Seymour Papert just rolled in his grave. Processing is great but it's far far from actually designed to teach programming. It stumbles into that rather than purposely gets there.
This paper goes over just some of the things wrong with Processing. Skip all the cool stuff on that page and just concentrate on the critiques of Processing
There isn't... as much as I love Bret Victor's work, Processing is out there today teaching people how to code so I take any criticism of it with a very large grain of salt.
Until someone puts the work into implementing some ideas from Learnable Programming, Processing is one of the best we have.
It's a fantastic way for people to approach programming in a very visual and progressive way.
When P5.js first came out, I was skeptical. But today with the power of javascript, I think it's just as fine for most applications.