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Welcome to the Kotlin PEG parser with Kotlin DSL!

The project is inspired by the pest parser and the kotlin-peg-dsl project.

Simple example

val num = Symbol.rule<Int>(name = "Num", ignoreWS = false) {
    seq {
        val sign = +char('+', '-').orDefault('+')
        val digits = +DIGIT.oneOrMore().joinToString()

        value { (sign.get + digits.get).toInt() }
    }
}

val sum = Symbol.rule<Int>(name = "Sum") {
    num.list(separator = char('+'), min = 1u).mapPe { it.sum() }
}


fun evalExpr(expression: String) =
    PegParser.parse(symbol = sum.value(), expression).getOrElse { null }

val results = listOf(
    evalExpr("1"),                         // 1
    evalExpr("+1"),                        // 1
    evalExpr("+ 1"),                       // null
    evalExpr("+1 +"),                      // null
    evalExpr("-17"),                       // -17
    evalExpr("-1 7"),                      // null
    evalExpr("1+2+3+4+5"),                 // 15
    evalExpr("1 + +2 + -3 + +4 + 5"),      // 9
    evalExpr("definitely not expression"), // null
    evalExpr(""),                          // null
)

for (res in results) {
    println(res)
}

Resources

• Documentation
• Examples
  • Simple calculator
  • Json parser
• About PEG
• PEG formal description
• Other useful papers

Things to improve before stable:

TODO

• add more docs
• add more tests, improve the code coverage
• add more built-in characters
• add ability to define Comment parsing expression
• better error messages and error handling
• support left recursion
• provide more examples
• multiplatform

Suggestions are welcome!