This would also allow things like a splice operator (mentioned here: http://arclanguage.org/item?id=540); if we had this (assuming that @x expands to (splice x)), you could write (let arglist '(4 5 6) (list 1 2 3 @arglist 7 8 9)) and get (1 2 3 4 5 6 7 8 9). This would actually be superior to apply in certain cases: (and x y @arglist) wouldn't have to evaluate y or the parts of arglist, whereas (apply and x y arglist) has the same effect in most cases, but does evaluate y, which can be problematic. I suppose one way to solve this would be to give values a "cer" (Current EnclosuRe) or some such; if lst were '(1 2 (a b) 3 4), then (cer x) = nil, (cer (car x)) = x, and (cer (car (list-ref 2))) = (list-ref 2). It's not clear what (cer (cdr x)) would be, but it would probably also be x.
Personally I'd still implement this as a macro form, such that we would have a (spliceable ...) form which would scan its contents for splice-macros. So the syntax would look approximately like:
(spliceable ...) would essentially be a generalization of the `() operator, except that ` will only scan for , while (spliceable ...) would scan for any splice-macros.
