diff --git a/src/java/com/samskivert/depot/impl/expression/Function.java b/src/java/com/samskivert/depot/impl/expression/Function.java
new file mode 100644
index 0000000..51b5c9b
--- /dev/null
+++ b/src/java/com/samskivert/depot/impl/expression/Function.java
@@ -0,0 +1,101 @@
+//
+// $Id: $
+//
+// Depot library - a Java relational persistence library
+// Copyright (C) 2006-2009 Michael Bayne and Pär Winzell
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.depot.impl.expression;
+
+import java.util.Collection;
+
+import com.samskivert.depot.PersistentRecord;
+import com.samskivert.depot.expression.FluentExp;
+import com.samskivert.depot.expression.SQLExpression;
+import com.samskivert.util.StringUtil;
+
+public interface Function
+{
+    String getCanonicalFunctionName ();
+
+    public static abstract class NoArgFun extends FluentExp implements Function
+    {
+        public void addClasses (Collection<Class<? extends PersistentRecord>> classSet)
+        {
+            // nothing to add
+        }
+    }
+
+    public static abstract class OneArgFun extends FluentExp implements Function
+    {
+        protected OneArgFun (SQLExpression argument)
+        {
+            _arg = argument;
+        }
+
+        public void addClasses (Collection<Class<? extends PersistentRecord>> classSet)
+        {
+            _arg.addClasses(classSet);
+        }
+
+        public SQLExpression getArg ()
+        {
+            return _arg;
+        }
+
+        public String toString ()
+        {
+            return getCanonicalFunctionName() + "(" + _arg + ")";
+        }
+
+        protected SQLExpression _arg;
+    }
+
+    public static abstract class TwoArgFun extends FluentExp implements Function
+    {
+        protected TwoArgFun (SQLExpression arg1, SQLExpression arg2)
+        {
+            _arg1 = arg1;
+            _arg2 = arg2;
+        }
+
+        public void addClasses (Collection<Class<? extends PersistentRecord>> classSet)
+        {
+            _arg1.addClasses(classSet);
+            _arg2.addClasses(classSet);
+        }
+
+        public String toString ()
+        {
+            return getCanonicalFunctionName() + "(" + _arg1 + ", " + _arg2 + ")";
+        }
+
+        protected SQLExpression _arg1, _arg2;
+    }
+
+    public static abstract class ManyArgFun extends ArgumentExp implements Function
+    {
+        protected ManyArgFun (SQLExpression... args)
+        {
+            super(args);
+        }
+
+        public String toString ()
+        {
+            return getCanonicalFunctionName() + "(" + StringUtil.join(_args, ", ") + ")";
+        }
+    }
+}
diff --git a/src/java/com/samskivert/depot/impl/expression/NoArgFun.java b/src/java/com/samskivert/depot/impl/expression/NoArgFun.java
deleted file mode 100644
index e69de29..0000000
diff --git a/src/java/com/samskivert/depot/impl/expression/OneArgFun.java b/src/java/com/samskivert/depot/impl/expression/OneArgFun.java
deleted file mode 100644
index e69de29..0000000
diff --git a/src/java/com/samskivert/depot/impl/expression/TwoArgFun.java b/src/java/com/samskivert/depot/impl/expression/TwoArgFun.java
deleted file mode 100644
index e69de29..0000000