Parser combinator not terminating - how to log what is going on?
parser-combinators, scala
Solution
Logging the attempts to parse `notComma` and `notEndLine` show that it is the end-of-file (shown as a CTRL-Z in the log(...)("mesg") output) that is being repeatedly parsed. Here's how I modified your parser for this purpose:
def text = rep(log(notComma)("notComma") | log(notEndLine)("notEndLine"))
I'm not entirely sure what's going on (I tried many variations on your grammar), but I think it's something like this: The EOF is not really a character artificially introduced into the input stream, but rather a sort of perpetual condition at the end of the input. Thus this never-consumed EOF pseudo-character is repeatedly parsed as "either not a comma or not an end-of-line."
Problem
I am experimenting with parser combinators and I often run into what seems like infinite recursions. Here is the first one I ran into: ``` import util.parsing.combinator.Parsers import util.parsing.input.CharSequenceReader class CombinatorParserTest extends Parsers { type Elem = Char def notComma = elem("not comma", _ != ',') def notEndLine = elem("not end line", x => x != '\r' && x != '\n') def text = rep(notComma | notEndLine) } object CombinatorParserTest { def main(args:Array[String]): Unit = { val p = new CombinatorParserTest() val r = p.text(new CharSequenceReader(",")) // does not get here println(r) } } ``` How can I print what is going on? And why does this not finish?