An example of how you can use Design by Contract macros and Non-nullable type macros in Nemerle to write more reliable code

gistfile1.n

        public FlushContentsTo([NotNull] outputStream : Stream) : uint
            requires outputStream.CanWrite
        {   
            def startPosition = 0;
            _heap.Seek(startPosition);
            outputStream.Seek(startPosition);

            def bytes = _heap.ToArray();
            def writer = BinaryWriter(outputStream);
            writer.Write(bytes);
            
            startPosition :> uint;
        }