diff --git a/stella/src/debugger/DebuggerParser.cxx b/stella/src/debugger/DebuggerParser.cxx
index bb1a3ecfd..c378b1f0e 100644
--- a/stella/src/debugger/DebuggerParser.cxx
+++ b/stella/src/debugger/DebuggerParser.cxx
@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: DebuggerParser.cxx,v 1.51 2005-07-12 02:27:06 urchlay Exp $
+// $Id: DebuggerParser.cxx,v 1.52 2005-07-13 02:54:13 urchlay Exp $
 //============================================================================
 
 #include "bspf.hxx"
@@ -876,6 +876,7 @@ bool DebuggerParser::validateArgs(int cmd) {
 
 // main entry point: PromptWidget calls this method.
 string DebuggerParser::run(const string& command) {
+	static Expression *lastExpression;
 	int i=0;
 
 	// special case: parser testing
@@ -884,7 +885,13 @@ string DebuggerParser::run(const string& command) {
 		int status = YaccParser::parse(command.c_str() + 5);
 		commandResult += debugger->valueToString(status);
 		commandResult += ", result==";
-		commandResult += debugger->valueToString(YaccParser::getResult());
+		lastExpression = YaccParser::getResult();
+		commandResult += debugger->valueToString(lastExpression->evaluate());
+		return commandResult;
+	}
+
+	if(command == "expr") {
+		commandResult = "result==" + debugger->valueToString(lastExpression->evaluate());
 		return commandResult;
 	}
 
