--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/plparser/PropertyListScope.java	Sat Aug 28 17:39:34 2010 +0900
@@ -0,0 +1,50 @@
+package plparser;
+
+import java.util.TreeMap;
+
+/*
+ * Scope mechanism for local variable
+ *    define("<>(x)","~(true& ~x)");
+ *    previous x token is stored in an association list
+ *    pop() remove local x token and restore previous x.
+ *    previous x may be null. We cannot use this scope
+ *    for quantifiers since our macro evaluator already
+ *    convert everything in symbols.
+ */
+public class PropertyListScope<Node> {
+	public TreeMap<String,Token<Node>> scope;
+	public Dictionary<Node> dict;
+	public PropertyListScope<Node> prev;
+	
+
+	public PropertyListScope(PropertyListScope<Node>prev, Dictionary<Node> dict) {
+		this.dict = dict;
+		this.prev = prev;
+		this.scope = new TreeMap<String,Token<Node>>();
+	}
+	
+
+	// enter the scope
+	public PropertyListScope<Node> push() {
+		return new PropertyListScope<Node>(this,dict);
+	}
+	
+	// exit the scope
+	public PropertyListScope<Node> pop() {
+		// restore local variable name
+		for(String name: scope.keySet()) {
+			Token<Node> t = scope.get(name);
+			dict.put(name, t); // overwrite
+		}
+		return prev;
+	}
+	
+	// make new local name in this scope
+	public Token<Node> getLocalName(String name) {
+		Token<Node> n = new Token<Node>(name);
+		Token<Node> t=dict.get(name);
+		scope.put(name, t); // remember original
+		dict.put(name,n);   // overwrite entry with new one
+		return n;
+	}
+}
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