This is about syntactic sugar only. Everything is still s-expressions underneath.
I don't know the right way to do this yet (mathematica is the best way I've seen so far) but one thing I'd like to implore Paul to do:
Forbid all special characters in symbol names. Nice as they are, they will be more valuable as syntactic sugar.
(Parting thought:
x*2+7 - f(5/2,y+8)
(- (+ (* x 2) 7) (f (/ 5 2) (+ y 8))) )