diff --git a/stella/src/debugger/EqualsExpression.cxx b/stella/src/debugger/EqualsExpression.cxx
new file mode 100644
index 000000000..be6f395ad
--- /dev/null
+++ b/stella/src/debugger/EqualsExpression.cxx
@@ -0,0 +1,27 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll       
+//  SS  SS   tt           ll   ll        
+//  SS     tttttt  eeee   ll   ll   aaaa 
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2005 by Bradford W. Mott and the Stella team
+//
+// See the file "license" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//
+// $Id: EqualsExpression.cxx,v 1.1 2005-07-13 02:54:13 urchlay Exp $
+//============================================================================
+
+#include "Expression.hxx"
+#include "EqualsExpression.hxx"
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+EqualsExpression::EqualsExpression(Expression *left, Expression *right)
+  : Expression(left, right)
+{
+}
+
diff --git a/stella/src/debugger/EqualsExpression.hxx b/stella/src/debugger/EqualsExpression.hxx
new file mode 100644
index 000000000..d7fdd4604
--- /dev/null
+++ b/stella/src/debugger/EqualsExpression.hxx
@@ -0,0 +1,39 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll       
+//  SS  SS   tt           ll   ll        
+//  SS     tttttt  eeee   ll   ll   aaaa 
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2005 by Bradford W. Mott and the Stella team
+//
+// See the file "license" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//
+// $Id: EqualsExpression.hxx,v 1.1 2005-07-13 02:54:13 urchlay Exp $
+//============================================================================
+
+#ifndef EQUALS_EXPRESSION_HXX
+#define EQUALS_EXPRESSION_HXX
+
+#include "Expression.hxx"
+
+/**
+  This class provides an implementation of an constant expression;
+  that is, one that consists solely of a constant integer value.
+
+  @author  B. Watson
+  @version $Id: EqualsExpression.hxx,v 1.1 2005-07-13 02:54:13 urchlay Exp $
+*/
+class EqualsExpression : public Expression
+{
+  public:
+    EqualsExpression(Expression *left, Expression *right);
+    int evaluate() { return myLHS->evaluate() == myRHS->evaluate(); }
+};
+
+#endif
+
diff --git a/stella/src/debugger/MinusExpression.cxx b/stella/src/debugger/MinusExpression.cxx
new file mode 100644
index 000000000..e2d6158ff
--- /dev/null
+++ b/stella/src/debugger/MinusExpression.cxx
@@ -0,0 +1,27 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll       
+//  SS  SS   tt           ll   ll        
+//  SS     tttttt  eeee   ll   ll   aaaa 
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2005 by Bradford W. Mott and the Stella team
+//
+// See the file "license" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//
+// $Id: MinusExpression.cxx,v 1.1 2005-07-13 02:54:13 urchlay Exp $
+//============================================================================
+
+#include "Expression.hxx"
+#include "MinusExpression.hxx"
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+MinusExpression::MinusExpression(Expression *left, Expression *right)
+  : Expression(left, right)
+{
+}
+
diff --git a/stella/src/debugger/MinusExpression.hxx b/stella/src/debugger/MinusExpression.hxx
new file mode 100644
index 000000000..8cf197ba9
--- /dev/null
+++ b/stella/src/debugger/MinusExpression.hxx
@@ -0,0 +1,39 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll       
+//  SS  SS   tt           ll   ll        
+//  SS     tttttt  eeee   ll   ll   aaaa 
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2005 by Bradford W. Mott and the Stella team
+//
+// See the file "license" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//
+// $Id: MinusExpression.hxx,v 1.1 2005-07-13 02:54:13 urchlay Exp $
+//============================================================================
+
+#ifndef MINUS_EXPRESSION_HXX
+#define MINUS_EXPRESSION_HXX
+
+#include "Expression.hxx"
+
+/**
+  This class provides an implementation of an constant expression;
+  that is, one that consists solely of a constant integer value.
+
+  @author  B. Watson
+  @version $Id: MinusExpression.hxx,v 1.1 2005-07-13 02:54:13 urchlay Exp $
+*/
+class MinusExpression : public Expression
+{
+  public:
+    MinusExpression(Expression *left, Expression *right);
+    int evaluate() { return myLHS->evaluate() - myRHS->evaluate(); }
+};
+
+#endif
+
diff --git a/stella/src/debugger/PlusExpression.cxx b/stella/src/debugger/PlusExpression.cxx
new file mode 100644
index 000000000..898f05ffa
--- /dev/null
+++ b/stella/src/debugger/PlusExpression.cxx
@@ -0,0 +1,27 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll       
+//  SS  SS   tt           ll   ll        
+//  SS     tttttt  eeee   ll   ll   aaaa 
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2005 by Bradford W. Mott and the Stella team
+//
+// See the file "license" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//
+// $Id: PlusExpression.cxx,v 1.1 2005-07-13 02:54:13 urchlay Exp $
+//============================================================================
+
+#include "Expression.hxx"
+#include "PlusExpression.hxx"
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+PlusExpression::PlusExpression(Expression *left, Expression *right)
+  : Expression(left, right)
+{
+}
+
diff --git a/stella/src/debugger/PlusExpression.hxx b/stella/src/debugger/PlusExpression.hxx
new file mode 100644
index 000000000..95dc1810a
--- /dev/null
+++ b/stella/src/debugger/PlusExpression.hxx
@@ -0,0 +1,39 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll       
+//  SS  SS   tt           ll   ll        
+//  SS     tttttt  eeee   ll   ll   aaaa 
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2005 by Bradford W. Mott and the Stella team
+//
+// See the file "license" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//
+// $Id: PlusExpression.hxx,v 1.1 2005-07-13 02:54:13 urchlay Exp $
+//============================================================================
+
+#ifndef PLUS_EXPRESSION_HXX
+#define PLUS_EXPRESSION_HXX
+
+#include "Expression.hxx"
+
+/**
+  This class provides an implementation of an constant expression;
+  that is, one that consists solely of a constant integer value.
+
+  @author  B. Watson
+  @version $Id: PlusExpression.hxx,v 1.1 2005-07-13 02:54:13 urchlay Exp $
+*/
+class PlusExpression : public Expression
+{
+  public:
+    PlusExpression(Expression *left, Expression *right);
+    int evaluate() { return myLHS->evaluate() + myRHS->evaluate(); }
+};
+
+#endif
+
diff --git a/stella/src/debugger/module.mk b/stella/src/debugger/module.mk
index dde32993a..eb070438e 100644
--- a/stella/src/debugger/module.mk
+++ b/stella/src/debugger/module.mk
@@ -6,6 +6,9 @@ MODULE_OBJS := \
 	src/debugger/EquateList.o \
 	src/debugger/Expression.o \
 	src/debugger/ConstExpression.o \
+	src/debugger/EqualsExpression.o \
+	src/debugger/PlusExpression.o \
+	src/debugger/MinusExpression.o \
 	src/debugger/PackedBitArray.o \
 	src/debugger/CpuDebug.o \
 	src/debugger/RamDebug.o \
diff --git a/stella/src/yacc/Makefile.yacc b/stella/src/yacc/Makefile.yacc
index 561f22185..4fd3da4ad 100644
--- a/stella/src/yacc/Makefile.yacc
+++ b/stella/src/yacc/Makefile.yacc
@@ -8,9 +8,9 @@ all: stella.y
 
