Scala: How to combine parser combinators from different objects
- by eed3si9n
Given a family of objects that implement parser combinators, how do I combine the parsers? Since Parsers.Parser is an inner class, and in Scala inner classes are bound to the outer object, the story becomes slightly complicated.
Here's an example that attempts to combine two parsers from different objects.
import scala.util.parsing.combinator._
class BinaryParser extends JavaTokenParsers {
def anyrep: Parser[Any] = rep(any)
def any: Parser[Any] = zero | one
def zero: Parser[Any] = "0"
def one: Parser[Any] = "1"
}
object LongChainParser extends BinaryParser {
def parser1: Parser[Any] = zero~zero~one~one
}
object ShortChainParser extends BinaryParser {
def parser2: Parser[Any] = zero~zero
}
object ExampleParser extends BinaryParser {
def parser: Parser[Any] = (LongChainParser.parser1
||| ShortChainParser.parser2) ~ anyrep
def main(args: Array[String]) {
println(parseAll(parser, args(0) ))
}
}
This results to the following error:
<console>:11: error: type mismatch;
found : ShortChainParser.Parser[Any]
required: LongChainParser.Parser[?]
def parser: Parser[Any] = (LongChainParser.parser1
||| ShortChainParser.parser2) ~ anyrep
I've found the solution to this problem already, but since it was brought up
recently on scala-user ML (Problem injecting one parser into another), it's probably worth putting it here too.
