PureParser

A parser combinators library built on PureLogic in Scala 3, featuring :

• Usual benefits of parser combinators (ease of use, reusability...)
• Accumulation of all relevant errors unlike short-circuiting behaviors like Either
• AST recovery so that even partially-invalid code still produces a partial output

These two last features make PureParser useful for implementing mature parsers for programming languages or LSP implementations.

Example

enum Expr:
  case Literal(value: Int)
  case Array(elements: List[Expr])
  case Invalid

val literalParser: Parser[Char, Expr] = Expr.Literal(
  Parser
    .regex("[+-]?[0-9]+")
    .toIntOption
    .getOrElse(Parser.abort)
)

val arrayParser: Parser[Char, Expr] = Expr.Array(
  Parser.inOrder(
    Parser.literal('['),
    Parser.separatedByUntil(exprParser, Parser.literal(','), Parser.literal(']')),
    Parser.literal(']')
  )
)

val exprParser: Parser[Char, Expr] = Parser.recoverWith(
  Parser.expect(Parser.firstOf(literalParser, arrayParser), "Valid expression"),
  RecoverStrategy.skipUntil(Parser.oneOf(",]"), Expr.Invalid)
)

// Literal(1)
println(Parser("1")(exprParser))

// Array(List(Literal(1), Literal(2)))
println(Parser("[1,2]")(exprParser))

// Array(List(Literal(1), Literal(2), Invalid, Literal(4), Invalid, Literal(5)))
// ParseError(expected = Label("Valid expression"), at = 5)
// ParseError(expected = Label("Valid expression"), at = 3)
println(Parser("[1,2,hello,4,there,5]")(exprParser))

Play with more examples on the example playground (sources).

Import in your project

SBT:

libraryDependencies += "io.github.iltotore" %% "pureparser" % "version"

Mill:

mvn"io.github.iltotore::pureparser:version"

Note: replace version with the version of PureParser you want to use.

PureParser supports Scala JVM and JS.

Useful links

• Website
• Scaladoc