Scala如何实现HashMap数据结构?

I have lately become obsessed with functional programming and I am really into Scala. Just out of curiosity I decided to start implementing my own data structures. I started with a SinglyLinkedList where I differentiated with two case classes the case Empty and the case Cons(head,tail). I was wondering if anybody could point me into how I could implement a HashMap? Thank in advance for you help :)