That's talked about in this recent article, "The History of Standard ML" https://dl.acm.org/doi/pdf/10.1145/3386336
There's also this video presentation, "The History of Standard ML: Ideas, Principles, Culture": https://www.youtube.com/watch?v=NVEgyJCTee4
[1] https://en.m.wikipedia.org/wiki/ML_(programming_language)