizer is a program that converts a sequence of characters (raw string) into a sequence of tokens.
SwiLex is a universal lexer which means that you can use it to build any lexer only by defining your tokens in a Swift enum (in few lines of code).
Combined with SwiParse it allows to build a full Parser. (learn more)
SwiLex is distributed as a Swift Package using SPM.
To install SwiLex, add the following line to the dependencies
list in your Package.swift
:
.package(url: "https://github.com/yassram/SwiLex.git", .upToNextMinor(from: "1.1.0")),
SwiLex will support other dependency managers soon.
Import SwiLex to use it:
import SwiLex
Define a SwiLaxable enum to list your possible tokens with their corresponding regular expressions:
enum WordNumberTokens: String, SwiLexable {
static var separators: Set<Character> = [" "]
case text = "[A-Za-z]*"
case number = "[0-9]*"
case eof
case none
}
Then create an instance of SwiLex and call the lex function:
var lexer = SwiLex<WordNumberTokens>()
let tokenList = try lexer.lex(input: " H3Ll0 W0r 1d 1234 aBcD ")
// returns [text[H], number[3], text[Ll], number[0], text[W], number[0],
// text[r], number[1], text[d], number[1234], text[aBcD]]
This will return a list of tokens with the type of the token and its value (the matched string).
SwiLex provides a mechanism for conditionally activating tokens. This tokens are only available for specific Mode
.
In the following example we want to make the .quotedString
token available only when the .quote
mode is active.
Start by defining the possible Mode
s.
enum Modes {
case normal
case quote
}
Then define a SwiLaxable enum to list the possible tokens with their corresponding regular expressions (like for a simple Lexer):
enum QuotedStringTextNumberTokens: String, SwiLexable {
static var separators: Set<Character> = [" "]
case text = "[A-Za-z]*"
case number = "[0-9]*"
case doubleQuote = "\""
case quotedString = #"[^"]*"#
case eof
case none
}
Next, define the tokens' availability for the possible modes by implementing the activeForModes
property:
extension QuotedStringTextNumberTokens {
var activeForModes: Set<Modes> {
switch self {
case .doubleQuote:
return [.quote, .normal]
case .quotedString:
return [.quote]
default:
return [.normal]
}
}
}
.doubleQuote
is available for both.normal
and.quote
modes allowing to switch between them (by defining the end and the begining of a quote)..quotedString
is only available for the.quote
mode.- All the other tokens are only availbale for the
.normal
mode.
The last step is to tell when to change the curent mode.
For that implement the function changeMode(current mode: Modes?) -> Modes?
:
extension QuotedStringTextNumberTokens {
func changeMode(current mode: Modes?) -> Modes? {
switch self {
case .doubleQuote:
return mode == .normal ? .quote : .normal
default:
return mode
}
}
}
Finally create an instance of SwiLex and call the lex function with the initial mode:
let input = #"4lb3rt Einstein said "If you can't explain it to a 6 year old, you don't understand it yourself.""#
var lexer = SwiLex<QuotedStringTextNumberTokens>()
let tokenList = try lexer.lex(input: input, initialMode: .normal)
// [number[4], text[lb], number[3], text[rt], text[Einstein], text[said], doubleQuote["],
// quotedString[If you can't explain it to a 6 year old, you don't understand it yourself.],
// doubleQuote["]]
This will return a list of tokens with the type of the token and its value (the matched string).
A documentation with more examples is available here
- Tokens defined using only a simple
SwiLexable
enum. - Support conditional tokens with custom modes.
- Support actions on each match by implementing the
onLex(raw: Substring)
function. - Errors with line number and the issue's substring.
- Add detailed documentation with more examples.
- Support Cocoapods and Carthage.
- π₯ SwiParse, a general-purpose parser generator that can be linked to SwiLex to generate a full parser. (released here) π₯
This is an open source project, so feel free to contribute. How?
- Open an issue.
- Send feedback via email.
- Propose your own fixes, suggestions and open a pull request with the changes.
Yassir Ramdani
MIT License
Copyright (c) 2020 yassir RAMDANI
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