- renamed 'parsers1.scala' to 'parsers2.scala'.

1 files changed, 63 insertions, 0 deletions

diff --git a/sources/examples/parsers2.scala b/sources/examples/parsers2.scala
new file mode 100644
index 0000000000..ee830b894f
--- /dev/null
+++ b/sources/examples/parsers2.scala
@@ -0,0 +1,63 @@
+package examples;
+
+object parsers2 {
+
+  abstract class Tree{}
+  case class Id (s: String)         extends Tree {}
+  case class Num(n: int)            extends Tree {}
+  case class Lst(elems: List[Tree]) extends Tree {}
+
+  abstract class ListParsers extends CharParsers {
+
+    def ident: Parser[Tree] =
+      for (
+        val c: char <- chr(Character.isLetter);
+        val cs: List[char] <- rep(chr(Character.isLetterOrDigit))
+      ) yield Id((c :: cs).mkString("", "", ""));
+
+    def number: Parser[Tree] =
+      for (
+        val d: char <- chr(Character.isDigit);
+        val ds: List[char] <- rep(chr(Character.isDigit))
+      ) yield Num(((d - '0') /: ds) ((x, digit) => x * 10 + digit - '0'));
+
+    def list: Parser[Tree] =
+      for (
+        val _ <- chr('(');
+        val es <- listElems ||| succeed(List());
+        val _ <- chr(')')
+      ) yield Lst(es);
+
+    def listElems: Parser[List[Tree]] =
+      for (
+        val x <- expr;
+        val xs <- chr(',') &&& listElems ||| succeed(List())
+      ) yield x :: xs;
+
+    def expr: Parser[Tree] =
+      list ||| ident ||| number;
+
+  }
+
+  class ParseString(s: String) extends Parsers {
+    type intype = int;
+    val input = 0;
+    def any = new Parser[char] {
+      def apply(in: int): Parser[char]#Result =
+        if (in < s.length()) Some(Pair(s charAt in, in + 1)) else None;
+    }
+  }
+
+  def main(args: Array[String]): unit =
+    Console.println(
+      if (args.length == 1) {
+        val ps = new ListParsers with ParseString(args(0));
+        ps.expr(ps.input) match {
+          case Some(Pair(list, _)) => Console.println("parsed: " + list);
+          case None => "nothing parsed"
+        }
+      } else "usage: java examples.parsers2 <expr-string>"
+    );
+
+}
+