packrat parsing

1 files changed, 48 insertions, 0 deletions

diff --git a/test/files/run/packrat1.scala b/test/files/run/packrat1.scala
new file mode 100644
index 0000000000..69eb8c5fc9
--- /dev/null
+++ b/test/files/run/packrat1.scala
@@ -0,0 +1,48 @@
+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 extends Application{
+  import grammars._
+
+  val head = phrase(term)
+
+  println(extractResult(head(new lexical.Scanner("1"))))
+  println(extractResult(head(new lexical.Scanner("1+2"))))
+  println(extractResult(head(new lexical.Scanner("9-4"))))
+  println(extractResult(head(new lexical.Scanner("9*9"))))
+  println(extractResult(head(new lexical.Scanner("8/2"))))
+  println(extractResult(head(new lexical.Scanner("4*9-0/7+9-8*1"))))
+  println(extractResult(head(new lexical.Scanner("(1+2)*3"))))
+}
+
+object grammars extends StandardTokenParsers with PackratParsers{
+
+  def extractResult(r : ParseResult[_]) = r match{
+    case Success(a,_) => a
+    case Failure(a,_) => a
+    case Error(a,_) => a
+  }
+
+  lexical.delimiters ++= List("+","-","*","/","(",")")
+  lexical.reserved ++= List("Hello","World")
+
+  /****
+   * term = term + fact | term - fact | fact
+   * fact = fact * num  | fact / num  | num
+   */
+
+
+ val term: PackratParser[Int] = (term~("+"~>fact) ^^ {case x~y => x+y}
+           |term~("-"~>fact) ^^ {case x~y => x-y}
+           |fact)
+
+ val fact: PackratParser[Int] = (fact~("*"~>numericLit) ^^ {case x~y => x*y.toInt}
+           |fact~("/"~>numericLit) ^^ {case x~y => x/y.toInt}
+           |"("~>term<~")"
+           |numericLit ^^ {_.toInt})
+ }