5 files changed, 40 insertions, 22 deletions
diff --git a/src/jcgp/function/Addition.java b/src/jcgp/function/Addition.java
index 45a8d35..f40bc24 100644
--- a/src/jcgp/function/Addition.java
+++ b/src/jcgp/function/Addition.java
@@ -3,19 +3,23 @@ package jcgp.function;
 import jcgp.population.Connection;
 
 public class Addition extends Function {
+	
+	private int arity = 2;
 
 	@Override
-	public int run(Connection... connections) {
-		if (connections.length > 0) {
-			return connections[0].getValue() + connections[1].getValue();
+	public Object run(Connection... connections) {
+		if (connections.length < arity) {
+			throw new InvalidArgumentsException("Not enough connections were given.");
+		} else if (connections[0].getValue() instanceof Integer) {
+			return ((Integer) connections[0].getValue()) + ((Integer) connections[1].getValue());
 		} else {
-			throw new InsufficientArgumentsException();
+			throw new InvalidArgumentsException("Wrong data type, this function takes Integer.");
 		}
 	}
 
 	@Override
 	public int getArity() {
-		return 2;
+		return arity;
 	}
 
 }
diff --git a/src/jcgp/function/Function.java b/src/jcgp/function/Function.java
index 4900c68..118131a 100644
--- a/src/jcgp/function/Function.java
+++ b/src/jcgp/function/Function.java
@@ -4,8 +4,8 @@ import jcgp.population.Connection;
 import jcgp.population.InsufficientConnectionsException;
 
 public abstract class Function {
-	
-	public abstract int run(Connection ... connections) throws InsufficientConnectionsException;
+		
+	public abstract Object run(Connection ... connections) throws InsufficientConnectionsException;
 	
 	public abstract int getArity();
 	
diff --git a/src/jcgp/function/InsufficientArgumentsException.java b/src/jcgp/function/InsufficientArgumentsException.java
deleted file mode 100644
index a591b20..0000000
--- a/src/jcgp/function/InsufficientArgumentsException.java
+++ /dev/null
@@ -1,10 +0,0 @@
-package jcgp.function;
-
-public class InsufficientArgumentsException extends RuntimeException {
-
-	/**
-	 * 
-	 */
-	private static final long serialVersionUID = 2675108124600817777L;
-
-}
diff --git a/src/jcgp/function/InvalidArgumentsException.java b/src/jcgp/function/InvalidArgumentsException.java
new file mode 100644
index 0000000..cf55937
--- /dev/null
+++ b/src/jcgp/function/InvalidArgumentsException.java
@@ -0,0 +1,20 @@
+package jcgp.function;
+
+public class InvalidArgumentsException extends RuntimeException {
+
+	/**
+	 * 
+	 */
+	private static final long serialVersionUID = 2675108124600817777L;
+	private String reason;
+	
+	public InvalidArgumentsException(String reason) {
+		super();
+		this.reason = reason;
+	}
+	
+	public String getReason() {
+		return reason;
+	}
+
+}
diff --git a/src/jcgp/function/Subtraction.java b/src/jcgp/function/Subtraction.java
index 8f107b1..d785614 100644
--- a/src/jcgp/function/Subtraction.java
+++ b/src/jcgp/function/Subtraction.java
@@ -4,18 +4,22 @@ import jcgp.population.Connection;
 
 public class Subtraction extends Function {
 
+	private int arity = 2;
+
 	@Override
-	public int run(Connection... connections) {
-		if (connections.length > 1) {
-			return connections[0].getValue() - connections[1].getValue();
+	public Object run(Connection... connections) {
+		if (connections.length < arity) {
+			throw new InvalidArgumentsException("Not enough connections were given.");
+		} else if (connections[0].getValue() instanceof Integer) {
+			return ((Integer) connections[0].getValue()) - ((Integer) connections[1].getValue());
 		} else {
-			throw new InsufficientArgumentsException();
+			throw new InvalidArgumentsException("Wrong data type, this function takes Integer.");
 		}
 	}
 
 	@Override
 	public int getArity() {
-		return 2;
+		return arity;
 	}
 
 }