diff --git a/parser/nodes.cc b/parser/nodes.cc
index f98008a..7af3eca 100644
--- a/parser/nodes.cc
+++ b/parser/nodes.cc
@@ -1,6 +1,11 @@
 
+#include <stdlib.h>
+
+#include <vector>
+#include <iostream>
+
 #include "nodes.h"
-#include <vector>
+
 using namespace std;
 
 void Node::addChildren(refptr<Node> other)
@@ -19,3 +24,23 @@ void Node::addChildren(refptr<Node> other)
 Node::~Node()
 {
 }
+
+double BinOpNode::getNumber()
+{
+    double o = one->getNumber();
+    double t = two->getNumber();
+    switch (m_op)
+    {
+        case '*':
+            return o * t;
+        case '/':
+            return o / t;
+        case '+':
+            return o + t;
+        case '-':
+            return o - t;
+        default:
+            cerr << "Error: BinOpNode created with op '" << m_op << "'" << endl;
+            exit(-3);
+    }
+}
diff --git a/parser/nodes.h b/parser/nodes.h
index 275b871..edca3b4 100644
--- a/parser/nodes.h
+++ b/parser/nodes.h
@@ -15,16 +15,17 @@ class Node
         void addChildren(refptr<Node> other);
         std::vector< refptr<Node> > & getChildren() { return m_children; }
 
-        virtual int getInteger() { return 0; }
-        virtual double getNumber() { return 0.0; }
-        virtual refptr<Vector> getVector()
+        virtual int getInteger() const { return 0; }
+        virtual double getNumber() const { return 0.0; }
+        virtual refptr<Vector> getVector() const
         {
             return refptr<Vector>(NULL);
         }
-        virtual bool isShape() { return false; }
-        virtual bool isMaterial() { return false; }
-        virtual bool isTransformBlock() { return false; }
-        virtual std::string getString() { return ""; }
+        virtual bool isShape() const { return false; }
+        virtual bool isMaterial() const { return false; }
+        virtual bool isTransformBlock() const { return false; }
+        virtual std::string getString() const { return ""; }
+        virtual bool isExpression() const { return false; }
 
     protected:
         std::vector< refptr<Node> > m_children;
@@ -375,5 +376,28 @@ class WidthNode : public IntegerNode
         WidthNode(int i) : IntegerNode(i) {}
 };
 
+/******** scripting nodes ********/
+
+class ExpressionNode : public Node
+{
+    public:
+        bool isExpression() const { return true; }
+        virtual double getInteger() { return getNumber(); }
+};
+
+class BinOpNode : public ExpressionNode
+{
+    public:
+        BinOpNode(char op, refptr<Node> one, refptr<Node> two)
+            : m_op(op), one(one), two(two)
+        {
+        }
+        virtual double getNumber();
+    protected:
+        char m_op;
+        refptr<Node> one;
+        refptr<Node> two;
+};
+
 #endif
 
diff --git a/parser/parser.lex b/parser/parser.lex
index 6b1ffc5..79cc0c7 100644
--- a/parser/parser.lex
+++ b/parser/parser.lex
@@ -14,7 +14,7 @@
 
 \+                  return PLUS;
 -                   return MINUS;
-\*                  return STAR;
+\*                  return TIMES;
 \/                  return DIVIDE;
 %                   return MOD;
 
diff --git a/parser/parser.yy b/parser/parser.yy
index ebcb092..9be6450 100644
--- a/parser/parser.yy
+++ b/parser/parser.yy
@@ -33,7 +33,7 @@ static refptr<Node> parsed_scene_node;
 
 %token PLUS;
 %token MINUS;
-%token STAR;
+%token TIMES;
 %token DIVIDE;
 %token MOD;
 
@@ -102,6 +102,10 @@ static refptr<Node> parsed_scene_node;
 
 %token IDENTIFIER;
 
+%left PLUS MINUS
+%left TIMES DIVIDE
+%left UMINUS
+
 %%
 
 scene: SCENE LCURLY scene_items RCURLY {
@@ -168,7 +172,7 @@ camera_item: POSITION vector3 {
            | UP vector3 {
                 $$ = new UpNode($2->getVector());
             }
-           | VFOV number {
+           | VFOV expression {
                 $$ = new VFOVNode($2->getNumber());
             }
            ;
@@ -219,7 +223,7 @@ intersect: INTERSECT LCURLY bool_items RCURLY {
             }
          ;
 
-jitter: JITTER number {
+jitter: JITTER expression {
         $$ = new JitterNode($2->getInteger());
       }
       ;
@@ -284,13 +288,13 @@ material_item: COLOR vector3 {
              | SPECULAR vector3 {
                     $$ = new SpecularNode($2->getVector());
                 }
-             | REFLECTANCE number {
+             | REFLECTANCE expression {
                     $$ = new ReflectanceNode($2->getNumber());
                 }
-             | SHININESS number {
+             | SHININESS expression {
                     $$ = new ShininessNode($2->getNumber());
                 }
-             | TRANSPARENCY number {
+             | TRANSPARENCY expression {
                     $$ = new TransparencyNode($2->getNumber());
                 }
              ;
@@ -310,16 +314,16 @@ number: DEC_NUMBER  { $$ = $1; }
       | REAL_NUMBER { $$ = $1; }
       ;
 
