Scala Parser Combinators: Parsing terms with optional initial character -

i'm working on parser parses few terms have optional initial character same terms. problem is, of terms first character same initial character. i'm trying avoid rewriting each term , without initial character. figured packrat parser sounded solution i've yet working way want. below minimal example of i'm trying accomplish.

import scala.util.parsing.combinator._ import scala.util.parsing.input._  object test extends app {   object myparser extends regexparsers packratparsers {     lazy val p1:parser[string] = "ab"     lazy val p2:parser[string] = "cd"     lazy val parser:packratparser[string] = ("a".?) ~> ( p2 | p1 )   }      def parsing[t](s: string)(implicit p: myparser.parser[t]): t = {       import myparser._       val phraseparser = phrase(p)       val input = new packratreader(new charsequencereader(s))       phraseparser(input) match {         case success(t, _) => t         case nosuccess(msg, _) => throw new illegalargumentexception(           "could not parse '"+s+"': "+msg)       }     }                                 //> parsing: [t](s: string)(implicit p: test.myparser.parser[t])t    implicit val parser = myparser.log(myparser.parser)("parser")   println(parsing("cd"))  /* works */   println(parsing("acd")) /* works */   println(parsing("aab")) /* works */    // should work doesn't.   println(parsing("ab"))  /* expected "ab" found "b" */ } 

after looking @ @ishaaq's answer came solution believe little more elegant.

implicit class parserextension[t](val p: parser[t]) extends anyval {   def ?~[u](q: => parser[u]): parser[option[t] ~ u] = {     ((p ^^ some.apply) ~ q) | (success(none) ~ q)   } } 

this implicit class adds method parsers can have optional parser tracking. can use so:

val a:parser[string] = "a" val parser:parser[option[string] ~ string] = ?~ ( p2 | p1 ) 

here gist full source example