diff --git a/src/com/annimon/ownlang/lib/ArrayValue.java b/src/com/annimon/ownlang/lib/ArrayValue.java
index 9c96199..427c17d 100644
--- a/src/com/annimon/ownlang/lib/ArrayValue.java
+++ b/src/com/annimon/ownlang/lib/ArrayValue.java
@@ -42,6 +42,11 @@ public final class ArrayValue implements Value, Iterable<Value> {
         this(array.elements);
     }
     
+    @Override
+    public int type() {
+        return Types.ARRAY;
+    }
+    
     public Value get(int index) {
         return elements[index];
     }
diff --git a/src/com/annimon/ownlang/lib/FunctionValue.java b/src/com/annimon/ownlang/lib/FunctionValue.java
index 29c7790..ac2b49f 100644
--- a/src/com/annimon/ownlang/lib/FunctionValue.java
+++ b/src/com/annimon/ownlang/lib/FunctionValue.java
@@ -14,6 +14,11 @@ public final class FunctionValue implements Value {
         this.value = value;
     }
     
+    @Override
+    public int type() {
+        return Types.FUNCTION;
+    }
+    
     @Override
     public double asNumber() {
         throw new RuntimeException("Cannot cast function to number");
diff --git a/src/com/annimon/ownlang/lib/MapValue.java b/src/com/annimon/ownlang/lib/MapValue.java
index fb54763..1c77a97 100644
--- a/src/com/annimon/ownlang/lib/MapValue.java
+++ b/src/com/annimon/ownlang/lib/MapValue.java
@@ -20,6 +20,11 @@ public class MapValue implements Value, Iterable<Map.Entry<Value, Value>> {
     public MapValue(Map<Value, Value> map) {
         this.map = map;
     }
+    
+    @Override
+    public int type() {
+        return Types.MAP;
+    }
 
     public Value get(Value key) {
         return map.get(key);
diff --git a/src/com/annimon/ownlang/lib/NumberValue.java b/src/com/annimon/ownlang/lib/NumberValue.java
index 0c522db..5744790 100644
--- a/src/com/annimon/ownlang/lib/NumberValue.java
+++ b/src/com/annimon/ownlang/lib/NumberValue.java
@@ -19,6 +19,11 @@ public final class NumberValue implements Value {
         this.value = value;
     }
     
+    @Override
+    public int type() {
+        return Types.NUMBER;
+    }
+    
     @Override
     public double asNumber() {
         return value;
diff --git a/src/com/annimon/ownlang/lib/StringValue.java b/src/com/annimon/ownlang/lib/StringValue.java
index 7b75ad0..59fed48 100644
--- a/src/com/annimon/ownlang/lib/StringValue.java
+++ b/src/com/annimon/ownlang/lib/StringValue.java
@@ -14,6 +14,11 @@ public final class StringValue implements Value {
         this.value = value;
     }
     
+    @Override
+    public int type() {
+        return Types.STRING;
+    }
+    
     @Override
     public double asNumber() {
         try {
diff --git a/src/com/annimon/ownlang/lib/Types.java b/src/com/annimon/ownlang/lib/Types.java
new file mode 100644
index 0000000..246b1c6
--- /dev/null
+++ b/src/com/annimon/ownlang/lib/Types.java
@@ -0,0 +1,12 @@
+package com.annimon.ownlang.lib;
+
+public final class Types {
+
+    public static final int
+            OBJECT = 0,
+            NUMBER = 1,
+            STRING = 2,
+            ARRAY = 3,
+            MAP = 4,
+            FUNCTION = 5;
+}
diff --git a/src/com/annimon/ownlang/lib/Value.java b/src/com/annimon/ownlang/lib/Value.java
index 9e8ea09..7f09b5f 100644
--- a/src/com/annimon/ownlang/lib/Value.java
+++ b/src/com/annimon/ownlang/lib/Value.java
@@ -9,4 +9,6 @@ public interface Value {
     double asNumber();
     
     String asString();
+    
+    int type();
 }
diff --git a/src/com/annimon/ownlang/parser/ast/ArrayAccessExpression.java b/src/com/annimon/ownlang/parser/ast/ArrayAccessExpression.java
index 4db62d0..45f65c4 100644
--- a/src/com/annimon/ownlang/parser/ast/ArrayAccessExpression.java
+++ b/src/com/annimon/ownlang/parser/ast/ArrayAccessExpression.java
@@ -2,6 +2,7 @@ package com.annimon.ownlang.parser.ast;
 
 import com.annimon.ownlang.lib.ArrayValue;
 import com.annimon.ownlang.lib.MapValue;
+import com.annimon.ownlang.lib.Types;
 import com.annimon.ownlang.lib.Value;
 import com.annimon.ownlang.lib.Variables;
 import java.util.List;
@@ -23,7 +24,7 @@ public final class ArrayAccessExpression implements Expression {
     @Override
     public Value eval() {
         Value container = Variables.get(variable);
-        if (container instanceof ArrayValue) {
+        if (container.type() == Types.ARRAY) {
             return getArray().get(lastIndex());
         }
         return consumeMap(container).get(indices.get(0).eval());
@@ -47,19 +48,17 @@ public final class ArrayAccessExpression implements Expression {
     }
     
     private ArrayValue consumeArray(Value value) {
-        if (value instanceof ArrayValue) {
-            return (ArrayValue) value;
-        } else {
+        if (value.type() != Types.ARRAY) {
             throw new RuntimeException("Array expected");
         }
+        return (ArrayValue) value;
     }
     
     public MapValue consumeMap(Value value) {
-        if (value instanceof MapValue) {
-            return (MapValue) value;
-        } else {
+        if (value.type() != Types.MAP) {
             throw new RuntimeException("Map expected");
         }
+        return (MapValue) value;
     }
     
