The whole [_ ...] thing is actually a suggestion I saw on a certain someone's who still needs to gives us a certain CROMA Lisp's blog.
It also appears to be in arc
from
http://ycombinator.com/arc/tut.txt
Since functions of one argument are so often used in Lisp programs,
Arc has a special notation for them. [... _ ...] is an abbreviation
for (fn (_) (... _ ...)). So our first map example could have been
written
arc> (map [+ _ 10] '(1 2 3))
(11 12 13)