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Modules/zaubertrank/old/Evaluator.java

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+/*   
+Evaluator.java
+ *    
+ *    Copyright (c) 2000, Benjamin Fallenstein
+ *
+ *    You may use and distribute under the terms of either the GNU Lesser
+ *    General Public License, either version 2 of the license or,
+ *    at your choice, any later version. Alternatively, you may use and
+ *    distribute under the terms of the XPL.
+ *
+ *    See the LICENSE.lgpl and LICENSE.xpl files for the specific terms of 
+ *    the licenses.
+ *
+ *    This software is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the README
+ *    file for more details.
+ *
+ */
+/*
+ * Written by Benjamin Fallenstein
+ */
+
+package org.zaubertrank;
+import org.gzigzag.*;
+import java.util.*;
+
+/** An evaluator for zaubertrank expressions.
+ */
+
+public class Evaluator {
+public static final String rcsid = "$Id: Evaluator.java,v 1.1 2001/04/02 20:29:05 bfallenstein Exp $";
+    public static boolean dbg = false;
+    static final void p(String s) { if(dbg) System.out.println(s); }
+    static final void pa(String s) { System.out.println(s); }
+
+    // XXX should be able to store the following in the structure for debugging
+    public Stack data = new Stack();
+    public Stack returns = new Stack();
+    public Stack frames = new Stack();
+    public Data frame;
+    public ZZCell pos;
+    public boolean failed = false;
+
+    public Evaluator(ZZCell what, Data args) {
+	pos = what.h("zaubertrank:rpn");
+	frame = args;
+    }
+
+    public void step() {
+	ZZCell root = pos.getRootclone();
+	Primitive p = PrimitiveSet.findPrimitive(root);
+	if(root == null) { // RETURN STEP -- XXX return cell in ztpart
+	    if(returns.empty()) return;
+	    pos = (ZZCell)returns.pop();
+	    frame = (Data)frames.pop();
+	} else if(p != null) {
+	    Object[] args = new Object[p.args()];
+	    for(int i=args.length-1; i>=0; i--) args[i] = data.pop();
+	    data.push(p.eval(new Data(args)));
+	} else if(root.s("d.zt-arg") != null) {
+	    int nr = Data.i(root.s("d.zt-arg"));
+	    data.push(frame.o(nr));
+	} else {      // FUNCTION CALL! (XXX need argument reads)
+	    throw new ZZError("Function calls aren't working yet!");
+/*
+	    Parser.DecNode dn = new Parser.DecNode(root);
+	    Object[] args = new Object[dn.params.length];
+	    for(int i=args.length-1; i>=0; i--) args[i] = data.pop();
+	    returns.push(pos);
+	    frames.push(frame);
+	    frame = new Data(args);
+	    pos = dn.c.h("zaubertrank:rpn"); // XXX fix
+*/
+	}
+	pos = pos.s(Parser.sequencedim);
+    }
+
+    static public Object eval(ZZCell what, Data args) {
+	Evaluator e = new Evaluator(what, args);
+	while(e.running()) e.step();
+	if(e.failed) return null;
+	return e.data.pop();
+    }
+
+    public boolean running() {
+	return (!failed && pos != null);
+    }
+    
+    public boolean finished() {
+	return (!failed && pos == null);
+    }
+}