Add ability to defined new parser combinators

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The current parser combinators library is flexible but lacks the ability to easily define new combinators. For example, in a grammar that supports JavaTokensParser.wholeNumber and JavaTokensParser.floatingPointNumber literals and an e .. e expression, 1..2 is ambiguous; and 1. is parsed as a floating point literal.

    import scala.util.parsing.combinator.JavaTokenParsers
    object R extends JavaTokenParsers with Application{
      def RANGE = ":"
      def range_expression = value_expression~RANGE~value_expression
      def value_expression = /* other stuff eventually working down to */ literal_expression
      def literal_expression = ( stringLiteral | floatingPointNumber | wholeNumber | ident )
      println(parseAll(range_expression, "1" + RANGE + "n"))
    }

I'm using 2.7.6-final and want to define a new combinator similar to ANTLR's lookahead guard.

   (Integer "..") => Integer // Prevent 1..2 from being tokenized as 1. followed by .2

Obviously, I can't use => in Scala, but I would like to define something like

  a<~~b

which will parse a and b but reset the Input to just after where a was found. In the 2.8 trunk there is a similar guard(Parser) combinator that is used as a<~guard(b) but that is not yet available.

Currently, it is not easy to add new combinators because other parsers/combinators return type Parser which does not see new combinators. I suppose implicits may help, or http://scala.sygneca.com/patterns/pimp-my-library but something built into the framework would be better, if possible.

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Imported From: https://issues.scala-lang.org/browse/SI-2420?orig=1 Reporter: @DavidBiesack

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@DavidBiesack said: Adriaan Moors adriaan.moors@cs.kuleuven.be said in email

Yep, feel free to file a ticket to request this enhancement and assign it to me so it won't be forgotten.

but I can't find an Adriaan in the list of users

Changed component to Standard Library