All 3 Uses of

function
in
Turtles All the Way Down

The Pickett estate wasn't in a nice neighborhood, exactly, but it was so gigantic that it functioned as a neighborhood unto itself.
p. 99.5

functioned = worked or operated

Can't kiss anyone, can't drive a car, can't function in the actual sensate populated world.
p. 227.0

function = work or operate (do the things that need to be done in life)

I could never become a functioning grown-up like this; it was inconceivable that I'd ever have a career.
p. 227.3 *

functioning = working (able to do the things that need to be done in life)

Definitions:

(1) (function as in: Its main function is to...)
purpose, job, or natural activity
(2) (function as in: can't function well without sleep)
work or operate -- sometimes to work or operate normally or in a particular way
(3) (function as in: I'm attending a function tonight)
a social event or ceremony -- especially one attended for work or out of a sense of duty
(4) (function as in: oxygen is a function of altitude)
saying one results from another; or saying that the amount of one thing is dependent upon the value of another.

If x is a function of y, then x results from y; or the amount of x can be calculated based on the amount of y.
(5) (function as in: Amazon's new search function)
computer code that performs a specific task
(6) (function as in: a mathematical function)
a formula or mathematical expression that describes a relationship between variables
(7) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

For more specialized meanings in math and chemistry, see a comprehensive dictionary.