 calctest: stella.y calctest.c YaccParser.cxx YaccParser.hxx
 	bison -y -d stella.y
-	g++ -DPRINT -O2 -c YaccParser.cxx
-	g++ -O2 -c calctest.c
-	g++ -O2 -Wall -o calctest calctest.o YaccParser.o
+	g++ -DPRINT -I../debugger -O2 -c YaccParser.cxx
+	g++ -DBM -I../debugger -O2 -c calctest.c
+	g++ -I../debugger -O2 -Wall -o calctest calctest.o YaccParser.o ../debugger/*Expression.o
 	strip calctest
 
 #clean:
diff --git a/stella/src/yacc/YaccParser.cxx b/stella/src/yacc/YaccParser.cxx
index a9ae5f7f6..4ecf52daa 100644
--- a/stella/src/yacc/YaccParser.cxx
+++ b/stella/src/yacc/YaccParser.cxx
@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: YaccParser.cxx,v 1.2 2005-07-03 14:18:54 stephena Exp $
+// $Id: YaccParser.cxx,v 1.3 2005-07-13 02:54:13 urchlay Exp $
 //
 //   Based on code from ScummVM - Scumm Interpreter
 //   Copyright (C) 2002-2004 The ScummVM project
@@ -21,21 +21,27 @@
 
 //#include "YaccParser.hxx"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+//#ifdef __cplusplus
+//extern "C" {
+//#endif
+
+#include "Expression.hxx"
+#include "PlusExpression.hxx"
+#include "MinusExpression.hxx"
+#include "EqualsExpression.hxx"
+#include "ConstExpression.hxx"
 
 namespace YaccParser {
 #include <stdio.h>
 #include <ctype.h>
 
-int result;
-//#include "y.tab.h"
+#include "y.tab.h"
+yystype result;
 #include "y.tab.c"
 
 
-int getResult() {
-	return result;
+Expression *getResult() {
+	return result.exp;
 }
 
 
@@ -72,12 +78,12 @@ int parse(const char *in) {
 
 int yylex() {
 	char o, p;
-	yylval = 0;
+	yylval.val = 0;
 	while(*c != '\0') {
 		//fprintf(stderr, "looking at %c, state %d\n", *c, state);
 		switch(state) {
 			case ST_SPACE:
-				yylval = 0;
+				yylval.val = 0;
 				if(isspace(*c)) {
 					c++;
 				} else if(isdigit(*c)) {
@@ -92,8 +98,8 @@ int yylex() {
 
 			case ST_NUMBER:
 				while(isdigit(*c)) {
-					yylval *= 10;
-					yylval += (*c++ - '0');
+					yylval.val *= 10;
+					yylval.val += (*c++ - '0');
 					//fprintf(stderr, "yylval==%d, *c==%c\n", yylval, *c);
 				}
 				state = ST_DEFAULT;
@@ -152,7 +158,7 @@ int yylex() {
 
 			case ST_DEFAULT:
 			default:
-				yylval = 0;
+				yylval.val = 0;
 				if(isspace(*c)) {
 					state = ST_SPACE;
 				} else if(isdigit(*c)) {
@@ -160,8 +166,8 @@ int yylex() {
 				} else if(is_operator(*c)) {
 					state = ST_OPERATOR;
 				} else {
-					yylval = *c++;
-					return yylval;
+					yylval.val = *c++;
+					return yylval.val;
 				}
 				break;
 		}
@@ -184,6 +190,6 @@ int main(int argc, char **argv) {
 #endif
 }
 
