Description:
Transforms a tree-list (i.e. a list of lists) into a flat list.
If <level> is 1 (resp n) remove 1 (resp. n) level(s) of list imbrication.
If <level> is NIL (default) remove all levels of imbrication, down to a purely flat list.
Ex. (flat '((a b) c ((d e) f))) => (a b c d e f)
Ex. (flat '((a b) c ((d e) f)) 1) => (a b c (d e) f) [1 level of parenthesis]
|