[throwaway81523]

Article is overall unpersuasive. The first part is silly: copying a whole array instead of using a functional data structure such as a red-black tree is just asking for a huge slowdown. The second part doesn't give enough detail to really make its case. Author's solution was a big tree with mutable nodes, but there's a cautionary tale in an old article[0] by Ramsey and Dias about using a zipper[1] as a functional representation for the control node graph of a C-- compiler.

[0] https://doi.org/10.1016/j.entcs.2005.11.042

[1] https://en.wikipedia.org/wiki/Zipper_(data_structure)