usage: (ledit object) h or ? -- help ok -- end q -- quit (not saved) p -- level print pp -- pretty print mark -- stack cur_pointer ^ or top-- top level < -- pop cur_pointer num -- into the num-th element - num -- into the num-th element from the last cdr -- into cdr part (bi n1 n2) -- both in from n1 to n2 elements (bo n) -- both out from n-th element (f s-exp) -- find s-exp (r s-exp s'-exp) -- substitute all s-exp to s'-exp (cdr n) -- n-th cdr (n s-exp) -- append s-exp to the last (num) -- delete num-th element (num { s-exp }) -- substitute num-th element to s-exp (-num { s-exp }) -- insert s-exp into num-th element (e { form1 .. formn }) -- eval from form1 to formn