Scala Parser Combinators: how to define a line

Question

I am trying to get my thick head around the following problem:

class LineParser extends JavaTokenParsers {
   def lines: Parser[Any] = rep(line)
   def line: Parser[String] = """^.+$""".r

}

object LineParserTest extends LineParser {
   def main(args: Array[String]) {
       val reader = new FileReader(args(0))
       println("input : "+ args(0))
       println(parseAll(lines, reader))
   }
}

Input file:

one
two

When I run the program, it gives me this error:

[1.1] failure: string matching regex `^.+$' expected but `o' found

one

^

Apparently, I did something stupid, but couldn't figure out why. Please advise.

The above is a simplified version of the real goal: to parse a cisco-like configuration file which include commands and sub-commands and build an AST. There are several commands that I don't care and would like to ignore them using the pattern """^.+$""" above.

Kolmar · Accepted Answer · 2015-06-02 05:02:05Z

2

You don't need ^ and $ in the regex. By default . doesn't match end of line, so the following will make it work:

def line: Parser[String] = """.+""".r

In Java, if you want ^ and $ to match the line terminator, you have to set the Pattern.MULTILINE flag. So the following definition will work as well:

def line: Parser[String] = """(?m)^.+$""".r

answered Jun 2, 2015 at 5:02

Kolmar

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