-#ifdef __cplusplus
-}
-#endif
+//#ifdef __cplusplus
+//}
+//#endif
diff --git a/stella/src/yacc/YaccParser.hxx b/stella/src/yacc/YaccParser.hxx
index 8e4280c8e..d7a84e489 100644
--- a/stella/src/yacc/YaccParser.hxx
+++ b/stella/src/yacc/YaccParser.hxx
@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: YaccParser.hxx,v 1.2 2005-07-03 14:18:54 stephena Exp $
+// $Id: YaccParser.hxx,v 1.3 2005-07-13 02:54:13 urchlay Exp $
 //
 //   Based on code from ScummVM - Scumm Interpreter
 //   Copyright (C) 2002-2004 The ScummVM project
@@ -22,17 +22,19 @@
 #ifndef PARSER_HXX
 #define PARSER_HXX
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+#include "Expression.hxx"
+
+//#ifdef __cplusplus
+//extern "C" {
+//#endif
 
 namespace YaccParser {
 	int parse(const char *);
-	int getResult();
+	Expression *getResult();
 };
 
-#ifdef __cplusplus
-}
-#endif
+//#ifdef __cplusplus
+//}
+//#endif
 
 #endif
diff --git a/stella/src/yacc/calctest.c b/stella/src/yacc/calctest.c
index a9aab6125..2e3a16101 100644
--- a/stella/src/yacc/calctest.c
+++ b/stella/src/yacc/calctest.c
@@ -11,13 +11,16 @@ int main(int argc, char **argv) {
 
 #ifndef BM
 	YaccParser::parse(argv[1]);
-	printf("\n= %d\n", YaccParser::getResult());
+	printf("\n= %d\n", YaccParser::getResult()->evaluate());
 #else
-	char buf[10];
+	char buf[30];
 
-	for(int i=0; i<1000000; i++) {
-		sprintf(buf, "(1<2)&(3+4)");
-		YaccParser::parse(buf);
+	sprintf(buf, "1+2+3+4+5+6+7");
+	YaccParser::parse(buf);
+	Expression *e = YaccParser::getResult();
+
+	for(int i=0; i<100000000; i++) {
+		printf("%d\n", e->evaluate());
 	}
 #endif
 
diff --git a/stella/src/yacc/stella.y b/stella/src/yacc/stella.y
index 3149bb085..720f58f78 100644
--- a/stella/src/yacc/stella.y
+++ b/stella/src/yacc/stella.y
@@ -13,7 +13,12 @@ void yyerror(char *e) {
 
 %}
 
-%token NUMBER
+%union {
+	int val;
+	Expression *exp;
+}
+
+%token <val> NUMBER
 %left '-' '+'
 %left '*' '/' '%'
 %left LOG_OR
@@ -24,45 +29,51 @@ void yyerror(char *e) {
 %nonassoc '<' '>' GTE LTE NE EQ
 %nonassoc UMINUS
 
+%type <exp> expression
+
 %%
-statement:	expression { result = $1; }
+statement:	expression { fprintf(stderr, "\ndone\n"); result.exp = $1; }
 	;
 
