01: /*
02: * Jatha - a Common LISP-compatible LISP library in Java.
03: * Copyright (C) 1997-2005 Micheal Scott Hewett
04: *
05: * This library is free software; you can redistribute it and/or
06: * modify it under the terms of the GNU Lesser General Public
07: * License as published by the Free Software Foundation; either
08: * version 2.1 of the License, or (at your option) any later version.
09: *
10: * This library is distributed in the hope that it will be useful,
11: * but WITHOUT ANY WARRANTY; without even the implied warranty of
12: * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13: * Lesser General Public License for more details.
14: *
15: * You should have received a copy of the GNU Lesser General Public
16: * License along with this library; if not, write to the Free Software
17: * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18: *
19: *
20: * For further information, please contact Micheal Hewett at
21: * hewett@cs.stanford.edu
22: *
23: */
24:
25: package org.jatha.machine;
26:
27: import org.jatha.Jatha;
28: import org.jatha.dynatype.*;
29:
30: // @date Sat Feb 1 22:18:53 1997
31: /**
32: * opRTN_IF returns from a function call if the
33: * value on the stack is NIL. (RTN-if-FALSE).
34: * It returns the value on the stack (NIL).
35: * Used in compilation of the AND function.
36: * Uses D register.
37: * Modifes S, E, C and D registers.
38: * @see SECDMachine
39: * @author Micheal S. Hewett hewett@cs.stanford.edu
40: */
41: class opRTN_IF extends SECDop {
42: /**
43: * It calls <tt>SECDop()</tt> with the machine argument
44: * and the label of this instruction.
45: * @see SECDMachine
46: */
47: public opRTN_IF(Jatha lisp) {
48: super (lisp, "RTN_IF");
49: }
50:
51: public void Execute(SECDMachine machine) {
52: LispValue save = machine.S.pop();
53:
54: machine.C.pop(); /* Pop the RTN_IF command. */
55:
56: if (save == f_lisp.NIL) {
57: machine.S.assign(f_lisp.makeCons(save, machine.D.pop()));
58: machine.E.assign(machine.D.pop());
59: machine.C.assign(machine.D.pop());
60: }
61: // else do nothing and continue processing.
62: }
63: }
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