4 files changed, 14 insertions, 3 deletions
diff --git a/src/jcgp/function/Addition.java b/src/jcgp/function/Addition.java
index faf11d5..45a8d35 100644
--- a/src/jcgp/function/Addition.java
+++ b/src/jcgp/function/Addition.java
@@ -9,7 +9,7 @@ public class Addition extends Function {
 		if (connections.length > 0) {
 			return connections[0].getValue() + connections[1].getValue();
 		} else {
-			return 0;
+			throw new InsufficientArgumentsException();
 		}
 	}
 
diff --git a/src/jcgp/function/Function.java b/src/jcgp/function/Function.java
index f2d1125..4900c68 100644
--- a/src/jcgp/function/Function.java
+++ b/src/jcgp/function/Function.java
@@ -1,10 +1,11 @@
 package jcgp.function;
 
 import jcgp.population.Connection;
+import jcgp.population.InsufficientConnectionsException;
 
 public abstract class Function {
 	
-	public abstract int run(Connection ... connections);
+	public abstract int run(Connection ... connections) throws InsufficientConnectionsException;
 	
 	public abstract int getArity();
 	
diff --git a/src/jcgp/function/InsufficientArgumentsException.java b/src/jcgp/function/InsufficientArgumentsException.java
new file mode 100644
index 0000000..a591b20
--- /dev/null
+++ b/src/jcgp/function/InsufficientArgumentsException.java
@@ -0,0 +1,10 @@
+package jcgp.function;
+
+public class InsufficientArgumentsException extends RuntimeException {
+
+	/**
+	 * 
+	 */
+	private static final long serialVersionUID = 2675108124600817777L;
+
+}
diff --git a/src/jcgp/function/Subtraction.java b/src/jcgp/function/Subtraction.java
index f8b9c7d..8f107b1 100644
--- a/src/jcgp/function/Subtraction.java
+++ b/src/jcgp/function/Subtraction.java
@@ -9,7 +9,7 @@ public class Subtraction extends Function {
 		if (connections.length > 1) {
 			return connections[0].getValue() - connections[1].getValue();
 		} else {
-			return 0;
+			throw new InsufficientArgumentsException();
 		}
 	}