[briantrice]

It would be good to tackle multiple-promises-dependencies that the when()/all() protocols achieve, compared to then().

[chaitanya]

I avoided it so that the post does not become very long and the main point doesn't get diluted. That said, I do use multiple-promise-depenencies to implement PCL:LET in the accompanying source https://github.com/chaitanyagupta/promises/blob/1.0/pcl.lisp... (ON-PROMISES does the same thing as when()/all()).