-expression:	expression '+' expression { fprintf(stderr, " +"); $$ = $1 + $3; }
-	|	expression '-' expression { fprintf(stderr, " -"); $$ = $1 - $3; }
-	|	expression '*' expression { fprintf(stderr, " *"); $$ = $1 * $3; }
+expression:	expression '+' expression { fprintf(stderr, " +"); $$ = new PlusExpression($1, $3); }
+	|	expression '-' expression { fprintf(stderr, " -"); $$ = new MinusExpression($1, $3); }
+	|	expression '*' expression { fprintf(stderr, " *");  }
 	|	expression '/' expression
 				{	fprintf(stderr, " /");
+/*
 					if($3 == 0)
 						yyerror("divide by zero");
 					else
 						$$ = $1 / $3;
+*/
 				}
 	|	expression '%' expression
 				{	fprintf(stderr, " %");
+/*
 					if($3 == 0)
 						yyerror("divide by zero");
 					else
 						$$ = $1 % $3;
+*/
 				}
-	|	expression '&' expression { fprintf(stderr, " &"); $$ = $1 & $3; }
-	|	expression '|' expression { fprintf(stderr, " |"); $$ = $1 | $3; }
-	|	expression '^' expression { fprintf(stderr, " ^"); $$ = $1 ^ $3; }
-	|	expression '>' expression { fprintf(stderr, " <"); $$ = $1 > $3; }
-	|	expression '<' expression { fprintf(stderr, " >"); $$ = $1 < $3; }
-	|	expression GTE expression { fprintf(stderr, " >="); $$ = $1 >= $3; }
-	|	expression LTE expression { fprintf(stderr, " <="); $$ = $1 <= $3; }
-	|	expression NE  expression { fprintf(stderr, " !="); $$ = $1 != $3; }
-	|	expression EQ  expression { fprintf(stderr, " =="); $$ = $1 == $3; }
-	|	expression SHR expression { fprintf(stderr, " >>"); $$ = $1 >> $3; }
-	|	expression SHL expression { fprintf(stderr, " >>"); $$ = $1 << $3; }
-	|	expression LOG_OR expression { fprintf(stderr, " ||"); $$ = $1 || $3; }
-	|	expression LOG_AND expression { fprintf(stderr, " &&"); $$ = $1 && $3; }
-	|	'-' expression %prec UMINUS	{ fprintf(stderr, " U-"); $$ = -$2; }
-	|	'~' expression %prec UMINUS	{ fprintf(stderr, " ~"); $$ = (~$2) & 0xffff; }
-	|	'<' expression { fprintf(stderr, " <"); $$ = $2 & 0xff; }
-	|	'>' expression { fprintf(stderr, " >"); $$ = ($2 >> 8) & 0xff; }
-	|	'(' expression ')'	{ fprintf(stderr, " ()"); $$ = $2; }
-	|	NUMBER { fprintf(stderr, " %d", $1); }
+	|	expression '&' expression { fprintf(stderr, " &"); }
+	|	expression '|' expression { fprintf(stderr, " |"); }
+	|	expression '^' expression { fprintf(stderr, " ^"); }
+	|	expression '>' expression { fprintf(stderr, " <"); }
+	|	expression '<' expression { fprintf(stderr, " >"); }
+	|	expression GTE expression { fprintf(stderr, " >="); }
+	|	expression LTE expression { fprintf(stderr, " <="); }
+	|	expression NE  expression { fprintf(stderr, " !="); }
+	|	expression EQ  expression { fprintf(stderr, " =="); $$ = new EqualsExpression($1, $3); }
+	|	expression SHR expression { fprintf(stderr, " >>"); }
+	|	expression SHL expression { fprintf(stderr, " >>"); }
+	|	expression LOG_OR expression { fprintf(stderr, " ||"); }
+	|	expression LOG_AND expression { fprintf(stderr, " &&"); }
+	|	'-' expression %prec UMINUS	{ fprintf(stderr, " U-"); }
+	|	'~' expression %prec UMINUS	{ fprintf(stderr, " ~"); }
+	|	'<' expression { fprintf(stderr, " <"); }
+	|	'>' expression { fprintf(stderr, " >"); }
+	|	'(' expression ')'	{ fprintf(stderr, " ()"); }
+	|	NUMBER { fprintf(stderr, " %d", $1); $$ = new ConstExpression($1); }
 	;
 %%
diff --git a/stella/src/yacc/y.tab.c b/stella/src/yacc/y.tab.c
index 58811ac0d..528b61126 100644
--- a/stella/src/yacc/y.tab.c
+++ b/stella/src/yacc/y.tab.c
@@ -28,8 +28,14 @@ void yyerror(char *e) {
 	fprintf(stderr, "%s\n", e);
 }
 
