The following program shows example functions with argument lists similar to those described above.

#!/usr/cogent/bin/gamma

function variable_args (x, y...)
{
  princ("---- Output from variable_args(x, y...) ---- \n");
  princ("The first arg: ", x, "\n");
  with a in y do
    {
      princ("One of the variable args: ", a, "\n");
    }
  princ("\n");  
}

function optional_args (x, y?, z=5)
{
  princ("---- Output from optional_args(x, y?, z=5) ---- \n");
  if (undefined_p(y))
    y = "This value has not been defined.";
  princ("The first arg: ", x, "\n");
  princ("The second arg: ", y, "\n");
  princ("The third arg: ", z, "\n");
  princ("\n");  
}

function no_eval(x, !y)
{
  princ("---- Output from no_eval(x, !y) ---- \n");
  princ("This argument was evaluated: ", x, "\n");
  princ("This argument was not evaluated: ", y, "\n");
  princ("\n");  
}

function many_args (fixed_arg, !y?... = nil)
{  
  princ("-- Output from many_args(fixed_arg, !y?... = nil) ---- \n");
  princ("fixed_arg: ", fixed_arg, "\n");
  princ("y: ", y, "\n");
  princ("The first y arg: ", car(y), "\n");
  with a in cdr(y) do
    {
      princ("The next y arg: ", a, "\n");
    }
  princ("\n");
}

variable_args("hello", 9, "world", 4 + 7, #x);
optional_args(1);
optional_args(1, 2);
optional_args(1, 2, 3);
no_eval(2+2, 3+3);
many_args("Fixed", "hello", 9, "world", 4 + 7, #x);

The output of this program is as follows:

---- Output from variable_args(x, y...) ---- 
The first arg: hello
One of the variable args: 9
One of the variable args: world
One of the variable args: 11
One of the variable args: x

---- Output from optional_args(x, y?, z=5) ---- 
The first arg: 1
The second arg: This value has not been defined.
The third arg: 5

---- Output from optional_args(x, y?, z=5) ---- 
The first arg: 1
The second arg: 2
The third arg: 5

---- Output from optional_args(x, y?, z=5) ---- 
The first arg: 1
The second arg: 2
The third arg: 3

---- Output from no_eval(x, !y) ---- 
This argument was evaluated: 4
This argument was not evaluated: (+ 3 3)

---- Output from many_args(!y?... = nil) ---- 
One of the args: hello
One of the args: 9
One of the args: world
One of the args: (+ 4 7)
One of the args: 'x