diff --git a/src/org/nwapw/abacus/number/Function.java b/src/org/nwapw/abacus/number/Function.java
index 9659c59..8b42124 100644
--- a/src/org/nwapw/abacus/number/Function.java
+++ b/src/org/nwapw/abacus/number/Function.java
@@ -2,14 +2,11 @@ package org.nwapw.abacus.number;
 
 public abstract class Function {
 
-    public int arity;
+    protected abstract boolean matchesParams(Number[] params);
+    protected abstract Number applyInternal(Number[] params);
 
-    protected abstract Number applyInternal(Number...params);
-
-    public Number apply(Number...params) throws IllegalArgumentException {
-        if(params.length != arity)
-            throw new IllegalArgumentException("Invalid number of arguments: Function takes "
-                    + arity + ", " + params.length + " provided.");
+    public Number apply(Number...params) {
+        if(!matchesParams(params)) return null;
         return applyInternal(params);
     }