> bad_user summed up a fundamental flaw Not really. I didn't see the author ever claim you could magically control external mutable state, indeed he explicit

> bad_user summed up a fundamental flaw Not really. I didn't see the author ever claim you could magically control external mutable state, indeed he explicitly acknowledged that: > Unfortunately, adding the toolbar bar to the window may not truly be an atomic operation down deep, but from your perspective it is, since you can't make the mutation operation any smaller. You may not have completely eliminated the chance of things going into a bad state, but you've minimized it as far as you can. He just says "do the best you can with your own software, and here are some ideas about it". It's an old article, appropriate for its time (detailed because many people were new to functional concepts) and yet surprisingly prescient (the rise of functional languages did occur). Nobody forced you to read it if you happen to be some whiz-functional programmer to whom all the points are intuitively obvious. Honestly, I don't understand the negative tone in many of the comments.