From a3d34c650abb28375a64b417b3c934d948f4fc69 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Wed, 2 Apr 2003 12:50:48 +0000
Subject: *** empty log message ***

---
 .../examples/expressions/expressions-current.scala | 63 ++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 sources/examples/expressions/expressions-current.scala

(limited to 'sources')

diff --git a/sources/examples/expressions/expressions-current.scala b/sources/examples/expressions/expressions-current.scala
new file mode 100644
index 0000000000..8783fc9544
--- /dev/null
+++ b/sources/examples/expressions/expressions-current.scala
@@ -0,0 +1,63 @@
+package test;
+
+abstract class Lang {
+  trait Visitor {
+    def caseNum(n: int): unit;
+  }
+
+  abstract class Exp {
+    def visit(v: visitor): unit;
+  }
+
+  type visitor <: Visitor;
+
+  class Num(n: int) extends Exp {
+    def visit(v: visitor): unit = v.caseNum(n);
+  }
+
+  class Eval(result: Ref[int]): visitor extends Visitor {
+    def caseNum(n: int) = result.elem = n;
+  }
+}
+
+abstract class Lang2 extends Lang {
+  abstract class Visitor2 extends Visitor {
+    def casePlus(left: Exp, right: Exp): unit;
+  }
+
+  type visitor <: Visitor2;
+
+  class Plus(l: Exp, r: Exp) extends Exp {
+    def visit(v: visitor): unit = v.casePlus(l, r);
+  }
+
+  class Eval2(result: Ref[int]): visitor extends Eval(result) with Visitor2 {
+    def casePlus(l: Exp, r: Exp) =
+      result.elem = { l.visit(this); result.elem } + { r.visit(this); result.elem }
+  }
+
+  class Show2(result: Ref[String]): visitor extends Visitor2 {
+    def caseNum(n: int) = result.elem = n.toString();
+    def casePlus(l: Exp, r: Exp) =
+	result.elem =
+	    "(" + { l.visit(this); result.elem } +
+            "+" + { r.visit(this); result.elem }+ ")";
+  }
+}
+
+object Main {
+
+  def main(args: Array[String]) = {
+    val l1 = new Lang { type visitor = Visitor }
+    val e1: l1.Exp = new l1.Num(42);
+
+    val iref = new Ref(0);
+    System.out.println("eval: " + { e1.visit(new l1.Eval(iref)); iref.elem });
+
+    val l2 = new Lang2 { type visitor = Visitor2 }
+    val e2: l2.Exp = new l2.Plus(new l2.Num(5), new l2.Num(37));
+    val sref = new Ref("");
+    System.out.println("eval: " + { e2.visit(new l2.Eval2(iref)); iref.elem });
+    System.out.println("show: " + { e2.visit(new l2.Show2(sref)); sref.elem });
+  }
+}
-- 
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