https://github.com/eratio08/kpars

Very simple parser combinator library in Kotlin
https://github.com/eratio08/kpars

applicative functional-parsing kotlin monad monadic-parser-combinators parser parser-combinators parsing

Last synced: about 1 month ago
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Very simple parser combinator library in Kotlin

• Host: GitHub
• URL: https://github.com/eratio08/kpars
• Owner: eratio08
• Created: 2024-04-06T22:01:02.000Z (9 months ago)
• Default Branch: main
• Last Pushed: 2024-04-08T15:59:53.000Z (9 months ago)
• Last Synced: 2024-04-08T23:24:44.140Z (9 months ago)
• Topics: applicative, functional-parsing, kotlin, monad, monadic-parser-combinators, parser, parser-combinators, parsing
• Language: Kotlin
• Homepage:
• Size: 72.3 KB
• Stars: 1
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Parser Combinator in Kotlin

A very simple [parser combinator](https://www.cs.nott.ac.uk/~pszgmh/pearl.pdf) library implementation in Kotlin.

## Example

The following grammar

```

expr ::= expr addop term | term

term ::= term mulop factor | factor

factor ::= digit | ( expr )

digit ::= 0 | 1 | . . . | 9

addop ::= + | -

mulop ::= * | /

```

Can be parsed and evaluated like this

```kotlin

// Parsers

fun add(a: Int, b: Int): Int = a + b

fun sub(a: Int, b: Int): Int = a - b

val addOp: Parser<(Int, Int) -> Int> =

    (symbol("+") keepRight return_(::add)) or (symbol("-") keepRight return_(::sub))

fun mul(a: Int, b: Int): Int = a * b

fun div(a: Int, b: Int): Int = a / b

val mulOp: Parser<(Int, Int) -> Int> =

    (symbol("*") keepRight return_(::mul)) or (symbol("/") keepRight return_(::div))

fun isDigit(c: Char): Boolean = when (c) {

    in '0'..'9' -> true

    else -> false

}

val digit = token(satisfies(::isDigit)) flatMap { x -> return_(x.code - '0'.code) }

fun expr(): Parser {

    val factor = digit or (symbol("(") flatMap { _ -> expr() keepLeft symbol(")") })

    val term = chainL1(factor, mulOp)

    return chainL1(term, addOp)

}

// Evaluation

val res = apply(expr())("1 + 3 * 3").firstOrNull()?.first

// -> 10

```