1 files changed, 53 insertions, 0 deletions
diff --git a/sources/examples/parsers.scala b/sources/examples/parsers.scala
new file mode 100644
index 0000000000..43a386e8db
--- /dev/null
+++ b/sources/examples/parsers.scala
@@ -0,0 +1,53 @@
+package examples;
+
+module Parse {
+
+  type Result = Option[List[Char]];
+
+  trait Parser extends Function1[List[Char],Result] with {
+    def &&& (def p: Parser) = new Parser {
+      def apply(in: List[Char]) = Parser.this.apply(in) match {
+        case Some(in1) => p(in1)
+        case n => n
+      }
+    }
+
+    def ||| (def p: Parser) = new Parser {
+      def apply(in: List[Char]) = Parser.this.apply(in) match {
+        case None() => p(in)
+        case s => s
+      }
+    }
+  }
+
+  val empty = new Parser { def apply(in: List[Char]): Result = Some(in) }
+
+  def fail = new Parser { def apply(in: List[Char]): Result = None() }
+
+  def chrWith(p: Char => Boolean) = new Parser {
+    def apply(in: List[Char]): Result = in match {
+      case List() => None()
+      case (c :: in1) => if (p(c)) Some(in1) else None()
+    }
+  }
+
+  def chr(c: Char): Parser = chrWith(d => d == c);
+
+  def opt(p: Parser): Parser = p ||| empty;
+  def rep(p: Parser): Parser = opt(rep1(p));
+  def rep1(p: Parser): Parser = p &&& rep(p);
+}
+
+module ExprParser {
+  import Parse._;
+
+  def letter    =   chrWith(c => c.isLetter);
+  def digit     =   chrWith(c => c.isDigit);
+
+  def ident     =   letter &&& rep(letter ||| digit);
+  def number    =   digit &&& rep(digit);
+
+  def expr:Parser =  expr1 &&& rep((chr('+') &&& expr1) ||| (chr('-') &&& expr1));
+  def expr1     =  expr2 &&& rep((chr('*') &&& expr2) ||| (chr('/') &&& expr2));
+  def expr2     =  ident ||| number ||| (chr('(') &&& expr &&& chr(')'));
+}