+
+#line 16 "stella.y"
 #ifndef YYSTYPE
-# define YYSTYPE int
+typedef union {
+	int val;
+	Expression *exp;
+} yystype;
+# define YYSTYPE yystype
 # define YYSTYPE_IS_TRIVIAL 1
 #endif
 #ifndef YYDEBUG
@@ -104,9 +110,9 @@ static const short yyrhs[] =
 /* YYRLINE[YYN] -- source line where rule number YYN was defined. */
 static const short yyrline[] =
 {
-       0,    28,    31,    32,    33,    34,    41,    48,    49,    50,
-      51,    52,    53,    54,    55,    56,    57,    58,    59,    60,
-      61,    62,    63,    64,    65,    66
+       0,    35,    38,    39,    40,    41,    50,    59,    60,    61,
+      62,    63,    64,    65,    66,    67,    68,    69,    70,    71,
+      72,    73,    74,    75,    76,    77
 };
 #endif
 
@@ -923,114 +929,118 @@ yyreduce:
   switch (yyn) {
 
 case 1:
-#line 28 "stella.y"
-{ result = yyvsp[0]; }
+#line 35 "stella.y"
+{ fprintf(stderr, "\ndone\n"); result.exp = yyvsp[0].exp; }
     break;
 case 2:
-#line 31 "stella.y"
-{ fprintf(stderr, " +"); yyval = yyvsp[-2] + yyvsp[0]; }
+#line 38 "stella.y"
+{ fprintf(stderr, " +"); yyval.exp = new PlusExpression(yyvsp[-2].exp, yyvsp[0].exp); }
     break;
 case 3:
-#line 32 "stella.y"
-{ fprintf(stderr, " -"); yyval = yyvsp[-2] - yyvsp[0]; }
+#line 39 "stella.y"
+{ fprintf(stderr, " -"); yyval.exp = new MinusExpression(yyvsp[-2].exp, yyvsp[0].exp); }
     break;
 case 4:
-#line 33 "stella.y"
-{ fprintf(stderr, " *"); yyval = yyvsp[-2] * yyvsp[0]; }
+#line 40 "stella.y"
+{ fprintf(stderr, " *");  }
     break;
 case 5:
-#line 35 "stella.y"
+#line 42 "stella.y"
 {	fprintf(stderr, " /");
-					if(yyvsp[0] == 0)
+/*
+					if($3 == 0)
 						yyerror("divide by zero");
 					else
-						yyval = yyvsp[-2] / yyvsp[0];
+						$$ = $1 / $3;
+*/
 				}
     break;
 case 6:
-#line 42 "stella.y"
+#line 51 "stella.y"
 {	fprintf(stderr, " %");
-					if(yyvsp[0] == 0)
+/*
+					if($3 == 0)
 						yyerror("divide by zero");
 					else
-						yyval = yyvsp[-2] % yyvsp[0];
+						$$ = $1 % $3;
+*/
 				}
     break;
 case 7:
-#line 48 "stella.y"
-{ fprintf(stderr, " &"); yyval = yyvsp[-2] & yyvsp[0]; }
+#line 59 "stella.y"
+{ fprintf(stderr, " &"); }
     break;
 case 8:
-#line 49 "stella.y"
-{ fprintf(stderr, " |"); yyval = yyvsp[-2] | yyvsp[0]; }
+#line 60 "stella.y"
+{ fprintf(stderr, " |"); }
     break;
 case 9:
-#line 50 "stella.y"
-{ fprintf(stderr, " ^"); yyval = yyvsp[-2] ^ yyvsp[0]; }
+#line 61 "stella.y"
+{ fprintf(stderr, " ^"); }
     break;
 case 10:
-#line 51 "stella.y"
-{ fprintf(stderr, " <"); yyval = yyvsp[-2] > yyvsp[0]; }
+#line 62 "stella.y"
+{ fprintf(stderr, " <"); }
     break;
 case 11:
-#line 52 "stella.y"
-{ fprintf(stderr, " >"); yyval = yyvsp[-2] < yyvsp[0]; }
+#line 63 "stella.y"
+{ fprintf(stderr, " >"); }
     break;
 case 12:
-#line 53 "stella.y"
