[plt-scheme] vectors by value

John, look at this mod of your code:

(define mylist '(hi-there))

(define (changemylist x)
  (begin
    (set! x '(yall))
    x))

(define myvector #(hi-there))

(define changemyvector
  (lambda (x)
    (vector-set! x 0 'yall)
    x))

mylist
(changemylist mylist)
mylist

myvector
(changemyvector myvector)
myvector

(define mylist '(whatcha-doin?))
mylist
(set! mylist '(nuthin))
mylist



Welcome to DrScheme, version 203.
Language: Pretty Big (includes MrEd and Advanced) custom.
(hi-there)
(yall)
(hi-there)
#1(hi-there)
#1(yall)
#1(yall)
(whatcha-doin?)
(nuthin)
> 

The 3rd `whatcha-doin?/nuthin' exchange shouldn't surprise you.

What's suprising is the first one, that `changemylist' didn't change
`mylist'!  If you a standard Scheme source, e.g.  R5RS or SICP, you'll
see that the usual explanation of this is in terms of environments:
that `changemylist' defines an environment and binds `x' to a
location, and stores first `hi-there' in this location, and then
stores `yall' in this location. but `changemylist' does nothing to the
global value of `mylist'.  Pretty mind-boggling stuff, and HtDP offers
a simplified semantics.