     @Override
diff --git a/src/com/annimon/ownlang/parser/ast/ArrayAssignmentStatement.java b/src/com/annimon/ownlang/parser/ast/ArrayAssignmentStatement.java
index 5a41a8a..b2222ac 100644
--- a/src/com/annimon/ownlang/parser/ast/ArrayAssignmentStatement.java
+++ b/src/com/annimon/ownlang/parser/ast/ArrayAssignmentStatement.java
@@ -1,6 +1,6 @@
 package com.annimon.ownlang.parser.ast;
 
-import com.annimon.ownlang.lib.ArrayValue;
+import com.annimon.ownlang.lib.Types;
 import com.annimon.ownlang.lib.Value;
 import com.annimon.ownlang.lib.Variables;
 
@@ -21,7 +21,7 @@ public final class ArrayAssignmentStatement implements Statement {
     @Override
     public void execute() {
         final Value container = Variables.get(array.variable);
-        if (container instanceof ArrayValue) {
+        if (container.type() == Types.ARRAY) {
             array.getArray().set(array.lastIndex(), expression.eval());
             return;
         }
diff --git a/src/com/annimon/ownlang/parser/ast/BinaryExpression.java b/src/com/annimon/ownlang/parser/ast/BinaryExpression.java
index 2e5f8ea..985e6b8 100644
--- a/src/com/annimon/ownlang/parser/ast/BinaryExpression.java
+++ b/src/com/annimon/ownlang/parser/ast/BinaryExpression.java
@@ -3,6 +3,7 @@ package com.annimon.ownlang.parser.ast;
 import com.annimon.ownlang.lib.ArrayValue;
 import com.annimon.ownlang.lib.NumberValue;
 import com.annimon.ownlang.lib.StringValue;
+import com.annimon.ownlang.lib.Types;
 import com.annimon.ownlang.lib.Value;
 
 /**
@@ -52,13 +53,15 @@ public final class BinaryExpression implements Expression {
         final Value value1 = expr1.eval();
         final Value value2 = expr2.eval();
         
-        if (value1 instanceof StringValue) {
-            return eval((StringValue) value1, value2);
+        switch (value1.type()) {
+            case Types.STRING:
+                return eval((StringValue) value1, value2);
+            case Types.ARRAY:
+                return eval((ArrayValue) value1, value2);
+            case Types.NUMBER:
+            default:
+                return eval(value1, value2);
         }
-        if (value1 instanceof ArrayValue) {
-            return eval((ArrayValue) value1, value2);
-        }
-        return eval(value1, value2);
     }
     
     private Value eval(StringValue value1, Value value2) {
@@ -81,7 +84,7 @@ public final class BinaryExpression implements Expression {
     private Value eval(ArrayValue value1, Value value2) {
         switch (operation) {
             case LSHIFT:
-                if (!(value2 instanceof ArrayValue))
+                if (value2.type() != Types.ARRAY)
                     throw new RuntimeException("Cannot merge non array value to array");
                 return ArrayValue.merge(value1, (ArrayValue) value2);
             case PUSH: 
diff --git a/src/com/annimon/ownlang/parser/ast/ConditionalExpression.java b/src/com/annimon/ownlang/parser/ast/ConditionalExpression.java
index c183806..5e8610b 100644
--- a/src/com/annimon/ownlang/parser/ast/ConditionalExpression.java
+++ b/src/com/annimon/ownlang/parser/ast/ConditionalExpression.java
@@ -2,6 +2,7 @@ package com.annimon.ownlang.parser.ast;
 
 import com.annimon.ownlang.lib.NumberValue;
 import com.annimon.ownlang.lib.StringValue;
+import com.annimon.ownlang.lib.Types;
 import com.annimon.ownlang.lib.Value;
 
 /**
@@ -56,7 +57,7 @@ public final class ConditionalExpression implements Expression {
         final Value value2 = expr2.eval();
         
         double number1, number2;
-        if (value1 instanceof StringValue) {
+        if (value1.type() == Types.STRING) {
             number1 = value1.asString().compareTo(value2.asString());
             number2 = 0;
         } else {
diff --git a/src/com/annimon/ownlang/parser/ast/FunctionalExpression.java b/src/com/annimon/ownlang/parser/ast/FunctionalExpression.java
index f86681e..800a2d2 100644
--- a/src/com/annimon/ownlang/parser/ast/FunctionalExpression.java
+++ b/src/com/annimon/ownlang/parser/ast/FunctionalExpression.java
@@ -3,8 +3,7 @@ package com.annimon.ownlang.parser.ast;
 import com.annimon.ownlang.lib.Function;
 import com.annimon.ownlang.lib.FunctionValue;
 import com.annimon.ownlang.lib.Functions;
-import static com.annimon.ownlang.lib.Functions.isExists;
-import com.annimon.ownlang.lib.UserDefinedFunction;
+import com.annimon.ownlang.lib.Types;
 import com.annimon.ownlang.lib.Value;
 import com.annimon.ownlang.lib.Variables;
 import java.util.ArrayList;
@@ -47,7 +46,9 @@ public final class FunctionalExpression implements Expression {
         if (Functions.isExists(key)) return Functions.get(key);
         if (Variables.isExists(key)) {
             final Value value = Variables.get(key);
-            if (value instanceof FunctionValue) return ((FunctionValue)value).getValue();
+            if (value.type() == Types.FUNCTION) {
+                return ((FunctionValue)value).getValue();
+            }
         }
         throw new RuntimeException("Unknown function " + key);
     }