Scala Parser Combinator define issues

Question

I've just started using Scala a few days ago and wanted to write my first parser.

the problematic code is as follows:

  val withoutZero: Parser[List[String]] = ("1" | "2" | "3" | "4").+
  val withZero: Parser[String] = "0" | withoutZero

the number string I'd like to parse can have multiple zeros and other numbers but I want to define two functions for it.

the combined withZero has to stay String (not List[String] or whatever else). at the moment I'm only parsing one zero because ("0").+ didn't work out.

my question: how am I able to adjust the withZero Parser to multiple zeros AND combining it with the withoutZero Parser still staying a Parser[String]

Can you give some examples of grammatical strings? It's not entirely clear to me from your description. — Travis Brown
– Travis Brown, Commented May 1, 2015 at 17:44
The stuff on either side of the | has to be the same type, so I still don't understand—it guess I'd still like to see actual strings. — Travis Brown
– Travis Brown, Commented May 1, 2015 at 18:21

Kolmar · Accepted Answer · 2015-05-01 18:22:29Z

1

I think this should work for 0+ | (1|2|3|4)+:

val withZero: Parser[String] = (literal("0").+ | withoutZero) ^^ (_.mkString)

It joins the list of Strings from some parser into a single String

edited May 1, 2015 at 18:22

answered May 1, 2015 at 18:12

Kolmar

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3 Comments

12dollar Over a year ago

thanks only problem: value mkString is not a member of java.io.Serializable

Kolmar Over a year ago

@TwelveDollar It's a member of scala.collection.TraversableOnce and via inheritance member of List and all other collections. Do you have anything else within parenthese? Some of the Parsers in the parentheses is not a Parser[List[String]], it seems. It works as seen here: tutorialspoint.com/…

12dollar Over a year ago

okay thanks, can't see any mistake copied your tutorialspoint code resulting in the same error. I'll fix that myself. code works as intended therefore answer accepted. (y)!

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