Scala Combinator Parser to Map problem

Question

I have been beating my head against a wall, trying to figure out how to get this to work. The initial parser worked great, but when I try to get a Map out of it, it is only giving the initial number value, but not he value blocks.

The format is "float: [label float: [optinallabel float:] ...]" like:

     412285.556: [Label 0.0:[Label1 1.0:][Label2 2.0:]

The parser to list is:

object ParseList extends JavaTokenParsers {
    def sep : Parser[String] = ":"
    def string : Parser[Any] = """[\.a-zA-Z0-9]+""".r
    def num: Parser[Any] =  floatingPointNumber <~ sep
    def valueBlock: Parser[Any] =  "["~>rep(valueBlock)<~"]" | string ~ floatingPointNumber <~ sep
    def expr: Parser[Any] = num ~ rep(valueBlock )
    def apply(in: String) = parseAll(expr,in)
}

Testing gives:

scala> ParseList("""412285.556: """)
res150: ParseList.ParseResult[Any] = [1.13] parsed: (412285.556~List())

scala> ParseList("""412285.556: [Label 1.0:]""")
res151: ParseList.ParseResult[Any] = [1.25] parsed: (412285.556~List(List((Label~1.0))))

scala> ParseList("""412285.556: [Label 0.0:[Label1 1.0:][Label2 2.0:]]""")
res152: ParseList.ParseResult[Any] = [1.51] parsed: (412285.556~List(List((Label~0.0), List((Label1~1.0)), List((Label2~2.0)))))

When I try to make it a Map, if only returns the number, but calls the member routine. See the debug output.

The Map parser:

object ParseMap extends JavaTokenParsers {
  // Seperator
  def sep : Parser[String] = ":"
  // string
  def string : Parser[String] = """[a-zA-Z][a-zA-Z0-9]+""".r
  // Block within [] with label value: and option additional blocks
  def valueBlock: Parser[(String,Any)] =
      member <~ rep(obj)
  // Member - value pair within a block
  def member: Parser[(String, Any)] =
    string ~ floatingPointNumber <~ sep ^^
        { case s ~ n => (s, n); println("In Member s=" +s+" n="+n); (s, n)} 
  def obj: Parser[Map[String,Any]] =
    "["~> rep(valueBlock) <~"]"  ^^ {Map() ++ _}
  // Initial number value of the data
  def num: Parser[(String, Any)] =
          floatingPointNumber <~ sep ~ rep(obj) ^^
          {  case floatingPointNumber => ("Num", floatingPointNumber) }
  // order of operations
  def value: Parser[Any] = (
      num
      | obj
      | member
      | floatingPointNumber
      | string
      )
  def apply(in: String) = parseAll(value,in)
}

The testing gives:

scala> ParseMap("""412285.556: """)
res154: ParseMap.ParseResult[Any] = [1.13] parsed: (Num,412285.556)

scala> ParseMap("""412285.556: [Label 1.0:]""")
In Member s=Label n=1.0
res155: ParseMap.ParseResult[Any] = [1.25] parsed: (Num,412285.556)

scala> ParseMap("""412285.556: [Label 0.0:[Label1 1.0:][Label2 2.0:]]""")
In Member s=Label n=0.0
In Member s=Label1 n=1.0
In Member s=Label2 n=2.0
res156: ParseMap.ParseResult[Any] = [1.51] parsed: (Num,412285.556)

All my attempts to get a single Map out of it, has failed. Any help would be greatly appreciated.

Rex Kerr · Accepted Answer · 2015-11-02 22:07:47Z

3

Scala's parser combinators are not the easiest thing to use, and they're extraordinarily slow. Try fastparse instead.

I can't quite figure out what you want from that data (it's a very strange format!), but there's a nice guide to getting started.

Your core label-interpreter will probably look something like

val Pair = P(Label ~ " " ~ Num ~ ":")
val MapLine = P("[" Pair ~ ("[" ~ Pair ~ "]").rep ~ "]").
  map{ case (pair, pairs) => pair :: pairs.toList }

answered Nov 2, 2015 at 22:07

Rex Kerr

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1 Comment

user190941 Over a year ago

Thanks, I was planning on looking at fastparse, once I figured this out.

Shadowlands · Accepted Answer · 2015-11-02 21:39:48Z

2

The main problem is your use of the <~ combinator in the num method - this throws away all parsed data that follows it (including the rep(obj) parse result that you want for your map). Modify that line to something like:

def num: Parser[(String, Any)] =
      floatingPointNumber ~ sep ~ rep(obj) ^^
      {  case floatingPointNumber ~ sep ~ objs => ("Num", (floatingPointNumber, objs)) }

and you start getting results like:

scala> ParseMap("""412285.556: [Label 0.0:[Label1 1.0:][Label2 2.0:]]""")
In Member s=Label n=0.0
In Member s=Label1 n=1.0
In Member s=Label2 n=2.0
res3: ParseMap2.ParseResult[Any] = [1.51] parsed: (Num,(412285.556,List(Map(Label -> 0.0))))

which, while it probably doesn't look quite like what you might be wanting, should give you a starting point to progress further.

answered Nov 2, 2015 at 21:39

Shadowlands

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1 Comment

user190941 Over a year ago

I think this will get me by this hurtle.

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