packrat parsing

1 files changed, 52 insertions, 0 deletions

diff --git a/test/files/run/packrat3.scala b/test/files/run/packrat3.scala
new file mode 100644
index 0000000000..34695ef2ed
--- /dev/null
+++ b/test/files/run/packrat3.scala
@@ -0,0 +1,52 @@
+import scala.util.parsing.combinator._
+
+import scala.util.parsing.combinator.syntactical.StandardTokenParsers
+import scala.util.parsing.input._
+import scala.util.parsing.syntax._
+
+import scala.collection.mutable.HashMap
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    import grammars3._
+
+    val head = phrase(AnBnCn)
+
+    println(extractResult(head(new lexical.Scanner("a b c"))))
+    println(extractResult(head(new lexical.Scanner("a a b b c c"))))
+    println(extractResult(head(new lexical.Scanner("a a a b b b c c c"))))
+    println(extractResult(head(new lexical.Scanner("a a a a b b b b c c c c"))))
+
+    println(extractResult(head(new lexical.Scanner("a a a b b b b c c c c"))))
+    println(extractResult(head(new lexical.Scanner("a a a a b b b c c c c"))))
+    println(extractResult(head(new lexical.Scanner("a a a a b b b b c c c"))))
+  }
+}
+
+object grammars3 extends StandardTokenParsers with PackratParsers {
+
+  def extractResult(r: ParseResult[_]) = r match {
+    case Success(a,_) => a
+    case Failure(a,_) => a
+    case Error(a,_) => a
+  }
+
+
+  lexical.reserved ++= List("a","b", "c")
+  val a: PackratParser[Any] = memo("a")
+  val b: PackratParser[Any] = memo("b")
+  val c: PackratParser[Any] = memo("c")
+
+  val AnBnCn: PackratParser[Any] =
+    guard(repMany1(a,b) ~ not(b)) ~ rep1(a) ~ repMany1(b,c)// ^^{case x~y => x:::y}
+
+
+  private def repMany[T](p: => Parser[T], q: => Parser[T]): Parser[List[T]] =
+  ( p~repMany(p,q)~q ^^ {case x~xs~y => x::xs:::(y::Nil)}
+   | success(Nil)
+  )
+
+  def repMany1[T](p: => Parser[T], q: => Parser[T]): Parser[List[T]] =
+   p~opt(repMany(p,q))~q ^^ {case x~Some(xs)~y => x::xs:::(y::Nil)}
+
+}