-{ fprintf(stderr, " >="); yyval = yyvsp[-2] >= yyvsp[0]; }
+#line 64 "stella.y"
+{ fprintf(stderr, " >="); }
     break;
 case 13:
-#line 54 "stella.y"
-{ fprintf(stderr, " <="); yyval = yyvsp[-2] <= yyvsp[0]; }
+#line 65 "stella.y"
+{ fprintf(stderr, " <="); }
     break;
 case 14:
-#line 55 "stella.y"
-{ fprintf(stderr, " !="); yyval = yyvsp[-2] != yyvsp[0]; }
+#line 66 "stella.y"
+{ fprintf(stderr, " !="); }
     break;
 case 15:
-#line 56 "stella.y"
-{ fprintf(stderr, " =="); yyval = yyvsp[-2] == yyvsp[0]; }
+#line 67 "stella.y"
+{ fprintf(stderr, " =="); yyval.exp = new EqualsExpression(yyvsp[-2].exp, yyvsp[0].exp); }
     break;
 case 16:
-#line 57 "stella.y"
-{ fprintf(stderr, " >>"); yyval = yyvsp[-2] >> yyvsp[0]; }
+#line 68 "stella.y"
+{ fprintf(stderr, " >>"); }
     break;
 case 17:
-#line 58 "stella.y"
-{ fprintf(stderr, " >>"); yyval = yyvsp[-2] << yyvsp[0]; }
+#line 69 "stella.y"
+{ fprintf(stderr, " >>"); }
     break;
 case 18:
-#line 59 "stella.y"
-{ fprintf(stderr, " ||"); yyval = yyvsp[-2] || yyvsp[0]; }
+#line 70 "stella.y"
+{ fprintf(stderr, " ||"); }
     break;
 case 19:
-#line 60 "stella.y"
-{ fprintf(stderr, " &&"); yyval = yyvsp[-2] && yyvsp[0]; }
+#line 71 "stella.y"
+{ fprintf(stderr, " &&"); }
     break;
 case 20:
-#line 61 "stella.y"
-{ fprintf(stderr, " U-"); yyval = -yyvsp[0]; }
+#line 72 "stella.y"
+{ fprintf(stderr, " U-"); }
     break;
 case 21:
-#line 62 "stella.y"
-{ fprintf(stderr, " ~"); yyval = (~yyvsp[0]) & 0xffff; }
+#line 73 "stella.y"
+{ fprintf(stderr, " ~"); }
     break;
 case 22:
-#line 63 "stella.y"
-{ fprintf(stderr, " <"); yyval = yyvsp[0] & 0xff; }
+#line 74 "stella.y"
+{ fprintf(stderr, " <"); }
     break;
 case 23:
-#line 64 "stella.y"
-{ fprintf(stderr, " >"); yyval = (yyvsp[0] >> 8) & 0xff; }
+#line 75 "stella.y"
+{ fprintf(stderr, " >"); }
     break;
 case 24:
-#line 65 "stella.y"
-{ fprintf(stderr, " ()"); yyval = yyvsp[-1]; }
+#line 76 "stella.y"
+{ fprintf(stderr, " ()"); }
     break;
 case 25:
-#line 66 "stella.y"
-{ fprintf(stderr, " %d", yyvsp[0]); }
+#line 77 "stella.y"
+{ fprintf(stderr, " %d", yyvsp[0].val); yyval.exp = new ConstExpression(yyvsp[0].val); }
     break;
 }
 
@@ -1265,5 +1275,5 @@ yyreturn:
 #endif
   return yyresult;
 }
-#line 68 "stella.y"
+#line 79 "stella.y"
 
diff --git a/stella/src/yacc/y.tab.h b/stella/src/yacc/y.tab.h
index eced98741..5f10ee2a1 100644
--- a/stella/src/yacc/y.tab.h
+++ b/stella/src/yacc/y.tab.h
@@ -1,10 +1,14 @@
 #ifndef BISON_Y_TAB_H
 # define BISON_Y_TAB_H
 
-# ifndef YYSTYPE
-#  define YYSTYPE int
-#  define YYSTYPE_IS_TRIVIAL 1
-# endif
+#ifndef YYSTYPE
+typedef union {
+	int val;
+	Expression *exp;
+} yystype;
+# define YYSTYPE yystype
+# define YYSTYPE_IS_TRIVIAL 1
+#endif
 # define	NUMBER	257
 # define	LOG_OR	258
 # define	LOG_AND	259