Programming Language Reminiscence: R-Technology

Nodes are program states and directed edges (arcs) are state transitions. The C code also has a more interesting R-program: building a full binary tree iteratively, without using stack — in constant memory, if we do not count the allocated tree nodes. I should also say that the tree builder (written for the sake of running the example and was not present in the original Algol-68 code) did take some thought: how many R-states I need, what is the point of each state, how much mutable state is enough.

Source: okmij.org