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Combinator Parsing Problem

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Partha Biswas

Posts: 3
Nickname: parthab
Registered: Jul, 2007

Combinator Parsing Problem

Posted: Apr 15, 2008 2:51 AM

Dear Everybody,
I was trying to parse various strings. One rule tells that the String must contain a smaller string like HGSDC:MSISDN=919810001671,SUD=OICK7-0; which can be described by a Java regular expression "HGS?[CEI]*".

I have written a code like following :

import scala.util.parsing.combinator._
import scala.util.parsing.combinator.syntactical._
import java.util.regex.{Pattern, Matcher}

object Test extends StandardTokenParsers with ImplicitConversions with Application {

lexical.delimiters ++= List(",", "?", "[", "]", ":", "=", ";", "-")

def expr: Parser[Any] = opt(startStop) ~> rep(member) <~ opt(startStop)

def startStop = "[" | "]"

def member: Parser[Any] = opt(numericLit) ~ ident ~ rep(opt(",") ~ opt(":") ~ ident ~ opt("=") ~ opt("-") ~ opt(numericLit) ~ opt(";") <~ opt("?"))

val lSTr = List("[ Hello,Hi How Do U D oo ?]",
"60 HGSSE:MSISDN=919810637917,SS=BAIC,BSG=TS10;",
"53 HGSDC:MSISDN=919810001671,SUD=OICK7-0;",
" XGSDW")

val pat = Pattern.compile("HGS?[CEI]*")
for (str <- lSTr) {
if(pat.matcher(str).find()) {
val tokens = new lexical.Scanner(str)
println("input: " + str)
val result = (phrase(expr)(tokens))
println(result)
}
}
}

The outpput lokks like :

input: 60 HGSSE:MSISDN=919810637917,SS=BAIC,BSG=TS10;
[1.55] parsed: List(((Some(60)~HGSSE)~List(((((((None~Some(:))~MSISDN)~Some(=))~None)~Some(919 810637917))~None), ((((((Some(,)~None)~SS)~Some(=))~None)~None)~None), ((((((None~None)~BAIC)~None)~None)~None)~None), ((((((Some(,)~None)~BSG)~Some(=))~None)~None)~None), ((((((None~None)~TS10)~None)~None)~None)~Some(;)))))
input: 53 HGSDC:MSISDN=919810001671,SUD=OICK7-0;
[1.49] parsed: List(((Some(53)~HGSDC)~List(((((((None~Some(:))~MSISDN)~Some(=))~None)~Some(919 810001671))~None), ((((((Some(,)~None)~SUD)~Some(=))~None)~None)~None), ((((((None~None)~OICK7)~None)~Some(-))~Some(0))~Some(;)))))

Requirements :
The String may or may not start with numeric literal. I want the output as a Array[String] or List[String] or a tuple. Also the elements should be as it is in the input, white spaces being the delimiter, like :
"60","HGSSE:MSISDN=919810637917,SS=BAIC,BSG=TS10;"

Firstly, how to use combinator.ImplicitConversions with ParseResult ( created by phrase(expr) ) ? Or, is there any other way ?

Also I was not comfortable using ":", "=", ";", "-" as lexical.delimiters, when they are really not delimiters in my case. I want to write 'member' cleanly. What I have built here ( the 'member' ) is on a trial and error basis. Could you please rectify that ? How could I use a Chainl1 , if required. Please help at the earliest. I am a neophyte in Scala, and I have started coding in Scala. I have requirement to parse a little different kind of String also, about which I will let you know in the next letter.

Thanks in anticipation and with earnest regards ~
Partha Biswas

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