* Tassilo Horn <t...@gnu.org> [2023-01-20 16:14]: > Jean Louis <bugs@gnu.support> writes: > > >> Yes, and I think it's seriously wrong with > >> > >> : (+) > >> -> NIL > >> > >> where its docs say > >> > >> Returns the sum of all num arguments. When one of the arguments > >> evaluates to NIL, it is returned immediately. > > > > For some reason PicoLisp is quite different than other Lisp. I have > > asked author about it. > > > > 15:09 <abu[m]> It is a "feature" that NIL propagates through > > arithmetics > > Well, but with (*) and (+), there is no single NIL involved! And in > Elisp (+ nil), where actually a nil is involved, you get an error.
What we can learn from PicoLisp is that there was no use for (*) ➜ 1 and that programs work, GUI applications and Android/Replicant work, and there was no use of (*) ➜ 1 so far. Similarly like author of PicoLisp finding use when (*) ➜ NIL, so I would also find (very rare) use with errors. Even if NIL, I find use as I will get error raised in combinations like (+ (*) (* 2 2)), because (+ nil 4) would raise error. > > 15:09 <jmarciano> How does it help instead of providing identity > > elements? > > 15:09 <abu[m]> (*) especially was not contemplated though, it is a > > pretty useless call > > [...] > > 15:12 <abu[m]> What is a call like (*) useful for? > > > > As you see, author also asked naturally why is it useful. > > So go and ask why he thinks (apply '+ ()) -> NIL is more useful than 0 > given that the sum of the empty set of numbers _is_ 0. I will ask. But docstring does not speak of empty sets. You introduce "sets" where there is not direct relation to it. (+ &rest NUMBERS-OR-MARKERS) Return sum of any number of arguments, which are numbers or markers. Of course I get confused. I ask A, but people say B. I ask A, but people say C. I ask A, but people say D. No answer about A. But there are many introductions of things not relevant to function itself. I still believe that there is some actual practical use. `apply' can be used with (apply '+ '(a b)) as why would you need in apply for addition two arguments? If list is with one argument, testing with `cadr' will be known, otherwise, I use `car' instead of `apply'. > >> So why does it return NIL? And why do you apparently consider that > >> useful? And can something be useful even though it is incorrect? > > > > I find it right as with error raising or nil I can find what is > > wrong. > > It's good to signal an error when the expression is wrong as does Elisp > with > > (+ nil) > (* 1 2 nil) > (apply #'+ (list 1 nil 19)) > (+ 2 "i am not a number") That is exactly my point, what you see useful there, I see too. Making it less error prone with useless default identity elements hides the real event preceding the operation. -- Jean Take action in Free Software Foundation campaigns: https://www.fsf.org/campaigns In support of Richard M. Stallman https://stallmansupport.org/
