A virtual code application in the following form causes a function with
non-nil virtual code f to be applied to every item
in a list.
map]] f = ((nil,nil),((nil,f),nil))
The map mnemonic is used in silly to express applications
in this form as map f. This operation is also well known to
lisp users and functional programmers. The semantics is determined by
these two operator properties (for non-nil f).
map]] f) nil = nil
map]] f) (x,y) = (f x,([[map]] f) y)
Note that the representation of lists described in Representation of Numeric and Textual Data, is assumed.