Deque

Deque is an ad-hoc example by Christopher Diggins for a concatenative language that is not a stack language. It uses a http://en.wikipedia.org/wiki/Deque instead.

To quote from his message to the concatenative mailing list:

• 1! — Pushes a one to the right of the deque
• !1 — Pushes a one to the left of the deque
• …
• add! — Adds the right two numbers of the deque
• !add — Adds the left two numbers of the deque
• …

3! !5 !2 sub! !add

If applied to an empty deque this will leave the value 4 on the deque.

A Python implementation was given by the streamer Tsoding https://github.com/tsoding/deque.py.