Just for the record, I never called them bills just because they contain a dollar sign! I was thinking of a short word which describes an expression who's evaluation changes depending on the local circumstances. Like a legal bill, not a dollar bill.
The name macro doesn't really work, as it's only an expression, it's not a code block.
The idea was never to start passing complex expressions around the place. It was just to allow a function to take an expression containing about one or two names, and evaluate the expression internally, so this...
func(lambda foo: foo > 0)
func($foo > 0)
Other uses are there, and might be helpful from time to time, but it's mainly about cleaning up APIs. I personally work with user facing Python APIs all day, and users are generally programming interactively, so perhaps my take is atypical.
What the hell is a thunk anyway? It's a horrible name.
On the jQuery like syntax, $(foo), that might work and might do away with the issue of expressions containing bills always evaluating to bills. I took that too far. Good point.