Based on the comments, the implementation of a single-ended queue as two stacks was somewhat mind-blowing for a number of readers. People, you ain’t seen nothing yet.

Good Monday morning all. I have received a lot of good comments on this series so far that I thought I would speak to a bit.

Last year we declared a relatively simple interface to represent an immutable binary tree. We noticed that it was different from every other interface that we’ve declared so far, in that it really said nothing at all about the immutability of the tree. One normally thinks of immutable data types not in terms of their shape, but rather in terms of what operations may be performed on the data type. Operations are usually either to query the object somehow, or to “modify” it by producing new modified versions of the old immutable object.