This is the 4th post in a series about migrating to functional programming. This week, I'll first implement the Dijkstra algorithm, then migrate the code to a more functional-friendly design. Dijkstra's algorithm allows to find the shortest path in any graph, weighted or not, directed or not. The only requirement is that weights must be positive.

Many functional programming articles teach abstract functional techniques. That is, composition, pipelining, higher order functions. This one is different. I...