How to define a variadic function

问题

I'm looking for something similar to Javascript's arguments array:

function parent(){
  child.apply(this.arguments);
}

I'm aware of the dot notation for variable argument lengths and also scheme's apply function.

This doesn't seem to work as the dot is taken to be the first argument:

(define (parent .) 
          (list .))

(parent 1 3 4 6 7)
Error: bad argument count - received 5 but expected 1: #<procedure (array arg-list)>

This works but isn't ideal. I'd like to call the function without the extra syntax to define the args list:

(define (parent args-list)
     (apply list args-list))


(parent 1 3 4 6 7)
Error: bad argument count - received 5 but expected 1: #<procedure (array args-list)>

(parent `(1 3 4 6 7))
(1 3 4 6 7)

回答1:

The correct syntax is:

(define (parent . args-list)
    <do something with args-list>)

Use it like this:

(parent 1 2 3 4 5)

Inside the procedure, all the arguments will be bound to a list named args-list. In the above snippet, args-list will have '(1 2 3 4 5) as its value. This is an example of how variadic functions work in Scheme.

For the sake of completeness, the same mechanism can be used for anonymous functions, too (notice that args-list is not surrounded by parenthesis):

((lambda args-list <do something with args-list>) 1 2 3 4 5)

回答2:

You want:

(define (parent . args) 
   args) ; args is a list

Which is infact the 'default' implementation of list.

(define (list . x) x)

The error message when applying (define (parent . ) ...) seems wrong, also, the code should not have compiled in the first place as it is invalid syntax. Might imply a bug with the version of Chicken Scheme you are using.

来源：https://stackoverflow.com/questions/12942127/how-to-define-a-variadic-function