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