Using regex parser within a JavaTokensParser subclass

Question

I am trying out scala parser combinators with the following object:

object LogParser extends JavaTokenParsers with PackratParsers {

Some of the parsers are working. But the following one is getting tripped up:

 def time  = """([\d]{2}:[\d]{2}:[\d]{2}\.[\d]+)"""

Following is the input not working:

09:58:24.608891

On reaching that line we get:

[2.22] failure: `([\d]{2}:[\d]{2}:[\d]{2}\.[\d]+)' expected but `:' found

09:58:24.608891

Note: I did verify correct behavior of that regex within the scala repl on the same input pattern.

val r = """([\d]{2}):([\d]{2}):([\d]{2}\.[\d]+)""".r
val s = """09:58:24.608891"""

val r(t,t2,t3) = s
t: String = 09
t2: String = 58
t3: String = 24.608891

So.. AFA parser combinator: is there an issue with the ":" token itself - i.e. need to create my own custom Lexer and add ":" to lexical.delimiters?

Update an answer was provided to add ".r". I had already tried that- but in any case to be explicit: the following has the same behavior (does not work):

def time = """([\d]{2}:[\d]{2}:[\d]{2}.[\d]+)""".r

user5504273 · Accepted Answer · 2015-10-29 23:07:03Z

1

I think you're just missing an .r at the end here to actually have a Regex as opposed to a string literal.

 def time  = """([\d]{2}:[\d]{2}:[\d]{2}\.[\d]+)"""

it should be

 def time  = """([\d]{2}:[\d]{2}:[\d]{2}\.[\d]+)""".r

The first one expects the text to be exactly like the regex string literal (which obviously isn't present), the second one expects text that actually matches the regex. Both create a Parser[String], so it's not immediately obvious that something is missing.

There's an implicit conversion from java.lang.String to Parser[String], so that string literals can be used as parser combinators.

There's an implicit conversion from scala.util.matching.Regex to > Parser[String], so that regex expressions can be used as parser combinators.

http://www.scala-lang.org/files/archive/api/2.11.2/scala-parser-combinators/#scala.util.parsing.combinator.RegexParsers

answered Oct 29, 2015 at 23:07

user5504273

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4 Comments

WestCoastProjects Over a year ago

actually I had already tried that .. I will update the OP including the .r to demonstrate it.

user5504273 Over a year ago

I see. Do you get any different error when trying that? Here is the minimal example I used to check, that works fine in isolation (the test passes). Maybe there is something around it that's making problems, not that particular parser itself: gist.github.com/anonymous/3dbc9556044c6629b117

WestCoastProjects Over a year ago

No, same behavior/error. I have also isolated that piece to a single parser expression: still no change.

WestCoastProjects Over a year ago

I appreciate your effort / gist and have upvoted for it. Your gist demonstrates that the standalone piece works. Man these combinators are brittle. I will not award (yet..) in case someone were to have additional input leading to a complete solution.

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