Actually, that's precisely why it has to be lower precedence: we want $.sin to turn into ($ sin), so as to get at trig from mzscheme; if it were to become (map .sin ...), things would die because of the malformed ssyntax in .sin. (I tried it both ways, which is how I figured this out.)
Ah, I think we have a misunderstanding here: from my point of view, objects earlier in the list have lower precedence to objects later in the list. ^^ So your "lower precedence" is my "higher precedence". Basically, it has to do with stuff like:
foo!bar:qux!quux
which is compiled as:
{{foo ! bar} : {qux ! quux}}
So !, which is listed later, has higher precedence (it gets grouped more tightly)