-ngon: NGON DEC_NUMBER COMMA number {
+ngon: NGON DEC_NUMBER COMMA expression {
         $$ = new NGonNode($2->getInteger());
         $$->addChild(new RadiusNode($4->getNumber()));
     }
     ;
 
-offset: OFFSET number {
+offset: OFFSET expression {
         $$ = new OffsetNode($2->getNumber());
       }
-      | OFFSET number LCURLY offset_items RCURLY {
+      | OFFSET expression LCURLY offset_items RCURLY {
         $$ = new OffsetNode($2->getNumber());
         $$->addChildren($4);
       }
@@ -333,7 +337,7 @@ offset_items: /* empty */
                 }
              ;
 
-offset_item: SCALE number {
+offset_item: SCALE expression {
                 $$ = new ScaleNode(new Vector($2->getNumber(), $2->getNumber(),
                     $2->getNumber()));
            }
@@ -371,7 +375,7 @@ options_item: WIDTH DEC_NUMBER {
             | MAXDEPTH DEC_NUMBER {
                     $$ = new MaxDepthNode($2->getInteger());
                 }
-            | EXPOSURE number {
+            | EXPOSURE expression {
                     $$ = new ExposureNode($2->getNumber());
                 }
             | AMBIENT vector3 {
@@ -396,7 +400,7 @@ plane_items: /* empty */
             }
            ;
 
-plane_item: POSITION vector3 COMMA number {
+plane_item: POSITION vector3 COMMA expression {
                 $$ = new PlanePositionNode($2->getVector(), $4->getNumber());
             }
           | shape_item { $$ = $1; }
@@ -419,7 +423,7 @@ polygon_items: /* empty */
 polygon_item: vector2 { $$ = $1; }
             ;
 
-radius: RADIUS number {
+radius: RADIUS expression {
             $$ = new RadiusNode($2->getNumber());
         }
       ;
@@ -508,13 +512,13 @@ subtract: SUBTRACT LCURLY bool_items RCURLY {
 transform: TRANSLATE vector3 {
                 $$ = new TranslateNode($2->getVector());
             }
-         | ROTATE number COMMA vector3 {
+         | ROTATE expression COMMA vector3 {
                 $$ = new RotateNode($2->getNumber(), $4->getVector());
             }
          | SCALE vector3 {
                 $$ = new ScaleNode($2->getVector());
             }
-         | SCALE number {
+         | SCALE expression {
                 $$ = new ScaleNode(new Vector($2->getNumber(),
                     $2->getNumber(), $2->getNumber()));
             }
@@ -524,7 +528,7 @@ transform_block: TRANSLATE vector3 LCURLY transform_block_items RCURLY {
                     $$ = new TranslateBlockNode($2->getVector());
                     $$->addChildren($4);
                 }
-               | ROTATE number COMMA vector3 LCURLY transform_block_items RCURLY {
+               | ROTATE expression COMMA vector3 LCURLY transform_block_items RCURLY {
                     $$ = new RotateBlockNode($2->getNumber(), $4->getVector());
                     $$->addChildren($6);
                 }
@@ -532,7 +536,7 @@ transform_block: TRANSLATE vector3 LCURLY transform_block_items RCURLY {
                     $$ = new ScaleBlockNode($2->getVector());
                     $$->addChildren($4);
                 }
-               | SCALE number LCURLY transform_block_items RCURLY {
+               | SCALE expression LCURLY transform_block_items RCURLY {
                     $$ = new ScaleBlockNode(
                         new Vector($2->getNumber(), $2->getNumber(),
                             $2->getNumber()));
@@ -559,20 +563,37 @@ union: UNION LCURLY bool_items RCURLY {
         }
      ;
 
-vector2: LESS number COMMA number GREATER {
+vector2: LESS expression COMMA expression GREATER {
             refptr<Vector> vec =
                 new Vector($2->getNumber(), $4->getNumber(), 0.0);
             $$ = new VectorNode(vec);
         }
       ;
 
-vector3: LESS number COMMA number COMMA number GREATER {
+vector3: LESS expression COMMA expression COMMA expression GREATER {
             refptr<Vector> vec =
                 new Vector($2->getNumber(), $4->getNumber(), $6->getNumber());
             $$ = new VectorNode(vec);
         }
       ;
 
+expression: term                    { $$ = $1; }
+          | expression TIMES term   { $$ = new BinOpNode('*', $1, $3); }
+          | expression DIVIDE term  { $$ = new BinOpNode('/', $1, $3); }
+          | MINUS expression %prec UMINUS {
+              $$ = new BinOpNode('-', new NumberNode(0.0), $2);
+          }
+          ;
+
+term: factor                        { $$ = $1; }
+    | term PLUS factor              { $$ = new BinOpNode('+', $1, $3); }
+    | term MINUS factor             { $$ = new BinOpNode('-', $1, $3); }
+    ;
+
+factor: number                      { $$ = $1; }
+      | LPAREN expression RPAREN    { $$ = $2; }
+      ;
+
 %%
 
 refptr<Node> parse(const char * fileName)