Apologies for bothering everyone with this. It took some research (there is surprising little discussion of the function online or even in most books), but I at least understand how it works now.
It seems that it is not often used in everyday programming: "It is a good idea to leave the use of NCONC, RPLACA, RPLACD, and DELETE to risk-loving programmers. Unless desperate for time or space saving, using them just leads to unnecessary bugs. "--Lisp (Winston, Horn) P. 117 /Lindsay On Thu, Feb 9, 2017 at 5:21 PM, Lindsay John Lawrence < lawrence.lindsayj...@gmail.com> wrote: > I tried conc to an empty list on both 32 and 64 bit versions of picolisp > I even installed SBCL just to try the similar 'nconc' on that platform. > > The results are consistent for all of them. > I just don't understand why.... Is it simply 'standard', historical > reasons? because of the way evaluation works? > > As it is, I would not be able to build a list 'destructively' without > conditional logic for the initial empty list. > conc works as expected when M is not empty. i.e M is rewritten. > > > # -------------------------------------------- > # Could also use NIL to represent the empty list ( > http://software-lab.de/doc/ref.html#nilSym) > : (setq M '() N '(A B C)) > -> (A B C) > : (conc M N) > -> (A B C) > : M > -> NIL > : N > -> (A B C) > > # This is even weirder to me... > # Again, I expected M, not N, to be rewritten > : (setq M NIL N '(A B C) L '(1 2 3)) > -> (1 2 3) > : (conc M N L) > -> (A B C 1 2 3) > : M > -> NIL > : N > -> (A B C 1 2 3) > : L > -> (1 2 3) > # --------------------------------------------- > > /Lindsay > > >
