Reminds me of the recursive let discussion (http://arclanguage.org/item?id=13748): when we're defining or setting a variable, and we have an expression which calculates the (new) value for the variable, which scope do we want the variables in the expression to come from?
Sometimes we'll want the variables to come from one scope and sometimes from another. But, I think you're right that a parallel = would be a useful default. It would be easy for me to write (= a x b y) as (= a x) (= b y) if I didn't want the variables to be set in parallel, but harder for me to get them to be evaluated in parallel when I wanted them to be without a facility to do it for me.
The definition is still a little 'lumpy' for my taste. But it'll smooth out with time. Besides, maybe it'll turn out to be a bad idea. No point prematurely optimizing for aesthetics.
