Well, it kinda "makes sense"...
#programming

@fuxoft So (println(+)) is what, 0?

@filiph Yes, it is!

@segedacz Not yet "user". We'll see about that. Do you know of something similar with similarly excellent documentation?

@segedacz How "new" is that? I've worked in Erlang about 5 years ago and the docs weren't exactly a walk in the park.

@fuxoft @filiph
And (and) is #t and (or) is #f.

@AverageDog @filiph That's a great sentence!

@fuxoft @filiph
:)

@AverageDog @fuxoft so wait, is it possible to evaluate any operand and function this way? What's (sin) and (cos) then? What's (/)? Do operands and functions need to deal with null arguments? Do they get to provide defaults?

@filiph @fuxoft
If a function has a neutral element, then applying it to zero arguments will return it. If a function has no neutral element, calling it with zero arguments is an error.
E.g.:
(sin) ==> error
(-) ==> error
(- 1) ==> -1
(- 1 1) ==> 0
(- 10 2 3) ==> 5
#scheme #lisp #functions

@filiph @fuxoft
When writing your own functions, you can have optional arguments. E.g.:
(define (f x . y)
(if (null? y)
(- x)
(- x (car y))))
(f 5) ==> -5
(f 5 2) ==> 3