seeking article on representing cyclic graphs using purely functional data structures

Some time ago I have seen an article reference on LtU that discussed representing cyclic graphs using purely functional data structures. The graph structure was something like flow graph or state machine.

The article discussed switch from implementation based on mutable variables to purely functional version, and the thesis of article was that the authors lived more happily with purely functional version afterwards.

I was unable to locate article using search (too many unrelated results), if somewhat remember the article or at least its title, please give me a reference.

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Thank you

Thank you. The first reference is what I wanted to find.