perhaps I've missed something ...

[John Clements <clements@xxxxxxxxxxx>]

... but I fail to see the appeal of this mechanism. As far as I can 
tell, a scheme implementation which conforms to this SRFI allows me 
to write

(set! (car x) 5)

rather than

(set-car! x 5)

To my eyes, the only effect of this change is to confuse the 
primitive which mutates bindings (set!) with a primitive that mutates 
values (set-car!).  Although these two are radically different 
beasts, beginning students often find it hard to understand the 
difference, and a change of this sort will only make it harder to 
teach them.

humbly yours,

john clements

ps. Since I am using a fixed-width font, I can see that the second 
one is actually two characters shorter.

pps. let and letrec are both binding constructs. I don't see why we 
need two different forms.  Why not just use 'let,' and if any of the 
right-hand-sides happen to refer to the name they're bound to, 
implicitly change the whole thing into a letrec?  I think this would 
be much simpler and avoid lots of confusion.